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UNIVERSITY OF CALIFORNIA. 
 
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 Clots No. 
 


A GUIDE 
 
 TO 
 
 ELEMENTARY CHEMISTRY 
 
 FOR BEGINNERS 
 
 BY 
 
 LE ROY C. COOLEY, PH.D., 
 
 PROFESSOR OF PHYSICS AND CHEMISTRY IN VASSAR COLLEGE 
 
 $3 
 
 pmntaiTT 
 
 NEW YORK .: CINCINNATI : CHICAGO 
 
 AMERICAN BOOK COMPANY 
 

 
 
 
 COPYRIGHT, 1886, 
 BY IV1SON. BLAKEMAN, TAYLOR, & TO. 
 
 M. i 
 
UNIVERSITY 
 
 PREFACE. 
 
 IN an Elementary Chemistry, written in 1872, it was my 
 purpose to give a short course, for beginners, in which the 
 experimental evidence, on which the most fundamental parts 
 of the science rested, should take the place of minute details 
 and advanced theoretical discussions, hoping in this way to 
 encourage the study of chemistry by experiment instead of by 
 books alone, as was so much the custom at that day. A Student's 
 Guide, printed for the use of my classes in 1878, contained a 
 course introductory to qualitative analysis, giving the student 
 nothing but an outline of experiments. He was expected 
 to make the experiments, to observe and describe his own- 
 results, and from these to construct for himself a plan for the 
 detection of the metals. I now combine the leading ideas of 
 those two books, and offer to my fellow-teachers a new volume, 
 in which they are more fully developed in ways suggested by 
 the unbroken experience of the intervening years. 
 
 Chemistry as a branch of study in the schools has two great 
 merits happily combined. One is to be found in the kind of 
 knowledge it offers, and the other in the peculiar mental 
 training it affords. Of these the latter is certainly not the 
 least important, because a person is well educated, not so 
 much in proportion to what he knows, as in proportion to 
 what he can do with his knowledge. Hence a chief purpose 
 
 iii 
 
IV PREFACE. 
 
 of the study of elementary chemistry in schools is to educate 
 the mind by giving it the right kind of exercise in the use of 
 its powers. 
 
 I have therefore tried to make a judicious selection of the 
 most fundamental facts and principles of chemistry, and to 
 present these in such a way that the student must constantly 
 use his senses to discover facts, his reason in drawing correct 
 inferences from the data he collects, and good English in ex- 
 pressing accurately what lie sees and thinks. 
 
 I know of but one way to teach a student how to acquire 
 a real knowledge of nature, and that is, to fix his mind habit- 
 ually on things and events brought under his own eye, and 
 direct him to the discovery of facts and principles for himself. 
 The use of apparatus is, of course, indispensable if the 
 student is thus to study phenomena instead of descriptions 
 of phenomena, and the use of apparatus, by himself, is with- 
 out doubt the method which is most certain to stimulate his 
 mind to the greatest activity. Laboratory study for students 
 in high schools is rapidly growing in favor, but unfortunately, 
 in many schools where chemistry is taught, the difficulties in 
 the way of this method are still thought to be real. Even in 
 these, chemistry to be truly useful should be presented as a 
 study of phenomena, by experiments, instead of what some- 
 body has said about phenomena in books. 
 
 I have therefore tried to construct a course of experiments 
 suited to the use of the beginner, at his laboratory desk, and 
 to the use of the teacher for his class of beginners, where 
 facilities for students to work for themselves seem to be out 
 of reach. 
 
 The study of any subject by experiment combines two kinds 
 of exercise; mechanical and mental operations go hand in 
 hand. On this account experimental investigation is a com- 
 
PREFACE. V 
 
 plex and difficult work. All that can be done to make it less 
 so for beginners is to make one or the other, the mechanical 
 or the mental processes, predominate in our elementary course 
 of instruction. Then which shall it be? The mechanical of 
 course stands first, in one sense, for there will be no phenomena 
 to study until apparatus is selected and arranged to exhibit 
 them. But, on the other hand, a wise selection of apparatus 
 and conditions cannot be made by one who has not already 
 acquired some skill in tracing the relations of cause and effect, 
 and some experience in the application of experimental 
 methods. I think we should first cultivate the power to 
 observe exhaustively and to detect relations, that we should 
 make the mental more prominent than the mechanical in the 
 elementary study of chemistry. Accordingly : 
 
 In this course of experiments the mechanical operations 
 are described in quite minute details. Exactly what is to be 
 done is told, but what is to happen, and the meaning of it, is 
 for a time withheld. Exceptions to this plan will be found 
 in the description of processes which are simply means to 
 secure conditions, and in the statement of facts which may be 
 needed for immediate use. But in general the phenomena 
 which hold the chemistry of substances or processes are left 
 for the student to discover. See, for example, page 35, or 
 pages 85, 86. 
 
 I know that much stress is, by many, laid upon the industrial 
 value of an instrument-making course in chemistry. But it 
 seems to me that the study of chemistry is not primarily to 
 teach mechanics, and that the use of tools and the possession 
 of mechanical ingenuity can be better acquired in the indus- 
 trial school or workshop, where these are the specific aims, 
 than in the laboratory of the high school or academy, where 
 the acquisition of knowledge for the sake of mental training is 
 
VI PREFA CE. 
 
 the chief purpose. Home-made apparatus is not to he de- 
 spised, but to he greatly respected, where nothing hetter can be 
 had, for much can be done with the most common utensils, 
 such as bottles, fruit-jars, tea-saucers, and oyster-cans. But 
 certainly beginners can do hetter work with good facilities than 
 with poor ones. And while there is so much in the market 
 which is at once scientific and inexpensive, the student should 
 be taught to reach more accurate results than are otherwise 
 possible by the use of it. Productive ingenuity and skill 
 must be founded on exact knowledge and clear thinking; they 
 cannot precede these. Therefore : 
 
 The apparatus called for in this course has been selected 
 from that which is made for, and approved by, chemists. The 
 pieces are neat, simple, easily put together, always in market, 
 and as cheap as possible for good scientific work. (See Appen- 
 dix, Fig. 69.) 
 
 A brief summary of the most important facts and principles 
 follows the experimental work, by which the student can check 
 and correct his results. In this summary will be found the 
 information which should be acquired by beginners in chem- 
 istry. I have tried to include in it only such things as will be 
 of most value to the many who will finish the study of chem- 
 istry in the high school, and to the few also who are there to 
 lay a foundation for college work. "Not how much w r e know 
 is the best question, but how we have got what we know, and 
 what we can do with it, and, above all, what it has made of 
 us." J. P. LESLIE. 
 
 It is not well to undertake too much. It is not best to have 
 the student's text-book burdened with matter which he is not 
 expected to master. There is more education to be gained by 
 extending the search for facts into other volumes than by 
 skipping parts of the book in .use. I have not given a long 1 
 
*. vn 
 
 list of experiments, but have tried to make a judicious selection, 
 believing that a few typical ones well made and thoroughly 
 studied, are far more useful than a larger number would be 
 if studied in haste. What I mean by the thorough study of a 
 few experiments in the treatment of a subject may be seen by 
 referring to " Substitution," pp. 19-21: "Decomposition of nitric 
 acid," pp. 92-95; or "Chlorides," pp. 141-145. 
 
 Additional work is better when provided by teachers for such 
 pupils or classes as have time or talent to undertake it. I 
 would make such work partake of the nature of research as 
 much as possible. A student may be given some question to 
 be answered by his own experiments, or two substances whose 
 mutual reactions and results he is directed to investigate, or 
 a single body whose properties he is asked to study and report. 
 Some work of this kind I have given under the head of " Ex- 
 ercises." (See, for examples, pp. 39, 82, 100.) 
 
 Next in value to research in the laboratory stands research 
 in the library. By all means teach the student how to make 
 the results of his study, with apparatus and the text-book, the 
 nucleus around which to group other facts, a center from 
 which to extend his knowledge. From the following works 
 the teacher can select abundant materials for this exercise, in 
 kind and quantity suited to the varying wants of different 
 individuals or of successive classes. Buckley's " Short History 
 of Natural Science." Wurtz' "History of Chemical Theory." 
 Wurtz' "Atomic Theory." Cooley's "New Text-Book of 
 Chemistry." Cooke's "New Chemistry." Remsen's "Or- 
 ganic Chemistry." Remsen's " Theoretical Chemistry." Ros- 
 coe and Schorlemmer's " Treatise on Chemistry." Fresenius' 
 "Qualitative Analysis." Douglas and Prescott's "Qualitative 
 Analysis." 
 
viii PREFACE. 
 
 1 have in all cases rejected dangerous experiments, but I 
 have in many cases devised simple, safe, and efficient ways to 
 study explosive and noxious substances. See, for examples, 
 Hydrogen, pp. 29, 30, and Chlorine, pp. 138, 139. 
 
 The wood-cuts which represent the experiments are, with 
 a single exception, Fig. 23, made from the photographs or 
 drawings of the apparatus in actual use. For the selected cuts, 
 which illustrate the descriptions of historical or industrial 
 work, I am unable to give the credit which is due to their 
 
 unknown authors. 
 
 L. C. C. 
 POCOHKEEPSIE, June, 1886. 
 
TJHI7BRSIT7 
 
 CONTENTS. 
 
 OBSERVATION AND EXPERIMENT. 
 
 PAGE 
 
 Chemistry : Observation ; experiment ; way to study . . 9 
 
 CHEMICAL, CHANGES. 
 
 Decomposition ; combination ; substitution ; double decom- 
 position ; heat and chemical action ; electricity and 
 chemical action; light and chemical action .... 13 
 
 Hydrogen: Preparation of; properties of; cause of the 
 explosion of; water a product of its combustion; heat a 
 product of its combustion 28 
 
 Oxygen: Preparation of; properties of; chemical actions 
 of; occurrence of; allotropism of; ozone 33 
 
 Exercises : Experimental study of chemical changes . . 39 
 
 CHEMISTRY OF COMBUSTION. 
 
 Burning of a candle ; burning of other substances ; material 
 products; heat also a product; light also a product; 
 structure of flame ; queries 41 
 
 CHEMISTRY OF WATER. 
 
 Analysis and synthesis; analysis of water; composition of 
 water by weight; percentage composition; composition 
 by volume; constant composition of water; constant 
 composition of other compounds ; the LAW of constant 
 composition ; water in nature ; solvent power of water ; 
 drinking waters ; mineral waters ; effect of cold on 
 water 50 
 
 Exercises : Experimental investigations 63 
 
 ix 
 
X CONTENTS. 
 
 CHEMISTRY OF THE ATMOSPHERE. 
 
 PAGE 
 
 Lavoisier's experiment; oxygen removed from air by sul- 
 phur and by phosphorus 65 
 
 Nitrogen: Preparation of; properties of; AIR: analysis 
 of; composition of; a mixture ; diffusion of gases ... 66 
 
 Respiration: Of animals; produces changes in air; 
 ventilation ; of plants 77 
 
 Exercises : Investigations the action of sulphuric on 
 oxalic acid and the action of phosphorus on air . . . 82 
 
 COMPOUNDS OF NITROGEN, HYDROGEN, AND OXYGEN. 
 
 Office of nitrogen in the air ; character of the compounds 
 of nitrogen 84 
 
 Ammonia: Production of ammonia; the nascent state; 
 ammonia in gas-works ; preparation of ammonia; prop- 
 erties of ammonia; its action on the acids; composition 
 by volume 84 
 
 Nitric Acid: Occurrence of, in nature; made from 
 sodium nitrate; properties of; decomposition of; the 
 nitrates 90 
 
 Nitrogen Oxides : Study of the decomposition of nitric 
 acid by copper ; proof that air takes part in the action ; 
 the several products; nitrous oxide; five nitrogen 
 oxides; the LAW of multiple proportions; combining 
 weights . . 92 
 
 Exercises : Investigation of tests 98 
 
 THE COMPOSITION OF PLANTS. 
 Decomposition of wood by heat ; constituents of plants . . 101 
 
 Carbon : Source of carbon in plants ; charcoal-making ; 
 lamp-black; action of charcoal on gases; action of 
 charcoal on colors ; action of charcoal on oxides ; the 
 diamond ; graphite ; allotropism of carbon 103 
 
CONTENTS. XI 
 
 PAGE 
 
 Carbon dioxide: Preparation of; properties of; carbon 
 monoxide ; compounds of carbon and hydrogen ; 
 methane 112 
 
 ELEMENTS, MOLECULES, AND ATOMS. 
 
 The number of the ELEMENTS; table of names, symbols, 
 and atomic weights ; three forms of matter ; facts, laws, 
 and theories, to be carefully distinguished. MOLE- 
 CULES; some facts about the expansion of gases; the 
 theory; chemical changes are changes in molecules; 
 ATOMS; "multiple proportions" explained; atomic 
 theory ; symbols ; formulas ; atomic weights ; molecular 
 weights; reactions 117 
 
 ACIDS, BASES, AND SALTS. 
 
 Acids; salts; hydroxides; reaction of acids and bases; 
 neutral compounds 129 
 
 Chemical names : Of acids ; of salts ; of bases .... 135 
 
 CHLORINE AND THE CHLORIDES. 
 Discovery of chlorine; preparation and properties of 
 chlorine ; bleaching ; the CHLORIDES ; chlorides by 
 chlorine water ; chlorides by hydrochloric acid; chlorides 
 by aqua regia ; two chlorides of one metal ; HYDROGEN 
 CHLORIDE : Preparation of; composition of; comparison 
 of volume; composition of compounds; the "two-vol- 
 ume " law deduced ; test for chlorine and the chlorides . 138 
 
 The Chlorine Group: Bromine; iodine; fluorine; 
 their hydrogen compounds ; relation of atomic weights 
 to properties 147 
 
 Exercises : Study of tests 151 
 
 SULPHUR AND ITS COMPOUNDS. 
 
 Native sulphur and sulphides; preparation of sulphur; 
 properties of sulphur; artificial sulphides; HYDROGEN 
 SULPHIDE : preparation and properties of; use of . . .154 
 
xii CONTENTS. 
 
 PAGE 
 
 The Sulphur Group: Selenium; tellurium; hydrogen 
 compounds; general behavior; relation of atomic 
 weights to properties 161 
 
 Sulphurous Oxide and Acid : Preparation of sulphur- 
 ous oxide; properties of sulphurous oxide; sulphurous 
 acid; bleaching 163 
 
 Sulphuric Acid and the Sulphates: Properties of 
 the acid ; uses of the acid ; test for the acid ; manufac- 
 ture of the acid ; the SULPHATES : sulphates by action 
 of the acid on metals ; by action of the acid on bases ; 
 two sulphates of the same metal ; other sulphur acids . 166 
 
 Exercises: Investigation of tests . . * 173 
 
 PHOSPHORUS, AND THE NITROGEN GROUP. 
 
 Discovery of phosphorus; properties; red phosphorus; 
 matches ; phosphorus oxides and acids ; the phosphates ; 
 manufacture of phosphorus 175 
 
 Arsenic: Arsenous oxide; arsenic oxide; arsenic and 
 hydrogen; Marsh's test 178 
 
 The Nitrogen Group : Members ; their hydrogen com- 
 pounds ; relation of atomic weights to properties . . 182 
 
 SILICON, AND THE CARBON GROUP. 
 
 Silicon : Its oxide ; the CARBON GROUP : members ; their 
 hydrogen compounds; their oxygen compounds; the 
 silicates 183 
 
 Boron : The element ; borax ; boric acid ; no hydrogen 
 compound 185 
 
 VALENCE. 
 
 A difference in atoms; valence defined; substitution 
 governed by valence; the valence of boron; valence 
 useful in study of reactions; valence of an element 
 changes . . 188 
 
CONTENTS. xiii 
 
 THE METALS. 
 
 PAGE 
 
 What is a metal? number and abundance of the metals; 
 occurrence in nature 192 
 
 THE POTASSIUM GROUP. 
 
 Potassium: Description of; chemical action on water; 
 occurrence in nature; potassium carbonate; potassium 
 hydroxide; experiments in the preparation of some 
 other salts ; flame test 195 
 
 Sodium: Description of; occurrence in nature; sodium 
 carbonate; sodium hydroxide; flame test; study of 
 reaction of sodium compounds 199 
 
 Ammonium: Facts about ammonia; comparison of 
 formulas; the hypothetical metal; its salts; the sul- 
 phides ; study of reactions of ammonium compounds . 201 
 
 The Potassium Group : Names of members ; compari- 
 son of properties 204 
 
 THE CALCIUM GROUP. 
 
 Calcium: The metal; its occurrence in nature; effect of 
 heat 011 the carbonate; effect of acids on the carbonate; 
 effect of water on the carbonate ; the sulphate ; to pre- 
 pare the insoluble compounds; to prepare the soluble 
 compounds 206 
 
 The Calcium Group: Names of the members; com- 
 parison of atomic weights and properties ; study of 
 characteristic reactions; flame colors 210 
 
 METALS OF THE ZINC GROUP. 
 
 Magnesium: The metal; its compounds ; study of reac- 
 tions of magnesium compounds 212 
 
 Zinc: The metal; manufacture of; uses of; compounds 
 of; preparation of insoluble compounds, and study of 
 characteristic reactions ; the zinc group 212 
 
XIV CONTENTS. 
 
 THE IRON GROUP. 
 
 PAGE 
 
 Manganese: The metal; its oxides; the potassium man- 
 ganate and permanganate; study of reactions with 
 manganese salts; COBALT; NICKEL 217 
 
 Iron: Occurrence of iron ; its ores; roasting and reducing 
 the ores ; cast-iron ; the three forms of iron ; manufac- 
 ture of wrought-iron; manufacture of steel, Bessemer 
 process; cementation; compounds of iron ; two classes; 
 the two chlorides; distinctive reactions for the two 
 classes ; general reactions of iron salts 220 
 
 Chromium: The metal ; its ore ; the potassium chromate ; 
 the dichromate ; reactions of chromium salts .... 229 
 
 The Iron Group : comparison of properties 231 
 
 ALUMINUM. 
 
 The metal; alum; aluminum oxide; study of reactions 
 of aluminum salts 233 
 
 THE ANTIMONY GROUP. 
 
 Antimony: The metal; alloys of; BISMUTH; the anti- 
 mony group ; the reactions of arsenic, antimony, and 
 bismuth compared 235 
 
 TIN AND LEAD. 
 
 Tin: Occurrence in nature; extraction from the ore; 
 properties of the metal ; compounds of tin ; distinctive 
 reaction for oiis and ic compounds ; general reactions of 
 the salts of tin 239 
 
 Lead: Occurrence in nature; extraction from the ore; 
 two methods ; lead oxides ; lead carbonate ; reactions of 
 the salts of lead 242 
 
 THE COPPER GROUP. 
 
 Copper: Occurrence in nature; extraction from its ores; 
 properties of the metal ; copper compounds ; the sul- 
 phate ; study of reactions of the salts of copper . . . 247 
 
CONTENTS. XV 
 
 PAGE 
 
 Mercury: Occurrence in nature; extraction from its ore; 
 properties of the metal; compounds of mercury; the 
 two chlorides; mercurous compounds; mercuric com- 
 pounds ; study of reactions 251 
 
 Silver: Occurrence in nature; extraction from its sul- 
 phide ; extraction from galena ; properties of the metal ; 
 compounds of silver ; reactions of the salts of silver . . 254 
 
 GOLD AND PLATINUM. 
 
 Gold: Occurrence in nature; obtained by "washing"; 
 
 obtained by " amalgamation " ; properties of gold . . 259 
 Platinum: Occurrence in nature; properties of the 
 
 metal; the platinum group 260 
 
 CLASSIFICATION. 
 
 Classes: How they are made; the classes of the non- 
 metals founded on valence; metals not always classed 
 in this way ; more than one way to group the metals ; 
 four principal ways to classify the metals 262 
 
 The Natural System: Classification by atomic weights; 
 Newland's discovery; Mendelejeft's extension; the spiral 
 of elements ; the vacant places 264 
 
 The Analytical System : Classification founded on solu- 
 bilities; analytical table drawn from the preceding ex- 
 periments in this course ; how to find out what metal a 
 compound contains ; making notes ; to identify the acid 
 part; to name the salt; hint for further work; form 
 of notes . . . . 268 
 
ELEMENTARY CHEMISTRY 
 
 OBSERVATION AND EXPERIMENT. 
 
 IN the study of Chemistry we are to learn some things 
 about the different kinds of matter. There are two ways 
 in which these things have been found out, and in these 
 same ways we can most easily learn what these things are. 
 These two ways of studying nature are called observation 
 and experiment. 
 
 Observation. When I look at something which is 
 going on, and watch carefully to see what happens, my act 
 is an observation. To look at an object so closely that we 
 can see its shape, its color, and whatever else is visible 
 about it, is an act of observation. 
 
 If, for example, I desire to know as much as possible 
 about a butterfly, the best way to learn it is to catch the 
 butterfly, look at it intently, note down and remember 
 what I see. The butterfly would show me that it has four 
 wings, six legs, two long hair-like bodies (antennae) reach- 
 ing forward from its head with knobs upon their ends, two 
 large, dark, and prominent eyes which do not close nor 
 turn, and that the beautiful colors of its wings are due to 
 a fine dust which is easily rubbed off by my fingers. All 
 these facts I could learn by holding the insect in the hand 
 and looking at it thoughtfully. 
 
 Knowledge which I get in this way is learned by obser- 
 vation. 
 
 9 
 
10 
 
 OBSERVATION AND EXPERIMENT. 
 
 Experiment. But if, instead of only looking at an 
 object as I find it, I do something to it to see how it will 
 behave or appear in different conditions, this operation is 
 an experiment. 
 
 Will 5 cubic centimeters of water dissolve as much as 10 
 grams of granulated sugar ? I cannot find out by simply 
 looking at sugar and water. In order to learn what the 
 fact is, I may put the two things together in the right 
 way, and if I do so I make an experiment. Thus: 
 
 Ex. 1. I take a tall glass cylinder, a, Fig. 1, which is 
 graduated to measure cubic centimeters, and pour in water 
 
 Fig. 1. 
 
 up to the 5 cc. mark. 1 I transfer this water to one of 
 the thin round-bottomed cylinders, b, called a test-tube. 
 I also weigh out 10 g. of granulated sugar 2 and put it 
 into the water in the tube b. 8 I now warm the tube in the 
 flume of a Bunsen lamp, c. There is danger of breaking 
 the tube if I heat it too suddenly, or too long in one spot, 
 
 1 If one must get along without a graduated cylinder, he may 
 obtain 5 cc. very nearly by filling his test-tube one inch above the 
 rounded bottom. The tube is supposed to be inch in diameter. 
 
 - If one must get along without a balance, he can obtain about 
 10 g. of dry sugar by filling a teaspoon twice. 
 
 8 Fold a narrow strip of paper into the shape of a trough and lay 
 this in the tube, which should be held in a slanting position. The dry 
 sugar will slide safely down this trough .instead of clinging to the wet 
 walls of the tube. 
 
OBSERVATION ANJ) EXPERIMENT. 11 
 
 and to avoid this danger I move it slowly in the flame to 
 heat all sides evenly. When the liquid begins to boil I lift 
 the tube into the hot air above the flame, where I can keep 
 it hot without boiling it too vigorously. I watch to see 
 
 Whether the sugar remains, or becomes less and less. 
 
 Whether it all finally disappears. 
 
 If the liquid at length becomes, as it will, almost or 
 quite transparent, we shall know that 5 cc. of hot water can 
 dissolve 10 g. of sugar. I will then stand the tube in the 
 tube-rack, and when it is cold I will look again and see 
 
 Whether 5 cc. of cold water can hold the 10 g. in solution. 
 
 Let us keep this syrup for use in another experiment. 
 
 The sap of some trees and the juices of some plants are 
 natural solutions of sugar in water, but 
 the quantity of sugar in 5 cc. of these 
 juices is very small. Nothing but an 
 experiment could have first shown that 
 5 cc. of water can dissolve so much 
 sugar as we have found it to do. 
 
 But in experiments we often put 
 things together in ways in which na- 
 ture never does. For example, I wish 
 to know how sugar will behave in strong sulphuric acid. 
 Nature never puts these two things together, arid the only 
 way I can find out how they will act in the presence of 
 each other is to bring them together. Thus: 
 
 Ex. 2. I measure out 5 cc. of strong sulphuric acid 
 with the cylinder a, Fig. 1, pour it into an empty test-tube, 
 then rinse the cylinder and stand it on a small plate, Fig. 2. 
 I now pour the sugar syrup made in the other experiment 
 into this cylinder. I am ready now to bring the two to- 
 gether. I pour the acid in a slender stream into the syrup, 
 and watch for every change that happens. I notice 
 
 A change in color. 
 
 0? TBM 
 
1- o /;>/; I M770.Y A XI) EXPERIMENT. 
 
 A change in volume (size). 
 
 A change in temperature (warmer or colder). 
 
 A new substance unlike sugar or syrup or acid. 
 
 As soon as the experiment is over I write, in my note- 
 book, a short account of what I did, and the results just as 
 I saw them. 
 
 The fact is that a coal-black, bulky mass of hot carbon 
 or charcoal is the result of bringing these two substances 
 together. 
 
 , The science of Chemistry is founded on facts which have 
 \ been discovered by experiment, and the most natural way 
 j to study Chemistry is by the same means. The best way for 
 tne student is to make the experiments himself. The sec- 
 ond best way is to see them made by a teacher. In either 
 case the student should remember that the object of mak- 
 ing experiments is to discover truth. An experiment may 
 be pretty and interesting, but its value does not lie in its 
 beauty. "No experiment is good for anything in the study 
 of Chemistry unless it helps to reveal some truth. 
 
 The student should reniember, also, that it is not what he 
 reads about experiments, or hears a teacher say about them, 
 that is going to give him the best and quickest insight into 
 Chemistry, but that which he sees with his own eyes and 
 describes in his own words. 
 
 To study Chemistry by experiment the student should 
 obey the following rules : 
 
 1. Arrange the apparatus and use it exactly as directed. 
 
 2. Watch carefully to see ever?/ change which takes place. 
 
 3. Note accurately on paper every Important change. 
 
 4. Compare these results with the facts stated in the 
 book, and correct those which are found to be wrong. 
 
 5. Study carefully to see how certain inferences may be 
 made from the results. 
 
CHEMICAL CHAXGES. 
 
 WE already know by observation that there are changes 
 ail the time going on in bodies of matter. Some things 
 change very rapidly, others very slowly. Wood changes 
 to smoke and ash sometimes in a few minutes ; a stone 
 crumbles to powder only after many years. But nothing 
 can forever stay exactly as it is. 
 
 The first thing we have to do in Chemistry is to become 
 acquainted with these changes. How do they differ ? How 
 are they brought about, and what terms are used to de- 
 scribe them ? 
 
 Ex. 3. I take a piece of magnesium wire or ribbon / 
 about six inches long, grasp one end with a pair of pincers, 1 
 and hold the other end for a moment in the flame of the 
 Bunsen lamp, Fig. 3. I see that 
 
 The metal becomes red hot, then bursts into flame. 
 
 Nothing finally remains but a crumbling white solid. 
 
 Ex. 4. J now in 
 
 the same way hold a 
 piece of iron wire in 
 the flame of the Bun- 
 sen lamp, and see that 
 
 The metal becomes red hot, but 
 does not burn. 
 
 And finally, when cold, is the 
 same substance as at first. 
 
 Both metals were changed by 
 the heat, but in very different 
 ways. The iron became hot in- F i s 
 
 1 A homely handle can be made by starting a split in one end of a 
 stick. The wire can be inserted in the split and held as with pincers. 
 
 13 
 
14 CHEMICAL C1IAX(,KS. 
 
 stead of cold, red instead of black, but it remained iron. 
 The magnesium did not remain magnesium, but was changed 
 into a new substance ; the crumbling white solid is a very 
 different thing from the tough, gray, and lustrous metal. 
 There was no change in the substance of the iron; there 
 was a change in the substance of the magnesium. 
 
 Observations. I watch the clouds and see them 
 change in size and shape, and oftentimes in color. But 
 their substance does not change, for clouds are made of 
 water-vapor, whatever may be their sizes, shapes, or colors. 
 
 To-day a piece of iron is smooth and bright, but if left in 
 moist air it will in time be found covered with iron-rust. 
 
 x 
 
 A part of the iron becomes changed into this very different 
 
 kind of matter. 
 
 Further observations show that there are changes going 
 on all the time around us which do not alter the 
 nature of substances, like the changes in the iron 
 wire when heated. All such changes are called 
 physical changes. There are others in which 
 the substance of bodies is changed into matter 
 of a different kind, like the burning of the 
 magnesium. All such changes are called chem- 
 ical changes . And so we learn that the multi- 
 " *' tudes of changes in the world of matter may be 
 
 grouped in two great classes. 
 
 If now we go on to compare one chemical change with 
 another we shall find that there are several different 
 varieties. 
 
 Decomposition. Ex. 5. I put one gram of " red oxide 
 of mercury'' into a side-neck ignition-tube, 1 Fig. 4, just 
 
 1 Ignition-tubes are made of "hard" glass while other tubes are 
 made of " soft " glass. Hard glass will stand a strong heat, while soft 
 glass will not. Common test-tubes may be used for heating liquids ; 
 ignition-tubes should be used for heating dry solids. 
 
CHEMICAL CHANGES. 
 
 15 
 
 Fig. 6. 
 
 about enough to fill the rounded bottom. I close the mouth 
 
 of the tube with a nicely fitting cork, and slip one end of 
 
 r i piece of rubber tubing, e, Fig. 5, over the end of the 
 
 side-neck. I then fix the 
 
 tube very obliquely in the 
 
 clamp of the support, f. 
 
 I next put a half-inch of 
 
 water into the test-tube , 
 
 and slip the free end of the 
 
 rubber tube down into it. 
 
 The oxide is now ready 
 to be heated, and if any- 
 thing shall be driven out 
 we may catch it in the 
 test-tube. 
 
 I now apply the flame of the lamp, and move it slowly 
 to heat the bottom of the tube evenly. The upper part of 
 the tube must not be heated. Now look for and describe 
 
 A change in the color of the oxide. 
 
 A coating which forms on the cold walls of the tube. 
 
 Bubbles which escape from the rubber pipe in the water. 
 
 A change in the quantity of the oxide. 
 
 Were the bubbles which came over through the water 
 anything more than air ? To answer this question I take 
 a splinter of wood, very slender, and long enough to reach 
 to the bottom of the tube, set fire to one end and watch 
 the spark very closely while I push it to the bottom of the 
 tube to see 
 
 Whether it burns just as it does in air. 
 
 THE FACTS. By heating the red oxide of mercury it is 
 first blackened and then broken into two kinds of matter 
 quite unlike itself. One of these appears in shining drop- 
 lets on the cold walls of the tube, the other goes off as a 
 
16 CHEMICAL CHANGES. 
 
 colorless gas which brightens the burning of a splinter. 
 The shining droplets which coat the cold walls of the tube 
 are mercury, and the gas in which a splinter burns with 
 unusual brightness is oxyyen. 
 
 This is a fine example of chemical change. But the most 
 important thing to notice is, that in this change one sub- 
 stance is broken into two which are entirely unlike itself 
 and unlike each other. Such a chemical change is called 
 deco mpos it to n . 
 
 Decomposition of Potassium Chlorate. Ex. 6. Po- 
 tassium chlorate is a white solid. Before I heat it the 
 coarse grains or crystals should be reduced to powder: I 
 grind it in a mortar (Fig. 6). I put two 
 grams of the powder into the ignition- 
 tube, 1 Fig. 4. This quantity will fill 
 about one inch of the tube. I put three 
 or four cubic centimeters of blue litmus 
 6 solution into one test-tube, I, and as much 
 
 lime-water into a second tube, c, Fig. 5, 
 and provide a good cork for each. I put the end of the 
 rubber tube into the litmus, and then heat the chlorate just 
 as I did the red oxide before. Watch for and describe 
 
 The changes in the chlorate. 
 
 The bubbles from the pipe in the litmus. 
 
 After a while I put a match-flame into the mouth of 
 the tube and see that it burns with unusual brightness. 
 This shows that the tube is filled with oxygen. 
 
 I then put the end of the rubber tube over into the lime- 
 water in c, and close b with its cork, in order to keep its 
 oxygen for use further on. 
 
 At length the boiling chlorate thickens, and soon after 
 
 1 The tube must be clean and dry. A piece of dry cloth, or a sponge 
 tied on the end of a wire or stick, is convenient for wiping tubes. 
 
CHEMICAL CHANGES. 17 
 
 dries up completely to a white solid. The work is done. 
 I stop the heat, remove the rubber tube, and cork the test- 
 tube c, to keep its oxygen also for future use. 
 
 Has any change been made in the litmus or the lime 
 water ? 
 
 THE FACTS. By heating potassium chlorate it is first 
 melted and afterward broken into two substances, unlike 
 itself and each other. One is the white solid, left in the 
 ignition-tube, and the other is oxygen. The chlorate is 
 decomposed. 
 
 Oxygen, which has appeared in both these experiments, 
 is an important substance, and as soon as we are through 
 with the special study of chemical changes we will examine 
 it fully. At present we will make two experiments with it. 
 
 Combination. What will happen if a bit of coal is 
 heated in oxygen ? 
 
 Ex. 7. I wind the end of a small wire around a little 
 splinter of charcoal, heat the charcoal until it holds a spark 
 of fire, and then lower it into the oxygen in the test-tube c, 
 Fig. 5, over lime-water. Notice 
 
 What effect is produced on the spark. 
 
 Whether the charcoal wastes away. 
 
 W r ill the oxygen brighten a match-flame afterwards ? 
 
 I now cover the mouth of the tube with my finger anJ 
 shake it briskly. 
 
 What change takes place in the lime-water ? 
 
 THE FACTS. Charcoal with a dull red spark will glow 
 brightly in oxygen and burn away rapidly ; the oxygen is 
 used up at the same time, and the lime-water afterward 
 becomes turbid and white. 
 
 But we know that oxygen will not whiten lime-water : 
 this was proved in Ex. 6. (How was it proved ?) Charcoal 
 also will not whiten lime-water. But the burning of the 
 
18 CHEMICAL CHANGES. 
 
 charcoal in oxygen yields something which will. It is a col- 
 orless gas called carbon dioxide. In place of charcoal and 
 oxygen we have carbon dioxide, which is very unlike both. 
 Now the thing most important to see in this case is that 
 two substances are changed into one. 
 
 Ex. 8. I take a piece of wire, perhaps a knitting- 
 needle, warm it a little, and then plunge it into some 
 flowers of sulphur. A thin layer of sulphur will cling to 
 the wire. I set fire to this sulphur, and then at once thrust 
 it into the test-tube b, containing oxygen and litmus, left 
 from Ex. (>. Notice and describe 
 
 The fine color of the flame. 
 
 The vapor which is produced. 
 
 I next close the tube with my finger and shake it to mix 
 the vapor with the litmus. 
 
 What change is made in the color of the litmus ? 
 
 Sulphur burns more freely in oxygen than in air, and 
 with a rich blue flame, filling the vessel with white vapor. 
 This vapor mixed with blue litmus solution changes the 
 color from blue to red. In place of the sulphur and oxy- 
 gen, both of which are used up, we have a new substance 
 quite different from either. This new substance into which 
 sulphur and oxygen are changed is called sulphur dioxide. 
 
 Now this change is like the change when the charcoal 
 was burned. It is another case in which two substances are 
 changed into one. Such a chemical change is called combi- 
 nation. 
 
 Decomposition or Combination? When ammonia 
 and hydrochloric acid are mixed a chemical change occurs ; 
 is it a chemical decomposition or a chemical combination '.' 
 
 Ex. 9. I put a cubic centimeter of strong ammonia 
 water into a tube or bottle, rinse it around to wet the sides, 
 and then pour it out. I put as much hydrochloric acid into 
 
CHEMICAL CHANGES. 19 
 
 another similar vessel and treat it in the same way. By 
 this means I fill the vessels with the colorless vapor of the 
 two substances. I next bring these two vessels 
 mouth to mouth and hold them one above the other 
 (Fig. 7). Notice and describe 
 
 The change which the colorless vapors undergo. 
 The two substances used are colorless, but a new 
 one is made which is seen as a white cloudlike mass, 
 which rolls down toward the bottom of the tube, 
 and will roll back again if the tubes be inverted. 
 In fact, the hydrochloric acid and ammonia com- 
 bine to form one thing, called ammonium chloride. Fi - 7 - 
 
 Substitution. All chemical changes are either decom- 
 positions or combinations. But in a great many cases the 
 two kinds take place at once. This is true in the action of 
 zinc and hydrochloric acid. 
 
 Ex. 10. I have a wide-mouth bottle which 
 will hold 200 cc. and a square of glass or of 
 heavy paper with which to cover it. 
 
 Into the bottle I put two or three pieces of 
 zinc, and just cover them with hydrochloric acid. 
 I then close the bottle with its cap of glass or 
 paper (Fig. 8). 
 Describe the action which sets in. 
 Feel the bottle, and what effect is discovered ? 
 I now bring a match-flame to the mouth of the bottle 
 while I lift the cover. 
 Describe the result. 
 
 A violent effervescence takes place whenever zinc and 
 hydrochloric acid are brought together. The vessel is 
 heated, and a gas escapes which takes fire with explosion. 
 This gas is hydrogen. Heat and hydrogen are two products 
 of the chemical action. Are there any others ? 
 
CHEMICAL CHANGES. 
 
 a 
 
 V 
 
 Fig. 9. 
 
 Ex. 11. To answer this question I examine the liquid 
 left in the bottle, when the bubbling of gas has come to an 
 end. I must first filter the liquid to rid it of black flakes, 
 which are only impurities of the zinc, and afterward 
 evaporate the liquid to recover any solid substance it may 
 contain. 
 
 1. Filtration. Cut a square of filter paper, A, Fig. 9, 
 about three inches on a side, a little less than twice the 
 
 length of the sloping side of 
 a funnel, /. Fold the square 
 into a triangle by bringing 
 corners d and a together. 
 Fold again, bringing corners 
 c and b together, making the 
 triangle B. 
 
 Then trim the edges along 
 the circular line e h. Open 
 
 the triangle (leaving three thicknesses of paper on one side 
 
 and one on the other), and we have a little 
 
 paper funnel, C, which will fit neatly in 
 
 the glass funnel, /. Press it in and wet 
 
 it with water. Then rest the funnel on a 
 
 test-tube and pour the liquid with its sedi- 
 ment into it. The liquid will run through, 
 
 but the sediment will stay on the filter. 
 
 2. Evaporation. Pour the clear 
 liquid into a porcelain dish and heat 
 it over a low flame, as shown in Fig. 
 10. It may boil, but should do so 
 very gently. The water will slowly 
 
 pass away as vapor, but any solid substance which is dis- 
 solved in it will stay in the dish. 
 
 I will evaporate the liquid left in Ex. 10, and just fil- 
 tered, down to about one-third its bulk, and then let it 
 
 Fig. 10. 
 
CHEMICAL CHANGE*. 21 
 
 stand until it is cold. A brown solid is now seen, if the 
 evaporation has gone far enough. This brown solid must 
 have been made by the action of the zinc on the hydro- 
 chloric acid in Ex. 10. It is called zinc chloride. 
 
 We began the experiment with zinc and acid ; we after- 
 wards find hydrogen, the brown solid, and heat, in place of 
 these twt) substances. 
 
 In all, we have now found three products of the chemical 
 action of zinc and hydrochloric acid. They are heat, hydro- 
 gen, and zinc chloride. 
 
 Now hydrochloric acid is a compound of the two ele- 
 ments hydrogen and chlorine, and the zinc just takes the 
 place of the hydrogen in it. In fact, the zinc has decom- 
 posed the hydrochloric acid and combined with the chlorine 
 of that substance. The hydrogen was driven out as a gas, 
 which burned quickly while the solid zinc chloride 1 stayed 
 behind in solution. 
 
 When one substance takes the place of another in a com- 
 pound, as the zinc took the place of hydrogen in the acid, 
 the action is called substitution. This is one of the most 
 common kinds of chemical action. 
 
 Double Decomposition. It often happens that when 
 two things are brought together both are decomposed. This 
 is the case with silver nitrate and sodium chloride. 
 
 Ex. 12. I take a small crystal of silver nitrate and drop 
 it into a test-tube with 5 cc. of water, and shake it until it 
 is dissolved. In another test-tube I dissolve some common 
 salt, which in chemistry is known as sodium chloride. I 
 now add a drop or two of the solution of salt to the silver 
 nitrate. After seeing, 
 
 What happens to show that a chemical action occurs ? 
 I go on adding the solution of salt carefully, drop by drop, 
 
 1 The solid is called zinc chloride because it is made up of zinc and 
 chlorine. When pure it u nearly white. 
 
CHEMICAL CHANGES. 
 
 watching to see whether still more of the new substance is 
 made by each addition; and that I may make no mistake 
 about this I shake the tube each time vigorously, and then 
 wait till the solid settles a little before I add the next 
 drops. I do this until a drop of the liquid gives no more 
 of the white solid, and stop with that drop. 
 
 If by accident I do get in a drop more than thte, I add a 
 drop of silver nitrate solution. 
 
 I then filter the mixture as in Ex. 11. The white solid 
 will be left on the filter-paper while a clear liquid will run 
 through. 
 
 I next evaporate this clear liquid, as shown in Fig. 10, 
 until but little is left, and then, when it cools, crystals 
 will appear. The new white solid is silver chloride, and 
 the crystals are sodium nitrate. 
 
 The silver nitrate and sodium chloride decompose each 
 other, and then the silver and sodium just change places 
 and form the two new compounds named above. The 
 names themselves show this double change, thus : silver 
 nitrate and sodium chloride become sodium nitrate and 
 silver chloride. 
 
 In all such cases as this, in which two substances decom- 
 pose one another and form two new ones, the action is 
 called double decomposition. We shall find another exam- 
 ple of double decomposition in the action of mercuric 
 chloride and potassium iodide. 
 
 Ex. 18. I take enough mercuric chloride in powder 
 to half-way fill the rounded bottom of a test-tube, cover 
 it with 5 cc. of water, and warm it until it is dissolved. 
 I take about twice as much potassium iodide in another 
 tube and dissolve it also in water. I put about JoO cc. 
 of water into a wide-mouth bottle, and add the mercuric 
 chloride solution. I now put in about one-half the solu- 
 tion of potassium iodide, little by little. 
 
CHEMICAL CHANGES. 23 
 
 Describe the result as it first appears. 
 And the curious change which soon occurs. 
 
 I go on adding the iodide, carefully noticing whether still 
 more of the new substance is made by each addition, and, 
 that I need make no mistake, I wait each time to let the 
 solid settle a little and the liquid clear before I add the 
 next drops. I do this until a drop of the iodide gives no 
 more of the colored solid, and stop with that drop. If by 
 accident I do get in too much, I will add drops of mercuric 
 chloride until the last drop has no effect. The scarlet solid 
 will soon settle and leave a clear liquid above it. 
 
 We find that when mercuric chloride and potassium 
 iodide are brought together in solution they yield a sub- 
 stance whose color, at first bright yellow, very soon changes 
 to a fine scarlet. The potassium iodide will give this sub- 
 stance just as long as there is any mercuric chloride in the 
 solution. When a drop fails, we may know that the chlo- 
 ride is all used up. The scarlet precipitate (as we call a 
 solid which comes by putting two liquids together) and 
 a solid substance which stays dissolved in the water are 
 the two new things into which the chloride and iodide 
 were changed. 
 
 Now the chemists tell us that mercuric chloride contains 
 mercury and chlorine, and that potassium iodide contains 
 potassium and iodine. When we put these two liquids to- 
 gether the chlorine and iodine changed places. Our scar- 
 let solid contains the mercury and iodine, and our white 
 solid contains the potassium and chlorine. In fact, loth of 
 the old substances were decomposed, and the two new ones 
 were made by their parts combining in different pairs. 
 
 SUGGESTION TO THE STUDENT. Notice all along how the 
 name of a substance tells us also the names of the simpler sub- 
 stances in it. When we see the name mercuric chloride we may 
 be reminded of the names of its parts, mercury and chlorine ; and 
 
24 CHEMICAL CHANGES. 
 
 in the same way potassium iodide suggests its parts, potassium 
 and iodine. So, too, our yellow solid made of mercury and iodine 
 is named mercuric iodide. 
 
 Definitions. A substance which is made up of two or 
 more kinds of matter quite unlike itself is called a com- 
 2)ound. Mercuric oxide is a compound of mercury and 
 oxygen. For the proof of this see Ex. 5. 
 
 The different kinds of matter of which a substance is 
 made are called its constituents. Mercury and oxygen are 
 the constituents of mercuric oxide ; sulphur and oxygen, of 
 sulphur dioxide (Ex. 8). 
 
 By far the larger number of substances are compounds ; 
 but there are a few which have never yet been decomposed, 
 and such are called elements. Mercury, oxygen, and sul- 
 phur are examples of elements. Some seventy of these 
 are now known, and out of this small number all the com- 
 pounds in nature are made. 
 
 But compounds rarely occur pure. Substances are min- 
 gled together two or more so completely that they seem 
 to be only one, and yet each still has all its properties 
 unchanged. Syrup of sugar is an example. The sugar and 
 the water are simply mixed together without change of 
 properties. Such substances are called mixtures. Brine is 
 another example. 
 
 All substances are either elements, compounds, or mix- 
 tures. 
 
 There are two ways of finding out what the constituents 
 of a compound are ; one is analysis, the other synthesis. 
 Any process in which we decompose a substance so as to 
 learn what it is made of is an analysis. Ex. 5 was an 
 analysis of mercuric oxide. Any process in which we 
 make a compound by putting its constituents together is a 
 synthesis. Ex. 8 was a synthesis .of sulphur dioxide, and 
 in Ex. 7 we found that carbon dioxide is composed of car- 
 
CHEMICAL CHANGES. 25 
 
 bon and oxygen by making these two elements combine. 
 This also was an example of synthesis. 
 
 Heat and Chemical Action Heat is very often pro- 
 duced by chemical changes. It was so in Ex. 10. It is so, 
 for another example, in the case of 
 
 SULPHURIC ACID AND WATER. Ex. 14- Into a wide- 
 mouth bottle I pour 40 cc. of cold water, and provide a rod 
 of glass, or of wood, with which to stir it. I then pour into 
 it gradually, while I stir it, 40 cc. of strong sulphuric acid. 1 
 Note the evidence that heat is produced as shown 
 
 By handling the bottle. 
 
 By inserting a test-tube holding a little alcohol. 
 
 These chemical changes need no extra heat to start them, 
 but yield heat as one of the products of the action. 
 
 There are other cases in which heat must be used to start 
 the change (Ex. 7 and Ex. 8), which once started produces 
 heat enough, and often more than enough, to keep the 
 action going. We touch the wood with a match-flame to 
 start a fire, but once begun the burning is kept up by the 
 heat of the chemical action itself. 
 
 There are still other cases in which heat must be applied, 
 not only to start the action, but also to keep it going (Ex. 5 
 and Ex. 6). In these cases heat is not produced, but ab- 
 sorbed, by the chemical action. 
 
 The fact is that every chemical action is a source of heat 
 or cold ; every change in the nature of a substance is accom- 
 panied by a change in temperature. 
 
 Electricity and Chemical Action. We are told in 
 the study of Pliysics, that if a strip of amalgamated zinc 
 and another of copper are put into a vessel of very dilute 
 acid they will yield a current of electricity. 
 
 1 The heat would be stronger if the water were poured into the acid. 
 This should never be done. Whenever strong sulphuric acid and water 
 are to be mixed always pour the acid gradually into the water while 
 von stir it. 
 
26 CHEMICAL CHANGES. 
 
 Ex. 15. I first make a little zinc-copper couple in this 
 way : I cut from a sheet of zinc, such as is used under 
 stoves, a strip four inches long by one-half inch in width 
 and bend it squarely at three-fourths inch from one end, ,v, 
 Fig. 11. I then amalgamate it. For this I take a few 
 cubic centimeters of the half-strong acid which was made 
 
 in Ex. 14, and add to 
 it five times as much 
 water in a saucer. I 
 must also have a little 
 mercury in a test-tube. 
 I first wet the zinc 
 with the acid. I next 
 pour the mercury first 
 upon one side, then upon the other, and rub the whole sur- 
 face gently with a piece of cloth. The surface of the zinc 
 should now shine like silver ; it is amalgamated. 
 
 I next take a piece of sheet-copper as wide as the zinc 
 and two and a half inches long, and fold one end, as shown 
 at c. I press the end of z into this fold and make the two 
 fit closely by pressing the fold carefully (not to break the 
 zinc) with pincers. The upright part of c is about two 
 inches long and stands facing the upright part of 2, as 
 shown at a, Fig. 11. 
 
 To prepare the dilute acid : I measure into the water-pan 
 p water enough to be a little deeper than the copper c is 
 high, and then add one-twentieth as much strong sulphuric 
 acid. 
 
 I shall also need a test-tube : to have it ready I lay one 
 in the water, let it fill and sink. 
 
 These preparations all made, I next stand the zinc-copper 
 in the acid water. 
 
 A torrent of bubbles rise alongside the copper. AY hut 
 are these bubbles ? To catch them I lift the test-tul>e, 
 
CHEMICAL CHANGES. 27 
 
 bottom upward, letting no air enter it, and bring its mouth 
 over the top of the copper, as shown at b. The bubbles 
 now rise into the tube, driving the water out at the rate of 
 1 cc. a minute, if everything works well. When the tube is 
 about half filled with gas I light a match, and lift the tube 
 slowly ; the water falls out, air takes its place, and as the 
 flame touches the mouth of the tube a sharp report occurs, 
 which says hydrogen ! 
 
 The acid water is decomposed and hydrogen, is set free. 
 But amalgamated zinc alone will not decompose the acid 
 (try it), nor will copper alone (try it). Is there anything, 
 more than zinc and copper, when they are together in the 
 acid? Yes, there is, as we are told, the current of elec- 
 tricity. The zinc-copper is a source of electricity, and the 
 hydrogen is set free by the action of electricity. 
 
 It is found that a great many chemical changes can be 
 made by means of electricity. And, on the other hand, a 
 great many chemical changes produce electricity. Like 
 heat, electricity is sometimes an agent and sometimes a 
 product in chemical action. 
 
 Light and Chemical Action Light is also a product 
 
 of chemical action. The light of our fires and the light of 
 our oil and gas lamps are examples. Remember, also, the 
 burning of sulphur in Ex. 8, and of charcoal in Ex. 7. 
 
 Light will also sometimes produce chemical changes. 
 
 Ex. 16. I first make some silver chloride by filling 
 a test-tube three-fourths full of water, adding a small crys- 
 tal of silver nitrate, shaking until the crystal is dissolved, 
 and then adding hydrochloric acid drop by drop. The white 
 cloud which rolls down is silver chloride. I now place the 
 tube in strong sunlight. 
 
 What change occurs in the color of the chloride ? 
 The change in color slowly from white to dark purple is 
 
CHEMICAL CHANGES. 
 
 a sign that a new substance is being made. In fact, light 
 decomposes the silver chkride. For other examples, and 
 for the explanation of this one, we must wait. 
 
 Heat, light, and electricity are agents which we can use 
 to bring about chemical actions which in their absence will 
 not occur. 
 
 Heat, light, and electricity are also products of chemical 
 action. They are just as important to the chemist as are 
 the material products, that is, the new substances, obtained 
 at the same time. 
 
 We now go on to examine hydrogen and oxygen gases 
 which we have met with in several experiments. 
 
 HYDROGEN. 
 
 Hydrogen may be made by zinc and hydrochloric acid, as 
 it was in Ex. 10. We may make and catch it as follows : 
 
 Ex. 17. I make enough dilute hydrochloric acid one 
 measure of strong acid to two 
 measures of water to fill the 
 -.^^^g water-pan about two inches deep. 
 I take the graduated cylinder, lay 
 Fig - 12 - it in the acid, as shown in Fig. 12, 
 
 and when it is thus filled with the liquid I lift it bottom 
 upward and let it stand mouth down 
 on the bottom of the pan, as in Fig. 
 13. I next drop a piece of granu- 
 lated zinc into the pan, and then 
 carry the mouth of the cylinder over 
 it. In all this work I use great care 
 to not let a bubble of air get into 
 the cylinder. The hydrogen bubbles 
 form on the zinc, rise in the cylin- ~ Fig. is. 
 
 der, and push the water down out 'of it, as shown in Fig. 14, 
 until finally the cylinder is filled with hydrogen. 
 
CHEMICAL CHANGES. 
 
 20 
 
 To Discover the Properties of Hydrogen 1 test 
 
 the gas by lighting a match, then lifting the cylinder out 
 
 of the liquid rather slowly, mouth 
 
 still downward, and then quickly 
 
 bringing the flame to the open 
 
 mouth. The gas takes fire with a 
 
 dull report. Compare this result 
 
 with that in Ex. 10. 
 
 Ex. 18. I fill the cylinder again 
 with the gas, and lift it from the rig. 
 
 water in the same way, then turn it over and let it stand 
 on the table open while I light a match. I bring the match 
 to the mouth of the jar. 
 Why is there no report ? 
 Which is heavier, hydrogen or air ? 
 What is the color of hydrogen ? 
 
 Ex. 19. I put 30 cc. of water into the mortar, Fig. 6, and 
 30 cc. strong hydrochloric acid. I drop into this a piece of 
 zinc, and then place a small funnel, mouth down, over the 
 zinc. I next bring the mouth of a test-tube 
 down over the stem of the funnel, as shown 
 in Fig. 15. The action should be brisk ; and 
 if it be so, then, after one minute, I slowly 
 lift the tube keeping its bottom up 
 carry it away from the stem, and then bring 
 a lighted match to its mouth. A dull explo- 
 sion proves that the tube is full of hydrogen. 
 The hydrogen rises through the air to the 
 top of the tube, collects there and gradually 
 pushes the air down and out at the bottom. If the explo- 
 sion is sharp, it shows that the tube was only partly filled. 
 Then repeat the experiment, and wait longer. 
 
 Other gases which are lighter than air may be collected 
 by this method, called upward displacement. Oxygen, which 
 
 Fig. 15. 
 
30 CHEMICAL CHANGES. 
 
 is Tieavier than air, is collected (Fig. 5) by downward dis- 
 placement. In Ex. 17 the gas was collected by displace- 
 ment of water instead of air, and this method may be used, 
 whether the gas is lighter or heavier than air. 
 
 WHAT CAUSES THE EXPLOSION? Ex. 20. I take a short 
 piece of glass tube, which is drawn out to a small jet at 01 it- 
 end, and fix it with a piece of rubber tubing 
 upon the stem of the funnel. I again put 
 dilute hydrochloric acid in the mortar, add 
 the zinc, and place the funnel over it. The 
 gas must come off very briskly ; and, if need 
 be to make it do so, I add more strong acid. 
 After about half a minute, if -the gas is com- 
 ing fast, and longer if not, so that the air 
 Fig. IB. shall be all driven out, I bring a match-flame 
 to the top of the jet on the end of the funnel. The gas 
 takes fire with the usual dull explosion, but goes on burn- 
 ing as quietly as a candle. Fig. 16 shows this result. 
 Then is hydrogen itself explosive ? 
 Note also if the flame is pale or brilliant. , 
 Is it a hot flame ? Try it with a small wire. 
 7r. 21. But what causes the explosion, if hydrogen 
 can burn without it ? I will collect a little hydrogen 
 over water, as in Ex. 17. But, instead of filling the cylin- 
 der with the liquid, I will leave it about two-thirds full of 
 air, filling only about one-third its height with the water. 
 The liquid will soon be driven out, and then the cylinder 
 is filled with a mixture of hydrogen and air. I now lift it 
 from the pan, and at once bring a match-flame below its 
 mouth. A sharp explosion follows. 
 
 What substances together explode in this case ? 
 Have these same ones been together before whenever the 
 explosion has occurred ? 
 
 What, then, is the material which explodes? 
 
CHEMICAL CHANGES. 
 
 31 
 
 What new Substance made by burning Hydrogen? 
 Ex. 22. To answer this question I must burn pure dry 
 hydrogen and catch the products. I will make the hydro- 
 gen as in Ex. 20, but before I light the jet I must dry the 
 gas, and I can do this by passing it over calcium chloride, 
 which absorbs water greedily. 
 
 I take a "drying-tube," a, Fig. 17, put a little cotton- 
 wool in the bulb loosely, drop in small pieces of calcium 
 chloride to fill the tube nearly full, and put a thin layer of 
 cotton over it. I next close the large end with a cork hav- 
 ing a hole, 1 through which I crowd the end of the stem of 
 the funnel, b, Fig. 17. 
 
 I now put several frag- 
 ments of the zinc into the 
 mortal' ; afterward place 
 the funnel over the zinc 
 and fix the drying-tube 
 firmly in the clamp of the 
 support s, as shown in 
 Fig. 17. This done, I 
 pour dilute hydrochloric 
 acid into the mortar. 
 
 Hydrogen is set free. 
 It goes up through the 
 calcium chloride, which 
 takes out the water. 
 The dry hydrogen escapes from the jet above. 
 
 After waiting until I am sure that the air is all driven 
 out, I set fire to the dry hydrogen at the top of the tube, 
 and then I hold a glass tumbler, or a wide-mouth bottle, 
 which is clean and dry, over the flame, as shown at c. 
 
 1 Holes are made through corks by means of " cork-borers," made 
 for the purpose. They may also be easily made by first running a hot 
 pointed wire through the cork, and then using a round file to enlarge 
 the hole. Each hole should be made to fit its tube very closely. 
 
 Fig. 17 
 
CHEMICAL CHANCES. 
 
 Notice a deposit of dew on the Avails of the bottle; it is 
 nothing but water. This is the substance made by burn- 
 ing hydrogen in air. 
 
 What are two other products ? See p. 28. 
 
 Description of Hydrogen. We have found that hy- 
 drogen is a gas without color, and when pure it is also 
 without odor and taste. It is very much lighter than air 
 (Exs. 18 and 19). An equal bulk of air is 14.44 times 
 heavier than this gas. In fact, hydrogen is the lightest 
 of known substances. 1 
 
 Hydrogen unmixed with air burns with a silent flame 
 (Ex. 20), but when mixed with air the mixture burns with 
 explosion (Ex. 21). The chemical action is the same in 
 both cases : water, heat, and light are the products of this 
 action (Ex. 22). There is nothing in this experiment to 
 show what the hydrogen combines with to make the water. 
 Let us remember this. 
 
 The flame of burning hydrogen is very hot (Ex. 20). In 
 fact, no other fuel gives so hot a fire as this. One gram of 
 this gas will yield enough heat in burning to boil 344.62 g. 
 of ice-cold water. 
 
 A unit of heat is so much heat as will raise the tem- 
 perature of 1 g. pure water 1 C. This unit is called a 
 calorie, just as the unit of weight is called a grant. The 
 heat of all chemical changes is measured by this unit. 
 The burning of the gram of hydrogen gives 34462 of these 
 units, or 34462 calories. 
 
 Hydrogen gas is very seldom found in nature ; it occurs 
 sometimes among the vapors which are thrown out of vol- 
 canoes. But the compounds of hydrogen are everywhere. 
 Water is only one of them. Nearly all animal and vege- 
 table bodies also contain hydrogen in large quantities. 
 
 1 One liter of hydrogen weighs .0805 g. when its temperature is 
 0^ C., and the pressure of the air 15 Ibs. per sq. inch. 
 
CHEMICAL CHANGES. 33 
 
 QUERY. A bottle stands mouth downward in water; it is full 
 of gas ; how would you decide whether it contains air or oxygen 
 or hydrogen? 
 
 OXYGEN. 
 
 Oxygen may be obtained by heating mercuric oxide, as 
 in Ex. 5, or potassium chlorate, as in Ex. 6. The latter 
 way is better, and a mixture of potassium chlorate with 
 " black oxide " of manganese is still better than the chlorate 
 alone. 
 
 To make Oxygen. Ex. S3. I take 4 g. of the chlo- 
 rate and grind it to powder in the mortar. To this I add 
 2 g. black oxide of manganese and mix the two powders. 
 I put this mixture into the side-neck tube, Fig. 4, which I 
 then cork tightly and fix in the clamp, as shown in the cut, 
 Fig. 19. 
 
 To catch and hold the gas, I use a set of flasks fitted up 
 as shown in Figs. 18 and 19. A conical flask 
 is provided with a soft rubber stopper with 
 two holes. A long glass tube passes through 
 one of these holes in the stopper, and almost 
 to the bottom of the flask ; a short glass tube 
 passes only through the stopper in the other. 
 I use four of these flasks, each holding about 
 200 cc. 1 and a small bottle, e. Into the first one, a, I put 
 sand enough to cover the bottom, and then some water, and 
 1 also put water into the bottle e. I then join them to- 
 gether, as shown in Fig. 19, the long tube of a with the 
 side-neck of the ignition-tube, i, and the long tube of each 
 
 1 This is a good size for the student's table. Larger ones may be 
 used by the teacher for the class-room, and a flask may be used 
 instead of the tube i for larger quantities. A set once fitted up is 
 a sort of general gas-works for the laboratory, for, as we shall see, this 
 method of collecting gas can be used for many other gases beside 
 oxygen. 
 
34 
 
 r / / KMICA L CIIA NGEfi. 
 
 of the others with the short tube of the one before it, 
 the last rubber tube simply dipping into the water of the 
 bottle. 
 
 The gas will be "washed" by bubbling through the 
 water in a, and then, too, one can tell by the bubbles in a 
 
 and in e whether 
 the gas is coming 
 off fast or slow, 
 and can regulate 
 the heat accord- 
 ingly. The use 
 of the sand will 
 be seen in Ex. 27. 
 All the flasks 
 must be closed air- 
 tight:; rubber stop- 
 pers easily make 
 air-tight joints. 
 I now go on to make the gas. I make the flame of the 
 Bunsen just high enough to not quite touch the ignition- 
 tube, then lift the lamp and heat the mixture, gently at 
 first, beginning at the part nearest the clamps, and mov- 
 ing the flame to heat the tube uniformly. The decomposi- 
 tion of the chlorate will gradually go on until it reaches the 
 bottom of the tube. If the gas comes off too fast at any 
 time I withdraw the heat for a moment. 
 
 The gas will bubble through the water in ., and grad- 
 ually fill that flask, pushing the air in it over into the next 
 one, b. When a is full, oxygen will go over to the bottom 
 of b, and will gradually fill that flask, pushing the air over 
 into c. From c the air is driven over to d, and from d into 
 e, the oxygen filling them all. One can be sure that the 
 vessels are all filled with this gas by putting a lighted 
 match into the mouth of e ; the flame will be brightened. 
 
 Fig. 19. 
 
CHEMICAL CHANGES. 35 
 
 When this test shows that the flasks are full of oxygen, 1 
 or when all the chlorate is decomposed, if in any case too 
 little is used, I withdraw the flame, and take off the rubber 
 tubes from all the flasks. 
 
 The Chemical Change Potassium chlorate is made 
 
 of potassium, chlorine, and oxygen. It gives up its oxygen 
 when heated, while the other two elements are left in the 
 tube combined with each other. The manganese oxide is 
 unchanged, and yet its presence is very useful, because it 
 compels the chlorate to give up all its oxygen more stead- 
 ily and with less heat. But just how it does this is not 
 known. This is one of the cases in which a substance 
 seems to act by its presence simply. A chemical action 
 like this, that is, one due to the presence of a substance 
 which remains unchanged, is called catalysis. 
 
 To discover the Properties of Oxygen The flasks, 
 
 used in Ex. 23 are full of oxygen. 
 
 What is the color of this gas ? 
 
 The bottle e is also full : what is the odor of oxygen ? 
 
 The bottle has now been standing some time open : is it 
 still full of gas ? If so, then which is heavier, oxygen or 
 air? 
 
 Ex. 24- I remove the stopper from flask d, hold the 
 flask bottom up for two minutes, then stand it on the table 
 and insert a lighted splinter of wood. 
 
 Does the gas remain in the flask? 
 
 Then which is heavier, oxygen or air? 
 
 Was this also shown by the bottle e? 
 
 OXYGEN AND THE MATCH. Ex. 25. I wind a small 
 copper wire (No. 20) around the white end of a burned 
 match. I then heat the black end to a glow, and lower it 
 a little way into the bottle e. The glow promptly becomes 
 
 1 The amount of chlorate used (4 g.) will yield more than enough 
 to fill these four flasks. 
 
CHEMICAL CHANGES. 
 
 a flame. I blow the flame out, and again lower the spark 
 into the oxygen ; the wood is promptly relighted. This may 
 be repeated many times with the same flask full of gas. 
 
 OXYGEN AND CARBON. Ex. 26. I take a piece of char- 
 coal of the bark, if I can get it and twist the end of a 
 piece of fine copper wire around it for a handle. I then 
 heat one corner of the charcoal until it glows and quickly 
 lower it into flask c. After the burning is over I pour a 
 little lime-water into the flask and shake it well. 
 What effect has oxygen on the burning of charcoal ? 
 What effect is produced on lime-water afterwards ? 
 What substance must be present, to do this ? (See p. 17.) 
 OXYGEN AND IRON. Ex. 27. I take a piece of small 
 iron wire (No. 23), and bind a piece of match to one end 
 of it. I then set fire to the match and place it in the 
 mouth of flask a, lowering it slowly 
 as it burns away. The burning 
 wood heats the iron until it too 
 takes fire, and it then burns with 
 surprising brightness. A slender 
 watch spring would burn with still 
 greater beauty. The sand catches 
 the melted globules of iron as they 
 fall, and may save the glass from 
 being broken. 
 
 OXYGEN AND HYDRO- 
 GEN. Ex. 28. Finally 
 in the flask b I will burn 
 a jet of hydrogen. 1 
 make the dry hydrogen 
 as in Ex. 22. The only 
 change in the apparatus 
 is the addition of the tube r t, Fig. 20 ; r is rubber and t is 
 glass, the lower end of which I held in the flame until the 
 
CHEMICAL CHANGES. 37 
 
 hole was nearly closed. Out of this small hole the gas 
 comes in a small jet. After the air has been all driven out 
 I set fire to the hydrogen and then plunge the small flame 
 down into the oxygen in the flask, as shown in the cut. 
 
 What change in the appearance of the flame ? 
 
 What is the new substance on the walls of the flask ? 
 
 What are the two constituents of this substance ? 
 
 What must have combined with the hydrogen in Ex. 22 ? 
 
 Where did the hydrogen there get it ? 
 
 Description of Oxygen. We have found that oxygen 
 has neither color nor odor nor taste. It is about 1.1 times 
 heavier than the same bulk of air. Oxygen combines read- 
 ily with many things. It does so very rapidly when heated, 
 and the chemical action yields both heat and light as well 
 as new substances. A chemical action which yields both 
 heat and light is called combustion. The heat and light of 
 all common fires are due to the action of oxygen, which 
 abounds in the air. 
 
 Bodies which burn at all in air will burn with much 
 more vigor in oxygen alone, as did the match and the char- 
 coal in Exs. 25, 26. And many things which do not burn in 
 air will burn freely in this gas, as did the iron in Ex. 27. 
 
 When a thing is combined with oxygen it is said to be 
 oxidized, and the new substance is called an oxide. Iron is 
 oxidized when it burns in dry oxygen, and the new sub- 
 stance made is the iron oxide. Carbon burned in oxygen 
 (Ex. 26) is oxidized and carbon dioxide is produced, which 
 will show its presence by whitening lime-water. 
 
 But most substances must be heated before they will 
 oxidize rapidly : neither wood nor coal nor iron will burn 
 unless first made much hotter than they can ever become 
 by exposure to the greatest summer heat. And yet the 
 oxygen of the air is all the time acting upon many things. 
 Wood decays and iron rusts ; these effects are due to 
 
Cl I EM 1C A L CHA NGES. 
 
 oxygen. But they are not produced quickly. Substances 
 are oxidized, at ordinary temperatures, slowly. 
 
 Oxygen in Nature. About one fifth part of all the 
 atmosphere is oxygen gas, and eight-ninths the weight of 
 all the water of the earth consists of this element. In 
 the bodies of animals and of plants oxygen is found in 
 large proportions, and in the rocks immense quantities are 
 combined. 
 
 QUERY. A bottle is full of a colorless gas ; how would you 
 decide whether it is air or hydrogen or oxygen? 
 
 Ozone. Oxygen is very strangely changed by the action 
 of electricity. If electric sparks are sent through oxygen, 
 the gas will be found to have a very strong and peculiar 
 smell, a little like that of burning sulphur. This strong- 
 smelling oxygen will tarnish silver, which remains bright 
 in oxygen that has not been electrified, and it will do much 
 other chemical work which common oxygen cannot. Two 
 cubic centimeters of it weighs as much as three cubic centi- 
 meters of oxygen. In weight and odor and in chemical 
 activity this electrified oxygen is as different from common 
 oxygen as if it were another substance. 
 
 And yet it can be nothing but oxygen. For the electric 
 sparks cannot add anything to the pure oxygen they pass 
 through, and so in going through it they cannot make a 
 compound of the oxygen. And if the oxygen was decom- 
 posed by the sparks, there would be at least another con- 
 stituent set free beside this one; but there is not. 
 
 We must confess that oxygen has two sets of properties ; 
 the gas may exist in two distinct forms. The heavy, active, 
 strong-smelling oxygen is called ozone. 
 
 Just how the electricity changes oxygen to ozone is not 
 known. But one thing is settled -by experiment, and that 
 is that the oxygen is condensed ; three volumes of oxygen 
 
CHEMICAL CHANG 
 
 will make only two volumes of ozone. The electricity con- 
 denses the oxygen in making ozone. 
 
 Ozone is also made when acid-water is decomposed by 
 electricity (Ex. 15). It is found in small quantities in the 
 atmosphere, especially after thunder-showers, on account 
 of the electric discharges, and its presence tends to purify 
 the air ; ozone oxidizes the impurities quickly and makes 
 them harmless. 
 
 Oxygen is not the only element 1 which can exist in two 
 forms, as we shall see. This property of an element is 
 called allotropism. Ozone is said to be an allotropic form 
 of oxygen. 
 
 EXERCISES IN CHEMICAL ACTION. 
 
 ! Study the action of hydrochloric acid on sodium car- 
 bonate by experiment. ProcSed as follows : 
 
 1. Bring the two substances together in a test-tube, and 
 describe the action which takes place. 
 
 2. Examine the gas which is given off to find out what 
 it is. 
 
 Note its color and its odor. 
 
 Test it with a flame ; is it oxygen or hydrogen ? 
 
 Is it heavier or lighter than air ? 
 
 Collect a little of the gas in another test-tube. To do 
 this, put a little of the carbonate into a side-neck tube, and 
 put the rubber tube from this down into a test-tube. Make 
 a very dilute acid by putting a cubic centimeter into the 
 graduated cylinder and filling with water up to 25 cc. ; this 
 dilute acid will not work quite so inconveniently fast as 
 the strong. Now pour three or four cubic centimeters 
 upon the carbonate, and cork the side-neck tube quickly. 
 When the action is nearly ended, add the acid again. Next 
 pour a little lime-water into the test-tube with the gas and 
 shake it well. 
 
 1 Sec definition of element on p. 24. 
 
40 CHEMICAL CHANGES. 
 
 What gas does it prove to be? 
 
 3. Examine the liquid which remains in the side-neck 
 tube to learn whether it contains any solid in solution. 
 Filter it (Fig. 9), if it is not already perfectly clear. Then 
 evaporate it (Fig. 10) until it is dry. 
 
 Compare the solid found with the carbonate used. 
 You can recognize this new substance by its taste. 
 
 4. Write out a short statement of the facts which you 
 have discovered about the action of hydrochloric acid on 
 sodium carbonate. 
 
 2. Study the action of hydrochloric acid on "Baking 
 soda." Do this by experiments in just the same way as 
 in Exercise 1. 
 
 What are the two proditcts of the action? 
 What, then, is "Baking soda"? 
 
 3. Study the action of dilute sulphuric acid on iron. 
 Do this by bringing the acid in contact with some very 
 small nails in a test-tube, closing the mouth of the tube, 
 but not quite air-tight, with the finger. Then 
 
 Find out whether the action is hastened by heat. 
 
 If a gas is produced, test it, and name it. 
 
 Find out by evaporation whether a solid is made also. 
 And finally write out a short statement of all the facts 
 which you have discovered about the action of dilute sul- 
 phuric acid on iron. 
 
 4. What is the difference between a physical change and 
 a chemical change? Between experiment and observa- 
 tion ? Between analysis and synthesis ? What are ele- 
 ments ? W T hat are compounds ? What are mixtures ? 
 AVhat, besides new substances, may be produced by chemi- 
 cal action ? What is combustion ? When is a substance 
 said to be oxidized '.' What is an oxide ? 
 
THE CHEMISTRY OF COMBUSTION. 
 
 IN ancient times only four elements were supposed to 
 exist, and these were fire, air, earth, and water. It is now 
 known that neither one of these is an element; and as 
 tojire, we know that it is not even a substance at all. Fire 
 is the light and heat produced by chemical action. The 
 chemical action which produces fire is called combustion. 
 
 Between what elements is this chemical action taking 
 place, and what new substances are made by it? These 
 are the questions we now set out to answer. 
 
 Combustion of a Candle. Ex. 29. I bring a clean and 
 dry bottle down over the flame of a burning candle and 
 hold it there for a little while, as shown in Fig. 21. 
 
 What is the effect on the flame ? 
 
 What gathers on the walls of the bottle ? 
 
 Will lime-water be whitened if shaken in the bottle? 
 
 Thus we find water and carbon dioxide both made by the 
 burning candle. But we know that it takes hydrogen and 
 oxygen to form water (Ex. 28), and also 
 that the air can furnish the oxygen 
 (Ex. 22). So, when the candle burns, the 
 air must furnish oxygen, and the can- 
 dle must furnish hydrogen to form the 
 water which it produces. 
 
 In Ex. 26 we found that carbon diox- 
 ide is made of carbon and oxygen. The 
 carbon dioxide of the candle-flame must 
 contain these same elements. The oxy- 
 gen could come from the air ; the carbon must have come 
 from the candle. Clearly the candle must contain carbon 
 and hydrogen among its elements. And when it burns, 
 
42 CHEMISTRY OF COMBUSTION. 
 
 the chemical action is" between oxygen of the air and these 
 elements of the candle. 
 
 Combustion in other Cases. Ex. 30. Burn a splin- 
 ter of wood, a small roll of paper, a bit of cotton on a wire 
 and moistened with alcohol, and a small jet of gas from 
 the Bunsen lamp, in dry bottles, and see whether you 
 lind the same two products in each case. 
 
 In the burning of a candle, of wood, of paper, of alcohol, 
 of gas, and in f act of all other common fuels, the com- 
 bustion is simply the combination of oxygen with the 
 constituents of these substances. 
 
 Carbon and hydrogen make up by far the larger part 
 of all the substances which are used for fuel, and when the 
 fuel burns carbon dioxide and water are always the chief 
 products. When wood burns it is first decomposed by 
 heat. Its carbon and hydrogen then take oxygen from the 
 air and make carbon dioxide and water-vapor, and these 
 two gases pass away in the smoke. 
 
 Why did the flames all go out in the bottle? 
 
 The black part of smoke is the carbon which goes off 
 without burning. 
 
 A smoky flame is one that gets too little air. A lamp 
 without a chimney smokes, but with a chimney the flame is 
 clear and bright. It is so because the hot chimney makes 
 a current of air sweep past the flame all the time, and this 
 large quantity of air gives oxygen enough to burn the 
 carbon completely. In every common fire much fuel is 
 wasted as smoke, because the furnace is not built in a way 
 to furnish air enough to burn up all the carbon. 
 
 Combustion is a mutual chemical action, generally be- 
 tween oxygen and some other substance, and which, when 
 rapid enough, evolves heat and light. 
 
 When a substance will burn in air, it is said to be cam- 
 
CHEMISTRY OF COMBUSTION. 43 
 
 bustible : the air at the same time is said to be the sup- 
 porter of combustion. But really there is no difference 
 in the part played by the two things in the action : the 
 chemical change is mutual. 
 
 Heat a Product of Combustion Fuel is burned for 
 
 the sake of the heat it can give, and not for the sake of 
 the new compounds which it yields. The hottest kind 
 of flame is that of hydrogen burning with oxygen. It is 
 called the ox //hydro yen flame. 
 
 Fig. 22 shows how this flame is obtained. The two gases 
 are in separate bags, H and 0, or sometimes in iron cylin- 
 
 Fig. 22. 
 
 ders. They are pressed out of these through separate tubes 
 into the " oxyhydrogen jet," where they mix just before 
 they reach the fire at the end of the jet. 
 
 The two gases unite to form water, which goes away as 
 vapor into the air. This chemical action is the source of a 
 heat so intense that wires or strips of iron, steel, copper, 
 zinc, and other things that do not burn at all in common 
 fires, will burn in it almost as fast as a cotton thread will 
 burn in a lamp-flame. 
 
 If we burn hydrogen in air instead of in oxygen the heat 
 is less intense because the chemical action is hindered by 
 the large quantity of nitrogen which air contains. 
 
44 CHEMISTRY OF COMBUSTION. 
 
 The quantity of heat will depend on the quantity of 
 hydrogen which burns. Two grams of hydrogen will yield 
 exactly twice as much heat as one gram, no matter whether 
 it burns slowly or swiftly. But if it burn swiftly, more 
 heat will be given in the same time, and the heat will be 
 more intense. 
 
 If a gram of hydrogen burns in the air instead of in 
 oxygen it will still give the same quantity of heat, and 
 yet the heat will not be as intense even if it burn in the 
 same time, because some part will be used in heating up 
 the large amount of nitrogen in air. 
 
 We may say the same things of the heat when carbon 
 or any other element is burned. The quantity of heat will 
 always be the same for the same weight of the element 
 burned, while the intensity of the heat will depend on the 
 time it takes to burn it. 
 
 But there is this difference, the gram of hydrogen will 
 give more heat than the gram of carbon. There is just 
 a certain amount of heat which the burning of a gram of 
 each element will give, but this quantity is not the same 
 for any two of them. 
 
 Heat Required to Start Combustion A jet of gas, 
 
 such as that from a chandelier, for example, escaping into 
 the air, shows no signs of "taking fire," but touch it witli 
 a match-flame, and it instantly springs into vivid combus- 
 tion. What has the match-flame done ? It has simply 
 heated the gas. Illuminating-gas will not burn until it has 
 a temperature of about 1000 F., and when the fire of the 
 match has heated the jet up to this temperature it bursts 
 into flame. 
 
 The temperature at which a substance begins to burn in 
 air is called its kindling-point. The kindling-point of most 
 of our ordinary fuels is about 1000 F., but some other 
 things begin to burn at a much lower temperature. Phos- 
 
CHEMISTRY OF COMBUSTION. 45 
 
 phorus, for example, kindles at a temperature little higher 
 than that of our fingers when we handle it. 
 
 The kindling-point of a substance is the temperature at 
 which it will begin to burn. 
 
 In lighting a gas-jet the match-flame is needed only to 
 heat the gas up to its kindling-point. 
 
 All Flames are Gas Flames. Let the wick of an alco- 
 hol-lamp be uncovered ; no signs of flame are to be seen, 
 but touch it with a lighted match, and very quickly an alco- 
 hol flame appears. Now, the wick, to begin with, is wet 
 with liquid alcohol. Then the heat of the match changes 
 this liquid into vapor, and afterward, quickly heats this 
 vapor up to its kindling-point. When this double work is 
 done the flame appears. 
 
 The alcohol is in a gaseous form when it burns with a 
 flame. 
 
 We will suppose, next, that we have a candle which has 
 been lighted and partly burned on some previous occasion. 
 Its wick is saturated with cold and solid wax. We touch it 
 with a match-flame. We notice that it takes more time to 
 fire it than it does a spirit-lamp or a gas-jet. The match 
 has more work to do. It first melts the wax ; it next 
 changes it into vapor ; and then, finally, it heats the vapor 
 up to its Idndliny-point. Not until this threefold work is 
 done does the candle-flame appear. The wax is in the form 
 of gas when it burns with flame. 
 
 The wax of the candle, and the alcohol of the lamp, are 
 changed into gases before any flame is seen, and this is 
 true of other fuels also. Whatever burns with a flame must 
 be at that moment in a (/aseous state. 
 
 Wood burns with flame, because it is first decomposed 
 by the heat. Gases are formed, and the burning of these 
 gases, and not of the solid wood, produces the flame. 
 
 Hard-coal is made up almost entirely of solid carbon. 
 
46 CHEMISTRY OF COMBUSTION. 
 
 which no furnace-heat can change into gas. As there are 
 no gases first made by the heat, so there can be no flame 
 produced in the burning. Hard-coal burns with a steady 
 glow without flame. 
 
 This is true if there is plenty of air for all the carbon, 
 but sometimes there is not, and then carbon dioxide is 
 formed, at first, as usual. But this afterward shares its 
 oxygen with more carbon and becomes carbon monoxide. 
 This carbon monoxide is a gas, and burns with a blue flame, 
 which may be often seen playing over the surface of a hard- 
 coal fire. 
 
 Light a Product of Combustion The very hot flame 
 
 of hydrogen gives very little light, but if I hold a small 
 iron wire in this flame the wire will quickly glow with 
 light of a bright-red color. If a piece of lime is held in the 
 oxyhydrogen flame it will shine with a dazzling brightness. 
 The light made in this way is the well-known " lime light," 
 also called the oxyhydrogen light. 
 
 In both these cases the light is made by heating a solid 
 substance which will not melt nor become a gas. Any 
 flame which contains a solid substance which will not 
 melt, nor become a vapor when heated, is a light-giving 
 flame. Is there such a solid substance in a candle or a 
 gas flame? 
 
 Ex. 31. I take a square of clean dry window-glass and 
 hold it for a very short time across a candle-flame, just be- 
 low the tip of it. I must remove it before it gets hot. 
 
 What products are deposited on the glass? 
 
 Ex. 32. I close the holes in the tube of the Bunsen 
 burner and the flame at once becomes bright. I next 
 press a clean dry cold glass down upon it as I did upon 
 the candle-flame before, and notice 
 
 Whether the same products are left on it. 
 
CHEMISTRY OF COMBUSTION. 47 
 
 7r. 33. Open the holes of the Bunsen burner and let 
 the air enter. It mixes with the gas in the tube, and there 
 is then oxygen enough among the particles of gas to satisfy 
 both the hydrogen and the carbon at once. 
 
 Compare the light with that when the holes are shut. 
 
 The candle-flame and the gas-flame both leave a black 
 coat upon the cold surface of the glass, and outside this 
 spot a ring of dew may be seen. The black substance is 
 carbon. The wax of the candle contains hydrogen and 
 carbon. Now, when these two are offered to oxygen the 
 oxygen will take hydrogen first. This is one fact. An- 
 other is, that carbon is a solid which will not melt. 
 
 We can now see how the light of a common flame is 
 made. The burning substance is decomposed into hydro- 
 gen and carbon. The oxygen of the air combines with the 
 hydrogen first, and produces water, and great heat. This 
 heats the particles of the carbon white-hot, so that they 
 shine with a bright light. 
 
 But the next moment this white-hot carbon unites with 
 oxygen of the air, and is changed at once into invisible 
 carbon dioxide. 
 
 If the hydrogen and oxygen both burn at the same in- 
 stant little light is given by the flame. The carbon changes 
 to carbon dioxide as fast as the hydrogen does ; its par- 
 ticles do not remain free long enough to shine. This is 
 also the reason that the Bunsen flame is smokeless. The 
 oxygen of air is mixed all through the gas and burns the 
 carbon as fast as it is set free. 
 
 But the heating of solid particles in a flame is not the 
 only cause of the light. It has been found that some of 
 the light comes from dense gases in the flame as well as 
 from the solid particles. This explains why a lamp-flame 
 is not so bright on the top of a high mountain as it is at the 
 base. The gases in the flames are denser at the base, where 
 
48 
 
 CHEMISTRY OF COMBUSTION. 
 
 the atmosphere is heavier, than they are at the top of the 
 mountain. 
 
 A Common Flame is Hollow. Ex. 34. I lay the 
 stick of a common match right across a good candle-flame, 
 just above the top of the wick, and leave it there only long 
 enough for the flame to scorch it. Where it is not scorched 
 of course there is no fire. 
 
 Where is the fire, as shown by the stick? 
 
 Ex. 35. I take a square of paper and press it down 
 upon the candle-flame almost to the top of the wick and 
 take it away again just as soon as I begin to see the upper 
 surface blacken, as shown in Fig. 23. 
 
 Where is the fire, as shown by the charred paper ? 
 
 
 Ex. 36. The larger flame of an alcohol-lamp is better 
 for the last two experiments than the candle. I plunge 
 
 the head of a match in- 
 to the dark center above 
 the wick. The wood of 
 the match burns in the 
 edge of the flame, but 
 the* head of the match 
 in the center does not. 
 
 What is lacking, heat 
 or air, or both ? 
 
 In a candle or lamp 
 flame the combustion goes on only around the outside, 
 in other words, the flame is hollow. There is no oxygen 
 in the center of the candle or the gas flame. The dark 
 space there is filled with the hot vapor of the wax or 
 with gas, and the combustion goes on only where the air 
 is in contact with the outside of this vapor. 
 
 The burner of a chandelier is made so as to spread the 
 illuminating-gas out into a fan-shaped sheet. This brings 
 
 Fig. 23. 
 
CHEMISTRY OF COMBUSTION. 49 
 
 a larger surface to the air and makes more light, but the 
 chemical action is only on the outside of this thin sheet. 
 The argand oil-burner does the same thing in another way. 
 Its wick is thin and cylindrical, and air is made to pass up 
 through the inside of it. The inside and outside together 
 form a large surface. And then by using a chimney a 
 draught is made by which more air than otherwise must 
 pass up over the surface of the flame. The best light is 
 produced by securing a full supply of air and a large 
 surface to the flame. 
 
 QUERIES. What will be the effect of cooling a flame to a tem- 
 perature below the kindling-point? 
 
 If a large piece of flat iron or stone is laid across a flame, as the 
 paper was laid in Ex. 35, the flame will not touch it ; a thin space 
 between them can be seen (try it). Why does the flame not touch 
 the solid? 
 
 Does a flame actually touch the bottom of a kettle in whicli 
 water is being heated? Why? 
 
 Why will a flame not pass through wire gauze ? But what if 
 the gauze becomes red-hot ? 
 
 Why does blowing a candle quench the flame ? Why does blow- 
 ing a fire make it burn more briskly ? 
 
THE CHEMISTRY OF WATER. 
 
 Analysis and Synthesis. We have seen that there 
 are two ways of finding the composition of a compound : 
 one is called analysis, the other synthesis. In analysis we 
 decompose the compound in such a way as to show what it 
 is composed of, while in synthesis we combine the con- 
 stituents in such a way as to show what they make. 
 
 Experiment 28 was a synthesis of water, because we 
 
 Fig. 24. 
 
 brought hydrogen and oxygen together and found that 
 they produced water when they combined. That experi- 
 ment proved that water is composed of hydrogen and oxy- 
 gen. But this is not enough. We wish to know whether 
 it makes any difference if we use more or less of these ele- 
 ments, and if it does, then we wish to know just how much 
 of each is needed. Now that we know, by synthesis, what 
 the elements of water are, \ve will try, by analysis, to find 
 DO 
 
CHEMISTRY OF WATER. 51 
 
 out whether there is any particular quantity of each, and if 
 so, then how much the water contains. 
 
 Analysis of Water. Ex. 87. How can we decompose 
 water ? We have already found in Ex. 15 that electricity 
 will set hydrogen free from acidulated water, and we will 
 try electricity for our purpose now. 
 
 APPARATUS NEEDED. We must have a battery, B, to 
 furnish the electricity; two wires, w w, to carry the elec- 
 tricity into the water ; two graduated cylinders, to catch 
 the gases, the water-pan and the support. All these are 
 shown in Fig. 24. 
 
 THE BATTERY. Two cells of any good battery will de- 
 compose water slowly, and a larger number more rapidly. 
 If a battery is not at hand, one can be easily made as 
 follows : l 
 
 TO MAKE THE TEST-TUBE BATTERY. Take 20 inches of 
 
 round " carbon pencil, " used in small electric lamps. It 
 should be about ^-inch diameter, and cost a few cents. 
 Saw this into five lengths of four inches each. 
 
 Find five nails, each about the same length as the car- 
 bons, and place them in a dish of dilute sulphuric acid. 
 The acid will dissolve off the smooth, hard surface of new 
 nails, so that they will act quickly when put into the bat- 
 tery-fluid by and by. 
 
 Get some flexible copper wire, No. 18 is a good size to 
 wind easily, and finally also get the rack of test-tubes 
 and a pair of pincers. 
 
 Take a piece of the wire about four inches long, and 
 wind one end of it around the end of a carbon rod twice, 
 as tightly as it can be drawn, and then, lapping the short 
 end over the wire, twist them with the pincers. This 
 makes a close, firm joint. See Fig. 25, c. Then take one 
 
 1 My test-tube battery is cheaply and easily made, and works vigor- 
 ously. It is fairly constant for an hour and a half. It will yield 
 hydrogen from acid-water at the rate of 1 cc. per minute. 
 
52 ciiKuisTiiY OF \\'ATh:n. 
 
 of the nails, ?i, and wind the other end of the wire around 
 it just below the head, drawing the wire as tightly as pos- 
 sible. Roll the wire upon the nail until the carbon and 
 nail are just far enough apart to let the couple hang close 
 against the inside of two tubes when they stand in the rack, 
 as shown at B, in Fig. 25 and Fig. 24. Make four of these 
 couples and hang them in the tubes, so that there will be 
 a carbon and a nail in each, except the first and the last. 
 The carbons and nails must not touch one another. Then 
 fix one carbon without a nail, and one nail without a car- 
 bon, C, Fig. 25. Put the carbon in the tube with the lone 
 nail, and the nail in that with the lone carbon, and put the 
 ends of their wires into the small holes h t Fig. 24, made 
 with an awl in the top of the rack. 
 
 THE WIRES. Cut two strips of platinum foil, each an 
 inch long and a little less than half an inch wide, and two 
 covered copper wires, say twenty. 
 inches long. Make one end of each 
 wire very bright ; crowd it through 
 a small hole near the end of a plati- 
 num strip, bend it back on the other 
 si^le, and press the loop carefully but 
 tightly together to hold the platinum 
 firmly. Now lay a thin piece of solder on the wire where 
 it touches the platinum, moisten it with a drop of hydro- 
 chloric acid, and then hold it in the blue flame of the Bun- 
 sen lamp until the solder melts, and no longer, lest the 
 solder corrode and ruin the foil. In this way the wire and 
 foil will be " soldered " together. 
 
 The ^junctions of the platinum and wires, and so much of 
 the wires themselves as will be in the water, must be well 
 covered with paraffine. Melt some paraffine over a gentle 
 heat, and before the liquid has 'become very hot put the 
 lower end of the platinum and wire into it. 
 See the foot-note on page 54. 
 
CHEMISTRY OF WATER. 53 
 
 THE GRADUATED CYLINDERS. Use two of the gradu- 
 ated cylinders shown at a, in Fig. 1. To support them : 
 saw two slots in a piece of thin board 
 (Fig. 26, ft), and then fasten it in the 
 clamp of the support /, Fig. 5. The 
 cylinders will hang bottom upward 
 through these slots, as shown in 
 Fig. 24. 
 
 THE WATER. Pure water will 
 not let electricity go through it, but 
 if it contains some sulphuric acid the electricity will go 
 freely. Use about one-thirtieth as much strong acid as 
 water, and fill the water-pan deep enough to cover the 
 tops of the platinum strips half an inch when they stand 
 upright, as shown in Fig. 26, a. 
 
 THE BATTERY FLUID. Dissolve 35 g. of powdered po- 
 tassium dichromate in 200 cc. of hot water. Then add 
 24 cc. of strong sulphuric acid very slowly? all the time 
 stirring the liquid. Use it when cold. 
 
 THE EXPERIMENT. Fill the cylinders by laying them 
 in the pan of water, and then, lifting them bottom up, care- 
 fully rest them in their support, as shown in Fig. 24. 
 
 Not a bubble of air should remain in either one. 
 
 Bend the wires to bring the platinum strips up under the 
 mouths of the cylinders, and fix them in place by bending 
 them tightly over the edge of the pan. See Fig. 26, a, and 
 Fig. 24. 2 
 
 1 Great heat is produced by adding the strong acid, and there is 
 danger that drops of the hot liquid will fly out of the vessel. Let the 
 acid run down the side of the vessel in a very small stream while 
 the red liquid is kept in motion. 
 
 2 Or, better, the wires may be passed up behind the cylinders 
 through small holes in the wooden support. The wires may be wedged 
 tightly in these holes, and the platinum strips will then be held in 
 place firmly while the wires are being handled during the experiment. 
 
54 CHEMISTRY OF WATER. 
 
 Next, fill the test-tubes nearly full of the battery fluid, 
 put globules of mercury into the holes h, and finally put 
 the ends of the wires from the water-pan into these holes, 
 noting by the watch the time when the last is inserted. 
 
 Bubbles of gas instantly form on the platinums, break 
 away, and rise into the cylinders; see that none escape 
 outside. 
 
 Note the number of cubic centimeters of gas in each 
 cylinder : 
 
 At the end of 2 minutes. 
 
 At the end of 5 minutes. 
 
 At the end of 10 minutes. 
 
 Do you find the larger quantity over the platinum which 
 is joined to the carbon or to the iron of the battery ? 
 
 Which is Hydrogen and which is Oxygen ? Ex. 38. 
 I test the gases with a match-flame. Holding a lighted 
 match in my right hand, I grasp the cylinder which is 
 over the plantinum of the wire which comes from the iron 
 of the battery, and, closing its mouth as well as I can 
 with my thumb, I lift it out of the water, turn it quickly 
 mouth upward, and at the same time bring the flame to 
 its mouth. The gas burns with explosion. 
 
 I next test the gas in the other cylinder in the same way ; 
 the match burns with unusual brilliancy, or a long splinter 
 of wood with a spark of fire thrust down into the gas 
 bursts into flame. 
 
 What are the relative volumes of hydrogen and oxygen ? 
 
 The Facts The current of electricity decomposes the 
 
 acid water. Hydrogen and oxygen are the only substances 
 produced. And there are always twice as many cubic cen- 
 timeters of hydrogen as of oxygen. 1 
 
 1 Oxygen combines with copper, and if the wires and solder are not 
 completely covered with paraffine where they touch the liquid, some of 
 the oxygen will be used up in this way. 
 
CHEMISTRY OF WATER. 55 
 
 These facts mean that water is made up of two measures 
 of hydrogen and one measure of oxygen. 
 
 A Source of Doubt But the water was not pure, and 
 
 some part of these gases may have come from the acid in it, 
 or have been used up by it. So this analysis alone does not 
 prove the composition of water beyond doubt. In fact, it is 
 only one source of evidence, while there are many others. 1 
 We may mention one. By measuring the hydrogen and 
 oxygen gases, and then passing an electric spark through 
 the mixture, they are made to combine, and in every case 
 it is found that just twice as many cubic centimeters of 
 hydrogen as of oxygen have been used to produce water. 
 
 All the facts when taken together prove that pure water 
 is composed of 
 
 Two volumes of hydrogen and one volume of oxygen. 
 
 Composition by Weight. But hydrogen is much 
 lighter than oxygen. In fact, it is found that one measure 
 of oxygen weighs eight times as much as the two measures 
 of hydrogen. So that by weight, pure water is composed of 
 
 One part of hydrogen and eight parts of oxygen. 
 
 One ninth part of any weight of water is hydrogen, and 
 the other eight ninths of it is oxygen. 
 
 Then how much of each must there be in 100 grams ? 
 One ninth of a hundred, or 11.11 of hydrogen, and eight 
 ninths of a hundred or 88.89 of oxygen. The chemist 
 writes this composition of water thus: 
 
 Hydrogen 11.11 
 
 Oxygen 88.89 
 
 Water 100.00 
 
 And this is called the percentage composition of water. 
 Composition by Volume. We have just seen that 
 water when it is decomposed yields just twice as many 
 1 See Roscoe and Schoiiemmer, pp. 204, 212. 
 
56 CHEMISTRY OF WATER. 
 
 cubic centimeters of hydrogen as of oxygen. When we 
 had 20 cc. of hydrogen we had also just 10 cc. of oxygen. 
 But we did not notice how much water gave us the 20 cc. 
 of one and the 10 cc. of the other. The fact is that it 
 takes only about fa part of 1 cc. of the liquid, and this is 
 so small a quantity that we do not see the loss of it in 
 the experiment. 
 
 But while 20 cc. of hydrogen and 10 cc. of oxygen will 
 make so little of the liquid water, they will of course make 
 a great deal larger volume of water vapor. It has been 
 found that they will make just 20 cc. The volume of the 
 water, in vapor, is just the same as the volume of the 
 hydrogen alone. The fact is that 
 
 Two measures of hydrogen and one measure of oxygen 
 make two measures of water-vapor. Or three volumes of 
 the constituents are condensed to two volumes of the com- 
 pound. 
 
 Make a note of this curious fact. 
 
 The Constant Composition of Water Water has 
 
 been analyzed over and over again with the same result. 
 The synthesis of water also has been repeated a great many 
 times, and the same proportions of the same elements have 
 always been found. It is, therefore, quite certain that pure 
 water is always made up of the same elements and in the 
 same proportions by volume and by weight. 
 
 The Constant Composition of other Compounds. 
 We may mention hydrochloric acid. It has been proved 
 by both analysis and synthesis that this acid is always 
 made up of hydrogen and chlorine, in the proportions of 
 1 part by weight of hydrogen to 35.5 parts of chlorine. 
 Its composition is as constant as that of water. 
 
 And common salt, from whatever source it comes, always 
 contains the same two elements, chlorine and sodium . 
 and always in the proportions of .'>.">. 5 parts of chlorine to 
 23 of sodium. 
 
CHEMISTRY OF WATER. 57 
 
 The Law of Constant Proportions. So many com- 
 pounds have, like these just named, been found to have a 
 constant composition, that the chemist is quite sure that 
 all compounds are alike in this respect, and he states this 
 conclusion as follows : 
 
 Any compound is ahvays made of the same constituents 
 and in the same invariable proportions. 
 
 This important statement of fact is known as the law of 
 constant proportions. 
 
 Water in Nature. Hydrogen and oxygen are the only 
 constituents of all pure water. Bat pure water 
 is not to be found in nature. Even the rain- 
 drop, which has never touched anything but the 
 air through which it falls, is not pure, and it is 
 still more impure after it has touched the earth. 
 Why is water always impure ? And what are 
 its impurities ? These are the questions which 
 we will try next to answer. 
 
 ]$ Xt QQ^ I fill a bottle three-fourths full of clear water. 
 I cover it with a piece of muslin loosely, and bind the cover 
 in place by a string around the neck. I put half a tea- 
 spoonful of powdered cochineal 011 the cover, and then pour 
 some clear water slowly upon it. The water very soon 
 trickles through the cover and falls into the water below. 
 But instead of being clear and colorless, it falls from the 
 cover in a crimson stream. Why ? 
 
 Ex. 40. I repeat Ex. 39, but in place of the cochineal 
 I use some powdered copper sulphate. The stream which 
 falls into the water is Hue. Why ? 
 
 Ex. 41. I prepare a flask of hydrochloric acid gas in 
 this way : I put 40 or 50 cc. of strong hydrochloric acid into 
 a side-neck flask, /, Fig. 28, and fix the flask in the clamp of 
 the support. 1 join the side-neck to the long tube of the 
 
58 CHEMISTRY OF WATER. 
 
 flask a, and the short tube of a with the long tube of b. 
 And now, all the joints being tight, I gently heat the acid. 
 
 Hydrochloric acid gas will 
 go over, driving the air be- 
 fore it, until the flasks are 
 full. When the gas issues 
 freely from b it will make 
 itself known ; then I with- 
 draw the flame, and at once 
 take both rubber tubes from 
 a. I then take the stopper 
 from the flask, and at the 
 same time cover its mouth 
 2 8- with the palm of my hand. 
 
 I now turn the flask bottom upward and lower its mouth 
 into t^e water of the pan, as shown in Fig. 29. The water 
 rises it should rise quickly into the flask. Why ? 
 
 Cochineal readily mixes with water, and gives it a crim- 
 son color. And yet not a particle of 
 cochineal can be seen in the crimson 
 liquid. It is divided into pieces too 
 small to be seen, and these pieces are 
 uniformly scattered, giving color to 
 every part. The cochineal was dis- " 29 
 
 solved by the water. The red liquid (Ex. 39) is a solution 
 of cochineal in water. 
 
 Water also dissolves copper sulphate (Ex. 40), and the 
 solution is blue. 
 
 Salt is also soluble in water; but its solution, brine, is 
 without color. A vast number of other solids are more or 
 less soluble in water. Some of them give it color ; others 
 give no visible sign of their presence. The most colorless 
 water may hold many and a great deal of these soluble 
 bodies. They arc its impurities. And all water that has 
 
CHEMISTRY OF WATER. 59 
 
 been in contact with soil and rock holds more or less of 
 these impurities. 
 
 Gases also are soluble in water. Hydrochloric acid gas 
 dissolves in large quantity (Ex. 41) ; 100 cc. of water will 
 take up 45,000 cc. of this gas at a temperature of 15 C., 
 more if it be colder and less if it be warmer. Hydrogen is 
 slightly soluble in water, oxygen a little more so ; 100 cc. 
 of water will take only about 3 cc. of oxygen. Water ab- 
 sorbs the gases of the atmosphere. These also are impuri- 
 ties in all natural water. 
 
 Mineral Waters. When water holds enough of any 
 one thing in solution to give it a peculiar taste it is called 
 mineral water. Such a water receives the name of the 
 substance in it, and so does the spring from which the 
 water issues. Sometimes a spring yields water in which 
 compounds of iron are dissolved ; it is then called an iron 
 spring, or a clialybeate spring. Sometimes the compounds 
 of sulphur are present in large quantity ; the water is then 
 a sulphur-water. 
 
 When water holds much lime or magnesia compounds in 
 solution it is called hard water ; when nearly free from 
 these it is called soft water. 
 
 Drinking- Water. Good water for household use always 
 contains air in solution. On standing quietly in a warm 
 place a vessel of water will show bubbles of air clinging to 
 the inside surface. Try it. This air if pure is not only 
 wholesome but helps to make the water palatable. But 
 water will absorb bad gases as freely as the good ; drinking- 
 water should not be allowed to stand in bad air. 
 
 Water which holds a small quantity of mineral matter in 
 solution is also wholesome, but never when it contains ani- 
 mal substances. Typhoid fever, diphtheria, and some other 
 diseases, are frequent where the Avater used in households 
 is charged with even very small quantities of animal sub- 
 stances. 
 
60 CHEMISTRY OF WATER. 
 
 Vegetable matter is less dangerous than animal matter, 
 but when much is present it likewise makes the water unfit 
 for household purposes. 
 
 Water which holds fine particles, whose impurities are 
 in the form of sediment, may be purified by filtration. On 
 a large scale, the water for cities is filtered through beds 
 of sand and gravel. 
 
 But the most deadly impurities of water are often in 
 solution, and these no such filter can take out. Charcoal- 
 filters may remove small portions, but they cannot be 
 trusted to purify bad waters for household use. 
 
 Distillation. Pure water can be obtained by boiling 
 common water and catching the steam in a cold vessel. 
 This process is called distillation. 
 
 Ex. Jf2. I place 50 cc. of water in my side-neck flask 
 and close it with a cork through 
 which I have pushed the stem of a 
 thermometer, as shown in Fig. 30. 
 To the side-neck I join a long glass 
 tube by slipping a short piece of 
 rubber tube over the end of each. 
 I put the end of 
 the glass tube 
 down into a test- 
 tube, which I lay 
 in the water-pan 
 nearly filled with 
 Fig - 30 - cold water, and 
 
 finally I heat the flask with a Bunsen lamp. 
 
 Note every effect you can see while the water is being 
 heated. 
 
 Keep watch of the mercury in. the thermometer before 
 the water boils. 
 
CHEMISTRY OF WATER. 
 
 61 
 
 Keep watch of the mercury in the thermometer after the 
 water boils. Note the temperature. 
 
 What happens in the test-tube ? 
 
 The Pacts. Long before water boils bubbles may be 
 seen escaping from it; these are bubbles of air which was 
 in solution. Afterward the water boils and the steam goes 
 over into the test-tube, where it is at once changed back 
 into water by cold. But it is only the water which goes 
 over as steam ; the solid impurities stay in solution in the 
 flask because they need so much more heat than water does 
 
 Fig. 31. 
 
 to change them into vapor. The water in the tube is nearly 
 pure; it is called "distilled water." And this way to 
 purify a liquid is called distillation. 
 
 The thermometer shows that in this process the water 
 becomes hotter and hotter until it boils, but not afterward. 
 When the thermometer marks 100 C. it goes no higher, 
 though the water boil never so hard. This temperature is 
 called the boiling-point of water. On a Fahrenheit ther- 
 
62 
 
 CHEMISTRY OF WATER. 
 
 mometer this point is marked 212. Other liquids also are 
 purified by distillation. 
 
 Fig. 31 shows a complete apparatus, used by chemists, 
 for the distillation of liquids. The liquid is boiled in the 
 flask. Its vapor goes through the inside tube of the con- 
 denser c, while .the larger tube outside it is kept full of 
 cold water. Here the vapor is changed back to liquid 
 
 Fig. 32. 
 
 and this liquid drops into the receiver R. Rubber tubes 
 carry the cold water to and from the condenser c. A ther- 
 mometer, t, may be used to show the boiling-point of the 
 liquid. 
 
 Effects of Cold. A given weight of water, say 10 g., 
 will grow smaller and smaller as we make it colder. Its 
 
CHEMISTRY OF WATEK. 63 
 
 volume will be less and less until its temperature is 4 C. 
 But if we cool it below this point the water will expand. 
 Its volume will then become greater and greater quite 
 regularly until it is cooled down to C. At the water 
 suddenly expands much more, and at the same time it 
 begins to freeze. This temperature at which water freezes 
 is called the freezing-point of water. It is C. or 32 F. 
 
 Ice is crystallized water. In blocks of ice the crystals 
 are so crowded together that their forms are lost. The 
 shapes of ice-crystals are seen in the beautiful frost-figures 
 on the window-pane in winter and in snow-flakes, some of 
 whose curious forms are shown in Fig. 32. 
 
 EXERCISES. 
 
 1. Study the effect of mixing snoiv and salt. 
 
 Take snow or pounded ice, add salt gradually, stirring 
 the two well together. 
 
 What change takes place in the two solids ? 
 Get the temperature of the mixture. 
 
 2. Compare the freezing and melting points of water. 
 
 1. Put a small bottle or a test-tube partly filled with 
 water into the freezing mixture just made, and stir this 
 water with the bulb of a thermometer carefully until it 
 begins to freeze. 
 
 At what temperature does the freezing begin ? 
 Does the temperature change afterwards ? 
 
 2. Fill a wide-mouth bottle with small pieces of ice and 
 let it stand. Afterward stir the ice about in the water 
 and take the temperature of the mixture. 
 
 At what temperature does the ice melt ? 
 Repeat these two experiments and decide whether they 
 show that there is, or is not, a difference between the 
 melting-point of ice and the freezing-point of water. 
 
64 CHEMISTRY OF WATER. 
 
 3. Find the boiling-point of alcohol. Fig. 30. 
 
 4. Find the boiling-point of a mixture of alcohol and water 
 
 made in the proportion of one volume of alcohol to 
 two volumes of water. 
 
 Use the apparatus shown in Fig. 30. 
 
 Note the temperature when the boiling begins. 
 
 Turn the lamp low and let the boiling go on slowly 
 until about 5 cc. of distillate is caught. Then change the 
 test-tube. 
 
 Note the boiling-point again. 
 
 Repeat this several times, and then compare the distil- 
 lates, by their odors and by means of a match-flame. 
 
 Which contains the most alcohol ? 
 
 Does the liquid in the flask still contain alcohol ? 
 
 The fact is that two liquids which have not the same 
 boiling-point can be roughly separated by this process of 
 distillation. It is called fractional distillation. 
 
 5. Find by evaporation, whether the water in use holds any 
 
 solid matter in solution. 
 
 How, by the use of the balance and the graduated cylin- 
 der, can you find how much of this mineral substance the 
 water contains? 
 
CHEMISTRY OF THE ATMOSPHERE. 
 
 NOT one hundred years ago the air was thought to be an 
 element ; that it is not was proved by the great French 
 chemist Lavoisier. 
 
 Lavoisier's Experiment. The apparatus which he used 
 was much like that shown in Fig. 33. A small quantity of 
 pure mercury was put into a flask which was placed over 
 a furnace. The flask had a long, slender neck, which 
 
 Fig. 33. 
 
 reached over into a pan of mercury. Standing mouth 
 downward in this pan was a jar filled with air, and the 
 neck of the flask was bent up into it. 
 
 When all was ready, Lavoisier lighted the fire in the 
 furnace and kept it burning all the time for twelve days. 
 On the second day he saw little red flakes of something 
 swimming around on the surface of the mercury. For four 
 or five days afterward the quantity of this red substance 
 
 65 
 
f>G CHEMISTRY OF 7777? ATMOSPHERE. 
 
 increased while the quantity of air in the receiver dimin- 
 ished. For some time longer the heat was kept up, but no 
 further change took place, and this part of the work was 
 done. He had less air in the apparatus than at first, shown 
 by the mercury rising in the jar, but instead of the air 
 which was lost he had the new red substance in the flask. 
 
 What was this red substance? To find out, Lavoisier 
 heated it in a tube so fixed that any gas which should be 
 produced would be caught in a vessel over mercury. The 
 red substance became black, then began to waste away 
 while bubbles of a colorless gas were caught in the vessel 
 prepared for the purpose, and globules of shining mercury 
 gathered on the walls of the tube above the heated part. 
 What was the colorless gas ? Lavoisier plunged a candle- 
 flame into it; the candle burned with a dazzling light. 
 The gas was oxygen. 
 
 But whence came this oxygen to combine with the mer- 
 cury when it was heated with air in Lavoisier's flask ? The 
 air must have given it to the mercury, and so the experi- 
 ment proved that oxygen is one constituent of air. 
 
 In the flask and the glass jar (Fig. 33) there was still left 
 a large quantity of air-like substance. But on plunging a 
 candle-flame into it the flame was put out as it would have 
 been in water. Plainly it was not air. In fact it was the 
 gas called nitrogen. 
 
 Lavoisier's experiment proved that oxygen and nitrogen 
 are two constituents of air. There are indeed a few other 
 gases in the atmosphere beside these, but in comparison 
 with these the quantity of them is small. Oxygen and 
 nitrogen are the two chief constituents of the air. 
 
 NITROGEN. 
 
 When a substance burns in air .it takes the oxygen and 
 leaves the nitrogen. Lavoisier burned mercury, but sul- 
 
CHEMISTRY OF THE ATMOSPHERE. 67 
 
 phur and some other things will burn more quickly, and 
 may be used instead. Let us try sulphur, and afterward 
 phosphorus. 
 
 Ex. 43. I cut a slice half an inch thick from a cork 
 which is much smaller than the 
 mouth of my bottle. I shape the 
 top of the cork into a shallow cup 
 and rub it well with crayon-powder, 
 or better with a paste of moistened 
 plaster of Paris. I put sulphur in 
 this cup, place the cup on the shal- 
 low water in the water-pan, set fire 
 
 to the sulphur, and put a bottle bottom upward over it, as 
 shown in Fig. 34. Describe 
 
 The flame of the sulphur. 
 
 The action of the water when the burning is over. 
 
 The change in the gas after long time standing. 
 
 Ex. 44. I use a piece of phosphorus, not larger than a 
 good-sized kernel of wheat, with another bottle holding 
 about 200 cc. I treat it just as I did the sulphur, and 
 again describe the flame, the action of the water afterward, 
 and the appearance of the gas inside after standing some 
 time over water. 
 
 But the handling of phosphorus is dangerous, unless it 
 is done with great care. Phosphorus takes fire easily and 
 burns the flesh cruelly. Cut it under water, lift the piece 
 with the knife-blade, dry it by gentle contact with filter- 
 paper, and put it into a dry cup. Never handle phosphorus 
 without using the greatest care. 
 
 Ex. 45- When the gas in the bottle used in Ex. 43 has 
 become clear I slip a square of glass or of cardboard under 
 the mouth of the bottle, lift it out of the water, turn it 
 mouth upward, stand it on the table and leave it covered. 
 
68 CHEMISTRY OF THE ATMOSPHERE. 
 
 I at once ignite a match, uncover the bottle, and insert 
 the flame ; the nitrogen will quench it. I leave the bottle 
 uncovered. I treat the bottle used in Ex. 44 in the same 
 way ; the nitrogen again puts out the flame. I leave this 
 bottle, also, uncovered. 
 
 Ex. 46- I now again insert a match-flame in the bottle 
 first left uncovered, and afterward in the other. The flame 
 is not quenched. 
 
 What does this prove? 
 
 Ex. 47. I now add a little blue litmus-water to the 
 water in the bottle in which sulphur was burned. 
 
 Note the change of color. Compare Ex. 8. 
 
 What causes this change of color? 
 
 Ex. 48. I add blue litmus-water to the water in the 
 second bottle which was left uncovered in Ex. 45; it 
 changes from blue to red. 
 
 Can you explain this change of color ? 
 
 Burning of Sulphur Sulphur, when burning with its 
 
 feeble blue flame, combines with oxygen, and the two 
 become sulphur dioxide. The water soon dissolves the 
 whitish vapor and rises into the vessel, and at last fills 
 just the space which the oxygen of the air occupied at 
 first, while the nitrogen of the same air remains above the 
 water (Ex. 43). 
 
 The sulphur dioxide shows its presence in the water by 
 reddening the blue litmus, Ex. 47, as it did in Ex. 8. 
 
 Burning of Phosphorus. When phosphorus is used 
 the action is much the same. It combines with the oxy- 
 gen of the air and forms phosphoric oxide, which fills the 
 vessel as a milk-white vapor. Water soon dissolves this 
 oxide, and the nitrogen of the air is left as before. 
 
 The phosphoric oxide also shows its presence in the water 
 by reddening blue litmus (Ex. 48). 
 
CHEMISTRY OF THE ATMOSPHERE. 69 
 
 Properties of Nitrogen Nitrogen is a colorless gas 
 
 (Exs. 43, 44). It is lighter than air (Ex. 46), but a liter of 
 it weighs fourteen times as much as a liter of hydrogen. 
 It will quench fire (Ex. 45), because it cannot unite with 
 the elements of the fuel as oxygen does. In fact, nitro- 
 gen is the least active of the elements. It will not only 
 quench fire, but if breathed instead of air it will quench 
 life also. Yet it cannot be poisonous, since we inhale it 
 with every breath without injury. It is the oxygen of the 
 air that sustains life, and it is the absence of oxygen, and 
 not the presence of nitrogen, which causes death when pure 
 nitrogen is breathed. 
 
 Other Constituents of Air. The air also contains 
 water in form of invisible vapor. This is proved by placing 
 a piece of caustic potash in an open dish. The potash 
 will very soon become wet, and if left for some time it 
 will be dissolved by the water which it takes from the air. 
 Try it. The moisture to be seen on the outside of a vessel 
 of ice-water in summer is the condensed water-vapor of the 
 air. Dew and hoar-frost are also the water of the air, 
 changed by cold from vapor to liquid and solid forms. 
 
 The air also contains carbon dioxide. This is shown by 
 lime-water, which if left exposed in an open vessel will 
 become covered in a few hours with a white crust. Try it. 
 This crust is the same substance which is seen in lime- 
 water after it has received carbon dioxide (Ex. 7). 
 
 The air also contains ammonia in very small quantities. 
 
 Nitrogen, oxygen, water-vapor, carbon dioxide, and am. 
 monia are the regular constituents of the atmosphere. Our 
 next question is, How much of each of these substances is 
 to be found in air ? 
 
 The Analysis of Air. We set out now to find how 
 many cubic centimeters of nitrogen and how many of oxy- 
 gen and carbon dioxide there are in 100 cc. of air. 
 
70 
 
 CHEMISTRY OF THE ATMOSPHERE. 
 
 To do this we will imprison a vesselful of air, and then 
 run into it a liquid which will absorb both the oxygen and 
 the carbon dioxide completely, and leave the nitrogen. We 
 can then measure the nitrogen which is left, and we can 
 find out how much there was of the other two, by measur- 
 ing the liquid which has gone into the tube to take their 
 place. 
 
 Ex. 49- OUR APPARATUS. I take a test-tube, t (Fig. 
 35) to hold the air. A six-inch tube, f inch in 
 j diameter, will do; an eight-inch tube of the same 
 \| diameter is better. The rubber stopper, c, is so 
 large that its small end will enter the tube only 
 about a half-inch. It has two holes ; to close 
 
 fone I have a solid rod of glass, s ; for the other, 
 a glass tube reaching just a very little below the 
 cork, as shown. A piece of thin rubber tubing, 
 &, A, is cut about six inches long. There is a pinch- 
 fp* cock, p, by which its walls may be pinched so as 
 Fi. 35. c ] ose ft completely. F is a small glass funnel. 
 The lower end of h I stretch over 
 the tube in the cork c, and its upper 
 end I fix over the stem of F, and then 
 I place the funnel in the clamp of the 
 support, as shown in Fig. 36, and re- 
 move the rod s. 
 
 THE LIQUID. To absorb the oxy- 
 gen and carbon dioxide gases I use 
 a mixture of pyrogallic acid and po- 
 tassium hydrate. 
 
 I take a small teaspoonful of the 
 solid acid and pour on it 10 cc. of 
 water ; it will soon dissolve. To this 
 I then add 5 cc. of strong solution of potassium hydrate, 
 and at once pour it into the funnel. Next, I hold the dish 
 
 Fig. 36. 
 
 
CHEMISTRY OF THE ATMOSPHERE. 
 
 71 
 
 Fig. 37. 
 
 below the cork and open the pinch-cock p a moment, to 
 
 let the liquid run down and fill the tubes completely. I 
 
 carefully take off the drop, which hangs 
 
 at the lower end of the tube below the 
 
 cork, with a piece of filter-paper. 
 
 I press the tube t up over the cork 
 
 until the joint is air-tight, as seen in 
 
 Fig. 37, and after a minute I put the 
 
 rod s into the open hole of the cork. 
 
 I have now imprisoned a tubeful of air ; 
 
 none can get out, and no more can 
 
 get in. 
 
 I left the hole in the cork open, be- 
 cause if it were not open the pressure 
 
 of the cork would crowd the air below, 
 
 and there would be too much in the 
 
 tube; and then, too, handling the tube warmed it, and the 
 volume of air changes with heat. 
 With the hole open, the air in the 
 tube soon comes to be just as warm 
 and just as much pressed as the air 
 outside. Whenever a gas of any kind 
 is to be measured its temperature and 
 pressure must be the same as those of 
 the air outside. 
 
 THE ABSORPTION. I now press 
 the pinch-cock p ; a little stream of 
 the liquid falls into t at once, and 
 then drops follow, or, if the tube be 
 slightly inclined, a slender stream will 
 flow down its side. It will continue 
 to enter as long as there is any oxy- 
 gen or carbon dioxide for it to absorb, and then stop. 
 
 The gas which is left in the tube is nitrogen. 
 
 Fig. 38. 
 
72 CHEMISTRY OF THE ATMOSPHERE. 
 
 But this gas is crowded down by the pressure of the 
 liquid in the rubber tube and funnel above, and so I take 
 hold of the cork c, and the rim of t, not to warm the gas 
 with my hand, and lift the tube bottom up, as shown at 
 T in Fig. 38, making the level of the liquid the same in 
 the tube and in the funnel. I then open the pinch-cock. 
 Some of the liquid will run out of T. When the liquid 
 stands at the same level in the tube and in the funnel, I 
 close the cock and bring the tube down again. 
 
 The almost black liquid in t has now taken out all the 
 oxygen and carbon dioxide from the tubeful of air, and 
 left all its nitrogen. 
 
 THE MEASURING. I must measure the liquid in the 
 tube to find how much oxygen was taken out, 1 and the 
 space above it to find how much nitrogen was left. 
 
 To do this I slip two small rubber rings up on the tube, 
 and make the upper edge of one mark the place of the 
 lower end of the cork, and of the other, the top of the 
 liquid. These rings must not afterward be disturbed. 
 
 I may now remove the cork, empty the tube, rinse it 
 with water, and then let the last drop of water drain away. 
 Finally, I use my graduated cylinder to find out exactly 
 
 How many cc. water will fill the tube to the first ring. 
 
 How many cc. water will fill the tube from the first to 
 the second ring. 
 
 THE CALCULATIONS. From these two numbers we can 
 find what part of the air is nitrogen and what part is 
 oxygen. For they help us to answer the following 
 questions, in their order, one after another, as shown 
 by an example below. 
 
 1 And carbon dioxide also. But the volume of the carbon dioxide, 
 in so small a quantity of air as we use, is so little that we cannot 
 measure it with our apparatus. We. may leave it out of account in 
 this experiment. 
 
CHEMISTRY OF THE ATMOSPHERE. 73 
 
 How many cc. of air were in the tube at first? 
 How many cc. of nitrogen did this air yield ? 
 How many cc. of oxygen did the same air yield? 
 Then what fractional part of the air is nitrogen? 
 What fractional part of the air is oxygen ? 
 And how many cc. nitrogen in 100 cc. of air ? 
 How many cc. of oxygen in 100 cc. of air ? 
 
 An Example. In an actual experiment it was found 
 to take of 
 
 Water to fill the tube to the first ring 6.0 cc. 
 
 Water to fill the tube from the first to second ring . 23.5 cc. 
 
 Hence the number of cc. of air taken 29.5 cc. 
 
 And the number of cc. of nitrogen found .... 23.5 cc. 
 And the number of cc. of oxygen found .... 6.0 cc. 
 
 Now this would show plainly that f $g of the air is nitro- 
 gen and 2%% of it is oxygen. Then in 100 cc. of air there 
 would be 
 
 Nitrogen 79.66 cc. 
 
 Oxygen 20.34 cc. 
 
 The Exact Composition of Air Some of the great- 
 est chemists have devoted much time to find out exactly 
 how much oxygen and nitrogen the air contains. The}' 
 have used other methods, more accurate than that of al> 
 sorption, and apparatus much more refined than that which 
 has answered our purpose. 1 They have found the per- 
 centage composition to be 
 
 Nitrogen 79.04 
 
 Oxygen 20.96 
 
 Air 100.00 
 
 1 For full description, see Roscoe and Schorleinmer, Vol. I. pp. 
 439-447. 
 
74 CHEMISTRY OF THE ATMOSPHERE. 
 
 When the gases are weighed instead of being measured 
 the numbers are different. Thus : 
 
 Nitrogen 77.00 
 
 Oxygen 23.00 
 
 Air 100.00 
 
 How much Water-vapor in Air? The quantity of 
 water-vapor in the air is all the time changing. There is 
 only a certain amount which air can hold at any given 
 temperature, and the only way to make it able to take 
 any more is to heat it. 
 
 But the atmosphere seldom has all that it can hold. 
 At 60 F. the quantity will be usually found between ^ 
 and ?fo of the bulk of the air. 
 
 "What Fraction of the Air is Carbon dioxide? 
 Sometimes as much as y^^ of the air is carbon dioxide; at 
 other times or places there may be no more than 5^0 . 
 Perhaps the average proportion may be 55^- 
 
 So small a quantity as one cubic inch of this gas in 
 twenty-five hundred cubic inches of air seems, at first 
 thought, too small to be worthy of notice. It is not so. 
 Carbon dioxide, little as there is of it, is one of the most 
 important substances in the atmosphere. Plants cannot 
 grow without it. It is a needful part of their food, and 
 they are, when growing, all the time taking it out of the 
 atmosphere. It is returned to the air by the breathing of 
 animals, by the burning of fuels, by the decay of plants, 
 and by volcanos. 
 
 We will shortly make a special study of this gas, but for 
 the present we go on with the description of air. 
 
 The Atmosphere a Mixture or a Compound ? It is 
 found that the carbon dioxide of the air makes lime- 
 water turbid just as the same gas from marble will do. The 
 water-vapor in the air may be condensed to liquid by cold, 
 
CHEMISTRY OF THE ATMOSPHERE. 75 
 
 just as water-vapor alone may be. Bodies burn in oxygen ; 
 they burn also in air, of which oxygen is a constituent 
 Nitrogen alone extinguishes fire completely, and nitrogen 
 in the air strives to do so, but succeeds only in making 
 them burn more feebly in the oxygen which is present. 
 In fact, the properties of the constituents of air can be 
 easily detected in the atmosphere itself. 
 
 But when substances combine they form a compound in 
 which their own properties are not to be found. We 
 therefore say that the atmosphere is not a compound, but 
 a mixture. 
 
 Constant and Uniform in Composition The pro- 
 portions of oxygen, nitrogen, and carbon dioxide are always 
 very nearly the same. Air on the tops of mountains, and 
 in the low places of the earth, and in different countries, 
 have all these constituents, and very nearly the same rela- 
 tive quantities of them. 
 
 The heavy carbon dioxide, the lighter oxygen, and the 
 still lighter nitrogen, are uniformly mixed together. Why 
 do they not separate into layers, as water and oil would do 
 after having been mixed never so perfectly? 
 
 Diffusion of Gases The fact is that gases will not 
 
 stay unmixed if they touch each other. We 
 may bring a light gas on top of a heavy one, 
 and find that a part of the light one will 
 sink, and a part of the heavy one will rise, 
 until the two are completely mixed. 
 
 Ex. 50. I will bring hydrogen to rest on 
 top of air. I select two wide-mouth bottles, 
 each holding about 200 cc., one with a neck 
 a little smaller than that of the other, so Fig - 39 - 
 that they may be put together, as in Fig. 39. The upper 
 bottle is to be filled with hydrogen, the lower one with air. 
 
 To FILL THE BOTTLE WITH HYDROGEN. I first fill it to 
 
76 CHEMISTRY OF THE ATMOSPHERE. 
 
 the brim with water ; cut a piece of heavy blotting-paper a 
 little larger than its mouth and slide it on as a cover and 
 smooth it down closely upon the glass (Fig. 40, a). I grasp 
 the bottle and turn it bottom upward over the pan, B, 
 lower it into the water, remove the paper cover, and 
 stand the bottle bottom upward in the water. The press- 
 ure of the atmosphere will safely hold the water in the 
 bottle while I invert it, and while its mouth is under water 
 in the pan. 
 
 I now put a few clippings of zinc into a side-neck flask 
 and fix the flask in the clamp, then join one end of a 
 
 Fig. 40. 
 
 rubber tube to the side-neck, the other to a glass tube 
 which reaches into the water of the pan. I pour some 
 dilute hydrochloric acid (half water) into the flask and cork 
 the neck at once. As soon as the air is driven out of the 
 flask I put the end of the glass tube under the mouth of 
 the bottle, 1 and collect the hydrogen as shown in Fig. 40. 
 
 1 A little shelf for the bottle to stand on may be made by bending 
 the ends of a strip of sheet-iron down to serve as feet to stand on the 
 bottom of the water-pan. 
 
CHEMISTRY OF THE ATMOSPHERE. 77 
 
 When the bottle is filled with gas I again slide the cover 
 of blotting-paper under its mouth, and hold it there while 
 I lift this bottle arid carry it over the mouth of the other. 
 I then remove the paper, and at once let the mouth of this 
 hydrogen-bottle down into that of the air-bottle, as shown 
 in Fig. 39. 
 
 After waiting ten minutes I lift the two bottles, hold 
 them over the water-pan, then separate them, and quickly 
 put them both, mouth down, in the water. 
 
 With a lighted match in one hand, I lift the hydrogen- 
 bottle and bring the flame to its mouth ; a small explosion 
 follows. I treat the air-bottle in the same way ; there 
 is another explosion. These explosions show that there 
 was a mixture of hydrogen and air in each bottle. 
 
 Now air is almost 14.5 times heavier than hydrogen, and 
 yet, to make that mixture, it must have risen into tho 
 upper bottle while the lighter hydrogen must have fallen 
 into the lower one. They have mixed in spite of their 
 difference in weight. 
 
 This mingling of gases, when they are simply brought 
 into contact with one another, is called the diffusion of 
 gases. The difference in weight of oxygen, nitrogen, and 
 carbon dioxide would arrange these gases in layers one 
 above another, the heaviest at the bottom, but the principle 
 of diffusion will not allow this separation ; it causes all 
 these gases to mix uniformly in every part of the atmos- 
 phere. 
 
 RESPIRATION. 
 
 Animals and plants need the gases of the atmosphere as 
 much as they need food and soil. Without food, an ani- 
 mal starves ; without air, its death would come still more 
 quickly. Pluck its roots from the soil, and a plant withers 
 and dies ; give it the most fertile soil, but take away the 
 air, and its death is just as certain. 
 
78 CHEMISTRY OF THE ATMOSPHERE. 
 
 Both animals and plants are able to take the air into 
 their bodies and then throw it out again. This act is called 
 respiration. 
 
 Respiration of Animals. When an animal breathes, 
 the air which goes to the lungs contains oxygen and nitro* 
 gen, with a little of carbon dioxide, water-vapor, and still 
 less of a few other gases. 
 
 But what comes from the lungs ? Large quantities of 
 water-vapor, as we know by observation, as in a cold Avinter 
 morning, when every breath looks like a cloud of steam. 
 We see the moisture of the breath at such times, because 
 the cold air condenses it and makes it visible. 
 
 But we can find this water, and something else, at the 
 same time by experiment. 
 
 Ex. 51. I take a clean and dry bottle, cover the lower 
 half of its mouth with my open lips while I pass a full 
 breath into it. Notice the deposit of dew on the walls of 
 the bottle. 
 
 I next pour a few cubic centimeters of lime-water into 
 the bottle and rinse the walls with it, and note the effect 
 on the lime-water. 
 
 Ex. 52. I pour 25 cc. strong lime-water into a clean 
 bottle and add 25 cc. of water. I take a glass tube, or a 
 straw, and, with one end in my mouth, the other in the 
 lime-water, I breathe through the transparent liquid per- 
 haps two or three times. 
 
 What is the effect on the lime-water ? 
 
 What two substances have we found which must have 
 been thrown out in the breath ? 
 
 Now, besides the carbon dioxide and water, which we 
 detect by these experiments, there is the nitrogen. The 
 fact is that while the nitrogen of the air is returned to the 
 air by the breath, the oxygen is used up in the body to 
 make carbon dioxide and water. 
 
CHEMISTRY OF THE ATMOSPHERE. 79 
 
 How is THIS BROUGHT ABOUT ? The air goes into the 
 lungs, and its oxygen passes through the pores of the 
 delicate membrane, of which the lungs are made, into the 
 blood. With the blood, as it goes from the lungs, this oxy- 
 gen is carried to every part of the whole body. It is while 
 in the blood, going from place to place, that the oxygen 
 meets the hydrogen and the carbon. 
 
 But how came these to be in the blood ? Every part 
 of our bodies is constantly wearing out. You cannot move 
 a filler without some of its particles being worn away. 
 You cannot step without some of the particles of the legs 
 be : ng worn out. Every breath, every motion, every thought, 
 renders useless some portions of the parts of the body 
 which aro acting at the time. 
 
 These worn-out particles are all the time going into the 
 blood. They consist chiefly of hydrogen and carbon, and it 
 is from these worn-out particles of our bodies that the oxy- 
 gen gets hydrogen and carbon to form the water-vapor and 
 the carbon dioxide which are thrown out at every breath. 
 
 Life itself depends upon this process. These waste par- 
 ticles are the impurities of the blood, and they must be 
 taken out or death will quickly come. As long as oxygen 
 is regularly supplied to the lungs it will change these im- 
 purities into water and carbon dioxide, and in these forms 
 they will be thrown out in the breath. 
 
 These two seem to be the most abundant substances 
 thrown out, but they are by no means the only ones. Many 
 other impurities are exhaled at the same time. Some of 
 these are very offensive, and all of them are very injur- 
 ious to health if taken again into the lungs. 
 
 Air spoiled by breathing Oxygen is the only thing 
 
 in the air that can purify the blood, and this element is 
 being taken from it by every breath. Once breathed, the 
 air is unfit, on this account, to be breathed again. 
 
80 CHEMISTRY OF THE ATMOSPHERE. 
 
 This is only one way, and that not the worst, in which 
 the act of breathing spoils the air. Every breath is pol- 
 luting all the air into which it is thrown, with the impuri- 
 ties of the blood. Air without its oxygen would not be 
 poisonous nor filthy, but air, with the abundant impurities 
 thrown into it with the breath, is both poisonous and 
 filthy. Were we able to see the impurities of air which 
 has been breathed, we would shun such atmosphere as we 
 now shun the water of a stagnant pool. Ought we to 
 shun it less because they are invisible? , .^ 
 
 Ventilation. It is necessary to change the air in the 
 rooms of our houses very often and very thoroughly, in 
 order to avoid being poisoned by our own breath. 
 
 The removal of foul air and the introduction of that 
 which is pure is called ventilation. Every room in which 
 human beings are expected to live ought to have some 
 means of ventilation. 
 
 Our chemistry teaches us these facts, but chemistry is 
 not left to do this alone. The same lesson is taught by 
 some of the most awful experiences. 
 
 Sometime more than a hundred years ago it happened 
 that, in Calcutta, one hundred and forty-six persons were 
 shut up for a night in a small room called the Black Hole. 
 At dawn of day only twenty-three remained alive. 
 
 The passengers on board a ship were all crowded into 
 the cabin, one stormy night. One hundred and fifty went 
 in, but only eighty came out alive. 
 
 Examples of less painful kind are much more common. 
 A schoolroom is unventilated ; the pupils become listless 
 and dull from the influence of bad air. A church or hall 
 is not ventilated, and a large audience becomes languid 
 and sleepy. A bedroom has its doors and windows tightly 
 shut; the sleeper awakes in the morning unrested and 
 with headache. 
 
CHEMISTRY OF THE ATMOSPHERE. 81 
 
 These are the effects of breathing air which has already 
 been breathed. 
 
 Every building in which people are to live, even for 
 short times, ought to have the means of ventilation "built 
 in," but if the builder of the house has not provided some 
 special means, then the windows and doors should be freely 
 used for the purpose. There should be two openings in 
 every inhabited room, one near the top, the other near the 
 bottom. Out of one of these the foul air may escape while 
 fresh air may come into the room through the other. A 
 window let down a little from the top, and raised a little 
 from the bottom, will meet this condition in a degree. 
 
 The Respiration of Plants Plants breathe. They 
 
 take air into their leaves and throw it back into the atmos- 
 phere again ; and this is respiration. 
 
 The leaves are curiously made. Look at one with a 
 good microscope, and we see that its surface is covered 
 with little openings, or pores. What a multitude of them ! 
 In some cases more than a hundred thousand in the small 
 space of one square inch ! They are found on both the 
 under and the upper side of the leaf. The air is taken 
 into these little mouths on the under side, while from those 
 on the upper side the gases are thrown out. 
 
 Animals breathe in order to get oxygen from the air ; 
 plants breathe in order to get water- vapor and carbon diox- 
 ide. The carbon dioxide is decomposed ; its carbon is kept 
 in the plant while its oxygen is thrown out. While the sun 
 shines this action goes on ; in the dark it does not, for it is 
 found that, at night, carbon dioxide is thrown out instead 
 of oxygen. 
 
 Animals are all the time using up the oxygen of the 
 atmosphere ; plants are by the help of sunlight throwing 
 it into the atmosphere. Animals are constantly giving 
 water-vapor and carbon dioxide to the atmosphere ; plants 
 
82 CHEMISTRY OF THE ATMOSPHERE. 
 
 are busy in taking these substances out. Thus do these 
 two great kingdoms of nature balance and sustain each 
 other. 
 
 EXERCISES. 
 1. Study the action of sulphuric, acid on oxalic acid. 
 
 1. Bring small quantities of the two substances together 
 in a test-tube, using the concentrated sulphuric acid, and 
 crystals of oxalic acid. Discover whether chemical action 
 will take place in the cold, the effect of heat, whether 
 a gas is set free, and any other facts you can. This work 
 will suggest the next step. 
 
 2. Proceed to collect some of the gas in order to learn 
 what it is. To do this, put 5 g. of oxalic acid, in crystals, 
 with 15 cc. of strong sulphuric acid into a side-neck flask, 
 to make the gas ; and to collect it, arrange two conical 
 flasks and one test-tube, which is fitted with a cork and 
 tubes in the same manner as the flasks. 
 
 8. Examine the gas. Put a flame into the mouth of the 
 first flask to learn whether the gas is combustible or other- 
 wise ; and for the name of the gas which gives the result 
 you get here consult p. 46. 
 
 Test the gas in the second flask with lime-water, and 
 name the gas which this test reveals. 
 
 Having now proved that the gas which is set free by the 
 action of the two acids is a mixture of carbon monoxide 
 and carbon dioxide, you can take the fourth step in your 
 investigation, which is to 
 
 4. Analyze the mixture. Do this by the method of 
 " absorption," the same as that used in the analysis of air 
 in Ex. 49. 
 
 Fill the funnel and the rubber tube, shown in Fig. 36, 
 not using the cork, with a strong solution of potassium 
 hydrate. This liquid will absorb carbon dioxide, but not 
 
CHEMISTRY OF THE ATMOSPHERE. 83 
 
 carbon monoxide. Then slip the end of the rubber over 
 the end of the long glass tube which passes into the test- 
 tube in which you caught the gas. Put a solid stopper in 
 place of the short glass tube, and then go on with the work 
 as in Ex. 49. When you come to measure the volumes do 
 not forget that you have used the long glass tube in the 
 test-tube full of gas. 
 
 5. Finally, write a brief account of your investigation 
 and its results. 
 
 2. Study the action of phosphorous on air. 
 
 We have seen that phosphorus burns in air when it is 
 heated (Ex. 44); but how will the two behave if no heat 
 is used ? Remember to handle phosphorus with great care. 
 See p. 67. 
 
 1. Place a small piece of phosphorus on the end of a 
 small wire, and put it into a bottle. Then invert the 
 bottle and leave it standing, mouth downward, in a vessel 
 of water several hours. Notice any evidence of chemical 
 change or of absorption, or of any other action which may 
 occur. 
 
 2. Remove the bottle from the water without losing any 
 part of what is in it, and at once test the gas which is left. 
 Decide what this gas is, and then what the phosphorus 
 must have done. 
 
 3. See if you can find out, by measuring, what fraction 
 of the air the phosphorus took out. 
 
 4. Write a brief account of your work and results. 
 
COMPOUNDS OF NITROGEN, HYDROGEN, 
 AND OXYGEN. 
 
 WE have seen that about four-fifths of the air is nitrogen 
 gas, and that its effect is simply to dilute the oxygen so 
 that combustion will be less furious than it would be in 
 oxygen alone, and so that the air may be mild enough for 
 animals to breathe. Nitrogen is just fitted to do this, 
 because it has so little affinity for other elements. 
 
 But nitrogen can be made to combine with other ele- 
 ments, and in fact there are a great many of its compounds 
 known. Many of these are strangely unlike the element 
 itself, for while it is the mildest of all things, these com- 
 pounds are among the most pungent and corrosive sub- 
 stances to be found. 
 
 AMMONIA. 
 
 Ammonia is the compound of nitrogen and hydrogen. 
 
 Produced in two Ways. There are two ways in which 
 these two elements can be made to combine: one is by 
 electricity. If we mix the gase^, and then send a silent 
 electric charge through the mixture for a long time, we 
 find some ammonia in the tube. 
 
 Ammonia in small quantities is found in the air, and it 
 is likely that the electricity of the atmosphere has pro- 
 duced it there. 
 
 The other way to make nitrogen and hydrogen combine 
 is to bring them together just at the moment when they 
 are set free from some other compounds. For example, 
 they are both found in animal bodies, such as horns, hoofs, 
 and flesh. Now, when these decay, the nitrogen and hydro- 
 gen are set free, but they are together at the same moment, 
 
 84 
 
NITROGEN, HYDROGEN, AND OXYGEN. 85 
 
 and combine with one another. Neither escapes alone, but 
 they go off together as ammonia. Ammonia may be found 
 in the air of stables, of farm-yards, and of other places 
 where animal matters are decomposing. 
 
 THE NASCENT STATE. These gases are not the only 
 things which combine most readily just at the moment 
 when they are set free from something else. Other ele- 
 ments also seem to be more active at that moment than 
 at other times. They are then said to be in the nascent 
 state. 
 
 FORMED IN GAS-WORKS. Gas for lighting towns and 
 cities is made by heating soft-coal to a cherry-red heat. 
 Among the gases and vapors driven off are ammonia and 
 some of its compounds. These are bad impurities, and in 
 the manufacture of gas they are washed out by cold water. 
 The ammonia, in this "ammonia water" of the gas-house, 
 is saved by making it combine with hydrochloric acid, 
 which changes it to ammonium chloride, or with sulphuric 
 acid, which changes it to ammoniu7n sulphate. This is the 
 source of nearly all the ammonia and its compounds, great 
 quantities of which are used annually. 
 
 Preparation of Ammonia Ammonia itself is made 
 
 by decomposing one of these com- 
 pounds by heating it with lime. 
 
 Ex. 53. I powder a very little 
 ammonium chloride and also a little 
 good quick-lime. I then mix them 
 well, and put into a clean and dry 
 test-tube enough to half fill the 
 rounded bottom. I fill the mortar 
 with water colored blue by litmus, 
 and add only a drop of hydrochloric Fig- * 1- 
 
 acid to redden it : let this stand ready for use when needed. 
 I take the tube between my fingers, with my thumb over 
 
86 NITROGEN, HYDROGEN, AND OYYGEN. 
 
 its mouth, leaving a small opening at the lower edge, and 
 hold it some time in the hot air above the flame, a little 
 inclined, as shown in Fig. 41. Note 
 
 The deposits of moisture on the cold parts of the tube. 
 
 The odor at the mouth of the tube. 
 
 This is the odor of ammonia. 
 
 What two substances seem to have been produced ? 
 
 By this time the decomposition of the mixture is at an 
 end, and I bring the mouth of the tube down into the red- 
 dened litmus-water, still holding the tube 
 so much inclined (Fig. 42) that the white 
 solid will not fall down into the water. 
 As the tube cools the red water rises in it. 
 But it will rise much further than it would 
 if the tube were heated without the mix- 
 ture. (Try an empty tube in the same way, and see how 
 far the water will rise.) 
 
 What property of the gas does this show ? 
 Note the change of color in the water. 
 Compare this change with that in Ex. 48. 
 
 THE FACTS. We find that by heating the ammonium 
 chloride with lime we get water, condensing in droplets on 
 the tube; ammonia, which we know by its familiar pun- 
 gent odor ; and a white solid left clinging to the bottom of 
 the tube, which is calcium chloride. 
 
 We see, too, that ammonia is a gas, but a gas which is 
 soluble in water. Now the so-called ammonia in commerce 
 is a liquid. It is, clearly, not the real ammonia. The fact 
 is, it is water with as much as it will hold of the ammonia 
 gas in solution. 
 
 One cubic centimeter of water at 15 C. will hold 783 cc. 
 of this gas, and, like all other gases, ammonia is more sol- 
 uble in colder water. At C. the cubic centimeter of 
 
NITROGEN, HYDROGEN, AND OXYGEN. 87 
 
 water will absorb 1148 cc. of this gas. This strong solu- 
 tion of ammonia is known as ammonium hydrate. 
 
 By warming this liquid ammonia, the gas itself can be 
 obtained in great abundance. 
 
 Ex. 54' To do this I arrange the apparatus as in Fig. 
 43. I put 10 cc. or 15 cc. of the liquid ammonia in the 
 side-neck flask, close its mouth 
 and connect it with the short 
 tube of a, whose long tube is 
 joined to the short one of b. 
 The stoppers must close the 
 flasks air-tight. 
 
 I put the short tube of a next 
 the flask, because this gas is 
 lighter than air. It will collect 
 in the upper part of a, and 
 push the air out through the 
 long tube into the upper part r1 *-* 3 - 
 
 of 6, and afterwards out of the long tube of b, until both 
 flasks are full. 
 
 I now make the lamp-flame very small, so that only a 
 current of hot air will warm the liquid in the flask. The 
 gas will soon escape freely. Some water-vapor goes over 
 with it, but 1 use as gentle heat as I can to keep it bub- 
 bling ; the water does not boil ; the bubbles are ammonia 
 gas, mixed with little vapor. 
 
 Note the odor of the gas which escapes from the open 
 tube of b; it will be more and more pungent until the air 
 is all out of the flask. 
 
 Ex. 55. Moisten a stick with hydrochloric acid and 
 hold it just above the tube of b. 
 
 What evidence of chemical action do you find ? 
 Compare this with Ex. 9. 
 
88 NITROGEN, HYDROGEN, AND OXYGEN. 
 
 Ex. 56. I take both rubber tubes from a, and at once 
 plunge the stoppered mouth of the flask down into a vessel 
 of water (Fig. 44). 
 What is the result ? 
 What does it teach about ammonia 
 gas? 
 
 Ex. 57. I redden some blue lit- 
 Fi - ** mus with as little hydrochloric acid 
 
 as will do it, and then pour into it some of the water which 
 has just now dissolved the gas in a. 
 
 How does the ammonia show its presence in the water ? 
 
 Has this ammonia-water any taste or odor? 
 
 THE FACTS. Dry ammonia-gas is invisible and much 
 lighter than air. Its solution in water has a caustic taste, 
 and will bring back the blue color of litmus which has been 
 reddened by acid. 
 
 Ammonia is a stimulating gas to breathe : on this ac- 
 count it is used to revive the faint, and sometimes to 
 overcome the effects of an anaesthetic, like ether or chlo- 
 roform. 
 
 Ammonia and hydrochloric acid combine at once, when- 
 ever brought together, and form ammonium chloride. The 
 white cloud in Ex. 55 was a cloud of ammonium chloride. 
 
 Ammonium Salts. Ammonia acts also on other acids, 
 and so forms a large number of compounds, which as a 
 class are called ammonium salts. 
 
 Ex. 58. I put 10 cc. of water into a small wide-mouth 
 bottle and add 2 cc. strong sulphuric acid. I place this in 
 a porcelain dish and drop into it a small clipping of blue 
 litmus-paper. 1 I now add strong ammonia water (ammo- 
 nium hydrate) little by little, shaking the mixture well 
 
 1 Filter-paper soaked in a strong solution of litmus and afterward 
 dried. 
 
NITROGEN, HYDROGEN, AND OXYGEN. 
 
 89 
 
 each time, until the red paper turns blue. If now I add 
 drop by drop of the dilute acid, I can reach the point 
 when the paper is just reddened by the last drop, and 
 when another drop of ammonia will make it blue again. I 
 do this. And then I put the dish over a small flame and 
 evaporate (Fig. 10) the liquid, until a white rim is seen 
 around its edge on the dish, and then let it cool. 
 
 While waiting for the liquid to evaporate I begin the 
 next experiment. 
 
 Ex. 59. I mix 5 cc. of water and 5 cc. strong nitric 
 acid, add the blue litmus-paper and then the ammonium 
 hydrate, until the last drop turns the paper blue. I then 
 evaporate this liquid to about one-fourth its bulk, and let 
 it cool. 
 
 If the liquids were evaporated enough, crystals of a white 
 solid will be seen in each when it is cold, or the whole may 
 become a solid white mass. 
 
 Ex 60. I take a little of one of these white solids to 
 test its action on litmus. I first pour upon it, and then 
 quickly off again, a little water just to wash it. And 
 then I add water to dissolve it. I take two clippings 
 of blue litmus-paper, moisten one with water, and then 
 redden it by holding it in the mouth of the bottle of 
 hydrochloric acid, and then put both into the solution. 
 No change of color should occur in either. 
 
 These white solids, made by the action of ammonia on 
 sulphuric and nitric acids, are examples of ammonium 
 salts. 
 
 But why did we use the litmus ? Simply to show 
 when the chemical change was ended. We have found 
 that blue litmus is reddened by an acid in every case, and 
 that ammonia will bring back the blue color. But when 
 there is just enough ammonia to use up all the acid, 
 
90 NITROGEN, HYDROGEN, AND 
 
 neither the blue nor the red is changed. The ammonia 
 and the acid neutralize each other, and the litmus shows 
 the end of this action. 
 
 Do not leave this until you see clearly why the two neu- 
 tralize each other. Consult p. 57 for the law. 
 
 Composition of Ammonia by Volume. It is found 
 by analysis that ammonia always yields just three times 
 as many cubic centimeters of hydrogen as of nitrogen. 
 Its composition by volume is : 
 
 3 measures hydrogen to 1 measure nitrogen. 
 
 But another question is, How much ammonia gas would 
 these 3 of hydrogen and 1 of nitrogen make ? It has been 
 found by analysis that 20 cc. of ammonia will give 30 cc. 
 of hydrogen and 10 cc. of nitrogen. That is to say, 30 cc. 
 of hydrogen and 10 cc. of nitrogen make 20 cc. of am- 
 monia. 
 
 Three measures of hydrogen and one measure of nitro- 
 gen make two measures of ammonia. Or four volumes of 
 the constituents are condensed to two volumes of the 
 compound. 
 
 Compare this curious fact with another noted under the 
 composition of water, p. 56. 
 
 NITRIC ACID. 
 
 Nitric acid is a compound of nitrogen, hydrogen, and 
 oxygen. It is one of the strongest of acids, and one of 
 the most useful. 
 
 Occurs in Combination. Very small quantities of 
 this acid exist, free, in the air: it is in its compounds that 
 it is mostly found. Two of these compounds occur in large 
 quantities in some parts of the earth : they are " saltpetre," 
 whose true name is potassium nitrate, and " Chilian salt- 
 petre," or sodium nitrate. 
 
NITROGEN, HYDROGEN, AND OXYGEN. 91 
 
 Made from Sodium Nitrate. To get the nitric acid 
 the sodium nitrate is heated with sulphuric acid. Sulphu- 
 ric acid is still stronger than nitric acid, and will drive the 
 latter out of the nitrate in order to take its place. The 
 nitric acid is driven out in the form of vapor, but it is 
 carried into a cold vessel, where the vapor is condensed 
 to a liquid. 
 
 Properties. Nitric acid when pure has no color, but 
 it is intensely sour and very corrosive. It will redden 
 litmus like other acids, but will not stop with this : it will 
 go right on to destroy the red color. Try this by putting 
 a piece of litmus-paper into a little of the strong acid. 
 It will first turn red, soon afterward yellow, and in a little 
 time the paper will easily break to pieces. In the same 
 way it will form yellow stains upon the fingers, and upon 
 the garments, and, in fact, upon all organic bodies. The 
 acid may be washed away by water, or it may be neutral- 
 ized by ammonia, but the yellow color will remain. 
 
 Ex. 61. Wet some pieces of woolen cloth with drops 
 of nitric acid, with drops of hydrochloric acid, and of 
 sulphuric acid. Wait until the color is changed by all, 
 and then try the effect of ammonia on them. Note the 
 difference. 
 
 The strong nitric acid in commerce is by no means pure : 
 in fact, it is almost half water, and there are several other 
 impurities besides water, in small quantities. By distil- 
 ling a mixture of this acid with strong sulphuric acid the 
 pure and concentrated nitric acid is obtained. 
 
 Decomposition of Nitric Acid. This acid is very 
 easily decomposed. It is decomposed by light. When 
 standing in the sunlight, the upper part of the bottle of 
 acid will, after a time, be seen full of a reddish vapor; 
 this is set free from the acid by light, and water is 
 formed at the same time. The yellow color of the com- 
 
92 NITROGEN, HYDROGEN, AND OXYGEN. 
 
 mon acid is due to this reddish vapor, some of which 
 is dissolved in the liquid. 
 
 THE NITRATES. Nitric acid is easily decomposed by 
 almost any metal. One can see this action by putting 
 small bits of copper or lead in a test-tube and covering 
 them with dilute nitric acid. But the fumes are very nox- 
 ious, and the experiment should be made on a small scale, 
 or else in the open air. The same red vapor, seen when 
 the acid is decomposed by light, is set free in abundance 
 by the metal. Water is also formed, and beside these a 
 salt of nitric acid is produced. These salts of nitric acid 
 are called nitrates. The salt made with copper is blue, and 
 it is called copper nitrate ; that made with lead is white, 
 and is called lead nitrate. 
 
 This decomposition of nitric acid by a metal will be 
 better understood further on, when we study Ex. 62. 
 
 These nitrates are all soluble in water, and so when a 
 metal is changed into a nitrate the metal seems to dis- 
 solve, but it is always the nitrate which is in solution, and 
 not the metal. 
 
 AQUA REGIA. Nearly all the metals are thus changed 
 into nitrates by nitric acid; but gold and platinum are the 
 exceptions. To dissolve these metals we need a mixture 
 of nitric and hydrochloric acids. Neither of these alone 
 can attack gold or platinum, but the two together will 
 dissolve them readily. The mixture of these two acids 
 is called aqua regia. But, as we shall see, the metals 
 dissolved in aqua regia are not changed into nitrates, but 
 into compounds of chlorine, called chlorides. 
 
 NITROGEN OXIDES. 
 
 Investigate the Decomposition of Nitric Acid 
 
 We have just seen that when nitric acid is decomposed 
 reddish vapors are set free. What are these vapors ? 
 
NITROGEN, HYDROGEN, AND OXYGEN. gj 
 
 Let us study the action by experiment. We will decom- 
 pose the acid by copper. 
 
 Ex. 62. I fit up my apparatus for making and collect- 
 ing gases as usual for a 
 gas heavier than air (Fig. 
 45), the long tubes of the 
 flasks a, b, c toward the 
 side-neck flask. Into both 
 a and b I put water, which 
 the cut shows only in 
 a, but none in c. After 
 the connections are made, 
 I put about seven grams 
 of small pieces of copper- : fjj 
 foil, or thin sheet-copper, Fig - 45> 
 
 in the side-neck flask, pour in about 25 cc. of dilute nitric 
 acid, half water, and close the flask with its air-tight stop- 
 per. The chemical action sets in at once. No heat is 
 needed to start it. 
 
 Note the change in the color of the acid. 
 
 Trace the changes of color as they occur in s, a, b } c. 
 
 We see that a red gas quickly fills the flask s, and goes 
 over into a, b, c, but that the red color disappears from 
 s, a, and b, and stays in c for a much longer time. 
 
 How many kinds of gas are evidently in the flasks ? 
 
 When a and b are clear, and c still full of red-brown gas, 
 I disjoin the rubber tube of c, remove the stopper carefully, 
 pour in gently a few cubic centimeters of water, and return 
 the stopper to its place as tightly fitted as before. I now 
 close the ends of both glass tubes with my finger, which 1 
 can easily do if they are at the same level, lift the flask 
 and shake it well. Note the disappearance of the red gas. 
 I next plunge the finger and tubes under water, and take 
 the finger away. Note the inrush of water. 
 
94 NITROGEN, HYDROGEN, AND OXYGEN. 
 
 Why did the color of the gas disappear with water ? 
 Why did the water rush in when the tubes were opened ? 
 What property of the red gas is thus discovered? 
 Ex. 63. I now disjoin the rubber tubes of I, and then 
 invert the flask and let the water run out of the short tube. 
 Of course air will run in through the long tube and mix 
 with the colorless gas within. The red gas is reproduced ! 
 This is an important discovery. If air will change the 
 colorless gas into the red gas, perhaps it was in this way 
 that the red gas was made in the flasks at first, for they 
 were full of air when the action began in s. If I could 
 keep the air away, while the copper and nitric acid act on 
 each other, would the red gas appear at all? 
 
 Now I can keep the air away, and answer this question, 
 by putting carbon dioxide into tlie flasks in place of the air. 
 Ex. 64- I disjoin the rubber tubes of a, and empty the 
 contents of * into a porcelain dish to be examined after- 
 ward. I then join the side-neck 
 with the long tube of another 
 flask (Fig. 46). I put 20 cc. 
 dilute nitric acid, half water, 
 into s, drop in gently two or 
 three pieces of marble as large 
 as peas, and close the flask. Car- 
 bon dioxide will be set free, 
 drive the air before it out at 
 the open short tube, and will 
 P> soon fill the flask. I then open 
 Tis - * 6 - s, drop in some bits of copper, 
 
 and quickly close it again. The nitric acid and copper now 
 act in the absence of air. Do they yield the red gas ? 
 None will be seen if the air was all expelled. Do they 
 yield the same colorless gas as before ? I mix air with the 
 gas in c ; the red gas instantly appears, as it did in Ex. 63. 
 
NITFJGEN, HYDROGEN, AND OXYGEN. 
 
 95 
 
 Our experiments clearly prove that when copper decom- 
 poses nitric acid, only a colorless gas is set free. But 
 when this colorless gas meets with air, another, a red- 
 brown gas, is formed. At the same time a blue compound 
 ^s made which stays in the liquid. The colorless gas is a 
 compound of nitrogen and oxygen, called nitric oxide, and 
 the red-brown gas is another compound of nitrogen and 
 oxygen, called nitroyen peroxide. The blue compound is 
 copper nitrate. It may be obtained in blue crystals by fil- 
 tering the liquid and evaporating it until, on cooling, the 
 crystals form. (Try it.) 
 
 When nitric oxide mixes with air it instantly combines 
 with oxygen and becomes nitrogen peroxide. 
 
 Nitrous Oxide. There is another compound of nitro- 
 gen and oxygen called nitrous oxide. It is not usually 
 made by the decomposition of nitric acid directly, but by 
 decomposition of ammonium nitrate, and this is done by 
 means of a gentle heat, which breaks the nitrate into water 
 and nitrous oxide. Thus : 
 
 Ex. 65. I put from 7 to 10 grams of ammonium nitrate 
 into the side-neck 
 flask, which should 
 be dry, and join the 
 flasks , b, c, as usual 
 for a heavy gas. To 
 condense the steam, 
 I put the empty flask 
 a into a dish of cold 
 water, ice-water is 
 best. It may be held 
 down in the water by 
 a cord passing over Fig - 47 - 
 
 the stopper and around under the heavy dish of water. To 
 decompose the nitrate 1 use the gentle heat of a small 
 
96 NITROGEN, HYDROGEN, A XI) OXYGEN. 
 
 flame, just hot enough to melt and keep it gently boiling. 
 The nitrate slowly wastes away, and when but about one- 
 fifth remains I withdraw the lamp. 
 
 Flasks s and a prove that water is produced. How ? 
 
 Test the gas in b with the flame of a splinter of wood. 
 
 Note the color, and the odor, of the gas in c. 
 
 THE FACTS. AmmQn^njn_ : Jiiteate contains nitrogen, hy- 
 drogen, and oxygen, and when it is decomposed the nitro- 
 gen and hydrogen separate, each taking a part of the 
 oxygen with it. The nitrogen and oxygen form the nitrous 
 oxide, while the hydrogen and oxygen form water. The 
 water is condensed in a (Fig. 47), while the nitrous oxide 
 is collected in a, b, and c. 
 
 Nitrous oxide is a colorless gas in which bodies will burn 
 with almost the same vigor as in oxygen itself. But its 
 most remarkable action is upon a person who breathes it. 
 Breathed in small quantities it intoxicates, and often causes 
 a disposition to laughter. On this account it is commonly 
 known as laughing-gas. But if its use be continued a few 
 minutes, it will produce complete insensibility, and if con- 
 tinued, death. It is much used to render patients insensi- 
 ble to pain in minor surgical operations, such as the extrac- 
 tion of teeth. The insensibility lasts a few minutes only ; 
 it is quickly banished by fresh air. 
 
 The Five Nitrogen Oxides. There are two other 
 compounds of nitrogen, making in all five. Here are five 
 entirely different kinds of substance made out of the 
 same two elements. But how can the same elements make 
 different compounds ? By combining in different propor- 
 tions. When the colorless nitric oxide touches the air it 
 takes in more oxygen and becomes the red nitrogen per- 
 oxide. Different weights of these elements unite. 
 
 Let N stand for nitrogen and for oxygen. By analy- 
 sis it has been found that 
 
NITROGEN, HYDROGEN, AND OXYGEN. 97 
 
 Nitrous oxide contains 28 of N and 16 of O 
 Nitric oxide 14 " " 16 " 
 
 Nitrous anhydride 28 " 48 
 Nitrogen peroxide " 14 " " 32 " " 
 Nitric anhydride " 28 " " " 80 " " 
 
 The properties of a compound depend on the relative 
 weights of the elements in it. This fact is clearly shown 
 by these nitrogen oxides. 
 
 The Law of Multiple Proportions It is a curious 
 
 fact that the relative quantities of oxygen in this table of 
 nitrogen oxides are all either 16, or else 2 or 3 or 5 times 
 16. So, too, in the case of the nitrogen the quantities are 
 either 14, or twice 14. In both cases alike, the larger 
 numbers are all exact multiples of the smallest. Now 
 chemists have found this to be true in a great many other 
 cases where two elements make more than one compound. 
 In fact they have met no exception. This causes them to 
 feel quite sure that all elements are alike in this respect, 
 and they state this conclusion as follows : 
 
 If one element combines with another in more than one 
 proportion, these proportions are all exact multiples of some 
 one fixed number. 
 
 And this important statement of fact is known as the 
 "law of multiple proportions." The student should now 
 remember the " law of constant proportions " ( p. 57), for 
 these two laws together cover the most vital facts about 
 the combination of elements. 
 
 Combination of Definite Weights These two laws 
 
 show very clearly that the elements never combine except 
 in certain definite weights. 
 
 The definite weights of oxygen and hydrogen in water 
 are in the ratio of 16 to 2. Sixteen grams of oxygen and 
 two grams of hydrogen will unite without leaving any of 
 either. But if we pass an electric spark through a mixture 
 
98 NITROGEN, HYDROGEN, AND OXYGEN. 
 
 of 16 g. of oxygen with 3 g. of hydrogen, just 1 g. of hydro- 
 gen will be left. 
 
 The definite weights in which oxygen and nitrogen 
 always combine have the ratio of 16 to 14. 
 
 The definite weights of hydrogen and chlorine which 
 make their compound, hydrochloric acid, are as 1 to 35.5. 
 In other compounds of chlorine the definite weight of 
 chlorine used may be 2 or 3 or some other whole number 
 of times 35.5. And in other compounds of hydrogen the 
 definite weight of hydrogen may be 2 or 3 or some other 
 whole number of times 1. 
 
 Combining Weights, These numbers which show the 
 ratios of the smallest definite proportions by weight in 
 which these elements ever combine with anything else, 
 are called combining weights. Thus we say 
 
 The combining weight of Hydrogen is ... 1 
 
 " " " " Oxygen " ... 16 
 
 " " Nitrogen " ... 14 
 
 " " " Chlorine "... 35.5 
 
 And we mean that the smallest weight, of chlorine for 
 example, which we can find in any compound is just 35.5 
 times as large as the smallest weight of hydrogen which 
 can be found in any of its compounds. 
 
 To find these numbers the combining weights is one 
 of the most difficult problems in chemistry. The student 
 is not yet ready to see how it is done. But it has been 
 done for the whole list of elements. Every element has a 
 combining weight assigned to it. 
 
 EXERCISES. 
 
 1. Make some Nessler's reagent as follows : 
 
 1. Make a solution of potassium iodide, say 6 g. in 20 cc. 
 of distilled water, or of the best spring water. 
 
NITROGEN, HYDROGEN, AND OXYGEN. 99 
 
 2. Make a strong solution of mercuric chloride, say 6 g. 
 in 60 cc. of water. 
 
 3. Add the mercuric chloride solution, little by little, to 
 the potassium iodide, until a small portion of the precipi- 
 tate will not disappear when shaken or stirred. 
 
 4. Make a strong solution of potassium hydrate, say 
 10 g. in 15 cc. of water, and when cold add this to the 
 mixture already made. 
 
 Finally, let this mixture stand until it is perfectly clear. 
 The clear liquid is called Nessler's reagent. 
 2. Study the effect of Nessler's reagent on solutions contain- 
 ing ammonia. 
 
 1. Add a drop or two of ammonium hydrate to a test- 
 tube nearly filled with distilled or spring water. Then add 
 1 cc. of the Nessler's solution. Mix it well, and note the 
 color of the mixture. 
 
 Find out whether less than a drop of ammonia will yield 
 this color in the same quantity of water. Or how little 
 you can use and still be able to detect the color. 
 
 2. Put a little solution of ammonium chloride in the 
 water, instead of ammonia, and test it with the Nessler's 
 solution. 
 
 Does the ammonia of the ammonium chloride yield the 
 same color ? 
 
 The fact is that Nessler's solution is the most delicate 
 test for ammonia, always showing the presence of that sub- 
 stance by a yellow color, which has a light straw tint 
 when very little ammonia is present, and a deep orange 
 tint when there is much. 
 
 8. Learn by this test whether rain-water contains am- 
 monia. 
 
 Why should rain-water contain ammonia ? 
 
 4- Test the drinking-water of the neighborhood for am- 
 monia. 
 
100 NITROGEN, HYDROGEN, AND OYYGEN. 
 
 3. Study the effect of nitric acid on ferrous sulphate, some- 
 times called " copperas. 11 
 
 1. Into a little dilute nitric acid in a test-tube drop a 
 good crystal of the ferrous sulphate. Do not shake it. 
 Notice the color which appears in the liquid around the 
 crystal. 
 
 2. See how dilute you can make the acid and still be 
 able to detect this color when a crystal of the sulphate is 
 used. 
 
 3. Try the solution of a nitrate, say potassium nitrate, 
 instead of nitric acid, in the same way. 
 
 Does the color now appear around the crystal ? If not, 
 there is probably little or no free nitric acid present. 
 
 4. Mix a little solution of the potassium nitrate with a 
 solution of the sulphate, incline the tube, and let a little 
 concentrated sulphuric acid run down the inside of the 
 glass, to the bottom. Do not shake it. * 
 
 The color should now appear as a ring, where the liquids 
 touch each other. 
 
 If so, then why did it not in the other case ? 
 
 The fact is that strong sulphuric acid decomposes the 
 nitrate and sets its nitric acid free. And then the free 
 nitric acid shows itself by the color it makes by acting on 
 the crystal. 
 
 5. Make the experiment again with potassium nitrate 
 and sulphuric acid, but add the ferrous sulphate to the 
 liquid when hot. 
 
 Ferrous sulphate is a delicate and much-used test for 
 nitric acid and the nitrates. It must be used in cold solu- 
 tions : the brown color disappears on heating. 
 
 6. Get a little of some white solid, the name of which 
 you do not know, from the teacher, or a friend who knows 
 what it is, and see if you can tell by the copperas test 
 whether it is a nitrate or not. 
 
THE COMPOSITION OF PLANTS. 
 
 THE substances which exist in plants, or which may be 
 made from them, are so many that we cannot undertake 
 to study them all. The most that we can do now is to 
 ascertain the elements of which plants are made, and per- 
 haps a few of their simpler compounds. 
 
 Let us examine a piece of wood as follows : 
 
 Ex. 66. I take a splinter of well-dried pine wood, 
 about as large and long as a common match, drop it into a 
 test-tube, and then heat it slowly by holding the tube 
 almost horizontally just above the tip of the lamp-flame, 
 and move the tube back and forth to heat the length of the 
 wood. 
 
 Notice the dew on the cold walls ; what does this show ? 
 
 Notice the vapors ; do they condense or go off as gases ? 
 
 Notice whether any other liquid than water is formed. 
 
 Describe the stick after the changes are over. 
 
 The Pacts. When Avood is heated in a close vessel, 
 where there is not air enough to burn it, there are many 
 new products of its decomposition. Some are gaseous ; 
 these escape into the air. Some are liquid; these con- 
 dense on the cold parts of the vessel. A black solid is 
 left which no heat seems to affect. Among the liquid 
 products is water, the dew seen on the walls of our 
 tube; and the black solid which was left behind is char- 
 coal, which is the element carbon, almost pure. But water 
 is always made up of hydrogen and oxygen, and as water 
 comes from the well-dried wood, the wood must contain 
 these elements also. Thus we prove that wood contains 
 carbon, hydrogen, and oxygen. 
 
 101 
 
102 COMPOSITION OF PLANTS. 
 
 By extending our experiments to other kinds of vege- 
 table matter we find in them the same elements : carbon, 
 hydrogen, and oxygen. Every blade of grass, every leaf 
 and flower, and every kind of seed and fruit, contain these 
 three elements, and they contain very little of any others. 
 
 Plants do indeed contain other elements than these. 
 Nitrogen is found in them ; in small quantities to be sure, 
 but it must not be overlooked, because it is one of the most 
 important elements in the vegetable food of animals. 
 
 Besides nitrogen there are several other elements in 
 minute quantities, which, with carbon, hydrogen, and oxy- 
 gen, enter into the composition of plants. 
 
 When wood or any other vegetable matter is burned, 
 these four elements disappear, and nothing but a little 
 ash remains ; but this ash contains all the other elements 
 of the substance. How small the quantity ! It seldom 
 amounts to one tenth of the whole. In every 100 pounds 
 of vegetable matter, from 90 to 97 pounds are made up of 
 carbon, hydrogen, oxygen, and nitrogen. All these facts 
 have been established by experiments. 
 
 The Food of Plants An animal, to live and grow, 
 
 must be supplied with food. The same is true of plants : 
 they must be supplied with nourishment which contains 
 all the elements they need to promote their growth. Now 
 carbon, hydrogen, and oxygen, with a little nitrogen, and 
 very small quantities of a few other elements, make up 
 every part of any plant. These the plant must get in 
 some way, else it cannot flourish. If any of them are 
 lacking, the plant suffers even if it does not die. The 
 food of plants must contain all these elements. 
 
 The plant gets its carbon from carbon dioxide. It gets 
 its hydrogen and oxygen from water. It gets its nitrogen 
 from ammonia, and as nine-tenths of the weight of 
 plants is made up of carbon, hydrogen, oxygen, and nitro- 
 
COMPOSITION OF PLANTS. 103 
 
 gen, it is easy to see that the three substances just named 
 must be the food upon which plants must chiefly live. 
 
 BUT HOW CAN A PLANT TAKE FOOD? Every plant has 
 a multitude of mouths. There is one at the end of every 
 little rootlet in the soil, and there are a host of them 
 on the under side of every leaf. Each little root-mouth 
 of a growing plant is taking in liquid food from the soil, 
 and each little leaf-mouth is at the same time taking 
 gaseous food from the air. 
 
 The liquid which enters the roots of a plant is water 
 in which many substances of the soil are dissolved. It 
 contains compounds of ammonia, from which the plant can 
 get nitrogen, and it also furnishes the plant with those 
 other elements which it needs in small quantities, those 
 which make up the ash which is left when the plant 
 is burned. 
 
 The gaseous food which enters the leaves of a plant 
 is the carbon dioxide and water-vapor of the air. From 
 these gases the plant gets carbon, hydrogen, and oxygen, 
 the three most abundant elements needed in its growth. 
 
 The food of plants must be decomposed before its carbon, 
 hydrogen, oxygen, and other elements can nourish them. 
 These elements then combine again in very different ways 
 to produce all the materials of which the parts of a plant 
 are made, such as starch, sugar, wood-fiber, gums, oils, and 
 coloring matters. 
 
 Among the four chief elements in plants, the only one 
 which we have hot studied is: 
 
 CARBON. 
 
 The Source of Carbon in Plants. Carbon dioxide 
 is one of the most important substances in the food of 
 plants. But the oxygen of this substance is of no use 
 to them ; they get enough of that from other sources ; 
 
104 
 
 COMPOSITION OF PLANTS. 
 
 it is the carbon which is useful. Now, every leaf of a 
 growing plant is taking the carbon dioxide of the air 
 which passes over it. We learned this when studying 
 the subject of respiration. This substance is decomposed 
 while in the leaf ; its oxygen is exhaled, but its carbon 
 remains to enter into combination as a part of the body 
 of the plant. 
 
 Charcoal-making. This carbon, which the plant has 
 taken from the atmosphere, and also the little which 
 it may have taken up through its roots, is obtained without 
 
 much difficulty, for use in the arts, and we are acquainted 
 with it under the name of charcoal. 
 
 The charcoal-maker piles his sticks of wood in the form 
 of a mound, and covers the whole with dirt and turf. He 
 leaves a few small holes for a little air to enter the pile 
 
COMPOSITION OF PLANTS. 105 
 
 at the bottom, and another at the top for the smoke to 
 escape, and in this way a half-smothered burning is kept 
 up for a long time, as shown in Fig. 48. 
 
 Now what change occurs ? A very simple one. The 
 wood is decomposed by the heat ; its gaseous constituents 
 are driven away, but its solid carbon is left behind. Not 
 all of it, to be sure, for a little of it unites with oxygen 
 and flies away as carbon dioxide. But the carbon which 
 is lost in this way is very little compared with the char- 
 coal which is left. 
 
 In appearance, the wood only seems to have changed in 
 color. It is black. In other things the charcoal looks like 
 the wood. There is the bark with all its knotty roughness. 
 There are the annual rings inside the bark, to be plainly 
 counted, and, if we look through a microscope, there are 
 the delicate cells, which the microscope could have shown 
 us in the wood before it was burned. Let us lift it, and 
 it is easy to feel that the wood has lost much of its weight, 
 but really it is not easy to see that it has lost much of 
 its size ; the stick of charcoal is very nearly as large as 
 the stick of wood from which it was made. 
 
 CHARCOAL is NOT QUTTE PURE CARBON. When pure 
 carbon burns it is wholly changed into carbon dioxide gas ; 
 no solid ash remains, but charcoal always leaves a little 
 ash, which proves it to be impure carbon. 
 
 OTHER IMPURE FORMS RESEMBLTXG CHARCOAL. Char- 
 coal is only one of the many common forms of carbon. 
 Among those most nearly like charcoal we may mention 
 now the hard coal, which is taken from mines for fuel; 
 coke, the black and porous solid left in the retorts of 
 gas-works ; bone-ldack, obtained by heating bones 111 close 
 vessels ; soot, to be found in chimneys ; and /amp-black, 
 so much used in the manufacture of printing-ink. 
 
 Lamp-black. Lamp-black is made by burning pitch 
 
106 
 
 COMPOSITION OF PLANTS. 
 
 or tar with little air. The pitch is put into an iron pot 
 and heated as shown at the left in the cut (Fig. 49). A 
 
 dense black smoke 
 is carried by the 
 draught over into 
 a large chamber. The 
 blackness of this 
 smoke is due to fine 
 particles of carbon. 
 This substance col- 
 lects on the Avails of 
 the chamber, and is 
 afterwards taken out 
 as a fine black powder. 
 This is lamp-black. 
 
 Printers' ink is a 
 mixture of lamp- 
 black and oil ; every 
 printed mark on this 
 page is a thin layer 
 of carbon clinging 
 tightly to the paper. 
 Action of Charcoal on Gases Charcoal is very por- 
 ous, and has remarkable power to absorb gases. Let us 
 study this action by experiment with ammonia. 
 
 Ex. 67. I must first heat the charcoal to redness to 
 drive out the air already in it. I select a piece that has 
 been well burned, make it about one inch long, and small 
 enough to slide easily into my graduated cylinder. I place 
 it in the bottom of my porcelain dish, or letter, in a large 
 iron spoon, cover it completely with fine sand, and put it 
 in a good fire. After it has been heated to full redness 
 for some time 1 let it cool, still protected by the sand. 
 
 While the spoon is cooling 1 fill my cylinder with am- 
 monia gas, in this way : 
 
COMPOSITION OF PLANTS. 
 
 107 
 
 Place the cylinder, inverted, through the ring of the sup- 
 port. Pour 5 cc. liquid ammonia into the side-neck tube, 
 
 and put the delivery 
 
 tube up into the cyl- 
 inder. Then gently 
 
 heat the liquid. I 
 
 can hold it by means 
 
 of a strip of paper 
 
 which I wind around 
 
 it, as shown in Fig. 
 
 50. Ammonia gas 
 
 will be driven over 
 
 into the cylinder, 
 
 and, being little 
 
 more than half as FI-. 50. 
 
 heavy as air, it will rise to the top and gradually expel the 
 
 air until the cylinder is filled. 
 
 I now place the cold charcoal in the mouth of the cylin- 
 der and then quickly lower it into a dish 
 of mercury. If the mercury rises in the 
 cylinder, as in Fig. 51, it will prove that 
 the ammonia gas is being absorbed by the 
 charcoal. 
 
 FACTS. Charcoal will take up 90 times 
 its own volume of ammonia gas, but only 
 8 or 9 times its volume of oxygen or nitro- 
 gen or carbon dioxide. This remarkable 
 power of charcoal makes it very useful in 
 hospitals and other places where offensive 
 
 odors are to be found. It will absorb the bad gases, and 
 
 thus purify the air. 
 
 Even animal substances, when decaying, lose their power 
 
 to offend us by their odor, if covered with a layer of good 
 
 charcoal. The decay will go on, but the odor will be lost. 
 
 Fig. 51. 
 
108 
 
 COMPOSITION OF PLANTS. 
 
 Action of Charcoal on Colors. Charcoal also has 
 the power to absorb many coloring matters. Animal char- 
 coal, or bone-black, possesses this property in higher degree 
 than wood charcoal. 
 
 Ex. 68. I prepare a filter, and rest the funnel in the 
 mouth of the cylinder. I fill the filter nearly full of bone- 
 black. Finally, I pour upon it some water colored with 
 blue litmus. If it comes through still colored, I pour it 
 back and let it run through a second time. Is the color 
 removed ? It has been absorbed by the charcoal. 
 
 Ex. 69. In the same way I filter some water colored 
 with cochineal. 
 
 Ex. 70. I try a solution of dark brown sugar. 
 Ex. 71. I try a solution of potassium chromate. This 
 is a mineral coloring-matter ; the others have been organic. 
 Is the color discharged in all these cases ? 
 APPLICATION. This power of charcoal makes it very 
 useful for taking the color out of liquids. Great quantities 
 
 are used to remove the 
 brown color from crude 
 sugar. After passing 
 the dark syrup through 
 a charcoal-filter it is 
 bright and colorless. 
 
 Charcoal filters are 
 much used to purify 
 drinking-water. The 
 
 ^^MP*--* a ^-,^^-iU-- charcoal gradually loses 
 ^^ "7^ its power as its pores 
 
 Flg M - are more and more 
 
 filled with the impurities. Fresh portions should then be 
 put in its place, or the same portion may be again heated 
 to redness, which will restore its power. 
 
COMPOSITION OF PLANTS. 109 
 
 Action of Charcoal on Oxides. Charcoal has a strong 
 attraction for oxygen, and when very hot it will decompose 
 many compounds of oxygen in order to unite with it. 
 
 Ex. 72. I make a mixture of 1 g. copper oxide with 
 about its own bulk of powdered charcoal, put it into the 
 side-neck ignition-tube, and place the end of the delivery 
 tube in some lime-water contained in a test-tube, as shown 
 in Tig. 52, and then apply the heat of the Bunsen lamp. 
 
 What is the effect on the lime-water ? 
 
 What, then, was the gas produced by the action ? 
 
 What are the elements of this gas ? 
 
 In what form were these elements in the mixture ? 
 
 Can you see any change in the black copper oxide ? 
 
 What, then, must have been the action of the carbon ? 
 
 THE FACTS. The black copper oxide is composed of 
 copper and oxygen, but when heated the carbon takes the 
 oxygen away from the copper and unites with it to form 
 carbon dioxide. This leaves the copper free. The carbon 
 dioxide whitens lime-water. The copper left behind should 
 appear distinctly reddish in the tube. 
 
 This power of carbon to decompose oxides makes it very 
 useful in the work of getting metals out of ores. Iron, for 
 example, is found in the mine in the form of iron oxide, 
 and by mixing this ore with coal, and then heating it 
 intensely in a furnace, its oxygen is taken away by the 
 carbon, and the iron is left in the metallic form. 
 
 The Diamond The diamond, most brilliant of gems, 
 
 is nothing but carbon. It is crystallized carbon. Dull, 
 black charcoal, very common and very cheap, and the beau- 
 tiful diamond, most costly of precious gems, are only two 
 different forms of the same element. 
 
 The diamond is the hardest known substance. It can- 
 not be cut or even scratched by any other. Very small 
 
110 
 
 COMPOSITION OF PLANTS. 
 
 and otherwise useless diamonds are set in the end of a 
 proper handle and are commonly used for cutting glass. 
 
 When found in the earth the diamond has the shape and 
 appearance of a roughly rounded pebble. This rough gem is 
 "cut" into one of two principal forms of jewel. They are 
 called the brilliant and the rose. The first of these is re- 
 garded as the finest. Its shape is well shown in Fig. 53. 
 t Ki Look at the gem sidewise, 
 
 and it appears as seen in 
 the upper part of the pic- 
 ture; look at the top of 
 it, and it appears as seen 
 in the lower part. The 
 form of the rose is seen in 
 Pig. 54 ; a side view above 
 and a top view below. 
 
 Graphite. Another 
 form of carbon is known 
 under the common name of 
 black-lead, and is very fa- 
 miliar to us in its most 
 useful shape, the lead of 
 our lead-pencils. This 
 name does not belong to 
 it properly, for it is not 
 lead. It has no proper- 
 ties like those of lead ex- 
 cept that which allows it 
 to leave marks upon paper. It is sometimes called plum- 
 bago; but the name by which it is generally known in 
 chemistry is graphite. 
 
 Graphite. is found in the earth. It is as black as coal, 
 but it has a dull shining appearance, which coal has not. 
 It is among the softest minerals to be found, and as per- 
 
 Fig. 53. 
 
COMPOSITION OF PLANTS. Ill 
 
 fectly opaque as can be. How unlike the hard and trans- 
 parent diamond in these respects ! 
 
 THREE FORMS OF THE SAME ELEMENT. All three of 
 these forms of carbon are alike in. some respects. No fire 
 can melt them. No liquid can dissolve them, if we except 
 melted iron, which seems to dissolve a little carbon. They 
 cannot be changed by exposure to the atmosphere ; they 
 suffer no decay, no rust. But let them be heated hot 
 enough, where oxygen is 
 present, and they will burn, 
 and the experiment shows 
 that they are not only much 
 alike in some respects, but 
 that they are actually the 
 same kind of matter. 
 
 For we have proved by 
 experiment, that when char- 
 coal burns carbon dioxide is 
 produced. By heating the 
 diamond to a white heat, in 
 oxygen gas, it will be con- 
 sumed, and carbon dioxide 
 will be found in its place. 
 Graphite has also been FiJ 64> 
 
 burned, and the same substance, carbon dioxide, produced 
 by its combustion. 
 
 Now we know that it takes carbon and oxygen always, 
 and nothing else, to make carbon dioxide. The carbon 
 must come from the fuel which burns. Hence charcoal, 
 diamond, and graphite are all the same element, carbon. 
 
 What other element have we found to exist in more than 
 one form ? What name is given to this property of ele- 
 ments ? 
 
 How this element has come to be in such wonderfully 
 
112 
 
 COMPOSITION OF PLANTS. 
 
 different forms we cannot tell. No chemist can change 
 charcoal into diamond, nor can any one tell us how it has 
 been done in the great laboratory of nature. 
 
 CARBON DIOXIDE. 
 
 Preparation. Carbon dioxide is the chief compound of 
 carbon and oxygen. It is most easily obtained by the 
 action of hydrochloric acid on marble. 
 
 Ex. 73. My apparatus is much the same as that used 
 in making oxygen (Ex. 23). It is shown in Fig. 55. A 
 
 little lime-water is 
 placed in the bottle 
 d, and clear water 
 in a, enough to 
 cover the end of the 
 glass tube. The 
 conical flasks are 
 joined by rubber 
 tubes, the long tube 
 in each to the short 
 tube of the one be- 
 fore it, and then 
 rl - " the long tube of a 
 
 to the side-neck of the flask s. The joints are all air-tight. 
 I put about 10 g. of marble in small pieces into the side- 
 neck flask and pour upon it about 25 cc. of dilute hydro- 
 chloric acid, half water, and at once close the flask with its 
 stopper. The gas, making in s, will drive the air before it 
 all out at d. The flame of a burning splinter thrust into d 
 will tell when the bottle is full of the carbon dioxide. 
 Then exchange this bottle for another having some blue 
 litmus-water instead of lime-water. 
 
 If the gas begins to come too slowly, I may remove the 
 cork of , add more acid, and replace it. Now consider 
 the following things: 
 
COMPOSITION OF PLANTS. 
 
 113 
 
 Fig. 56. 
 
 Describe the action which took place in s. 
 What effect was produced in the lime-water ? 
 What is the effect of this gas on flame ? 
 What is the effect of it on blue litmus ? 
 Why does the gas stay in the open bottle ? 
 Ex. 74- What if the vessel of carbon dioxide is open 
 downward ? I remove the tubes 
 and cork from flask c, Fig. 55, and 
 then hold the flask's mouth upon the 
 lip of a small wide-mouth bottle, as 
 if to pour the gas, as shown in Fig. 
 56. After a minute I place the flask 
 upon the table and plunge the flame 
 of a splinter down into the bottle, 
 and afterward into the flask. The 
 flame shows that the gas was actu- 
 ally poured, like water, from c into the bottle. 
 
 Ex. 75. Is this gas soluble in water? The gas bub- 
 bled through the water in a, Fig. 55, and I test that water 
 to see whether there is carbon dioxide 
 in it. I put some lime-water in a test- 
 tube, and, after taking the rubber tubes 
 from a, I lift the flask and pour water 
 from it into the lime-water, as shown in 
 Fig. 57. 
 
 If the water in a has dissolved carbon 
 dioxide, the lime-water will be whitened. 
 
 DESCRIPTION. Carbon dioxide is a compound of 
 carbon and oxygen: this was proved by Ex. 26. We 
 see that it is a colorless gas, and much heavier than air 
 (Exs. 73, 74). In fact it is about one and one-half times 
 heavier than air (1.529). It whitens lime-water by com- 
 bining with the lime and making the white solid called 
 calcium carbonate, which the water cannot dissolve, and it 
 
 Fig. 57. 
 
114 COMPOSITION OF PLANTS. 
 
 reddens blue litmus-water (Ex. 73), for a reason which will 
 appear by and by. 
 
 This gas will put out a fire (Ex. 73) just as quickly as 
 will water, and for the same reason. A body will not burn 
 without oxygen, and when covered with water the oxygen 
 of the air cannot get to it. So when in carbon dioxide, no 
 oxygen can reach the body, and the fire dies. 
 
 So, too, this gas will cause death, just as will water. An 
 animal must have oxygen to breathe, or it must die. It 
 drowns in water because water keeps the air away from 
 its lungs; carbon dioxide will do the same thing. There 
 is too little of this gas in the open air to do harm, but 
 where it collects in large quantities an animal dies because 
 it can get too little oxygen to keep it alive. 
 
 It sometimes collects in mines, and the miners call it 
 ckoke-damj). It sometimes collects in wells, and makes 
 them dangerous to enter ; a lighted candle will tell a work- 
 man whether this gas is present in dangerous quantities. 
 It often collects in school-rooms and churches and other 
 unventilated houses, but not often enough of it to do much 
 harm. The truth is that the breath of people is full of 
 other gases, some of which are very poisonous, and the 
 mischief in unventilated rooms is done by these compan- 
 ions of the carbon dioxide instead of by this gas itself. 
 
 Carbon dioxide is soluble in water (Ex. 75). It is found 
 that water will usually dissolve about its own volume. But, 
 like all gases, more will dissolve in colder water, and still 
 more when under greater pressure. Nearly all water con- 
 tains this gas, but the quantity in solution is generally 
 small. In some springs, however, it is very abundant. It 
 is so in the noted mineral springs of Saratoga. And the 
 refreshing summer drink soda-water is nothing but 
 water charged with a large quantity of this gas which has 
 been forced into it by great pressure. 
 
COMPOSITION OF PLANTS. 115 
 
 Carbon Monoxide Besides carbon dioxide there is 
 
 another compound of carbon and oxygen called carbon 
 monoxide. See p. 82. It is a colorless gas. It takes fire 
 easily, and burns with a pale blue flame ; this is the flame 
 which is often seen playing over the surface of a new- 
 made coal-fire. When the coal burns at the bottom of 
 the grate it produces carbon dioxide, as usual, but as this 
 carbon dioxide goes up through the hot coal above it 
 gives up a part of its oxygen and becomes carbon mon- 
 oxide. And then when this monoxide comes out into hot 
 air, at the surface, it takes oxygen and becomes carbon 
 dioxide again. 
 
 This gas is very likely to escape being burned. There 
 may not be air enough, or there may not be heat enough 
 to burn it. This should be remembered when coal is 
 used for warming rooms, for carbon monoxide is a very 
 poisonous gas. Accidents have many times happened 
 from burning charcoal in open fires with poor draught. 
 This poisonous gas escaping into the room destroys life. 
 
 COMPOSITION OF THE TWO OXIDES. It is found by 
 analysis of the two gases that the carbon monoxide con- 
 tains just one-half as much oxygen as the carbon dioxide. 
 The proportions are as follows : 
 
 In carbon monoxide there are 16 of O combined with 12 of C 
 dioxide " " 32 " O " " 12 " C 
 
 What law does this illustrate ? 
 
 Compounds of Carbon and Hydrogen. No other ele- 
 ments form so many compounds with one another as do 
 carbon and hydrogen. Of carbon and oxygen there are 
 only two. Of nitrogen and oxygen there are five, and 
 this is rather an unusual number for two elements only. 
 But of carbon and hydrogen the compounds are many 
 scores in number. They are called hydrocarbons. Just 
 now we will study only one of these. 
 
116 COMPOSITION OF PLANTS. 
 
 Methane This is the simplest one of the hydrocar- 
 bons. It is commonly called marsh-gas, which is a very 
 appropriate name, because it is abundant in marshy 
 places. Have you never seen the water of ponds and 
 quiet pools stirred by bubbles of gas breaking at the sur- 
 face ? It is a very common thing to be seen in water 
 standing over muddy bottoms. The bubbles are of marsh- 
 gas. They are set free by the decay of vegetable sub- 
 stances in the mud below. 
 
 Marsh-gas flows from coal-beds into the mines where 
 the laborers are at work. The most awful effects are 
 then sometimes produced by it. It is very combustible, 
 and, more than this, when mixed with air it is terribly 
 explosive. Fancy it flowing into a mine, mixing with the 
 air around the miners, and the mixture then touching 
 the flame of the miner's lamp! The lamps and the lives 
 of the miners are then extinguished at once by a terrible 
 explosion. 
 
 The miners have given this gas the name of fire-damp. 
 
 It is found by analysis that methane is made of carbon 
 and hydrogen only, and in quantities by weight which are 
 as 12 to 4. 
 In methane there are 12 parts of C combined with 4 parts of H. 
 
 How many combining weights of carbon in the 12 of C ? 
 How many combining weights of hydrogen in the 4 of 
 H? 
 
ELEMENTS, MOLECULES, AND ATOMS. 
 
 The Number of the Elements We have already 
 
 seen, p. 24, that an element is a substance which has never 
 yet been decomposed. 
 
 At present (July, 1886) seventy-one elements are known. 
 Some of these have been discovered very lately, and per- 
 haps others may be found in the future. On the other 
 hand some so-called elements have been found to be com- 
 pounds, and it may be that some of the seventy-one shall 
 yet be decomposed. All that we can say is that there are 
 seventy-one kinds of matter which chemists to-day are not 
 able, by any means in their power, to break into simpler 
 bodies. As out of twenty-six letters of the alphabet all 
 the words in the English language are made, so out of 
 these seventy-one elements all the compounds in nature 
 are formed. 
 
 But only a few of this small number are at all abundant. 
 In fact, the larger part of the earth, and all it contains, is 
 made up of only about a dozen elements. All the water on 
 the globe consists of oxygen and hydrogen. Four-fifths of 
 the air is nitrogen. These three, with carbon, make up by 
 far the larger part of all plants, and the bodies of animals. 
 And as for rocks and soils, they consist chiefly of those 
 just named, with eight others, sulphur, silicon, potas- 
 sium, sodium, calcium, magnesium, aluminum, and iron. 
 With these exceptions, the elements are not common, and 
 one-third of the whole number are very rare. 
 
 The names of all the elements now known are given in 
 the following table. The symbols and atomic weights 
 will be explained soon. 
 
 117 
 
118 
 
 ELEMENTS, MOLECULES, AND ATOMS. 
 
 THE SEVENTY-ONE ELEMENTS. 
 
 
 
 NAMES. 
 
 Symbols. 
 
 Atomic 
 Weights. 
 
 NAMES. 
 
 Symbols. 
 
 Atomic 
 Weights. 
 
 Aluminum . . 
 
 Al. 
 
 27.3 
 
 Molybdenum . 
 
 Mo. 
 
 96. 
 
 Antimony , \ 
 
 Sb. 
 
 120. 
 
 Nickel ... 
 
 Mi. 
 
 58. 
 
 Arsenic . . . 
 
 As. 
 
 75. 
 
 Nitrogen . . . 
 
 N. 
 
 14. 
 
 Barium . . . 
 
 Ba. 
 
 137. 
 
 Osmium . . . 
 
 Os. 
 
 198.6 
 
 Beryllium (') . 
 
 Be. 
 
 9. . 
 
 Oxygen . . . 
 
 0. 
 
 16. 
 
 Bismuth . . . 
 
 Bi. 
 
 208. 
 
 Palladium . . 
 
 Pd. 
 
 106. 
 
 Boron . . . 
 
 B. 
 
 11. . 
 
 Phosphorus 
 
 P, 
 
 31. 
 
 Bromine . . . 
 
 Br. 
 
 80. 
 
 Platinum . . 
 
 Pt. 
 
 195. 
 
 Cadmium . V .J 
 
 Cd. 
 
 112. 
 
 Potassium . . 
 
 K. 
 
 39.1 
 
 Csesium . . . 
 
 Cs. 
 
 1*3. 
 
 Rhodium . . 
 
 Rh. 
 
 104. 
 
 Calcium . . , l 
 
 Ca. 
 
 40. 
 
 Rubidium . . 
 
 Rb. 
 
 85.5 
 
 Carbon . . . 
 
 C. 
 
 12. 
 
 Ruthenium. . 
 
 Ru. 
 
 103.5 
 
 Cerium . . . 
 
 Ce. 
 
 141. 
 
 Samarium . . 
 
 Sin. 
 
 150. 
 
 Chlorine . . . 
 
 Cl. 
 
 35.5 
 
 Scandium . . 
 
 Sc. 
 
 44. 
 
 Chromium . . 
 
 Cr. 
 
 52. 
 
 Selenium . . 
 
 Se. 
 
 79. 
 
 Cobalt . . . 
 
 Co. 
 
 69. 
 
 Silicon . . . 
 
 Si. 
 
 28. 
 
 Columbium ( 2 ) . 
 
 Cb. 
 
 94. 
 
 Silver. . . . 
 
 Ag. 
 
 108. 
 
 Copper . . . 
 
 Cu. 
 
 63.3 
 
 Sodium . . . 
 
 Na. 
 
 23. 
 
 Decipium . . 
 
 Dp. 
 
 ? 
 
 Strontium . . 
 
 Sr. 
 
 87.5 
 
 Didymium ( 3 ) . 
 
 Di. 
 
 142.3^ 
 
 Sulphur . . . 
 
 S. 
 
 32. 
 
 Erbium . . , 
 
 Er. 
 
 106. 
 
 Tantalum . . 
 
 Ta. 
 
 182. 
 
 Fluorine . . . 
 
 F. 
 
 19. 
 
 Tellurium . . 
 
 Te. 
 
 125. 
 
 Gallium . . . 
 
 -Ga. 
 
 69. 
 
 Terbium . . . 
 
 Tb. 
 
 ? 
 
 Germanium. . 
 
 Gr 
 
 72.75? 
 
 Thallium . . 
 
 Tl. 
 
 204. 
 
 Gold .... 
 
 An. 
 
 196.5 
 
 Thorium . . . 
 
 Th. 
 
 232. 
 
 Hydrogen . . 
 
 H. 
 
 1. 
 
 Thulium . . . 
 
 Tm. 
 
 i 
 
 Indium . . . 
 
 In. 
 
 113.6 
 
 Tin .... 
 
 Sn. 
 
 118. 
 
 Iodine . . . 
 
 I. 
 
 127. 
 
 Titanium . . 
 
 Ti. 
 
 48. 
 
 Iridimu . . , 
 
 Ir. 
 
 193. 
 
 Tungsten ( 4 ) . 
 
 W. 
 
 184. 
 
 Iron .... 
 
 Fe. 
 
 56. 
 
 Uranium. . . 
 
 U. 
 
 240. 
 
 Lanthanum 
 
 La. 
 
 138.2 
 
 Vanadium . . 
 
 V. 
 
 51.2 
 
 Lead . . . . 
 
 Pb. 
 
 207. 
 
 Ytterbium . . 
 
 Yb. 
 
 178. 
 
 Lithium . . . 
 
 Li. 
 
 7. 
 
 Yttrium . . . 
 
 Yt. 
 
 89. 
 
 Magnesium . . 
 
 Mg. 
 
 24. 
 
 Zinc .... 
 
 Zn. 
 
 65. 
 
 Manganese . . 
 
 Mn. 
 
 55. 
 
 Zirconium . . 
 
 Zr. 
 
 90. 
 
 Mercury . . . 
 
 Hg- 
 
 200. 
 
 
 
 
 (') Beryllium is also called Glucinum, with the symbol Gl. 
 
 (2) Columbian! is also called Niobium, with the symbol Nb. 
 
 ( 3 ) The announcement ha* come from Vienna that Didymium lias been decom- 
 posed. See Chemical News, vol. 52, and Nature, vol. 3'J, p. 435. 
 
 ( 4 ) Tungsten has also been called Wolt'ramiuiu. 
 
ELEMENTS, MOLECULES, AND ATOMS. 119 
 
 The Three Forms of Matter Earth, water, and air 
 
 represent the solid, liquid, and gaseous forms of matter. 
 So far as we know, all kinds of matter are in one or another 
 of these three conditions. But ice and water and steam 
 are all one kind of matter, and yet one is a solid, another 
 is a liquid, and another a gas. 
 
 Ice, when heated, melts into water, and water when 
 heated to a higher temperature boils into steam. We 
 tind that many other solids are like ice in this respect 
 they melt when heated, and that other liquids are like 
 water they may be changed into vapor by heat. 
 
 These are facts. We know them to be so, because we 
 have seen these changes happen over and over again. 
 Indeed, so many substances have been tried and found to 
 be solid at low temperature, liquid at some higher tempera- 
 ture, and gaseous at some temperature higher still, that 
 we feel quite sure that the facts are the same for all ; and 
 so we say that 
 
 The solid, liquid, and gaseous forms of matter depend on 
 the amount of heat in them. 
 
 This one statement, made out of many facts, is a law. 
 
 Another Effect of Heat If we warm a piece of 
 
 iron it will become larger, and if we cool it it will become 
 smaller. The same thing is true of a piece of wood ; it is 
 larger when it is hot than when it is cold. A given weight 
 of water, or of air, is found to be larger and larger as it is 
 heated more and more. These are facts. They have been 
 proved to be true of the substances named, and of a great 
 many more beside. Now let us put all such facts together 
 into one statement by saying that 
 
 Heat makes a body larger without changing its weight. 
 
 This is a law. A law, in science, is simply a single 
 statement which covers a large number of facts. 
 
120 ELEMENTS, MOLECULES, AND ATOMS. 
 
 THE REASON. A body is larger when it is hot ; can 
 we tell why it is so ? Nobody knows with absolute cer- 
 tainty why bodies should expand when heated. But the 
 best way to account for it is to suppose that matter is 
 made up of very small particles which are quite separate 
 from one another, so that they may be driven farther apart 
 or crowded nearer together. Heat drives them farther 
 apart and makes them till more space, and cold allows 
 them to fall more closely together, and thus to fill a smaller 
 space. Surely this is a very good reason why heat should 
 make a body larger, and cold should make it smaller. If a 
 body were made up of separate particles it would behave 
 just as we see that it does behave when heated and cooled, 
 and so we may suppose that it is made up of such particles. 
 Perhaps it is so. 
 
 If we imagine every body to be made up of small parti- 
 cles which are quite separate, we can understand many 
 other facts beside expansion by heat. Take, for example, 
 the fact that you make an india-rubber ball smaller 
 when you squeeze it. If we are right in supposing that 
 the ball is made up of a great multitude of small, separate 
 particles, the hand would make it smaller by crowding 
 them closer together. The ball acts just (ts if it were made 
 up of separate particles. Probably it is so. 
 
 In a great many other ways bodies behave exactly as if 
 they were made up of such separate particles. Indeed, so 
 i'ar as they have been examined, the facts are always just 
 what we should expect if matter be made up of small par- 
 ticles which are some distance apart. On this account we 
 believe it to be so. 
 
 Now, something which is believed because it gives good 
 reasons for a large number of facts is called a theory. 
 That all bodies are made up of minute particles which do 
 not touch one another is our theory of matter. 
 
ELEMENTS, MOLECULES, AND ATOMS. 121 
 
 The student cannot too early nor too carefully fix in his 
 mind the difference between facts and theories. Facts are 
 things known to be true ; theories are things believed to be 
 true. 
 
 Molecules. According to the theory of matter just 
 stated, all bodies are made up of separate particles. These 
 particles cannot be seen. They are so small as to be 
 quite beyond our sight with the best microscope. They 
 are the very smallest pieces of a substance which can pos- 
 sibly exist, so that to divide them into parts will change 
 the substance into something else. They are called mole- 
 cules. A molecule is a particle of substance so small that 
 it cannot be divided without changing the nature of the 
 substance. Molecules of the same substance are all alike, 
 but the molecules of different kinds of matter are not alike. 
 
 Some Facts about the Expansion of Gases It has 
 been found by very careful and repeated experiments that 
 if we take 273 cc. of air as cold as freezing water, C. 
 and warm it just 1 C., it will become just 274 cc. Add 
 another degree of heat and it will become 275 cc., and so 
 on, each degree of heat expanding it just 1 cc. In other 
 words, one degree of heat will always expand air just 
 27TT f what its volume is at C. 
 
 The rate has been found also for many other gases, and 
 it is the same for all. This is a very important fact. It 
 is not so among solids and liquids ; no two solids expand 
 exactly alike ; no two liquids. Why do all gases expand 
 alike when heated, while solids and liquids do not ? 
 
 Again, if air is pressed in a close vessel it will be 
 crowded into smaller volume ; but, on the other hand, if 
 we put less pressure on it the air will expand. Other 
 gases behave in the same way. And the same change of 
 pressure will change the volume of one just exactly as 
 much as another. This is another important fact. It is 
 
122 ELEMENTS, MOLECULES, AND ATOMS. 
 
 not a fact for solids and liquids ? Why should the same 
 pressure condense all gases exactly alike ; and the removal 
 of the same pressure expand all gases exactly alike ? 
 
 The Theory. These and other facts led Avogadro, in 
 1811, to suppose that when two gases are equally warm, 
 and under the same pressure, a cubic inch of one contains 
 just as many molecules as a cubic inch of the other. And 
 since all gases behave, in so many respects, just as they 
 would be expected to do if this famous hypothesis were 
 true, it is believed to be as Avogadro supposed. 
 
 Equal volumes of all gases, at the same temperature and 
 pressure, contain the same number of molecules. 
 
 This is Avogadro's theory : but it is often called Avo- 
 gadro's law. 
 
 Chemical Changes are Changes in the Molecules. 
 When water is decomposed by electricity (Ex. 37) it is 
 broken into two parts ; one part is hydrogen, the other is 
 oxygen. The change is believed to take place in each sep- 
 arate molecule. When mercuric oxide is heated (Ex. 5) 
 every molecule of it is broken into two parts ; one is mer- 
 cury, the other oxygen. When marble and hydrochloric 
 acid act (Ex. 73) every molecule of these two substances 
 is broken into two parts, and then those parts fall together 
 again, in a different way, and make the molecules of two 
 new kinds of matter. 
 
 Atoms. Now what shall we call the smaller particles 
 in a molecule ? They are atom.s. These are the very 
 smallest pieces of matter that take part in a chemical 
 change. They cannot be divided by any known process 
 whatever. All bodies are made up of molecules, and mole- 
 cules are made up of atoms. 
 
 If the atoms of a molecule are alike, the substance is 
 an element, but if the atoms in a molecule are not all alike 
 the substance is a compound. 
 
ELEMENTS, MOLECULES, AND ATOMS. 123 
 
 The Explanation of the Law of Multiple Propor- 
 tions The law of multiple proportions is the statement 
 
 of a fact. We know that the combining weight of an ele- 
 ment is never divided in chemical changes ; can we tell why ? 
 
 The most natural reason is found by supposing the 
 combining weight to be the weight of a particle of mat- 
 ter which cannot be divided, that is, of an atom. Such 
 particles will pass unbroken from one kind of compound 
 into another. One of them may go alone, or some whole 
 number of them may go together. The weight of one of 
 them is the combining weight of the element, and of any 
 whole number of them, is a multiple of that combining 
 weight. And so 
 
 If jone element combines with another, in more pro- 
 portions than one, these proportions must be multiples of 
 its combining weight. 
 
 The Atomic Theory. This theory of matter is known 
 as the Atomic Theory. Its main points are these : All 
 bodies are made up of molecules, and molecules are made 
 up of atoms. All chemical changes are changes in the 
 arrangements of the atoms, and the combining weights 
 of the elements are the relative weights of their atoms. 
 
 The theory of atoms was first proposed in 1808 by John 
 Dalton. He was the first to see clearly that the combi- 
 nation of the elements, in definite and in multiple pro- 
 portions, are facts which seem to show that there are 
 particles of matter which cannot be divided. The atomic 
 theory was made to explain these laws of combination, and 
 it is well fixed in chemistry, because it not only explains 
 these, but has been found to explain new facts, as fast as 
 they have been discovered, down to the present time. 
 
 Symbols of Elements Instead of writing the full 
 
 name of the element hydrogen, we may simply write 
 the first letter, H, to represent it. H is then called the 
 
 if 
 
124 ELEMENTS, MOLECULES, AND ATOMS. 
 
 symbol of hydrogen. In the same way is the symbol of 
 oxygen, N of nitrogen, and C of carbon. 
 
 Sometimes the names of two or more elements begin 
 with the same letter, as carbon, calcium, and copper. In 
 this case a small letter is used with the large initial, thus : 
 the symbol of calcium is Ca, and that of copper is Cu. 
 The latter is from the Latin name of copper, which is 
 Cuprum. A symbol represents the name, and also just 
 one atom of an element. 
 
 Formulas of Compounds. Instead of writing the full 
 name mercuric oxide, we may simply write the symbols 
 of the elements of this compound, side by side, Hg for 
 mercury and for oxygen, making HgO to represent it. 
 Hg O is then called the formula for mercuric oxide. H Cl 
 is the formula for hydrochloric acid. 
 
 The formula of a compound represents one molecule of it. 
 
 H 2 is the formula for water ; the small figure 2 means 
 that there are two atoms of hydrogen combined with one 
 of oxygen in the molecule. C 2 is the formula for carbon 
 dioxide, and shows that one molecule contains one atom 
 of carbon and two atoms of oxygen. H 2 S 4 is the formula 
 for sulphuric acid ; what does it show ? 3 H 2 S O 4 means 
 three molecules of sulphuric acid, and 2H 2 O means two 
 molecules of water. Notice the different meaning of 
 figures placed before the formulas and those placed at the 
 right and a little below the symbols, in the formula. 
 
 In reading symbols and formulas, the names of the sub- 
 stances, and not the letters used, should always be given. 
 We should use symbols and formulas to shorten writing, 
 but not to shorten speech. 
 
 Atomic Weights. We have learned that hydrochloric 
 acid contains 35.5 times as much chlorine as hydrogen ; we 
 may say this of any quantity ; it is true of one molecule, 
 which contains one atom of chlorine and one of hydrogen. 
 
ELEMENTS, MOLECULES, AND ATOMS. 125 
 
 These numbers, 1 and 35.5, are called the atomic weights 
 of hydrogen and chlorine, because they are supposed to 
 represent the relative weights of the atoms of these two 
 elements. We have no idea how much, or rather how 
 little, the atom of hydrogen really weighs, but we do be- 
 lieve that, whatever it does weigh, the atom of chlorine 
 weighs 35.5 times as much. We cannot tell the weight 
 of either, in fractions of a gram or ounce, but we can call 
 the weight of the hydrogen atom 1, without saying what, 
 and then we can say that an atom of chlorine weighs 35.5. 
 
 These numbers are the same as those which have been 
 called combining weights, p. 98. We know that they are the 
 smallest relative weights of these elements which combine ; 
 this is a fact discovered by experiment. It is believed that 
 they represent the weights of the atoms of these elements. 
 This is a part of the atomic theory. 
 
 And now we see that the symbol of an element not 
 only represents one atom, but also one atomic weight. 
 
 Molecular "Weights If a molecule is made of atoms 
 we can find its weight by adding the weights of its atoms 
 together. There are three atoms in a molecule of water, 
 H 2 0, two of hydrogen and one of oxygen. The weight 
 of an atom of hydrogen is 1, and of an atom of oxygen 
 is 16, and the weight of all three atoms together must be 
 18. The molecular weight of water, H 2 0, is therefore 18. 
 It is not 18 grams, nor 18 grains, but simply 18 times as 
 much as the weight of an atom of hydrogen. 
 
 The atomic weights are given in the table on p. 118, and 
 these will enable one to find the molecular weight of any 
 substance whose formula is known. Try it in the follow- 
 ing examples. 
 
 What is the molecular weight of hydrochloric acid, HC1? 
 
 " " " " sodium chloride, NaCl? 4" 
 
 " " " " mercuric oxide, Hg O ? j 
 
 " " " " sulphuric acid, H 2 SO 4 ? a $ 
 
126 ELEMENTS, MOLECULES, AND ATOMS. 
 
 Reactions. Chemical changes are also called reactions. 
 Now chemical changes are changes in the molecules of sub- 
 stances, and we can show what they are by making changes 
 in the formulas which represent the molecules. In this 
 way symbols and formulas are a great help in the study 
 of experiments. 
 
 For example, suppose we wish to know all about the 
 reaction of sodium and hydrochloric acid. We must 
 begin by making the experiment. We may then study 
 the results by the help of symbols and formulas. 
 
 REACTION OF SODIUM AND HYDROCHLORIC ACID. Ex. 
 76. I measure 2 cc. of strong hydrochloric acid into a 
 test-tube which stands in the rack, drop in upon it a piece 
 of sodium as large as a small pea, and loosely cover the 
 mouth of the tube with a piece of paper. After half a 
 minute, I push the flame of a lighted match down into 
 the tube. When the sodium has disappeared, I drop in 
 another piece of about the same size. 
 
 What gas is set free by the chemical action ? 
 
 What proof is seen that another substance is produced ? 
 
 To find out what is this second product, I first let it 
 settle to the bottom of the tube, and then pour off the 
 liquid so carefully that I leave the solid behind almost dry. 
 In this way I get rid of most of the acid which was not 
 decomposed. I then add three or four cubic centimeters 
 of water, to dissolve the white solid, pour the solution 
 into a small porcelain dish, and heat it over a small flame 
 until the water is all driven off and the solid remains dry 
 and white. The dish must now stand until cold, after 
 which I add a few drops of water in which the white solid 
 again dissolves. By tasting this liquid you may learn 
 
 What is this second product of the chemical action. 
 
 We have now got the facts about the reaction we are 
 studying. To get the facts is always the first step in an 
 investigation. 
 
ELEMENTS, MOLECULES, AND ATOMS. 127 
 
 NEXT WRITE THE REACTION. Now that we know what 
 substances were used and what new substances were made, 
 the next step is to use formulas and signs to show what 
 happened. 
 
 We added sodium to the hydrochloric acid in the tube ; 
 we can show that fact by writing the symbol of sodium, 
 which is Na, and the formula of the acid, which is H Cl, 
 with the sign of addition between them, thus : Na + H Cl. 
 We know by the taste, and by the explosion, that common 
 salt and hydrogen were produced. We can show this by 
 writing the formula of common salt, or sodium chloride, 
 Na Cl, and the symbol of hydrogen, H, with the sign of 
 addition between them, thus: NaCl + H. We know that 
 there is no loss nor gain of matter in any chemical change. 
 The new substances must contain every atom of the old, 
 and no others. We can show this by writing the old sub- 
 stances and the new, with the sign of equality between 
 them. Thus we have 
 
 Na + H Cl = Na Cl + H 
 
 We read this reaction in this way : one atom of sodium, 
 with one molecule of hydrochloric acid, yield one mole- 
 cule of sodium chloride, and one atom of hydrogen. This 
 describes the chemical change which took place. 
 
 Now USE ATOMIC WEIGHTS. This chemical expression 
 may be changed into numbers by writing the atomic weight 
 of each element, under its symbol, wherever that symbol 
 appears. Thus 
 
 Na + HC1 = NaCl -f H 
 23 + (1 + 35.5) = (23 + 35.5) + 1 
 23 + 36.5 = 58.5 + 1 
 
 If we had to make a quantity of common salt by this 
 process this last equation would be very useful because it 
 tells us just how much of the substances to use. We may 
 
128 ELEMENTS, MOLECULES, AND ATOMS. 
 
 call these numbers grains or grains or pounds, or any other 
 weights we please. The equation shows that if we use 23 
 grains of sodium and 36,5 grams of hydrochloric acid, we 
 can get just 58.5 grains of salt and 1 gram of hydrogen. 
 Knowing this it is easy to find how much of the constit- 
 uents to take for any desired quantity whatever of the 
 compound. 
 
 FINALLY SOLVE A PROBLEM. How much sodium would 
 be needed to make 100 g. of common salt by reaction with 
 hydrochloric acid ? 
 
 If for 58.5 g. of salt we need 23 g. of sodium, then for 
 100 g. of salt we should need fcy x 23, which is 39.31 + . 
 
 ANOTHER EXAMPLE. Let us study the decomposition of 
 mercuric oxide by heat. We have made the experiment 
 already. In Ex. 5 it was found that mercury and oxygen 
 were the products. We take the symbols from the table, 
 p. 118, and write the reaction thus : 
 
 Hg O = Hg + O 
 
 Read this equation in full. Refer to the table of ele- 
 ments, p. 118, for the atomic weights, and put them under 
 the symbols. What does this new equation show ? 
 
 How much mercury could be obtained from 100 g. of the 
 oxide ? And how much oxygen ? 
 
ACIDS, BASES, A1ST> SALTS. 
 
 Acids. We have already made use of several substances 
 called acids. We now set out to discover just what is 
 meant by the term acid. Let us examine a few of these 
 substances for this purpose. 
 
 Ex. 77. I fill a bottle two-thirds full of water and add 
 enough solution of blue litmus to color it distinctly. I 
 next add dilute sulphuric acid, 1 of acid to 10 of water, 
 drop by drop, and note the change in color. 
 
 I now add a drop or two of the same acid to a test-tube 
 nearly full of water, and touch a drop of this dilute solution 
 to my tongue, and note the taste of the acid. 
 
 I finally pour 5 cc. of strong sulphuric acid into 40 cc. 
 of water in a bottle, drop into it a clipping of sheet-zinc, 
 and cover the bottle with a square of heavy paper. In a 
 few moments I bring a lighted match to the mouth of the 
 bottle, lifting the cover at the same time, and note the 
 combustion which takes place. What is this gas which 
 is set free by the metal ? ft I 
 
 Ex. 78. I now use hydrochloric acid instead of sul- 
 phuric, and again note the 
 
 Change in the color of the blue litmus. 
 Taste of the acid. 
 Action with zinc. 
 
 Ex. 79. I next try acetic acid, and use magnesium 
 instead of zinc. I put 10 cc. of the acid in a test-tube, and 
 drop upon it a short piece of magnesium ribbon. Note 
 whether the same gas is given off as in the other cases. 
 Note also the taste of the acid, and its action on blue litmus. 
 
130 ACIDS, BASES, AND SALTS. 
 
 Ex. 80. I repeat the experiment with acetic acid, but 
 use iron instead of magnesium. I add the iron in the form 
 of filings, or the smallest tacks, and gently heat the liquid. 
 
 Is there any gas set free ? Is it hydrogen ? 
 
 Ex. 81. I use acetic acid again, but this time I add 
 small clippings of zinc, and heat the acid. Is the action 
 the same as before ? 
 
 We find that sulphuric acid, hydrochloric acid, and acetic 
 acid are alike in three things : they are all sour to the taste, 
 will redden blue litmus, and yield hydrogen by the action 
 of a metal. There are many other substances having these 
 same characters. All such are called acids. 
 
 THE CHIEF CHARACTERISTIC. The following table shows 
 the composition of several acids, by formulas: 
 
 Nitric acid . . . . .... .," H N O 3 
 
 Sulphuric acid ..'.... H 2 S O 4 
 
 Phosphoric acid . . . ....;;. . . H 8 PO 4 
 
 Hydrochloric acid H Cl 
 
 Hydroiodic acid . . '. . . . *'-.-. . HI 
 
 Hydrobromic acid H Br 
 
 and a glance at these symbols shows that hydrogen, H, is 
 a constituent in every one. Every acid contains hydrogen. 
 
 But there are many compounds containing hydrogen 
 which are not acids. An acid is a compound containing 
 hydrogen, which may be driven out by a metal, as in our 
 experiments. This is the chief character of an acid. 
 
 THE TWO CLASSES. Look at the two sets of formulas 
 in the table. In each acid of the first set, oxygen, O, is 
 present; it is not to be found in those of the second. 
 
 Now we may learn from this that there are two classes 
 of acids. One class contains the element oxygen, the other 
 does not. 
 
ACIDS, BASES, AND SALTS. 131 
 
 % 
 
 Salts. When in Ex. 77 our zinc drove the hydrogen 
 out of sulphuric acid, zinc sulphate was also made. 
 If we write the reaction 
 
 it shows how zinc and sulphuric acid may yield hydrogen 
 and zinc sulphate. 
 
 We see that 1 atom of the metal, Zn, takes the place of 
 2 atoms of hydrogen, H 2 , in the molecule of acid, so that 
 instead of H 2 S 4 we have Zn S 4 . 
 
 We should be careful to notice that the metal puts itself 
 in the place of the hydrogen of the acid to form the new 
 molecule. 
 
 The action is the same when zinc acts on other acids 
 instead of sulphuric. The zinc drives hydrogen out and 
 puts itself in the place of it. 
 
 Many other metals have the same power to act upon 
 acids. Not every metal can do this to every acid (Ex. 81), 
 but the power to put itself in the place of hydrogen in 
 acids is very common among the metals. 
 
 The new compounds, formed by this action of the metals, 
 are called salts. When sodium and hydrochloric acid are 
 used, the new compound, as we have seen, is common salt ; 
 you have only to evaporate the liquid to get the familiar 
 white solid. Every acid would yield a different kind of 
 salt with sodium. Each different metal also yields a 
 different salt with every acid on which it acts. 
 
 DEFINITION. A salt is a com^pound formed by putting a 
 metal in the place of hydrogen in an acid. 
 
 Hydroxides -- Some metals act on water very much 
 as the metals act on acids, but the new compounds will be 
 of a quite different character. Thus : 
 
 Ex. 82. I fill a bottle half full of water; add just 
 enough litmus to color it distinctly ; change its color to red 
 
132 ACIDS, BASES, AND SALTS. 
 
 by stirring it with a rod moistened with an acid, and then 
 drop upon its surface a bit of sodium. Note the change 
 in color, and prove that hydrogen is set free. 
 
 Ex. 83. I repeat the experiment, but use 25 cc. of 
 water without the litmus. When the sodium is gone, I 
 examine the liquid in three ways: 
 
 1. I moisten the end of a rod with the liquid, touch my 
 tongue with it, and note the taste. 
 
 2. I try its action on blue litmus-water. I then try it on 
 red litmus-water in this way: I take a little water in a 
 tube, blue it with litmus, and then redden it with a rod 
 moistened with acid. To this I add a few drops of the 
 liquid, and note the change in color. 
 
 3. I put the rest of the liquid in a porcelain dish and 
 evaporate it to dry ness, using a small flame toward the 
 end of the operation, and note the appearance of the solid 
 left behind. 
 
 THE FACTS. The sodium decomposes the water, and 
 the two new substances are hydrogen gas, and a white 
 solid which is very "alkaline" to the taste, and able to 
 restore the blue color to reddened litmus. 
 
 We may write the reaction in the usual way: 
 
 Na + H 2 NaHO + H 
 
 Sodium Water Sodium hydroxide Hydrogen 
 
 and this shows that 1 atom of the metal, Na, takes the 
 place of 1 atom of the hydrogen, H, in the molecule of 
 water, and makes a new molecule of what is called sodium 
 hydroxide, Na H O. This sodium hydroxide is the white 
 substance left behind in the dish. 
 
 It is named for the elements in it sodium, hydro- 
 gen, and oxygen. The last two names are combined in 
 hydroxide, and so we get the name sodium hydroxide. 
 
 In like manner we have potassium hydroxide, K H 0, 
 and ammonium hydroxide, Am HO. 
 
ACIDS, BASES, AND SALTS. 133 
 
 Ex. 84. I half fill two bottles with litmus-water red- 
 dened by acid, and then to one I add drops of potassium 
 hydroxide (caustic potash) solution to the other drops of 
 ammonium hydroxide (ammonia). 
 
 Note the change in the color of each. 
 
 Carefully learn the taste of each. 
 
 THE FACTS. These three hydroxides are alike, very 
 alkaline in taste, and alike able to restore the blue of red- 
 dened litmus. They restore the blue color by decomposing 
 the acid which reddened it. In this way they neutralize 
 the acids. This is their chief characteristic. 
 
 It has been found by experiment, that nearly all metals 
 have compounds of this kind. The hydroxides are a very 
 large class indeed. 
 
 DEFINITION. A hydroxide is a compound of a metal 
 with hydrogen and oxygen, which will neutralize an acid. 
 
 OTHER NAMES. These substances are also called hy- 
 drates ; instead of sodium hydroxide we may say sodium 
 hydrate. They are also called bases.. 
 
 Reaction of Bases and Acids. But how does a base 
 or hydroxide neutralize an acid ? Take the sodium hy- 
 droxide and hydrochloric acid for example. 
 
 Ex. 85. I put 15 cc. of hydrochloric acid into a bottle 
 and drop into it a small bit of litmus-paper, 1 which in- 
 stantly becomes red. I next add a solution of sodium 
 hydroxide little by little, shaking or stirring the liquid 
 well after each addition. I watch the color of the litmus- 
 paper : it will after a while show signs of turning blue. 
 I then add the hydroxide, a drop at a time, until after the 
 last drop the paper remains blue. By this sign I know 
 that the acid is neutralized. 
 
 1 Litmus-paper is made by soaking filter-paper in a strong solu- 
 tion of litmus in water and then drying it; the paper has a deep blue 
 color. 
 
134 ACIDS, BASES, AND SALTS. 
 
 I next search for the product of the action. I put tL<; 
 liquid into a porcelain dish and evaporate it down care- 
 fully until dry. Let it cool, and then examine the residue. 
 Note its color and its taste. By its taste we know what 
 this new substance is. 
 
 We find that common salt (Na Cl) is one product of the 
 action of these two liquids. By writing the reaction, we 
 may discover that there should be another. For we must 
 have new substances enough to contain all the atoms in the 
 old ones. Thus, if we write 
 
 HC1 + NaHO = NaCl + HHOorH 2 O 
 acid base salt water 
 
 we see that water must be a product of the action. In 
 this case the acid and the base neutralize each other by 
 forming a salt and water. 
 
 In other cases the action is the same. It is a fact that 
 when an acid arid a base act upon each other the result is 
 to produce a salt and water. There are few exceptions 
 (p. 95) to these important facts, viz. : 
 
 When a metal acts on an acid a salt and hydrogen are 
 produced. When a base acts on an acid a salt and water 
 are produced. 
 
 Neutral Compounds. Water is a good example of 
 bodies which are neither acids nor bases nor salts. It 
 will not change the color of litmus either to red or blue. 
 It is not sour to the taste like the acids, nor caustic like 
 the bases, nor is it made by putting a metal in the place 
 of hydrogen in the acids, as the salts are. There are a 
 great many other compounds like water in these respects. 
 Bodies which will not change the color of either blue or red 
 litmus are called neutral bodies. 
 
ACIDS, BASES, AND SALTS. 135 
 
 CHEMICAL NAMES. 
 
 The names of chemical compounds are not invented 
 to simply suit the fancy of the chemist ; they are made 
 by certain rules, and are meant to show the composition of 
 the substances to ivhich they are given. 
 
 The Names of Acids Sulphuric acid is made up of 
 
 sulphur, oxygen, and hydrogen; its name is so made that 
 the presence of these three things is shown. 
 
 The presence of sulphur is shown by using the name 
 of that element. The presence of oxygen is shown by 
 the ending ic. The presence of hydrogen is shown by the 
 word acid, because all acids are known to contain this 
 element. 
 
 Sulphurous acid is another compound of these same 
 elements, sulphur, oxygen, and hydrogen. Sulphur is 
 shown by its own name as before. Oxygen is shown by 
 the ending ous. Hydrogen is shown by the word acid as 
 before. 
 
 It will be seen that sulphuric acid and sulphurous acid 
 are made of the same elements. The first contains a larger 
 proportion of oxygen than the other, and this is their only 
 difference in composition. Now ic is used in the name of 
 the one that contains the larger proportion of oxygen, and 
 ous in the name of the other. 
 
 In the same way we have two acids of phosphorus : 
 they are called phosphoric acid and phosphor us acid. The 
 first contains a larger proportion of oxygen than the last. 
 This fact is shown by using the ending ic in the name of 
 the first, and ous in the name of the last. 
 
 In some cases more than two acids are made of the same 
 elements. Prefixes are then used in addition to the end- 
 ings ic and ous. These prefixes are hypo and per. There 
 is, for example, the hyposulphurous acid. It contains a 
 
136 ACIDS, BASES, AND SALTS. 
 
 less proportion of oxygen than the sulphurous acid, and 
 this is shown by the prefix hypo. The prefix per means 
 a larger proportion of oxygen. There is, for example, 
 the perchloric acid. It contains a larger proportion of 
 oxygen than the chloric acid: this is shown by the pre- 
 fix per. 
 
 The Names of Salts. The name of a salt is intended 
 to show the names, of the metal and the acid, by which the 
 salt is supposed to be made. If sodium act on sulphuric 
 acid, hydrogen is liberated and a salt is at the same time 
 formed ; this salt is called sodium sulphate. It is easy to 
 see that this name suggests tho name of the acid and also 
 of the metal. When sulphuric acid is used the salt which 
 is made is called a sulphate, no matter what metal is 
 employed. 
 
 But sulphurous acid yields a class of salts which are 
 called sulphites. Notice the difference: 
 
 Sulphuric acid yields sulphates. 
 Sulphurous acid yields sulphites. 
 
 The same difference is found in other cases. A salt 
 formed by chloric acid is called a chlorate; but one formed 
 by chlorous acid is called a chlorite. Nitric acid yields 
 nitrates, but nitrous acid yields nitrites. 
 
 The rule is this: if the name of the acid ends in ic, 
 the names of its salts shall end in ate; but if the name 
 of the acid ends in ous, the names of its salts shall end 
 in ite. 
 
 The Names of Bases All bases are made up of 
 hydrogen, oxygen, and a metal, and their names show this 
 fact. The word hydroxide suggests hydrogen and oxygen, 
 and hydroxide is the name of this whole family of com- 
 pounds. Each individual member of this family is dis- 
 tinguished by the name of the metal which is in it. 
 
ACIDS, BASES, AND SALTS. 137 
 
 The following examples will make this method clear. 
 See how the names of the elements suggest the name of 
 the base which they form, and how the name of the base 
 also suggests the names of the elements of which it is 
 
 made. 
 
 Sodium, hydrogen, oxygen, form the Sodium hydroxide. 
 Potassium, " " " " Potassium hydroxide. 
 
 Calcium, " Calcium hydroxide. 
 
 Iron, " " " Ferric hydroxide. 
 
 Iron, - " Ferrous hydroxide. 
 
 There are in many cases two hydroxides of the same 
 metal, and the endings w and oiis are used to distinguish 
 them. The names of the iron hydroxides illustrate this : 
 
 Ferric hydroxide . .' . ' : ^ . . Fe 2 (HO) 6 
 Ferrous hydroxide . S ... . . Fe (Hit)), 
 
CHLORINE AND THE CHLORIDES. 
 
 MORE than a hundred years ago it was in 1774 the 
 Swedish chemist Scheele was studying the action of hy- 
 drochloric acid on a black powder known as the "black 
 oxide of manganese." To his surprise a heavy greenish 
 gas was produced. Sir Humphry Davy afterward called 
 this gas chlorine. 
 
 Chlorine is a very suffocating substance, and in all experi- 
 ments with it we must be careful to not breathe it. When 
 we make the gas, and when we use it, there must be the 
 utmost care to have our apparatus air-tight, and to prevent 
 the escape of this noxious gas. 
 
 The following arrangement of our gas-making apparatus 
 will enable chlorine to show several of its properties with- 
 out escaping to poison the atmosphere of the room. 
 
 Preparation of Chlorine. We will adopt the original 
 method, and make the gas by the action of "black oxide 
 
 of manganese" 
 on hydrochloric 
 acid. 
 
 Ex. 86. In- 
 to a I put 50 cc. 
 water, and close 
 the flask tightly 
 with its stop- 
 per. By means 
 of a piece of 
 small wire I 
 hang a strip of 
 moist blue litmus-paper to the stopper of I, and press it 
 down into the flask. 
 
CHLORINE AND THE CHLORIDES. 139 
 
 I fix a piece of " gold leaf " (Dutch metal) in the same 
 way, and enclose it in c. I fill the bulb of a drying-tube 
 loosely with cotton, and then fill the wide part of the 
 tube with dry slaked lime and cork it tightly. 
 
 I then join all these parts, as shown in the cut, by means 
 of rubber tubing, the side-neck with the long glass tube 
 of a, the short tube of a with the long tube of b, the 
 short tube of b with the long tube of c, and the short tube 
 of c with that of the drying-tube, the small end of which 
 I place in a bottle, d. 
 
 Finally, to make the chlorine I put 25 g. of manganese 
 dioxide, Mn0 2 , into the side-neck flask, pour in upon it 
 100 cc. strong hydrochloric acid, press home the solid 
 rubber stopper, and apply a small flame of the Bunsen. 
 The heat must be gentle. The chlorine will slowly drive 
 the air over from flask to flask, and out at d; but if the 
 joints are as tight as they may be, no chlorine will escape 
 into the room. 
 
 The chlorine soon fills the side-neck flask, as may be 
 seen by its color, and then bubbles through the water in 
 a, and passes slowly on toward d. 
 
 What is the action of Cl and H 2 O, shown in flask a ? 
 What is the effect of Cl on the color of litmus, shown in b? 
 What is the effect of Cl on Dutch metal, shown in c f 
 Why are there no bubbles of Cl in the bottle d f 
 
 THE FACTS. The chlorine comes from the hydrochloric 
 acid. The reaction may be written as follows: 
 
 Mn0 2 + 4HC1 = MnCl 2 + 2H 2 O + 2C1 
 Manganese dioxide Hydrochloric acid Manganese chloride Water Chlorine 
 
 Chlorine is a greenish-yellow gas, whose odor is pungent, 
 and suffocating in the highest degree. Cold water dis- 
 solves about two and one-half times its own bulk of chlo- 
 rine, and then has the same color as the gas itself. This 
 
140 CHLORINE AND THE CHLORIDES. 
 
 chlorine-water may be used instead of the gas for many 
 purposes ; it will cause the same chemical actions. We see 
 also (flask b) that chlorine destroys the color of litmus, 
 and (flask c) that it combines with " gold leaf," and that 
 it is greedily absorbed by the lime in the " drying-tube." 
 
 The actions of chlorine on colors and on the metals are 
 important. Let us study them further. 
 
 Bleaching Chlorine destroys the color of litmus (b). 
 
 Will it also bleach other colors ? 
 
 Ex. 87. I fill a test-tube half-full of water, and color 
 it with black writing-ink. I slip the rubber tubes off 
 from the glass tubes of flask a, and then, carefully invert- 
 ing the flask over the mouth of the test-tube, as in Fig. 57 
 I let a few drops of chlorine-water run into the black liquid. 
 
 Ex. 88. I use cochineal, or an aniline dye, or the petal 
 of a flower, or a piece of calico cloth, instead of the inky 
 water in the last experiment. 
 
 Ex. 89. I take a piece of paper covered with writing in 
 red ink, and a piece of newspaper covered with printing, 
 and moisten both with the chlorine-water. 
 
 Is the color discharged in both cases ? 
 
 What is the coloring matter of printers' ink? 
 
 THE FACTS. This power of chlorine to destroy color- 
 ing matters is made use of on a large scale in the art of 
 bleaching. All colors which are made from vegetable or 
 animal substances will be removed by chlorine in the 
 presence of water : dry chlorine does not bleach. Nor are 
 mineral colors (carbon of printers' ink) disturbed by it. 
 The bleaching of linen and cotton goods and paper is done 
 by the use of chlorine. 
 
 Chlorine also destroys bad odors, and it is much used in 
 hospitals and elsewhere for this purpose. It is the most 
 powerful disinfectant. 
 
CHLORINE AND THE CHLORIDES. 141 
 
 Chlorine destroys colors and odors, by taking hydrogen 
 away from them. In some cases the color or the odor 
 gives up its hydrogen directly to the chlorine, but in 
 others it is water which gives up its hydrogen to the 
 chlorine, and then the oxygen which is set free attacks 
 the substance of the color or the odor and decomposes it. 
 
 BLEACHING POWDER. Chlorine is absorbed quite greedily 
 by slaked lime. The product is called bleaching powder, and 
 this, instead of chlorine-water, or the gas itself, is used in 
 the arts. 
 
 Ex. 90. I remove a part of the lime from the drying- 
 tube, Ex. 86, to a dish and cover it with water. After 
 stirring it well, I pour it on a filter, and catch the filtrate 
 in a test-tube. I then add a little of this clear solution to 
 some inky water or litmus solution in another tube. 
 
 By passing chlorine-gas over dry lime in large chambers, 
 instead of in a tube, immense quantities of this powder 
 are made, to be used as a bleaching agent and disinfectant. 
 
 The Chlorides Chlorine readily combines with the 
 
 metals and changes them into chlorides. This action took 
 place in flask c (Ex. 86). The leaf of " Dutch metal " is 
 said to be made of zinc and copper, and if so, the white 
 residue is made up of zinc chloride and copper chloride. 
 Let us search for the copper chloride. 
 
 But we should first examine some copper chloride itself, 
 so that we may be able to identify it. 
 
 Ex. 91. I put a little of a known specimen of copper 
 chloride into a test-tube and add a little water. It easily 
 dissolves. 
 
 What is the color of the strong solution ? 
 What is the color if more and more water be added ? 
 What happens if a piece of clean iron is left in the 
 solution ? 
 
142 CHLORINE AND THE CHLORIDES 
 
 I next add to some solution in another tube a little 
 ammonia, and then add more, and more, until the blue 
 precipitate made at first is dissolved to a clear, fine blue 
 liquid. 
 
 A compound of copper may be known by the green or 
 blue color of its solution, by the metallic copper set free by 
 iron, and by the action of ammonia. 
 
 Ex. 92. I now carefully take the stopper and tubes 
 from the flask c ; the white residue of the metal is lifted 
 out with them. I carefully wash this residue into a porce- 
 lain dish with as little water as will remove it. I look for 
 the color, and if I find none I evaporate the solution down 
 to a small bulk. Finally, I insert a bright clean needle or 
 knife-blade and leave it a few minutes. 
 
 Compare these results with those in Ex. 91, and decide 
 whether the chlorine produced copper chloride in the 
 flask c, in Ex. 86. 
 
 CHLORIDES BY CHLORINE WATER. Metals are changed 
 to chlorides, not only by chlorine gas, but also by chlorine 
 water. Thus : 
 
 Ex. 93. I put a leaf of "Dutch metal," about two square 
 inches, into a test-tube and pour upon it 5 cc. chlorine-water 
 from a, and shake it until dissolved. I then carefully 
 slide a clean iron nail down into the solution. 
 
 Does the color of the solution indicate a copper com- 
 pound ? Does the action of the iron prove its presence ? 
 
 After half an hour take out the iron, and put in a fresh 
 bright piece. If the action is over no copper will now be 
 deposited. Keep this liquid for Ex. 97. 
 
 CHLORIDES BY HYDROCHLORIC ACID. But the most 
 usual way of changing metals to chlorides is by means of 
 hydrochloric acid. Thus: 
 
 Ex. 94- Into 5 cc. strong hydrochloric acid I put several 
 
CHLORINE AND THE CHLORIDES. 143 
 
 small bits of iron, such as small tacks. Hydrogen escapes 
 with effervescence. I let the tube stand until the action is 
 over. 
 
 Note the color of the iron chloride now in solution. 
 
 Get the solid chloride out, by evaporating the liquid. 
 
 The reaction may be written in this way : 
 
 Fe + 2 H Cl = Fe C1 2 + 2 H 
 
 Iron Acid Ferrous chloride Hydrogen 
 
 which shows that an atom of iron, Fe, takes the place 
 of two atoms of hydrogen in the acid, and makes a new 
 molecule of ferrous chloride, setting two atoms of hydro- 
 gen free. Thus the iron is changed into a chloride. 
 
 Iron has a stronger attraction for chlorine than hydrogen 
 has, and can take the chlorine away from the* hydrogen in 
 the acid. This is also true of many other metals beside 
 iron. 
 
 CHLORIDES BY AQUA REGIA. When strong hydrochloric 
 acid is mixed with nitric acid, they decompose each 
 other; chlorine is set free, but stays in the solution. 
 Now this mixture will do what neither of the acids sepa- 
 rately can do : it will dissolve gold and platinum, changing 
 them into chlorides. Gold has been called the king ot 
 metals, and this liquid which dissolves it is called aqua 
 regia, the meaning of which is " royal water." Aqua regia 
 is the most powerful of all agents for changing metals into 
 their chlorides. For example : 
 
 Ex. 95. I put 2 cc. strong hydrochloric acid into a test- 
 tube and add about one-fourth as much strong nitric acid. 
 Into this I drop two or three small "tacks." Chemical 
 action is evident at once, and the iron slowly wastes away. 
 The liquid changes color as the iron chloride increases, 
 and toward the end orange vapors of a suffocating odor 
 may appear. Keep this liquid. 
 
144 CHLORINE AND THE CHLORIDES. 
 
 Two Chlorides of one Metal The color of the liquid 
 
 containing the iron chloride made by aqua regia is quite 
 different from that of the iron chloride made by hydro- 
 chloric acid. Let us try to find the reason. 
 
 Ex. 96. I repeat the experiment with hydrochloric 
 acid (Ex. 94), and when the action is over compare the 
 liquid with that made by aqua regia in Ex. 95. 
 
 Note the difference in color. 
 
 I next test a part of each of these two solutions sepa- 
 rately with ammonia, just as I did the copper solution in 
 Ex. 91. 
 
 Note the great difference in the two results. 
 
 Do the two solutions contain the same or different sub- 
 stances ? 
 
 THE FACTS. The iron chloride, made by hydrochloric 
 acid, is green, while that made by aqua regia is yellow. 
 When ammonia is added they behave very differently : the 
 first gives a light green precipitate, while the last gives one 
 that is reddish-brown. These differences lead us to think 
 that there must be two different chlorides of iron, and 
 this is true. 
 
 The green chloride is FeCl 2 , called ferrous chloride. 
 
 The yellow chloride is Fe 2 Cl 6 , called ferric chloride. 
 
 In the names of the two chlorides of iron the endings ic 
 and otts show the two proportions of chlorine, ic the larger 
 and ous the smaller. With many other metals, also, 
 chlorine forms both ic and ous chlorides. 
 
 Ex. 97. When the iron, in Ex. 93, took the copper out 
 of the copper chloride, what else occurred ? To the liquid 
 kept from that experiment add ammonia, and from the 
 color of the result decide 
 
 Whether it contains copper chloride or iron chloride. 
 
 Whether it contains ferrous or ferric chloride. 
 
CHLORINE AND THE CHLORIDES. 145 
 
 You can then understand just what happened in Ex. 93. 
 .For if the ammonia gives the green precipitate, then fer- 
 rous chloride is present, and the iron must have changed 
 the copper chloride into it. Thus : 
 
 CuCl 2 + Fe = FeCl 2 -f Cu 
 
 Copper chloride Iron Ferrous chloride Copper 
 
 Atoms of iron took the place of atoms of copper, and 
 changed the copper chloride to the ferrous chloride. 
 
 Hydrogen Chloride This is another name for hydro- 
 chloric acid, one of the strongest and most useful of all 
 acids. It is made on a large scale from common salt by 
 the help of sulphuric acid. On a small scale we may pre- 
 pare it with the apparatus used for chlorine, leaving out 
 only the drying-tube, as shown in Fig. 59. 
 
 Ex. 98. I put 50 cc. strong sulphuric acid in a, press 
 its stopper home, and join its long tube with the side- 
 neck. I leave b 
 empty (it should 
 be dry), close 
 it with the stop- 
 per and join to 
 
 a. I put a strip 
 of moist blue lit- 
 mus-paper in c, 
 and join it with 
 
 b. The bottle d 
 contains water, 
 into which the 
 
 tube from c is Fig s3 
 
 put with its end scarcely more than covered. Finally I 
 put the materials, dry salt, 5 g., and strong sulphuric acid, 
 10 cc., into the side-neck, and close it tightly. The reac- 
 tion sets in at once; but to keep it up, I apply a very gen- 
 
146 CHLORINE AND THE CHLORIDES. 
 
 tie heat so that bubbles will be seen in a a little faster 
 than one can count. The acid in a is used to absorb mois- 
 ture which comes over with the gas ; the gas will be dried 
 by the acid if it does not come over too fast. 
 
 Note the action of the hydrochloric acid on litmus. 
 
 Note the color of the gas. 
 
 What is the effect of the water in the bottle d? 
 
 Ex. 99. I remove the cork and tubes from flask b, and 
 then invert the flask with its mouth in a vessel of water. 
 The water quickly rises to almost fill the flask. 
 
 How can you account for this result ? 
 
 THE FACTS. The reaction when sodium chloride, Na Cl, 
 and sulphuric acid H 2 S O 4 , are gently heated is this : 
 
 NaCl + H 2 S0 4 = HNaS0 4 + 
 
 The hydrochloric acid, H Cl, is a colorless gas which in- 
 stantly reddens litmus and dissolves with great freedom 
 in water. The so-called hydrochloric acid, of commerce and 
 the laboratory, is a solution of this gas in water. 
 
 Composition of Hydrochloric Acid by Volume. If 
 hydrogen and chlorine gases are mixed, they will combine 
 when exposed to light, and, by measuring the gases, it has 
 been found that it takes just as many cubic centimeters of 
 hydrogen as of chlorine. Pure hydrochloric acid contains 
 
 1 volume of hydrogen and 1 volume of chlorine. 
 
 But now, how much hydrochloric acid will these two 
 volumes of its elements make ? It has been found that if 
 10 cc. of hydrogen and 10 cc. of chlorine are used, there 
 will be just 20 cc. of the hydrogen chloride made. 
 
 One volume hydrogen and 1 volume chlorine make 2 vol- 
 umes hydrogen chloride. 
 
 Now compare this fact with another noted under the 
 
CHLORINE AND THE CHLORIDES. 147 
 
 composition of water, p. 56, and still another noted under 
 the composition of ammonia, p. 90. 
 We see that in the case of 
 
 H Cl, 2 volumes of the elements make 2 volumes of compound. 
 H 2 O, 3 " 2 
 
 H 8 N, 4 " " " " 2 
 
 Just two volumes of the compound gas is made every 
 time ! The same thing is found true of other compound 
 gases also. Take the five compounds of nitrogen and oxy- 
 gen, for example : 
 
 2 volumes N and 1 volume O make 2 volumes nitrous oxide. 
 
 1 volume N ' ; 1 volume O " 2 " nitric oxide. 
 
 2 volumes X " 3 volumes O " 2 " nitrous anhydride. 
 
 1 volume N " 2 volumes O " 2 " nitrogen peroxide. 
 
 2 volumes N " 5 volumes O " 2 " nitric anhydride. 
 
 These are the results of experiments. And so, whether 
 we have two volumes of the constituents, as in the second, 
 or seven volumes, as in the fifth, there are just two volumes 
 of the compound made when they combine. If we put 
 all these facts into one statement, we have this law: The 
 volume of a compound gas is TWO, whatever may be the 
 number of volumes of the elements in it. 
 
 Test for Chlorine and the Chlorides Let a drop of 
 
 silver nitrate solution be added to a solution of chlorine 
 or of any chloride, and a white cloud or precipitate will ap- 
 pear. This white precipitate is silver chloride. It will 
 become dark colored if left a little while in the sunlight. 
 Try this test on several chlorides. 
 
 THE CHLORINE GROUP. 
 
 There are three other elements which are so much like 
 chlorine, that the four are together called the chlorine 
 group. They behave so nearly like chlorine, and their 
 
148 CIILOKINE AND THE CHLORIDES. 
 
 uses are so much less important, that we need not stop 
 long with them in our study. 
 
 Bromine A little more than half a century after the 
 
 discovery of chlorine it was in the year 1820 M. 
 Balard, a French chemist, found another element, with 
 properties much like those of chlorine. Its odor was 
 found to be so strong that, in honor of this characteristic 
 the element was called bromine. The word is from the 
 Greek word fipaifioz (bromos), which means stench. 
 
 Bromine is not very abundant, but it does exist in the 
 waters of some mineral springs, and in larger quantities 
 in the waters of the sea. It is always found in combina- 
 tion, and its compounds are called bromides. 
 
 Bromine is a lif/uid, but a very gentle heat changes it 
 to gas. It has a beautiful dark-red color. 
 
 This element readily combines with hydrogen and with 
 metals; in this respect it is like chlorine, and like that 
 element it is able to remove colors and to destroy bad 
 odors. 
 
 Iodine M. Courtois was a chemical manufacturer in 
 
 Paris. He was engaged in making soda, and was using 
 the ashes of sea-weeds for this purpose. A dark-colored 
 liquid was left in his kettles, and attacked the metal of 
 which they were made. When some sulphuric acid was 
 put with it, this liquid gave up a substance which, when 
 heated, changed to a beautiful violet-colored vapor. It 
 proved to be a new element, and it was called iodine. 
 This, from the Greek word iwdqg (iodas), means viof.et- 
 colored. 
 
 Iodine is a constituent of sea-plants, as we may know 
 from the story of its discovery. The sea contains it in 
 small quantities, and so do the waters of some mineral 
 springs. It is an element in sponges, and in oysters, and 
 in some fishes. It is always found in nature, combined 
 with other substances. 
 
CHLORINE AND THE CHLORIDES. 149 
 
 Iodine is a solid. A gentle heat melts it, and a little 
 higher temperature changes it into its beautiful vapor. 
 
 Water dissolves it, but a single grain will take no less 
 than 7000 grains of water to dissolve it. How small this 
 proportion of iodine, and yet it gives to the whole body 
 of the water a brownish-yellow color ! Alcohol will dis- 
 solve it in large proportions. This solution in alcohol is 
 the "tincture of iodine," used in medicine. 
 
 Iodine combines with hydrogen and with many metals. 
 In this respect it is much like chlorine and bromine. Its 
 compounds are called iodides. 
 
 Some of its compounds with the metals are remarkable 
 for their very brilliant colors (Ex. 13). 
 
 But there is one effect of iodine which neither chlorine 
 nor bromine can produce: it is the fine blue color it gives 
 to starch. Thus : 
 
 Ex. 100. I boil a bit of starch in a half test-tubeful 
 of water t and after it has become cold I add a little iodine- 
 water, made by vigorously shaking a crystal of iodine in 
 water. Note the blue color produced. 
 
 Compounds of iodine do not blue the starch ; the experi- 
 ment may be made with potassium iodide. But if one of 
 these can be decomposed the free iodine will show itself 
 by the color ; the experiment may be made by adding drops 
 of nitric-acid to the solution of potassium iodide, and then 
 adding the starch. The test for free iodine is starch. 
 
 The physician finds iodine -very useful as a medicine. 
 
 The photographer finds it very valuable in the art of 
 picture-making. 
 
 The element itself is sometimes used in medicine, but 
 its compounds are more generally used in the arts. 
 
 Fluorine. This element is found in combination with 
 the metals, and all attempts to get it free have failed. Its 
 chemical attractions are so strong, that if it be set free it 
 
150 CHLORINE AND THE CHLORIDES. 
 
 immediately combines with something else ; even with the 
 substance of the vessel in which the work is done. And 
 yet it is remarkable that this is the only element which 
 is not known to combine with oxygen. Its strongest 
 affinities are for hydrogen and the metals. We cannot 
 say whether fluorine is a gas, or would be if out of 
 combination, as chlorine is. It is supposed that it 
 would be, because it is a much lighter substance than 
 chlorine. It is only nineteen times heavier, while chlo- 
 rine is 35.5 times heavier than an equal bulk of hydrogen. 
 
 The mineral called fluor spar, CaF 2 , is the most abund- 
 ant compound of fluorine. When this is treated with 
 sulphuric acid the fluorine leaves the calcium, Ca, and 
 combines with hydrogen. This gives a gas, the hydro- 
 fluoric acid, HF. This acid gas is useful in the art of 
 etching glass; for wherever it touches glass the fluorine 
 leaves the hydrogen to unite with the elements of the 
 glass instead. 
 
 Hydrogen Compounds. Fluorine, chlorine, bromine, 
 and iodine behave toward hydrogen very much alike. 
 Each one forms a single compound with that element, and 
 each one combines with the hydrogen, atom for atom. 
 Their names and formulas plainly show this fact. Thus: 
 
 Hydrochloric acid II Cl 
 
 Hydrobromic acid . . H Br 
 
 Hydroiodic acid HI 
 
 Hydrofluoric acid . . ,- *.,; .w ;... HF 
 
 This is a very interesting fact, for there is no other 
 non-metal, besides these four, that will combine with hy- 
 drogen atom for atom. In the case of oxygen, for example, 
 the compound is water, H 2 0, in which an atom of oxy- 
 gen takes two atoms of hydrogen. An atom of oxygen 
 refuses, absolutely, to ever take any less than two of 
 hydrogen. 
 
CHLORINE AND THE CHLOUWEX. 151 
 
 General Behavior. These four elements behave very 
 much alike in other respects. This is, to be sure, not quite 
 so marked in the case of fluorine as in the other three, 
 but in general they combine witlrthe same elements and in 
 the same 'proportions. And they are able to do the same 
 kinds of work ; as, for instance, chlorine bleaches colors ; so 
 does bromine, and iodine also, when in solution. 
 
 Chlorine is a better bleacher than bromine, it is more 
 powerful, and bromine is a better bleacher than iodine. 
 But they are all bleachers. 
 
 Atomic Weights and Properties In general it is 
 
 true in other cases, as well as in bleaching, that the chem- 
 ical action of chlorine is more vigorous than that of 
 bromine, and of bromine more vigorous than that of iodine. 
 In fact, bromine will drive iodine out of combination and 
 take its place, and chlorine will treat bromine in the same 
 way. Now this order of chemical strength is just the 
 order of their atomic weights, beginning with the smallest. 
 Thus : 
 
 Atomic weight of Cl 35.5, with most vigorous chemical action. 
 Atomic " " Br 80 " less " " " 
 
 Atomic " " I 127 " least " " " 
 
 Their forms, gaseous, liquid, and solid, are in the same 
 order ; so are the densities of these elements. In fact, the 
 properties of these elements seem to depend, in some way, 
 on their atomic weights. 
 
 EXERCISES. 
 
 1. Study the actions of chlorides, bromides, and iodides on 
 
 silver nitrate. 
 
 1. Arrange three test-tubes, one with a little solution 
 of sodium chloride, another with as much solution of 
 potassium bromide, and another with as much solution of 
 
 O 0^ TBOi ^^ 
 
152 CHLORINE AND THE CHLORIDES. 
 
 potassium iodide. Add silver nitrate drop by drop, shak- 
 ing the tube vigorously after each addition, until a drop 
 fails to make a precipitate. Describe the precipitates. 
 Note the effect of shaking them. Look carefully for some 
 difference in their colors. 
 
 Then expose the tubes to sunlight, or for some time to 
 diffuse light, and note the changes which occur in the 
 colors. 
 
 2. Next test the solubility of these precipitates in am- 
 monium hydrate. To do this, make a little fresh precipi- 
 tate, and keep it from light as much as possible. When 
 the precipitate has settled, decant the liquid, that is, pour 
 it away carefully so as to leave the precipitate in the tube. 
 Then pour upon it ammonium hydrate gradually, with 
 shaking, until you can decide whether the precipitate dis- 
 solves. Do they all dissolve? Does one dissolve more 
 easily than another ? 
 
 3. Write a brief statement of all the facts which you 
 have discovered, noting particularly the points of difference 
 among the three compounds. 
 
 2. Study the action of chlorides, bromides, and iodides on 
 starch. 
 
 1. Make a very thin starch-water, by boiling a minute 
 piece of starch in considerable water, and cooling the 
 liquid. 
 
 2. Dissolve a chloride, a bromide, and an iodide, each in 
 water. 
 
 3. To a part of each solution add a few drops of nitric 
 acid, and afterward add a little of the starch-water. There 
 should be a difference in color produced ; note it carefully. 
 
 To another part of each solution add a little of the cold 
 starch-water, without the nitric acid. By this means you 
 can decide whether nitric acid is necessary to bring out the 
 colors observed before. 
 
CHLORINE AND THE CHLORIDES. 153 
 
 4- Add the starch-water to hot solutions instead of cold 
 ones, and let them become cold. By this means yon will 
 learn the effect of heat. 
 
 5. Write a brief statement of all the facts which you 
 have discoverd. 
 
 Chlorine, bromine, and iodine behave so very much alike, 
 that it is not always easy to distinguish their compounds 
 one from another. And then, too, there is another class of 
 compounds called cyanides, which might be mistaken for 
 some of these. Still the " silver-nitrate," and the " starch 
 test," will help one to identify these three classes of com- 
 pounds. In the case of the nitrate test, the pure precipi- 
 tates differ a little in color, and more in solubility in 
 ammonia, the chloride being easily soluble, the bromide 
 much less so, and the iodide almost not at all. In the 
 starch test, nitric acid must be used to decompose the com- 
 pounds, because it is only the free iodine which gives the 
 blue, and the free bromine which gives the brown color. 
 
 3. Take a few substances from the teacher, or a friend who 
 knows what they are, and see if you can decide whether 
 each is a chloride, bromide, or an iodide. 
 
SULPHUR AND ITS COMPOUNDS. 
 
 Native Sulphur Sulphur seems to have been known 
 
 and used in the most ancient days of which we have any 
 account. The element itself, and its compounds also, are 
 very abundant in the earth. The element itself, or native 
 sulphur, is found in the neighborhood of volcanos, or where 
 these fire-mountains have been active in time past. Large 
 quantities are taken from mines in Sicily ; in fact, a great 
 part of the sulphur in commerce comes from this source. 
 
 Native Sulphides. Sulphur is found combined with 
 metals in the rocks and soils almost everywhere. These 
 compounds are called sulphides. 
 
 The sulphide of iron is a good example. It is a brassy- 
 looking substance, very common in many rocks. It is often 
 found in the form of little cubes, as perfect as if they 
 had been chiselled by an artist. Sometimes it is found in 
 the form of thin, shining, yellow scales. It has been 
 called "fool's gold," because the ignorant have been de- 
 ceived by its color. It is iron disulphide, FeS 2 , and is 
 commonly called iron pyrites. 
 
 The sulphides are the substances from which the useful 
 metals are often obtained. Lead, for example, is taken 
 from the mineral called galena, but galena is the lead sul- 
 phide, Pb S. Silver, copper, and zinc are also among the 
 useful metals, found in the rocks in combination with 
 sulphur. 
 
 Preparation of Sulphur. In its native state, as found 
 in the mines of Sicily, sulphur is not combined with any- 
 thing, but yet it is very far from being ready for the mar- 
 ket. It is not in comlination, but it is mixed with a great 
 deal of earthy impurities from which it must be separated. 
 
 154 
 
SULPHUR AND ITS COMPOUNDS. 155 
 
 This is easily done, because sulphur is easily changed into 
 vapor by heat, while the earthy impurities are not. Let 
 the mixture be heated, then, and the sulphur-vapor will 
 pass away and leave the impurities behind. The vapor, 
 being cooled again, is sulphur, which is very much more 
 free from earthy matter than before. 
 
 It is heated a second time to remove the impurities 
 which the first process did not. This time the vapor is 
 run into a large chamber, and it is condensed upon the 
 cold walls in very fine powder. This powder is the " flowers 
 of sulphur " which is so common. 
 
 When the chamber is smaller, its walls become too hot to 
 collect the powder, which then melts, and the liquid runs 
 down upon the floor. It runs into channels in the floor 
 which lead it out of the chamber into moulds. In this way 
 the familiar sticks of " roll brimstone " are made for the 
 market. 
 
 Effects of Heat on Sulphur. Ex. 101. I reduce a 
 piece of brimstone to coarse powder and half fill a test-tube 
 with it. I hold the tube in the hot air above the lamp-flame, 
 and thus keep it from contact with too strong a heat, but 
 lower it until I find the heat intense enough to melt the 
 sulphur. The liquid should not be darkened, but be yellow 
 and limpid. 
 
 Ex. 102. I place the tube with the limpid yellow liquid 
 where it will not be shaken, and watch the liquid while it 
 slowly cools. 
 
 In what form does the sulphur solidify ? 
 
 Ex. 103. I now carefully re-melt the sulphur, and then 
 make the yellow liquid a little hotter, only a little. 
 
 Note the change in color. 
 
 I continue to heat the liquid gradually and incline the 
 tube from time to time, and observe that the color deepens 
 and the sulphur grows viscid until it refuses to flow at all. 
 
136 SULPHUR AND ITS COMPOUNDS. 
 
 I then heat it still more, and notice that the half-solid 
 sulphur re-melts. 
 
 I continue to apply heat to find out whether the sulphur 
 can be boiled, and what is the color of the vapor. 
 
 I then pour the liquid in a small stream into a vessel of 
 cold water, and examine the sulphur after this sudden 
 cooling. 
 
 THE FACTS. Sulphur at ordinary temperature is a 
 bright yellow solid, but when heated a little hotter than 
 boiling water (114.5 C.) it melts to a limpid yellow liquid. 
 Some care is required to preserve this yellow color, since 
 it easily changes if the heat be much greater. 
 
 At a higher temperature, about 132, the sulphur begins 
 to grow viscid as well as dark colored. Darker and thicker 
 it becomes as it gets hotter, until, at about 230, it is almost 
 black, and is so very viscid that it will not flow from the 
 vessel even if turned bottom upward. Make the hot sul- 
 phur still hotter, and the dark-colored, almost solid sub- 
 stance grows less viscid again ; it will flow in the vessel 
 very much like thick syrup. 
 
 At a higher temperature, about 450, the sulphur boils. 
 The hot vapor is colorless, but if cooled a little it is con- 
 densed and becomes yellow. 
 
 PLASTIC SULPHUR. If melted sulphur, just below its 
 boiling-point, be poured into cold water, it cools into a sub- 
 stance which looks like India-rubber. If we handle it, we 
 find that it is like India-rubber in other things besides its 
 color: it is tough and elastic. This unusual form of sul- 
 phur is called plastic sutyhiu: It will not stay in this 
 condition, but gradually it will become again yellow and 
 brittle as at first. This plastic sulphur is almost as unlike 
 the common form as if it were another element. In these 
 two forms we find a good example of allotropism, p. 39. 
 
 CRYSTALS OF SULPHUR. If melted sulphur, limpid and 
 
SULPHUR AND ITS COMPOUNDS. 157 
 
 yellow, be allowed to cool slowly (Ex. 102), fine needle- 
 shaped crystals will be seen to shoot out from the walls of 
 the vessel. They will increase in number and size, until 
 finally, when cold, the solid mass of sulphur will be made 
 up of these slender prisms interlaced and crowded together. 
 
 Crystals of sulphur are also found in nature, but their 
 shape (rhombic octohedra) is quite unlike that of the arti- 
 ficial crystals obtained by fusion. In these two forms of 
 sulphur we have a good example of dimorphism) the prop- 
 erty in virtue of which a substance may crystallize in two 
 distinct forms. Sulphur is called a dimorphorus element, 
 because it crystallizes in two shapes. 
 
 Artificial Sulphides. A sulphide of copper can be 
 made as follows : 
 
 Ex. 104- I prepare a small coil of fine copper wire, 
 No. 30, by winding the wire around a small lead-pencil or 
 glass tube. I put a few fragments of sulphur into a tube, 
 and then insert the coil and heat the sulphur to boiling. 
 Watch for any sign of chemical action, and notice that, 
 once well started, it will run to the upper end of the coil 
 without the further aid of the flame. 
 
 Compare the substance of the coil now with the copper 
 and the sulphur which were used. 
 
 Ex. 105. The experiment may be made by mixing 4 g. 
 flowers of sulphur with 8 g. of fine copper-filings, and heat- 
 ing this mixture in a test-tube. 
 
 THE FACTS. When copper and sulphur are heated to- 
 gether they unite and form a compound which is grayish- 
 black, and brittle. The lamp-flame brings them to the 
 right temperature, when at once the action sets in. - A 
 vivid red glow begins, and goes quickly to the end of the 
 coil or mixture. This glow is not due to the lamp-flame, 
 because it goes on even if the flame is taken away. The 
 
158 SULPHUR AND ITS COMPOUN])S. 
 
 additional heat to make the glow must l>e caused by the 
 chemical action itself. Thus : 
 
 Materials. Products. 
 
 Cu + S CuS + heat 
 
 Many other metals, like copper, will become sulphides 
 when heated with sulphur. If a white-hot rod of iron is 
 used to stir melted sulphur, the iron will become iron 
 sulphide, and if zinc and sulphur are properly heated, zinc 
 sulphide is obtained. 
 
 These artificial sulphides are not always the same as 
 the native sulphides of the same metals. This artificial 
 sulphide of iron, for example, is very different from the 
 native pyrites. It is Fe S, while the native sulphide is 
 FeS 2 ; the first is the ferrous sulphide, while the second 
 is the ferric sulphide. 
 
 Hydrogen Sulphide. The ferrous sulphide is very 
 easily decomposed by acids. 
 
 Ex. 106. I put a piece of ferrous sulphide, 1 not larger 
 than a grain of wheat, into a test-tube, and pour upon it 
 1 cc. dilute hydrochloric acid (half water). 
 
 Notice the effervescence : what does it show ? 
 
 Notice the odor in the tube. 
 
 Notice the color of the liquid when the action is over. 
 
 Add ammonia to the liquid and compare with Ex. 96. 
 
 THE FACTS. By the action of the acid and sulphide a 
 gas is set free with effervescence, and its bad odor 
 like that which arises from the putrefaction of certain 
 things, such as eggs proves this gas to be hydrogen sul- 
 phide. The ammonia test suggests the presence of ferrous 
 chloride in the liquid. Hence the reaction is as follows: 
 
 FeS + 2HC1 = FeCl 2 + H 2 S 
 
 1 This substance is sold in the form of "sticks," which is very 
 much better than the powder or the granular form. 
 
SULPHUR AND ITS COMPOUNDS. 159 
 
 The H 2 S is the hydrogen sulphide: it is also called 
 sulphuretted hydrogen. 
 
 This gas is found in the waters of "sulphur springs." 
 All the sulphur which such springs contain is in the form 
 of this gas. They owe their nauseous taste and odor, and 
 their medicinal value, to hydrogen sulphide dissolved in 
 their waters. 
 
 This gas is a powerful agent for changing the metals 
 into sulphides; no other substance is so valuable to the 
 chemist for this purpose. 
 
 Preparation and Properties. In order to study the 
 behavior of this gas without being annoyed by its escape 
 into the room, we may employ our usual form of gas ap- 
 paratus. 
 
 Ex. 107. Put 40 cc. water into a, Fig. 60, to cover 
 the lower end of the long tube. Add a cubic centimeter 
 of solution of lead 
 acetate, and a drop 
 or two of hydrochlo- 
 ric acid to 40 cc. 
 of water, and put 
 the mixture into b. 
 Into c put 40 cc. 
 water containing 
 some arsenious ox- 
 ide solution, and 
 several drops of 
 acid, and into d put 
 20 cc. dilute ammo- rig ' 60 ' 
 
 nium hydrate (half water). Connect the parts of the ap- 
 paratus, and be sure that the joints are tight. 
 
 Finally, put 10 g. ferrous sulphide, in small pieces, into 
 the side-neck flask, and pour upon it 30 cc. of dilute hydro- 
 chloric acid (half water), and stopper the flask at once. 
 
100 SULPHUR A XI) ITS COMFWXDS. 
 
 The air will be gradually driven out of the flasks, and 
 then the H 2 S will begin to show its presence by its ac- 
 tion on the liquids through which it passes. 
 
 Note its color as seen above the liquids. 
 
 Note the results of its action on the lead compound. 
 
 Note its different action on the "arsenic." 
 
 Note the effect of the ammonium hydrate. 
 
 Let the action go on until the effervescence stops. Then 
 take flask a out of the series, and transfer a little of its 
 water to tubes for the following purposes. 
 
 What is the odor of this water? 
 
 What is the effect of adding to it drops of H Cl and 
 then of lead acetate ? 
 
 What is the effect of adding to it drops of H Cl and 
 then of arsenic solution ? 
 
 Does the water have the same effects as the gas itself ? 
 
 THE FACTS. Sulphuretted hydrogen is a colorless gas 
 which is dissolved by water quite freely (a). The gas in 
 solution behaves just like the gas alone, readily changing 
 metallic compounds into sulphides. 
 
 This gas is also very soluble in ammonium hydroxide 
 (e), but in this case the solution is not a simple one, as 
 in water : there is chemical action between the two sub- 
 stances, and the result is ammonium sulphide. 
 
 Use in Analysis. It is easy to see (flasks b and c) that, 
 if one has a solution which contains either lead or arsenic, 
 without knowing which, sulphuretted hydrogen will help 
 him to decide, for lead sulphide is black while arsenious 
 sulphide is yellow. So this gas is often used to identify 
 the metals in the work of analysis. 
 
 But it is still more often used by the chemist to separate 
 two or more metals whose compounds are mixed. An 
 example will show how this may be done. 
 
SULPHUR AND ITS COMPOUNDS. 161 
 
 Ex. 108. I mix 1 cc. strong solution of copper chloride 
 and 1 cc. strong solution of zinc chloride, and then add 
 10 cc. H 2 S solution freshly made (Ex. 107). I let the black 
 precipitate settle and then add drops more of the H 2 S 
 solution, to see whether more precipitate forms. I must 
 add the hydrogen sulphide as long as it will make the pre- 
 cipitate, but when it refuses to do more I filter the whole 
 into a clean tube or bottle. I now have the black pre- 
 cipitate in the funnel, and the clear liquid in the vessel 
 below. 
 
 This liquid should contain all the zinc and none of the 
 copper. Test it by adding a few drops of ammonium 
 hydroxide : the presence of zinc and absence of copper 
 is shown by a white precipitate, without the blue which 
 copper would yield. 
 
 The black precipitate should contain all the copper and 
 none of the zinc. Test it by putting a little in a tube 
 and warming it with a few drops of nitric acid to dissolve 
 it, then adding a little water, and finally adding am- 
 monium hydroxide. The copper will be shown by the 
 familiar blue color. 
 
 THE SULPHUR GROUP. 
 
 There are three other elements whose chemical actions 
 are very much like those of sulphur. These are selenium, 
 tellurium, and oxygen. 
 
 Selenium. Selenium is a rare element, which is found 
 in combination with some metals, such as copper and iron. 
 These compounds are called selenides. The element is a 
 solid. It burns in the air with a reddish-blue flame, and 
 an odor peculiarly offensive, even worse than that of burn- 
 ing sulphur. It is a conductor of electricity, if it be first 
 melted and then slowly cooled, but not a conductor if 
 cooled quickly. Its symbol is Se. 
 
162 SULPHUR AND ITS COMPOUNDS. 
 
 Tellurium. Tellurium is even more rarely found than 
 selenium. The element is bluish-white, and has a fine 
 luster. Like sulphur and selenium, it is found in the earth 
 combined with metals, such as gold, silver, and lead. Its 
 symbol is Te. 
 
 Their Hydrogen Compounds. Sulphur, selenium, and 
 tellurium unite with hydrogen, and in the same propor- 
 tions. Each one combines with the hydrogen, not atom for 
 atom, but one atom for two. In this respect they are like 
 oxygen. Their names and formulas plainly show this fact. 
 Thus : 
 
 Hydrogen oxide H 2 O 
 
 Hydrogen sulphide H 2 S 
 
 Hydrogen selenide H 2 Se 
 
 Hydrogen telluride H 2 Te 
 
 Now these four are the only non-metals which combine 
 with hydrogen in this way one atom with two. But 
 these do so always. 
 
 General Behavior These four elements act very 
 
 much alike in other respects. They combine with the same 
 things and in the same proportions. This is not quite so 
 well marked in the case of oxygen, which stands a little 
 apart from the rest ; but still the likeness is very strong, 
 and these four form a well-marked natural group. 
 
 Atomic Weights and Properties. The order of the 
 atomic weights in this group is as follows: 
 
 O S Se Te 
 
 16 32 79 125 
 
 This is also the order of their specific gravities. When 
 equal volumes are weighed, O is found to be the lightest, 
 and S, Se, and Te are heavier in this order. It is also the 
 order of their melting-points ; oxygen melts at a very low 
 temperature, S melts at about 114 C., Se at 217, and Te 
 
SULPHUR AND ITS COMPOUNDS. 163 
 
 at 500. It is also the order of their energy in chemical 
 action, that of O being greatest and of Te least. The 
 gradually varying properties of this set of elements stand 
 in the order of their atomic weights. This is the second 
 case of this kind (see p. 151). Are there other instances ? 
 We shall see. 
 
 SULPHUROUS OXIDE AND ACID. 
 
 Burning of Sulphur. We have found (Ex. 8) that 
 sulphur will burn freely in oxygen, with a rich blue flame, 
 and that the product will dissolve in water, which will then 
 redden blue litmus. We have also found (Ex. 43), that 
 sulphur will readily burn in air. The product of combus- 
 tion, in both cases, is sulphur dioxide, SO 2 , which is more 
 commonly called sulphurous oxide. 
 
 Preparation of SO 2 This oxide is easily made by 
 heating sulphuric acid with copper. 
 
 Ex. 109. I put 10 g. of copper, in small pieces, such as 
 clippings of sheet-copper or wire, into the side-neck flask 
 
 Fig. 61. 
 
 of the gas apparatus (Fig. 61), and pour upon it about 20 cc. 
 of strong sulphuric acid. 
 
104 svLPJin; .i.v/> ITS 
 
 I put 15 cc. of water in a, 15 cc. of sulphuric acid in b, 
 and 50 cc. of water in e, and I then join the series , t>, r, 
 rf, e, as usual, the long tube of each with the short tube of 
 the one in front of it, and a with the side-neck. 
 
 I now heat the side-neck flask with a small flame until 
 effervescence begins, and afterwards just enough to keep 
 the action going. The liquid will froth over if the heat is 
 too strong. A little white vapor of sulphuric acid goes over 
 into a, but the true appearance of the oxide should be seen 
 in b, and in the other flasks. 
 
 What is the color of sulphurous oxide ? 
 
 Can you decide whether the gas is absorbed by H 2 in e? 
 
 To discover the Properties of Sulphurous Oxide 
 
 When the action is over I at once take all the flasks apart, 
 and then examine the gas they contain. 
 
 Ex. 110. I thrust a strip of moist blue litmus-paper 
 into a and leave it hanging, held by the stopper which I 
 press in beside it. I suspend a strip of dry blue litmus- 
 paper in the same way in b. Note any difference in the 
 action of the moist and dry gas. 
 
 Ex. 111. I lower the flame of a small taper, or of a 
 splinter of wood, into the gas in a, and decide 
 What is the effect of sulphurous oxide on flre ? 
 
 Ex. 112. If I boil a few small chips of logwood in 
 water I get a rich wine-colored solution. I do this, and 
 then, taking a test-tube half full of the colored water, I add 
 some of the water from flask e. 
 
 What is the effect of S O 2 on this color ? 
 
 Ex. 113. I transfer a little of the water from e to a, 
 dish or tube, and test it to learn 
 Whether it has the odor of the gas. 
 Whether it is an acid. 
 
SULPHUR AND ITS COMPOUNDS. 165 
 
 Ex. 114- At this point I take the tubes from c and d, 
 and, closing the flasks with solid corks, I stand them aside 
 for use at another time (Exs. 117, 118). I pour the brown 
 liquid carefully out of the side-neck flask, leaving the almost 
 black sediment behind, and then put in about 50 cc. of 
 water, shake it well, and filter the whole into a dish or 
 bottle. I keep this deep-blue liquid also for use at a future 
 time (Ex. 121). Pour the liquids from , b, e into the 
 waste, take out their stoppers and stand the flasks mouth 
 down in water, and leave them until the noxious gas is 
 absorbed. 
 
 THE FACTS. Sulphurous oxide is a gas with no color, 
 but possessing an odor of the most pungent and suffocat- 
 ing kind, the odor of a burning "Lucifer match." The 
 dvy gas will not redden blue litmus, but when moist it 
 will do so readily. It dissolves in water very freely, and 
 this solution is an acid. It will also bleach the color of 
 logwood and many other substances ; this the dry gas will 
 not do. 
 
 Sulphurous Acid The dry gas, and its solution, act 
 
 quite differently on litmus, and also on coloring matter, 
 and by this we know that the gas is not simjrly dissolved 
 in the water, as in the case of chlorine, and of hydrogen 
 sulphide, but that a chemical change has taken place. 
 
 The fact is, that the gas unites with water ; 
 
 SO 2 4- H 2 O = H 2 SO 8 
 
 Sulphurous oxide Water Sulphurous acid 
 
 and while the oxide itself is not an acid, its compound 
 with the elements of water is. 
 
 There are many other oxides like the sulphurous oxide 
 in this respect, they will combine with the elements of 
 water, and thus form acids. All such oxides are called 
 anhydrides. 
 
166 SULPHUR AXD ITS COMPOUNDS. 
 
 This one is called the sulphurous anhydride, because it 
 unites with the elements of water, and becomes sulphur- 
 ous acid. 
 
 Bleaching. The power of moist sulphurous oxide to re- 
 move colors makes this substance very valuable for bleach- 
 ing. Articles of straw, silk, and wool are bleached on a 
 large scale, by first moistening them and then hanging 
 them hi chambers in which sulphur has been burned. 
 The sulphurous oxide does not act on the color itself, but 
 it decomposes water and sets free a part of the hydrogen. 
 This hydrogen then acts on the colors, and changes them to 
 colorless compounds. Unfortunately these colorless com- 
 pounds will be decomposed on exposure to air and light, 
 and then the color returns. 
 
 Sulphurous oxide will not burn, nor will it allow the 
 combustion of anything else ; the fumes of burning sulphur 
 will extinguish fire. 
 
 SULPHURIC ACID AND THE SULPHATES. 
 
 Some Properties of the Acid If we examine a 
 
 specimen of strong sulphuric acid, which can be found 
 in every laboratory, we find that it is a heavy oily-acting 
 liquid. For this reason it is called oil of vitriol. If we 
 taste it which we must not do without first diluting it 
 with a large quantity of water we find it to be sourer 
 than the strongest vinegar. If we touch it, we find our 
 fingers smarting almost as if it had been fire. If we drop 
 it upon our garments, we find them turning red wherever 
 touched by it, and that, some days after, the red spots 
 crumble into holes. 
 
 When mixed with water the strong acid unites with it 
 at once, and the mixture is heated as if by fire (Ex. 14). 
 This violent attraction between the acid and water throws 
 light upon some well-known facts, thus : 
 
SULPHUR AND ITS COMPOUNDS. 167 
 
 Ex. 115. I put 2 or 3 cc. of oil of vitriol into a test- 
 tube and place in it the end of a clean pine stick. After 
 a few minutes I find the wood to be as black as if it had 
 been scorched. Indeed, the wood is changed very much 
 as it would be by fire. For by fire a black coal is left, 
 while the other elements are driven away. 
 
 What are the elements in wood? See p. 101. 
 Which one of these is left behind by the acid ? 
 Then which ones are taken out by it ? 
 Why does the acid extract these ? 
 
 One of our earliest experiments showed the singular 
 effects of this acid on sugar (Ex. 2), and now you can 
 no doubt find in the composition of the sugar, and this 
 property of the acid, a good explanation of that action. 
 Do so. 
 
 Some uses of Sulphuric Acid The chemist very 
 often needs the gases, with which he works, to be per- 
 fectly dry ; he remembers this strong attraction between 
 sulphuric acid and the elements of water, and makes his 
 gas bubble through some of the acid. It comes off dry. 
 
 Sulphuric acid is used in making a great many materials 
 used in the arts, such as soap, soda, alum, and other kinds 
 of chemicals. 
 
 It is used also in coloring cloth, in printing calico, and 
 then, at other times, it assists in the work of bleaching. 
 
 Many thousands of tons a week, of sulphuric acid, are 
 made and distributed over the world to be used for these 
 and other purposes in the arts. The manufacture of sul- 
 phuric acid is one of the most important industries. 
 
 Test for Sulphuric Acid. If, to any liquid which 
 contains this acid, a solution of barium chloride is added, 
 a white precipitate will be made, which cannot be dis- 
 solved by water or acids. Thus: 
 
168 SULPHUR A XI) ITS COMPOUNDS. 
 
 Ex. 116. To half a test-tube full of water I add a drop 
 of H 2 S0 4 , and a half cubic centimeter of H Cl, and then I 
 add a solution of barium chloride (Ba C1 2 ) drop by drop. 
 The white precipitate (BaS0 4 ) which comes, in spite of 
 the hydrochloric acid, shows the presence of H 2 SO 4 . Try 
 this test on a solution of any of the sulphates. 
 
 The Manufacture of Sulphuric Acid. The process 
 is founded on a few simple facts, which we can easily 
 demonstrate, and for this purpose we have the flasks full 
 of S 2 kept over from Ex. 114. The S O 2 may be made by 
 burning sulphur in oxygen (Ex. 8 ), or in air (Ex. 43), but 
 we may use that already made in the other way. The 
 question is now, How can this sulphurous oxide be changed 
 into sulphuric acid ? 
 
 Ex. 111. I wet a shaving or splinter of wood with 
 strong nitric acid and thrust it into the sulphurous ox- 
 ide of flask d (Ex. 114), and leave it there awhile. 
 
 Notice the colored fumes which are produced. 
 
 What is the meaning of these ? See Ex. 62. 
 
 It may be well to insert the splinter, wet with nitric 
 acid, a second time. But finally I take it out, pour 10 cc. 
 of water into the flask, and shake it well, to dissolve as 
 much as possible of the contents, then pour it into a test- 
 tube and label ^it d. 
 
 Ex. 118. And now to find out whether the sulphur- 
 ous oxide has been changed by the nitric acid I will dis- 
 solve the gas, which still remains in flask c (Ex. 114) in 
 10 cc. water, and then compare this solution with the 
 other, labelled d, in this way : I first add -a half cubic 
 centimeter of hydrochloric acid, and then add drops of 
 barium chloride, to each of my two solutions. 
 
 Note the difference in results. 
 
 What substance did the solution d contain ? 
 
SULPHUR AND ITS COMPOUNDS. 169 
 
 The Changes. When we bring sulphurous oxide and 
 nitric acid together yellowish-red fumes appear (Ex. 117), 
 and by these colored fumes we know that the nitric acid is 
 being decomposed. Sulphurous oxide in water will yield 
 no white precipitate with a mixture of hydrochloric acid 
 and barium chloride, but after this action of nitric acid the 
 solution will (Ex. 118). By this we know that the S O 2 
 has been so changed that its solution in water is sulphuric 
 acid. 
 
 If now we could only take the water out of the sul- 
 phuric acid again, we could see what the S O 2 had been 
 changed into. Unfortunately we cannot do this by experi- 
 ment, but, fortunately, we can represent the process by 
 formulas, as, in arithmetic or algebra, we often show by 
 signs, the work which we do not actually do. From sul- 
 phuric acid, H 2 SO 4 , let us subtract water, H 2 0. 
 
 H 2 S0 4 -H 2 = S(> 3 
 
 It must have been S O 3 which, when dissolved in water, 
 gave the sulphuric acid which we found in e/, and hence 
 the SO 2 must have been changed into SO 3 by the nitric 
 acid. 
 
 This S0 3 is called sulphuric oxide. It is also called sul- 
 phuric anhydride, because it combines with water to make 
 sulphuric acid. 
 
 THE FACTS. What, then, are the facts which we have 
 found ? They are as follows : 
 
 1. The burning of sulphur yields sulphurous oxide. 
 
 2. ^Sulphurous oxide will take oxygen from nitric acid 
 and become sulphuric oxide. 
 
 3. Sulphuric oxide dissolves in water and becomes sul- 
 phuric acid. 
 
 APPLICATION OF THESE FACTS. These are the facts 
 on which the manufacture of sulphuric acid is founded. 
 
170 SULPHUR AND ITS COMPOUNDS. 
 
 In the actual process there are a few others, but for the 
 full details you may refer to some larger chemistry. 1 
 
 The acid is made in immense lead-lined chambers. Such 
 a chamber may be 100 feet long, 20 feet wide, and almost 
 as high as it is wide. Sulphurous oxide goes over into 
 this chamber from a furnace where sulphur, or iron 
 pyrites, is burning. Xitric acid, made on the spot, also 
 enters the chamber, while jets of steam are blown in, and 
 a full supply of air is kept up. 
 
 The acid, which is made in this chamber, is too dilute 
 for use, and it is made stronger by evaporation in lead 
 pans, and then still stronger by evaporation in vessels of 
 glass or platinum. These must be used instead of lead 
 pans toward the last, because the strong acid will corrode 
 the lead. 
 
 The Sulphates. The salts made by sulphuric acid are 
 called sutyhates. We may study these as follows : 
 
 Ex. 119. To MAKE ZINC SULPHATE. I dilute some 
 strong sulphuric acid by pouring 5 cc. of it into 40 cc. of 
 water contained in a wide-mouth bottle, and drop into 
 this small pieces of zinc. I let the action go on until the 
 acid is used up, adding more zinc if necessary. When the 
 effervescence has almost stopped, with zinc still left in 
 the bottle, I filter the liquid to get rid of the black flakes 
 which come from impure zinc. I next evaporate the liquid 
 to one-half its bulk, and then let it cool. While it cools, 
 crystals will be seen forming in the liquid. These crystals 
 are zinc sulphate. 
 
 Ex. 120. To MAKE FERROUS SULPHATE. I make 
 some dilute sulphuric acid, as in the last experiment, and 
 
 1 In Hoscoe and Schorlemmer, Vol. I. pp. 319-338, is a full 
 account. In Cooley's Text-Book of Chemistry, p. 108, the reactions 
 are given briefly. 
 
SULPHUR AND ITS COMPOUNDS. 171 
 
 drop into it small iron nails, such as small "tacks." I 
 cover the bottle with a plate of glass or a square of heavy 
 paper, and, after the action has gone on for some time, 
 I lift the cover, and at the same time bring a match-flame 
 to the mouth of the bottle and discover 
 
 What gas is set free by the action? 
 
 When the action is over I filter the liquid, and then 
 evaporate it down to half its bulk, and let it cool. If the 
 evaporation has gone far enough, crystals will appear. 
 These crystals are ferrous sulphate. 
 
 Ex. 121. To MAKE COPPER SULPHATE. For this 
 purpose the strong acid is needed instead of the dilute, 
 and heat must be used. This work was done in experi- 
 ment 109, and if the deep blue liquid has been kept (Ex. 
 114), we need not now repeat the experiment. Sulphurous 
 oxide was set free instead of hydrogen, and the blue liquid 
 contained the copper sulphate. Perhaps by this time blue 
 crystals have made their appearance, but if not, I evaporate 
 the liquid to smaller bulk and let it cool. The blue crystals 
 are copper sulphate. 
 
 Ex. 122. To PROVE THAT THE BLUE CRYSTALS ARE 
 
 COPPER SULPHATE. I dissolve a crystal in water and 
 then add ammonia, as in Ex. 91, and also into another 
 portion of the solution I put a piece of iron. 
 
 What are the proofs that the blue crystals are a com- 
 pound of copper ? 
 
 I dissolve another crystal and add a little hydrochloric 
 acid and barium chloride (Ex. 116). 
 
 What is the proof that the blue crystals are a compound 
 of sulphuric acid? 
 
 But a compound of copper and sulphuric acid must be 
 the copper sulphate : the crystals are copper sulphate. 
 
172 SULPHUR AND ITS COMPOUNDS. 
 
 Different Ways to make Sulphates. Many sulphates 
 may be made by the action of the sulphuric acid on the 
 metals directly. In the case of zinc and iron the action 
 goes on in the cold, and yields hydrogen beside the sul- 
 phate. But in the case of copper, heat must be used to 
 produce the sulphate, and sulphurous oxide and water, in- 
 stead of hydrogen, are set free. 
 
 Silver, mercury, and some other metals are like copper 
 in this respect. When heated with strong sulphuric acid 
 they yield sulphates, sulphurous oxide, and water. 
 
 The sulphates may be made also by letting the acid 
 act on the oxides or the hydrates of the metals, instead 
 of on the metals themselves. 
 
 It is also found that this acid will sometimes yield two 
 salts of the same metal. 
 
 It will do this with sodium, for when the acid is gently 
 heated with common salt, as in Ex. 98, we get one salt 
 of sodium, but when the heat is much stronger we get 
 another. How can this be ? Well, we see that the mole- 
 cule of the acid, H 2 S0 4 , has two atoms of hydrogen, and 
 if the heat be gentle an atom of sodium, Na, takes the 
 place of only one of them, and we have NaIISO 4 , but if 
 the heat be strong both atoms of hydrogen are driven out 
 by two of sodium, and we get Na 2 SO 4 . 
 
 The first, NaIISO 4 , is the acid sodium sulphate. 
 The second, Na 2 SO 4 , is the noiinal sodium sulphate. 
 
 These two kinds of salts may come from any other 
 acid in whose molecules there are two atoms of H, which 
 may be driven out by a metal. All such acids are 
 called dibasic acids. Sulphurous acid, H 2 S0 3 , and carbonic 
 acid, H 2 CO 3 , are dibasic. They are dibasic, not because 
 they have two atoms of H in a molecule, but because they 
 have two atoms of H which metals can displace. 
 
SULPHUR AND ITS COMPOUNDS. 173 
 
 Acetic acid, H 4 C 2 2 , is monobasic. Its molecule con- 
 tains four atoms of H, but with metals it will give up 
 only one. 
 
 An acid salt is one which still contains a part of the hy* 
 drogen which a metal can displace. A normal salt is one 
 which contains none of the hydrogen which a metal can 
 displace. The normal salts are generally neutral to litmus- 
 paper, and are often called neutral salts. 
 
 OTHER SULPHUR OXACIDS. 
 
 The sulphurous and sulphuric acids are the most impor- 
 tant oxygen acids of sulphur ; but besides these two there 
 exists no less than six others. Look at their names and 
 formulas. 
 
 Hyposulphurous acid, H 2 S() 
 
 Pyrosulphuric acid, 1I 2 S 2 <)~ 
 Thiosulphuric acid, H 2 S 2 O 8 
 
 Dithionic acid, H 2 S 2 O 6 
 Trithionic acid, H 2 S 3 O 6 
 Tetrathionic acid, H 2 S 4 O 6 
 
 Only one of these needs to be noticed any further at 
 present, and that is the thiosulphuric acid. The sodium 
 salt of this acid is very useful in photography : it dissolves 
 away from the glass or paper the silver salts which have 
 not been acted upon by light, and which, if left, would 
 cause the picture to blacken. It is known as "hyposul- 
 phite of soda," but its true name is sodium thiosulphate. , 
 
 EXERCISES. 
 
 1. Study the action of dilute acids on sulphides, sulphites, 
 
 and sulphates. 
 
 1. Put a little of the powder of some specimen of each 
 of these compounds into a tube, moisten it with water, and 
 add a little dilute hydrochloric acid. Watch for efferves- 
 cence, or any other evidence of chemical action. Xotice the 
 odor of any gas which may be set free. If no action begins 
 soon, heat may be used. 
 
174 SULPHUR AND ITS COMPOUNDS. 
 
 2. Use dilute sulphuric acid, making the experiments 
 in the same way. 
 
 3. Write a brief statement of your results, pointing out 
 the differences in the behavior of these three kinds of com- 
 pounds. 
 
 2. Study the action of barium chloride on sulphites and sul- 
 
 phates. 
 
 1. Add drops of barium chloride to a solution of a sul- 
 phite and to a solution of a sulphate. Then compare the 
 precipitates which appear. 
 
 . Learn, by experiment, whether these two precipi- 
 tates are alike soluble in hydrochloric acid. 
 
 8. See whether both these precipitates will appear if 
 you add the hydrochloric acid to the solutions before you 
 add the barium chloride. Compare Ex. 118. 
 
 4. Write a brief statement of your results, pointing out 
 the difference in the behavior of the sulphites and the 
 sulphates. 
 
 3. Take from the teacher, or a friend who knows what 
 
 they are, a few substances, and see if you can decide 
 whether each is a sulphide, a sulphite, or a sulphate. 
 
PHOSPHORUS, AND THE NITROGEN GROUP. 
 
 IN 1669 a man by the name of Brandt, in Hamburg, was 
 making experiments, hoping to find the "philosopher's 
 stone," by the touch of which he would be able to turn 
 any substance into gold. What he actually did find was 
 a waxy-looking solid, yellow by daylight, but shining 
 with a pearly white light in the dark. It burned furi- 
 ously at the least provocation by warmth, and, on the 
 whole, was so strange in its actions that the superstitious 
 chose to name it " The Son of Satan." It proved to be an 
 element, and it has since been known as phosphorus. 
 
 Properties. Phosphorus comes to market in the form 
 of round "sticks," four or five inches long, and about 
 a half-inch in diameter. In color it is like yellow wax, 
 but it is much harder than that substance, although soft 
 enough to be easily cut with a knife. 
 
 Its most remarkable property is its strong attraction for 
 oxygen. If brought into the air it begins at once to unite 
 with oxygen, and waste away by a "slow combustion." 
 But if gently heated at the same time, its combustion 
 becomes rapid and furious. 
 
 To rub it with the warm fingers will inflame it. The 
 friction of a knife-blade in cutting it will sometimes pro- 
 duce heat enough to set it on fire. 
 
 Such a substance can be safely handled only when it is 
 under water. It is kept under water, and it ought to be 
 cut under water, to avoid accident. 
 
 This element is a powerful poison. 
 
 Red Phosphorus. Let some phosphorus be put into 
 a vessel full of carbon dioxide or nitrogen, which will 
 not act upon it, and then let heat be applied. In this 
 
 175 
 
176 PHOSPHORUS, AND THE NITROGEN GROUP. 
 
 case the phosphorus will not burn, no matter how hot 
 it becomes. But at a temperature of 240 C. a curious 
 change takes place. "The melted phosphorus becomes 
 solid, opaque, and of a deep red color." It is phosphorus 
 in an allotropic form. 
 
 This " red phosphorus " may be exposed to the air and 
 handled with very little danger. 
 
 The common and the red are not the only allotropic 
 forms in which this extraordinary element exists. There 
 is a white and flaky form, lately discovered by Remsen, 
 and a black variety has been described by Thenard. 
 
 Matches Phosphorus is used, in large quantities, in 
 
 making friction-matches. These are of several kinds, 
 among which is the sulphur ("Lucifer") match, the par- 
 affine match, and the safety match. 
 
 The sulphur match is made by dipping the end of a pine 
 stick in melted sulphur, and then into a paste made of 
 phosphorus and a little nitre, KN 3 , mixed in gum-water. 
 Now, by rubbing the end of the match, we produce heat 
 enough to set the phosphorus on fire ; the burning of the 
 phosphorus produces more heat, by which the sulphur is 
 set on fire, and then the sulphur burning with still more 
 heat sets fire to the wood. 
 
 The paraffine match is made in the same way, but par- 
 affine is used instead of sulphur. 
 
 In this way the troublesome odor (S O 2 ) of burning 
 sulphur is avoided. Sometimes potassium chlorate is used 
 in the mixture, and then the match burns with a slight 
 explosion. 
 
 The safety-match has no phosphorus in its tip; this 
 element is spread on the side of the box instead. Red 
 phosphorus is used. The match-stick is tipped with a 
 mixture of sulphur or antimony sulphide, and potassium 
 chlorate, and sometimes red lead or some other coloring 
 substance is added. 
 
PHOSPHORUS, ANl> THE NITROGEN GROUP. 177 
 
 To "light" this match, it must be rubbed against the 
 phosphorus surface of the box. 
 
 Phosphorus Oxides. There are two compounds of 
 this element with oxygen. 
 
 Phosphorus oxide ^ 2 O 3 
 
 Phosphoric oxide I*aO 5 
 
 The first is made when phosphorus is simply exposed 
 to the air. The second is made by burning phosphorus 
 in oxygen or air. 
 
 Let a small piece of phosphorus be hung, by a fine wire, 
 inside a bottle ; white vapors of P 2 O 3 will fall from it and 
 slowly fill the bottle. If then a little water is shaken in 
 the bottle, some of these vapors are dissolved, and by 
 adding a few drops of blue litmus solution, we prove the 
 presence of an acid. Thus: 
 
 Phosphorus oxide . . P 2 O 3 -f 3 H 2 O = 2 H 3 P O 3 . . Phosphorus acid. 
 
 Let a small piece of dry phosphorus be placed on a little 
 cup on a plate. Let it be touched with a hot wire, and 
 immediately covered with a dry glass jar. Clouds of milk- 
 white vapor are quickly formed, and, if everything is dry, 
 snow-white flakes will soon be seen, some clinging to the 
 walls of the jar, others falling like snow upon the plate. 
 This snow-white solid is phosphoric oxide, P 2 O 5 . 
 
 Let a little water be poured on the plate, and the white 
 solid will instantly dissolve with a hissing sound, like the 
 sound of a hot iron in water. A little blue-litmus is red- 
 dened by this solution, proving the presence of an acid. 
 Thus: 
 
 Phosphoric oxide . . P 2 O 5 -f- 3 H 2 O = 2 H 3 P O 4 . . Phosphoric acid. 
 
 There is a third acid in this series ; it is the hypo- 
 phosphorus acid, H 3 P0 2 . But of these three we shall 
 
178 PHOSPHORUS, AND THE NITROGEN CROUP. 
 
 notice further only the phosphoric acid, which is important 
 on account of its useful salts, the phosphates. 
 
 The Phosphates. These are found in rocks and soils, 
 in plants and in animals. It is in the form of phosphate 
 that phosphorus exists most largely in nature. We find 
 it more abundant in the seeds of plants than in other parts, 
 and in the brain, the blood, and the bones of animals ; and, 
 accordingly, we find that the phosphates are much used to 
 fertilize soils on which grain is to grow, and that they 
 are also needful constituents in the food of man. 
 
 Manufacture of Phosphorus Phosphorus is itself 
 
 extracted from bones. Almost half the weight of the 
 bones in animals is calcium phosphate, Ca^ (PO 4 ) 2 , and 
 about one-fourth of the weight of this phosphate is pure 
 phosphorus. 
 
 If the skeleton of a man weighs 12 Ibs. it contains about 
 one and a half pounds of this element. 
 
 To obtain phosphorus from bones they are first burned ; 
 in this process they become very white and very brittle. 
 They are afterwards crushed to powder; this powder is 
 called bone-ash, and it is chiefly calcium phosphate. 
 
 From the bone-ash the phosphorus is obtained 1 by 
 
 1. Treating it with sulphuric acid. 
 
 2. Evaporating the solution to dryness. 
 
 3. Heating the residue nearly to redness. 
 
 4. Heating to redness with charcoal. 
 
 ARSENIC. 
 
 The element arsenic is a solid substance with a steel- 
 gray color, and a luster like the metals. It is very brittle 
 and easily powdered. Its powder is sometimes sold under 
 the false name "cobalt," to be used as a fly-poison. 
 
 1 For details and explanations consult Roscoe and Schorlemmer, 
 Vol. I. p. 460. 
 
PHOSPHORUS, AND THE NITROGEN GROUP. 179 
 
 This element is sometimes found in the earth not com- 
 bined with anything, but such native arsenic, as it is called, 
 is not common. It is mostly found in combination with 
 metals and sulphur. 
 
 In Silesia, Germany, there is found a mineral which con- 
 tains arsenic with iron and sulphur ; it is called mispickel, 
 and its formula is Fe As S. This mineral is the source 
 from which most of the arsenic of commerce is obtained. 
 
 The chief use of arsenic is in making shot. A small 
 quantity of the element is melted with the lead. Lead 
 alone is too soft ; the arsenic hardens it. 
 
 Arsenous Oxide. This is the principal compound of 
 arsenic in commerce. Its formula is As 2 3 , and it is also 
 called arsenic trioxide, because its molecule contains three 
 atoms of oxygen. In the drug-stores it is often called 
 white arsenic, but more generally simply " arsenic." 
 
 This oxide is made directly from arsenical pyrites, 
 another name for mispickel. 
 
 To get the oxide from mispickel the mineral is roasted, 
 that is to say it is heated in a current of air. The hot oxy- 
 gen of the air takes the arsenic from the hot mineral, and 
 the two elements combine ; arsenous oxide is the result. 
 
 This substance is a white solid; it can be dissolved in 
 hot water, in cold water not so well. Its solution is almost 
 tasteless and colorless, and without odor. It is a most 
 fearful poison. 
 
 But while this compound is so fatal to the life of an 
 animal, it has a strange power to prevent decay. It is 
 used to destroy rats, mice, insects, and sometimes for the 
 terrible purpose of taking the lives of men. On the other 
 hand, it is made to do good service in the preservation of 
 the stuffed or dried objects -of natural history to be found 
 in museums. 
 
 Arsenous oxide is an anhydride, that is to say, it be- 
 
180 PHOSPHORUS, AND THE NITROGEN GROUP. 
 
 comes an acid by combining with the elements of water. 
 By so doing it forms arsenous acid. Thus : 
 
 As 2 O 3 + 3H 2 O = 2H 3 AsO 3 
 
 From this arsenous acid, H 3 AsO 3 , a large number of 
 salts, the arsenites, may be made. Sodium arsenite is 
 very useful in calico-printing; it helps to "fix" the color, 
 in other words, prevent its fading. The common Paris- 
 green is copper arsenite and copper acetate together. 
 
 Arsenic Oxide. There is also arsenic oxide ; its for- 
 mula is As 2 5 . It is, like the other, an anhydride, for with 
 water it yields arsenic acid, H 3 AsO 4 . 
 
 Arsenic and Hydrogen. There is one compound of 
 these two elements, a gas called arsine. It is made by the 
 action of nascent hydrogen on a soluble compound of arsenic. 
 It is very poisonous; Gehlen, who 
 discovered it, lost his life by acci- 
 dentally breathing a bubble of this 
 gas. It burns freely, and, if made 
 in the laboratory, it should be burned 
 as fast as it forms. 
 
 Ex. 123. To make and burn 
 this gas I use the simple hydrogen- 
 flame apparatus of Ex. 20, shown 
 again in Fig. 62. Before putting 
 the zinc into the hydrochloric acid 
 in the mortar to ma'ke the hydro- 
 gen, I dissolve a little arsenous 
 oxide in water, by putting a very 
 little of the powder not more 
 than will lie on the tip of a penknife-blade into one or 
 two cubic centimeters of water in a test-tube and boiling it. 
 I then drop several fragments of zinc into the dilute 
 acid in the mortar, and at once lower the funnel to cover 
 
 Fij. 62. 
 
PHOSPHORUS, AND THE NITROGEN GROUP. LSI 
 
 them. Hydrogen is rapidly set free. It drives the air out 
 of the apparatus, and when this is done I set fire to the 
 jet. I now hold the bottom of a cleata, dry porcelain dish 
 right across the flame for a moment ; no dark stain should 
 be left upon it. 
 
 Then I pour the arsenous oxide solution into the mortar. 
 Very soon the color of the flame becomes bluish-white. 
 Again I press the cold porcelain for a moment down into 
 the flame ; a lustrous brown stain is left upon it. I let 
 the flame play on other parts of the dish, touching it here 
 and there on the inside also. A large surface may be thus 
 covered with the brown arsenical mirror. 
 
 At the moment when hydrogen is set free by the zinc 
 it attacks the arsenous oxide and changes the arsenic into 
 arsine, AsH 3 , and its oxygen into water. 
 
 The arsine burns with a livid flame, thus : 
 
 2AsH 8 + 60rrAs 2 3 + 3H 2 O 
 
 arsenous oxide and water being the products of the action. 
 But the cold porcelain cools the flame, and then only the 
 hydrogen of the arsine burns, while the arsenic is deposited 
 on the dish in the form of a lustrous mirror. This mirror 
 will appear, even when the quantity of arsenic used in the 
 experiment is astonishingly small. In fact, this experi- 
 ment is a most excellent way of testing for arsenic in any 
 suspicious substance. It is known as Marsh's test. 
 
 The chemist has studied the compounds of arsenic, until 
 he has so well learned their characters, that he can tell with 
 great certainty whether they are present in a substance or 
 not, and Marsh's test is his most trusted method. It is 
 true that antimony will also give a stain on porcelain in 
 the same way, but its color is velvety black, and there are 
 other well-marked differences which are well known to 
 every practical chemist. 
 
182 PHOSPHORUS, AND THE NITROGEN GROUP. 
 
 THE NITROGEN GROUP. 
 
 PHOSPHORUS and arsenic are much alike in their chemi- 
 cal actions, and in some things both resemble nitrogen: 
 these three are the members of the nitrogen group of non- 
 metals. 
 
 Their Hydrogen Compounds. These elements unite 
 with hydrogen, and in the same proportions. The names 
 and formulas of their compounds plainly show this fact. 
 We have 
 
 Ammonia (amine) . . H 3 N 
 
 Phosphine H 3 P 
 
 Arsine H 3 As 
 
 We see that, in this group, each element unites with 
 hydrogen, one atom for three. In other respects the 
 resemblance among them is not so striking as it is in the 
 chlorine group or in the sulphur group. 
 
 The order of their atomic weights is as follows: 
 
 N P As 
 
 14 31 75 
 
 This is also the order of their densities. The strength 
 of their attraction for hydrogen is less, as the atomic 
 weight is greater, in the same order. But among these 
 elements the relation of properties to atomic weights is 
 not so close as in the cases of the chlorine and the sul- 
 phur groups. 
 
, AND THE CARBON GROUP. 
 
 Silicon. The element silicon is in many respects very 
 much like carbon. 
 
 It is usually a dark-colored powder, but it has two other 
 forms, which are a little like graphite and diamond. 
 
 Silicon, next to oxygen, is the most abundant element 
 in the world, but it is never found alone ; it is combined 
 with oxygen, and the two are not easily separated. Im- 
 mense quantities of silicon, in this condition, are hidden in 
 the sandstone rocks, so very common, yet very few persons 
 who are not chemists have ever seen the element itself. 
 
 Its Oxide. The compound of silicon and oxygen is 
 known as silica. Its true chemical name is silicon dioxide ; 
 its formula is Si0 2 . Common sand is chiefly silica, and 
 the sandstone rocks are masses of silica, mixed with many 
 impurities to be sure, but chiefly silica. And besides, there 
 are many purer forms, such as the following: 
 
 Flint is a kind of very hard stone which is sometimes 
 white, sometimes brown or black, but it is always silica, 
 and a much purer form than sandstone. In some places 
 very fine transparent diamond-shaped crystals are found ; 
 they are called rock-crystal, and consist of pure silica. 
 The common name of these hard varieties of silica is 
 quartz. 
 
 The beautiful amethyst is quartz crystal, with a delicate 
 purple color. 
 
 The precious opal, the chrysoprase, and the bloodstone 
 are little else than silica. 
 
 Jasper is a very fine-grained form of silica, colored gen- 
 erally red, but sometimes black. 
 
 183 
 
184 SILICON, AND THE CARBON GROUP. 
 
 The agate is a form of silica in which many tints of 
 color are delicately arranged in stripes or bands. When 
 the colors are few and very regularly arranged the agate 
 is called an onyx. When the color is uniform, and a 
 pearly white, the stone is a chalcedony, but when red it 
 is called carnelian. 
 
 THE CARBON GROUP. 
 
 Silicon behaves very much like carbon in its chemical 
 actions. The two are much more like each other than 
 like any other non-metals, and they together are called 
 the carbon group. 
 
 Their Hydrogen Compounds. These elements unite 
 with hydrogen in the same proportions. They yield 
 
 Methane (carbon hydride) . , . . , . . . . C H 4 
 Silicon hydride . . . * /;;:*> v<. ; >. ..;.-:. . Si H 4 
 
 We see that, in this group, each element unites with 
 hydrogen, one atom with four. 
 
 Their Oxygen Compounds They are not only alike 
 
 in their combination with hydrogen, but also with oxygen, 
 for we have carbon dioxide, C O 2 , and silicon dioxide, SiG 2 . 
 And then, just as from carbon dioxide we get carbonic 
 acid, by its union with water, thus : 
 
 C0 2 + H 2 = H 2 C0 3 
 
 The dioxide Water The acid 
 
 so from silicon dioxide we get silicic acid, 
 Si0 2 + II 2 = H 2 Si0 3 
 
 The dioxide Water The acid 
 
 The likeness does not stop here, for just as carbonic 
 acid yields salts the carbonates, so silicic acid yields 
 salts the silicates. 
 
 The Silicates. These salts are very abundant in na- 
 
SILICON, AND THE CARBON GROUP. 185 
 
 ture, and very useful in the arts. The natural silicates 
 occur in soils : clay is one of them. They also make up 
 large rock masses : the slates are of this kind. Clay and 
 the slate rocks alike are made chiefly of aluminum silicate. 
 
 Artificial silicates are easily made. It is only necessary 
 to melt together some silica, say fine white sand, and 
 potassium, or sodium, or calcium carbonate, to produce 
 the potassium, sodium, or calcium silicate. These arti- 
 ficial silicates are called glass. 
 
 In each different kind of glass there are at least two 
 kinds of silicate. In common "window glass" there are 
 sodium and calcium silicates; in "flint glass" there are 
 potassium and lead silicates. Most ornamental glassware, 
 such as vases, fine goblets, and decanters, are made of 
 flint glass. 1 
 
 BORON. 
 
 The Element The element boron can be obtained 
 in two forms ; as a dark-brown powder and as fine crys- 
 tals, almost as hard as diamond. It is never found free 
 in nature, but some of its compounds are quite abundant 
 The most interesting are boric acid and borax. 
 
 Borax. There is a lake in California (Borax Lake) 
 whose waters hold a large quantity of borax in solution, 
 and borax for the market is obtained by evaporating this 
 water. It comes out in the form of a mass of white 
 crystals. The chemical name of this substance is sodium 
 biborate. But the pure and dry biborate is not quite the 
 same as the crystals, for they hold a large portion of water 
 in combination, while the biborate has none. 
 
 This is shown by the formulas, 
 
 Sodium biborate ........ Xa 2 B 4 O 7 
 
 Borax crystals . . . ...... Na 2 B 4 O 7 + 10 H 2 O 
 
 1 Roscoe and Schorlemmer, Vol. II., Ft. I., pp. 462 to 490. 
 
186 SILICON, AND THE CAKBON GROUP. 
 
 Now, this water is a part of the crystal, for if we 
 it away by heat the borax is no longer crystalline. This 
 water is, therefore, called the water of crystallization. The 
 crystals of a great many other things also hold water of 
 crystallization. 
 
 Ex. 124. I make a solution of 5 g. of borax in 20 cc. 
 of hot water in a porcelain dish, and then add to it, in 
 small portions, 1 cc. strong sulphuric acid. I let this stand 
 until cold. Then notice and describe the crystals which 
 form. Are they crystals of borax ? 
 
 Ex. 125. To answer this question I put some of the 
 crystals into one porcelain dish, and as much borax into 
 another, and pour upon each 10 cc. of strong alcohol. I stir 
 them well, and then fire them both with a match-flame, and 
 notice the color of the flames, especially around the edges. 
 
 What evidence that the crystals are not borax ? 
 
 Boric Acid. Borax is changed to boric acid by the 
 action of strong sulphuric acid. Boric acid when dry ap- 
 pears in the form of glistening scale-like crystals (Ex. 124). 
 These dissolve in alcohol, and tinge the flame of alcohol 
 with green (Ex. 125). 
 
 Boric acid is sometimes made on a large scale in this 
 way, that is by the action of a strong acid on borax. But 
 it is also obtained by evaporating natural waters which hold 
 it in solution. Such water is found in Tuscany. It is in 
 a volcanic region, and jets of volcanic steam, out of the 
 earth, are directed into this water. The water evaporated 
 by the volcanic heat leaves boric acid. 
 
 No Hydrogen Compound. Boron is the only non- 
 metal which does not combine with hydrogen. We have 
 seen that elements, which combine with hydrogen in the 
 same way, are very much alike also in most of their chem- 
 ical actions. Now here is an element which seems to have 
 
SILICON, AND THE CARBON GROUP. 187 
 
 no disposition at all to unite with hydrogen, and, curiously 
 enough, we find it standing apart from all the other non- 
 metals in other respects too. When free, it is a little like 
 carbon and silicon. In some of its properties it resembles 
 the nitrogen group; in others it is more like the metals 
 than the non-metals. 
 
 Boron does not fairly belong to either group of non- 
 metals, but on the whole it stands nearer to the nitrogen 
 group than to others, and it is usually named in the list 
 of that group. 
 
 But, in both its forms, it differs from the members of 
 that group. For example : the crystallized variety will 
 not readily combine with oxygen, while the elements of 
 the nitrogen group, except nitrogen itself, will ; and the 
 other variety the brown powder when heated to red- 
 ness, will combine with nitrogen ; this the other members 
 of the nitrogen group will not do. 
 
VAI/ENCE. 
 
 WE have seen that every one of the non-metals, except 
 boron, will combine with hydrogen. But we have found 
 that they do not all combine with it in the same propor- 
 tions. In some cases they combine with it, atom for atom 
 (p. 150), in others one atom for two (p. 162), and in other 
 cases the proportions are still different (pp. 182, 184). 
 What is the meaning of this ? 
 
 A Difference in Atoms. The proportions of the ele- 
 ments, in these compounds of the non-metals with hydro- 
 gen, are found by actual analysis, and then they may be 
 shown by their formulas, each symbol of an element 
 standing for one combining weight. Let us take one 
 formula from each of the four groups which we have 
 studied, as an example, 
 
 HC1 H 2 H 8 N H 4 C 
 
 and we see that one combining weight of chlorine combines 
 with one of hydrogen, but that one of oxygen is not sat- 
 isfied with so little ; it must have two. One combining 
 weight of nitrogen refuses to unite with less than three of 
 hydrogen, while one of carbon demands four. 
 
 But we may as well say atoms, as combining weights, 
 for, by the atomic theory, a combining weight of an ele- 
 ment represents one atom. If so, the formulas show that 
 one atom of chlorine can hold one atom of hydrogen, 
 that an atom of oxygen is able to hold two, while an 
 atom of nitrogen is able to hold three, and an atom of 
 carbon, still more powerful, is able to hold four. In this 
 way it appears that these atoms differ in their power to 
 hold atoms of hydrogen in combination in a molecule. 
 
VALENCE. 189 
 
 VALENCE. Now this power of an atom to hold a defi- 
 nite number of other atoms in a molecule is called its 
 valence. 1 
 
 The valence of an atom is measured by the number of 
 hydrogen atoms which it can hold in combination. Thus 
 the valence of chlorine is 1, of oxygen is 2, of nitrogen 
 is 3, and of carbon is 4. 
 
 The valence of an atom is described by a prefix. Thus 
 chlorine is said to be uratvalent, oxygen fa'valent, nitrogen 
 fr'ivalent, and carbon quadrivalent. 
 
 The valence of an atom is shown to the eye usually by 
 primes or dashes, written with the symbol, thus : 
 
 Cl' or Cl_ shows that chlorine is a univalent element. 
 ()" " O = " " oxygen " bivalent " 
 
 X'" " N= " " nitrooren " trivalent " 
 
 (j"" (j = carbon " quadrivalent " 
 
 The place of the dashes is of no consequence ; they may 
 be written above the symbol, below, at the right, or at 
 the left of it. Thus : 
 
 Cl O N C 
 
 It is the number of dashes which shows the valence of 
 the element. 
 
 Substitution is Governed by Valence. Chlorine 
 will take the place of hydrogen in methane. To bring this 
 about it is only necessary to mix the two gases and put the 
 mixture in diffuse light. When this is done, it is found 
 that the chlorine will take the place of the hydrogen grad- 
 ually, until none is left. Methane, CH 4 , may as well be 
 written C H H H H. Then it is found that, 
 
 1 This property is also called quantivalence, and equivalence, and 
 valency, by different writers. To call it valence is one of the later 
 suggestions, and one worthy of general adoption. 
 
190 VALENCE. 
 
 C HH II H is first changed to C II H II Cl 
 CHHHC1 " then " CHHC1C1 
 CHHC1C1 " " CHC1C1C1 
 
 CHC1C1C1 " " " " CC1C1C1C1 
 
 Notice that the substitution of Cl for H goes on grad- 
 ually, atom for atom. The carbon gives one atom of hydro- 
 gen for one of chlorine every time. 1 
 
 The chlorine and hydrogen atoms have the same valence. 
 Like bronze and copper pennies, they are different kinds 
 of matter, but have the same value in making change. 
 One atom of chlorine may be exchanged for one atom of 
 hydrogen, and no more, in any chemical action. In fact, 
 all univalent substances displace one another atom for 
 atom. 
 
 But a bivalent atom is worth as much as two univalent 
 atoms, and, in chemical action, the exchange must be made 
 one atom for two. So one quadrivalent atom is worth two 
 that are bivalent, and two trivalent atoms are worth three 
 that are bivalent, in all chemical changes. 
 
 What is the Valence of Boron? Boron will not com- 
 bine with hydrogen, but it will with chlorine. The chlo- 
 ride is BC1 3 . Here we see one atom of boron holding 
 three univalent atoms of chlorine, which shows that boron 
 is trivalent. 
 
 In this way the valence of many other elements has been 
 found ; if they have no hydrogen compounds their chlorine 
 compounds, or their compounds with some other element 
 whose valence is known, may be used instead. The val- 
 ence of the metals has been found in this way. 
 
 Valence Useful in Writing Reactions The valence 
 
 of the elements tells us how many atoms must take part 
 in a reaction, and helps one to see how many molecules of 
 
 1 The H which is driven out combines with other atoms of Cl to 
 form HC1. 
 
VALENCE. 191 
 
 each substance are involved in the change which goes on. 
 For example : 
 
 We have found that sodium with hydrochloric acid yields 
 sodium chloride and hydrogen (Ex. 76). But sodium is 
 univalent, and so we write 
 
 Na' + H'Cl'^NaCl + H 
 
 So also zinc and hydrochloric acid yield zinc chloride 
 and hydrogen (Ex. 78). Shall we write 
 
 Zn + HC1 = ZnCl + H 
 
 No, because zinc is bivalent ; one atom of zinc is worth 
 two atoms of hydrogen, and must take the place of two. 
 But there is only one in one molecule of H Cl, and there- 
 fore we must write 
 
 Zn" + 2H'Cr = Zn"Cl' 2 -f 2H 
 
 Many reactions already studied will now seem clearer in 
 the light of this explanation, furnished by valence, and 
 in the future study of chemical actions valence will help 
 us much. 
 
 The Valence of an Element changes But the val- 
 ence of the same element is not always the same. It de- 
 pends partly on the other substance with which it acts. 
 Sulphur is bivalent with hydrogen, H 2 S", but it is quad- 
 rivalent with oxygen S' V 0" 2 . And nitrogen, a trivalent 
 element, sometimes has a valence of five. Still the changes 
 in valence are very regular, and they do riot greatly hinder 
 our using valence as a guide in writing common reactions. 
 
METALS. 
 
 What is a Metal? We think of a metal as a sub- 
 stance which is heavy, hard, and lustrous, and a good 
 conductor of electricity and heat, because most of the 
 common metals have these properties in high degree. 
 
 But there are some metals which are as soft as wax and 
 lighter than water. In some conditions, metals are not 
 at all lustrous, and some are not very good conductors. 
 We must look further than to these properties for a real 
 difference between metals and non-metals. It will be found 
 in their chemical actions. 
 
 The compounds of other non-metals with hydrogen and 
 oxygen are acids, while the compounds of metals with 
 hydrogen and oxygen are bases. Remember that acids 
 and bases are just opposite in character, and yet both 
 contain hydrogen and oxygen. The other element which 
 is combined with these two must be very different, in 
 order to make an acid in one case and a base in another. 
 And those which form the acids are the non-metals, while 
 those which form the bases are the metals. 
 
 A metal is an element whose compound with hydrogen and 
 oxygen is a base. 
 
 There is another chemical action in which metals and 
 non-metals differ. Remember what has been said about 
 salts, that they are made by putting another element 
 into an acid in place of the hydrogen. Now, these ele- 
 ments which can take the place of the hydrogen in acids 
 are the same ones which, united with hydrogen and oxy- 
 gen, form the bases; they are the metals. This gives us 
 another definition: 
 
 192 
 
METALS. 193 
 
 A metal is an element which will take the place of hydro- 
 gen in an acid and form a salt. 
 
 Accordingly the chemist divides the seventy-one elements 
 into two classes, metals and non-metals, and in a general 
 way the division is right. But nature does not draw any 
 such sharp line of division through the list of elements. 
 There are some elements whose compounds with hydrogen 
 and oxygen are sometimes bases and sometimes acids. 
 This is true of iron. The fact is, that while some of the 
 elements are perfect non-metals, and some are perfect 
 metals, there lie, between these, others which are less and 
 less perfect, and some which are almost as much one as 
 the other. In nature there is a gradual difference, in the 
 properties of the elements, running from one end of the 
 list to the other. 
 
 Number and Abundance of the Metals. We have 
 seen that the non-metals are included in four groups, and 
 that they number only fifteen. All others of the seventy- 
 one elements are metals. 
 
 Most of this large number of metals are rare substances 
 seldom seen or little used. Not more than fifteen or 
 twenty are abundant in nature or useful in the arts. 
 
 In our study of the metals we will select those which 
 will teach us the most chemistry, are the most abundant, 
 and the most useful. The study of the complete list of 
 metals and their compounds need be attempted only by 
 students who are to become chemists. To such this pres- 
 ent course is simply a preparation. 
 
 Occurrence of Metals in Nature There are a few 
 
 metals which are sometimes found free in the earth, not 
 pure, but simply mixed with other things. Gold and 
 silver and copper are examples. Metals when found in 
 this condition, uncombined with other elements, are called 
 native metals. 
 
194 METALS. 
 
 But the metals are usually found in combination with 
 non-metals. In fact, the solid earth is made up of such 
 compounds. But the rocks generally contain so much 
 besides these compounds, or it is so difficult to get the 
 metals out of them, that they are worthless for this pur- 
 pose. 
 
 There are, however, some parts of the rocky masses, 
 which are made up of metallic compounds, so rich in metal 
 that they are valuable substances from which to get the 
 metals themselves. Such compounds of the metals are 
 called ores. 
 
 The work of taking these ores out of the earth is 
 mining, and that of getting the metal out of the ore is 
 metallurgy. Mining is a mechanical operation, and we 
 will not stop to describe it, but metallurgy is a chemical 
 art, and we will study it in connection with several of 
 the common and the useful metals when we reach them, 
 as a good example of the application of chemistry to 
 useful purposes. 
 
 The most valuable ores of the metals are the oxides, 
 the sulphides, the chlorides, and the carbonates. 
 
THE POTASSIUM GROUP. 
 
 POTASSIUM. JF. 
 
 Description of the Metal. Most metals are very hard, 
 but potassium is as soft as wax. It is easily moulded by 
 the fingers or cut with a knife. When freshly cut, the sur- 
 face shines with a blue-white luster. 
 
 Most metals are heavy, but this one is lighter than 
 water. A piece dropped on water will float like cork. 
 Nor is this the only thing that will surprise one, who for 
 the first time drops potassium on water; the metal will 
 instantly take fire. Violet-colored flames will burst from 
 it, while the melted globule will run wildly over the water, 
 wasting away all the time, until, when nearly all gone, it 
 will usually put a stop to the action by a small explosion. 
 
 Its Chemical Action on Water The product of this 
 
 action is found to be a base. (How would you prove it ?) 
 It is the potassium hydroxide. We may write the reaction 
 
 II HO + K KHO + H 
 
 Water Potassium 1 Potassium hydroxide Hydrogen 
 
 The atom of potassium is univalent. It takes the place 
 of one of the two atoms of hydrogen in a molecule of water, 
 and forms a molecule of the hydroxide. 
 
 Hydrogen and much heat are also set free ; in fact, heat 
 enough to set the hydrogen on fire. A little of the potas- 
 sium itself also burns, and it is this which gives violet color 
 to the flame. 
 
 Occurrence in Nature Compounds of this metal 
 
 are present in all fertile soils, and from the soil they pass 
 
 1 The Latin name of potassium is Kalium, and the symbol, K, is 
 taken from this. 
 
 195 
 
196 THE POTASSIUllf GROUP. 
 
 into the bodies of plants. In some places potassium nitrate 
 is found in the earth in large quantities ; this is true of 
 the dry tropical countries like Egypt and India. It is 
 very soluble, and can be easily washed out by water. It 
 is known in commerce as nitre or saltpetre. Potassium 
 compounds are obtained for commerce either from plants 
 or from the soils which contain them in large enough 
 quantities. 
 
 Potassium Carbonate. K 2 C O 3 . When wood is burned 
 the compounds of potassium in it are all changed to potas- 
 sium carbonate, which becomes a part of the ash. To get 
 it out, the ashes are washed with hot water, for it is well 
 known that the carbonate is soluble, and then, to get it 
 in solid form, the solution is evaporated until the car- 
 bonate crystallizes out. Of course everything else in the 
 ashes, which is soluble, will conie out with the carbonate. 
 The product is very impure ; it is called potash. 
 
 The only chemical action in this process is the burning 
 of the wood. The method of getting the potash out of 
 the ashes may always be used to separate a substance 
 which is soluble when it is mixed with others which are 
 not. 
 
 Many of the other useful compounds of potassium are 
 made from the carbonate by chemical processes. 
 
 Potassium Hydroxide. K H O. Potassium will drive 
 the metal calcium out of combination with hydrogen and 
 oxygen, and take its place. This fact being known, the 
 chemist uses it to get potassium hydroxide. 
 
 He mixes slaked lime, Ca"H 2 O 2 , with potassium car- 
 bonate in water, and boils the mixture. The metals simply 
 change places. 
 
 Ca"H 2 2 + K' 2 C0 3 = CaC0 8 + 2KHO 
 
 Calcium Potassium Calcium Potassium 
 
 with become. and 
 
 Hydroxide Carbonate Carbonate Hydroxide 
 
THE POTASSIUM GROUP. 197 
 
 The calcium carbonate is a white solid which falls to 
 the bottom, while the potassium hydroxide stays in solu- 
 tion. This liquid is then boiled down in iron pans. 
 
 Potassium hydroxide is the same as caustic potash. It 
 has a remarkable attraction for water. It cannot be kept 
 except in tight bottles, for if left in the open air it will 
 take moisture enough to completely dissolve it. Some 
 other things have this same property; they dissolve in 
 water which they get out of the air. Such substances are 
 said to be deliquescent. 
 
 Other Compounds made from K 2 CO 3 . There are 
 a great many compounds of potassium which can be made 
 by starting with the K 2 C 3 . 
 
 Ex. 126. Make a little potassium chloride. To do this, 
 first dissolve K 2 C0 3 , as much as you can, in say 50 cc. of 
 water. Then add H Cl slowly, until, after shaking it, the 
 liquid will redden a bit of blue litmus-paper. Finally 
 evaporate the liquid to a small bulk and let it cool. Pour 
 the liquid away from the crystals, and dry them on filter- 
 paper. Keep this potassium chloride, K Cl. 
 
 Why was the litmus-paper used ? 
 
 What reaction took place ? 
 
 Ex. 127. Make some potassium nitrate in the same 
 way, only use nitric instead of hydrochloric acid. If the 
 evaporation is carried far enough, you can watch the crys- 
 tals growing in the liquid while it cools. Keep this KN0 3 . 
 
 Ex. 128. Make a little acid potassium tartrate. To do 
 this first make a strong solution of K 2 C 3 in one tube or 
 bottle, and a strong solution of tartaric acid in another. 
 Then add the acid to the carbonate, until a piece of litmus- 
 paper is reddened by the mixture. A white crystalline 
 precipitate, or solid, will be made. This is the acid potas- 
 sium tartrate, known in the shops as "cream of tartar." 
 Keep this. 
 
198 THE POTASSIUM GROUP. 
 
 When the two liquids were put together in the last 
 experiment a solid made its appearance. Any solid made 
 in this way is called a precipitate. It takes the solid form 
 because it is not soluble in the liquids. This, and one or 
 two others, are the only precipitates which we can make 
 from potassium compounds, because the acid tartrate and 
 one or two others are the only potassium compounds which 
 do not readily dissolve. Even these dissolve a little, and 
 on this account no precipitate will come unless the solu- 
 tions used are strong. 
 
 Flame Color. The flame of potassium is violet, and 
 this color is seen when any compound of this metal is de- 
 composed by heat. Thus : 
 
 Ex. 129. I take a piece of platinum-wire and bend one 
 end into a round loop about as large 
 as this O- I moisten this loop and 
 plunge it into the K Cl made in Ex. 
 126. A little of the salt will cling 
 to the wire, and I hold it in the 
 mantle of a colorless flame (Fig. 
 63), and notice the violet color of 
 F1 - * 3 - ' the flame above. 
 
 Look at this colored flame through a piece of cobalt-blue 
 glass. Is the violet visible ? 
 
 Ex. 130. Thoroughly clean the loop so that it will not 
 color the flame, and then try the K N Os of Ex. 127 in the 
 same way. 
 
 Try also the acid tartrate of Ex. 128. 
 
 The color will sometimes come more surely if the loop 
 is moistened with hydrochloric acid. Try K 2 C 3 without 
 hydrochloric acid and then with it. 
 
 None but potassium compounds will give this color. 
 
THE POTASSIUM GROUP. 199 
 
 SODIUM. Na. 
 
 The metal sodium is so much like potassium that a 
 separate description is scarcely needed. Moreover, the 
 student has already seen or handled it in several experi- 
 ments of this course, and can remember its appearance 
 and actions. 
 
 Sodium in Nature Common salt is made of sodium 
 
 and chlorine, it is sodium chloride, Na Cl. Immense quan- 
 tities of this are in the seas, and large beds of it are found 
 in the earth. It is also in the salt-springs which are found 
 here and there. Many other compounds of sodium also 
 occur, in large* quantities, in the earth ; the carbonate and 
 the nitrate may be mentioned. 
 
 Sodium Carbonate. Na 2 CO 3 . This, next to com- 
 mon salt, is the most important compound of the metal. 
 It may be made from the ashes of sea-plants, just as 
 K 2 C0 3 is made from the ashes of land-plants, but enough 
 of it could not be had from this source, for it is used in 
 making glass, and soap, and in other large industries. 
 
 For these uses it is made from common salt. About 
 half a ton of salt is heated in a furnace with sulphuric 
 acid. This changes the salt into sodium sulphate and sets 
 hydrochloric acid free. Thus : 
 
 H 2 SO 4 + 2XaCl = Xa 2 SO 4 + 211 Cl 
 
 Then this sulphate, Na 2 S0 4 , also called "salt-cake," 
 is mixed with coal and fragments of limestone, and heated 
 intensely until the whole is melted. 
 
 The sulphate is decomposed by the carbon, which seizes 
 its oxygen and flies away as carbon monoxide gas, while 
 sodium sulphide is left behind. Thus : 
 
 Na 2 SO 4 + 40 = Na a S + 4CO 
 
200 THE POTASSIUM GROUP. 
 
 The sodium sulphide, Na,j S, and the limestone, Ca C 3 , 
 then attack and decompose each other, 
 
 Na a S + CaCO 3 = Na 2 CO 3 + CaS 
 
 and a mixture of sodium carbonate and calcium sulphide, 
 NagCOg and CaS, called "black-ash," is left. 
 
 The carbonate is then dissolved out of the black-ash 
 by water, after which, by evaporating the water, the car- 
 bonate comes out as crystals. The sodium carbonate made 
 in this way is known in commerce as soda-ash. 
 
 There is another carbonate of soda which is made by 
 running carbon dioxide through a solution of NasCCV it 
 is the acid carbonate, NaHC0 3 . This is "baking-soda." 1 
 It is much used in "baking-powders," and to furnish the 
 carbon dioxide gas for making "soda-water." 
 
 Sodium Hydroxide. NaHO. This substance is so 
 much like potassium hydroxide that either may be used 
 for the same purposes in the laboratory and in the arts. 
 Both are used in soap-making. They combine with the 
 acids which are in fats and oils, and the salts which are 
 thus made are called soaps. There is this difference, 
 however: the potassium hydroxide makes the soft soaps, 
 while the sodium hydroxide yields the hard soaps. 
 
 The " caustic soda," or sodium hydroxide, is made from 
 Nag C 3 in the same way (how ?) that " caustic potash " is 
 made from K 2 CO 3 . 
 
 The compounds of sodium are all quite freely soluble 
 in water. (Can a precipitate be obtained from a solution 
 of any of them by tartaric acid, as in Ex. 128?) 
 
 1 In the exercises, pp. 39 and 40, the student must have come to 
 the conclusion that " baking-soda" is a sodium carbonate. Having 
 now gathered more facts, he finds that his conclusion was true, but that 
 it was not the whole truth. Wholly reliable conclusions can never be 
 reached until " the facts are all in." ;.. 
 
THE POTASSIUM GROUP. 201 
 
 Flame Color. The flame of sodium is pure yellow, 
 and any of its compounds decomposed, by heat, will yield 
 this color intensely. Thus : 
 
 Ex. 131. Wash the platinum loop and hold it in the 
 Bunsen flame. Is not the flame tinged yellow? Wash 
 the wire, and burn it repeatedly until it does not give the 
 yellow tint, and then use any sodium compound. Note 
 the rich color it imparts. 
 
 Look at this colored flame through cobalt-blue glass : 
 is the yellow color to be seen ? 
 
 There is a little sodium in the air, in the dust of the 
 room, and almost everywhere. The yellow tint of sodium 
 may be given by this small quantity that is ever present. 
 Only a deep, rich yellow can be trusted to show the pres- 
 ence of a sodium salt in quantity. 
 
 Ex. 132. Make a mixture of a sodium and a potassium 
 salt and burn the mixture on the platinum loop. 
 
 Which color, yellow or violet, can you get with the 
 naked eye ? 
 
 Which, if you look through cobalt glass ? 
 
 Ex. 133. Make a strong solution of some of the mix- 
 ture, and then add a little tartaric acid. Does a precipi- 
 tate form in the liquid ? Is this precipitate made by the 
 potassium or the sodium salt ? What is it ? 
 
 AMMONIUM (?) NH 4 . 
 
 We have seen that from ammonia, NH 3 , we may get 
 a class of salts called the ammonium salts. Is there a 
 metal in these salts ? 
 
 Some Facts Ammonia, NH 3 , is very soluble in 
 
 water (Ex. 56), and this solution will restore reddened 
 litmus to blue, and it also neutralizes acids. This shows 
 
202 THE POTASSIUM GROUP. 
 
 that it is a base, and yet it is made up of nothing but 
 nitrogen, hydrogen, and oxygen, all non-metals, 
 
 NH 8 + H 2 O = NH 4 HO. 
 
 Ammonia combines with hydrochloric acid (Ex. 0), to 
 make what is called ammonium chloride. This is a white 
 solid, which has all the properties of a salt, resembling the 
 chlorides of sodium and potassium, and yet it is made up 
 of nothing but nitrogen, hydrogen and chlorine, all non- 
 metals. 
 
 Ammonia solution neutralizes nitric acid and forms am- 
 monium nitrate (Ex. 59), and this is as much a salt as 
 is any other nitrate, but yet it is made of only nitrogen, 
 hydrogen, and oxygen, all non-metals. We find no metal 
 in these ammonium compounds. 
 
 Comparison of Formulas. Let us now compare these 
 compounds with those which do contain a metal, say the 
 metal potassium. 
 
 Potassium hydrate, K H O, and Ammonium hydrate, N H 4 H O 
 Potassium chloride, K Cl, and Ammonium chloride, N II 4 Cl 
 Potassium nitrate, K N O 8 , and Ammonium nitrate, N H 4 X O s 
 
 Notice that instead of K in the potassium compounds 
 we find N H 4 in the ammonium compounds. The N H 4 
 acts just like the metal potassium in making salts, and 
 this leads us to say that N H 4 may be a metal also. 
 
 A HYPOTHETICAL METAL. But we cannot get the NH 4 
 separate, as a metal. These atoms hang together well 
 while in the salts, and in reactions, but part at once if 
 driven out together. In chemical changes the group acts 
 as if it were a metal, and we may suppose it to be one. 
 We call it ammonium, and may give it a symbol, Am. 
 
 Its Salts. The ammonium salts are numerous. Am- 
 uiouium chloride, Am Cl, Ammonium carbonate, Am 4 C O 3 , 
 
THE POTASSIUM GROUP. 203 
 
 and ammonium sulphide, Am 2 S, may be mentioned. The 
 source of these salts in commerce has been already given, 
 and should now be recalled by the student, p. 85. 
 
 THE SULPHIDES. Only the sulphides need a word more. 
 There is more than one ammonium sulphide, but they are 
 all made by dissolving hydrogen sulphide gas in ammonia 
 water. Large volumes of gas will be absorbed. Thus : 
 
 H 2 S + N H 3 = N H 4 H S, Ammonium hydrosulphide. 
 
 But if ammonia is also present with this N H 4 H S, they 
 combine. Thus : 
 
 N H 4 H S + N H 8 = (N H 4 ) 2 S, Ammonium sulphide. 
 
 The solution of these two sulphides is colorless, but if 
 any free sulphur is in it, the liquid becomes yellow. The 
 sulphur unites with the sulphide. Thus: 
 
 (N H 4 ) 2 S + S = (N H 4 ) 2 S 2 , Ammonium disulphide. 
 
 This last-named suljjhide is yellow. 
 
 The ammonium sulphide solution is one of the most 
 useful reagents, as the student will soon find. But this re- 
 agent, called ammonium sulphide, is not a single compound ; 
 it is a mixture of all these. We may study the ammonium 
 compounds further, and compare them with potassium and 
 sodium, as follows : 
 
 Ex. 134. Add some tartaric acid solution to a strong 
 solution of any ammonium salt. 
 
 Note whether a precipitate comes as with potassium. 
 
 Ex. 135. Find out whether an ammonium salt will 
 give any particular flame-color. 
 
 Ex. 136. Mix a little solid or liquid ammonium salt, 
 of some kind, with a little K H 0, and gently heat it in a 
 test-tube. 
 
 Notice the odor ; what substance is set free ? 
 
204 THE POTASSIUM GROUP. 
 
 Ex. 137. Place a little solid ammonium salt in a por- 
 celain dish, and gradually heat it. 
 
 Does it melt ? What change does occur ? 
 
 THE FACTS. Tartaric acid gives a white precipitate in 
 strong solutions of ammonium salts, because the acid tar- 
 trate of ammonium is not very soluble. But the ammo- 
 nium salts generally are very soluble, and on this account 
 they need not be expected to give precipitates. They give 
 no color to the flame. They are decomposed when heated 
 with caustic potash, and then yield ammonia gas, known 
 by its odor. Heat alone drives them into vapor completely, 
 leaving nothing behind. 
 
 The change of a solid directly to vapor, without first 
 melting, is called sublimation. Camphor is the most fa- 
 miliar example of substances which sublime when heated. 
 The ammonium salts, as a class, do this. 
 
 THE POTASSIUM GROUP. 
 
 Potassium, sodium, and ammonium (?) are very much 
 alike, and besides these there are three other metals, 
 whose salts are less common and useful, also like these 
 in chemical character. They are lithium, caesium, and 
 rubidium. These six form a single family of metals, 
 generally called the Metals of the Alkalies. 
 
 These elements are all soft, light, and silvery white. 
 They lose their luster at once in air, because they have 
 so strong attraction for oxygen that the surface is tar- 
 nished with oxide. They cannot, therefore, be kept in air, 
 but must be put up in naphtha, a liquid which has no 
 oxygen in it. They decompose water whenever they touch 
 it, and form bases by the action. 
 
 These are the most powerful bases known, the most 
 caustic and the most ready to neutralize acids. They 
 
THE POTASSIUM GROUP. 205 
 
 form the same classes of salts, and these salts are much 
 alike in properties. These metals are all univalent. 
 
 QUERY. By what experiments would you find out whether 
 a given salt is a potassium, a sodium, or an ammonium com- 
 pound? 
 
 APPLICATION. Take from the teacher, or a friend who knows 
 what they are, some substances, and see if you can decide 
 whether each is a potassium, or a sodium, or an ammonium com- 
 pound. 
 
THE CALCIUM GROUP. 
 
 CALCIUM. Ca". 
 
 THE metal calcium is about as hard as gold, and shines 
 with a yellow luster. It tarnishes quickly in air. No 
 use has ever been made of the element itself, but its 
 compounds are not only very useful, but very abundant. 
 
 Occurrence in Nature Calcium carbonate, Ca"C0 3 , 
 
 is one of the largest constituents of the earth. Marble is 
 its purest natural form, but limestone is chiefly the same 
 thing, and the limestone rocks make up a large part of 
 the earth's crust. Calcium carbonate is the starting-point 
 in the manufacture of the useful salts of this metal. 
 
 The Effect of Heat on the Carbonate When a piece 
 
 of marble is heated intensely, it will not be much changed 
 in looks; its size will be the same, its color somewhat 
 whiter. But it will be found to be more easily crushed, 
 and it is easily shown that a chemical change has occurred. 
 This may be done by treating it with water. Very soon 
 after being wetted, the stone begins to swell and crack and 
 crumble, while volumes of steam arise, and when all is over 
 a fine white powder remains. 
 
 The fact is, that heat decomposes the marble, and drives 
 off carbon dioxide. Thus : 
 
 CaC<) 3 + heat = CaO 4- C O 2 
 
 and the white mass left behind is the calcium oxide, Ca O. 
 The common name of this oxide is quick-lime. 
 
 By this simple chemical process large quantities of 
 quick-lime are manufactured. The furnaces are * called 
 lime-kilns. 
 
 206 
 
THE CALCIUM GROUP. 207 
 
 The white powder made by the action of water on 
 quick-lime is called slaked-lime. The water actually com- 
 bines with the oxide. Thus : 
 
 CaO + H 2 O = CaH 2 O 2 + heat 
 
 We see by the formula that slaked lime is calcium 
 hydroxide. The heat of this chemical action is remarkable. 
 
 Among many uses of slaked-lime, we may mention that 
 of making mortar for building purposes. Mortar is made 
 by mixing slaked-lime and sand, and it is used to cement 
 together the bricks or stones in the walls of buildings. 
 Fresh mortar is very weak; it becomes a strong cement 
 after it is laid up in the walls. The chemistry of the 
 change is this : 
 
 Calcium hydroxide absorbs the carbon dioxide of the air, 
 when exposed, and is slowly changed by it into calcium 
 carbonate, which is hard and stony, and this, filled in with 
 grains of sand, becomes a strong and solid mass which 
 cements the bricks or stones together. 
 
 The calcium hydroxide, CaH 2 O 2 , is slightly soluble in 
 water: the solution is known as lime-water, and is very 
 useful to the chemist (Exs. 6, 26, 73), and to some extent 
 in medicine. 
 
 Effect of Acids on the Carbonate Even the weaker 
 
 acids will decompose marble, and in fact most other car- 
 bonates. Water and carbon dioxide are produced by this 
 action and the escape of this last in bubbles is the effer- 
 vescence which always occurs. Turn back, now, to the 
 preparation of carbon dioxide (Ex. 73). We wanted the 
 C0 2 then, and did not take account of anything else. But 
 we can now see what the complete reaction really was. 
 Thus : 
 
 Ca"CO 3 + 2IIC1 became CaCl 2 + H 2 O + CO 2 
 
208 THE CALCIUM GROUP. 
 
 and this illustrates the action of other acids on this sub- 
 stance. Carbon dioxide, water, and a salt of calcium are 
 the products. 
 
 Effect of Water on the Carbonate Pure water will 
 
 not dissolve this carbonate, but water holding CO 2 in 
 solution dissolves it quite readily. Let the C O 2 escape, 
 or drive it out by heat, and the carbonate reappears. 
 
 This action goes on in nature. Rain-water contains 
 C O 2 , taken from the air, and as this water runs over the 
 lime-rocks it dissolves and carries some of their substance 
 along. But when this solution is exposed to air, the C O 2 
 escapes, and the water then drops the solid carbonate. 
 This occurs in caverns where the water trickles through 
 their roofs. Each drop leaves a little solid carbonate 
 behind when it falls, and an icicle-like mass slowly grows 
 from the roof. This is called a stalactite. Another grows 
 up from the floor, this is called a stalagmite. 
 
 The Sulphate. CaSO 4 4- 2H 2 O. This is known as 
 gypsum, a crystalline mineral found in some abundance, 
 and, when ground to powder, quite useful as a fertilizer. 
 This mineral gives up its water, 2 H 2 O, when strongly 
 heated, and crumbles to a fine white powder called " Plas- 
 ter of Paris." Wet this plaster of Paris, and it combines 
 with water again and hardens into stone. This curious 
 property makes the sulphate useful for making casts. 
 
 Glass contains calcium silicate, combined with silicates 
 of sodium or potassium (see p. 185), and bleaching powder is 
 a mixture of calcium hypochlorite and calcium chloride. 
 How is it prepared ? See p. 141, and Ex. 86. 
 
 To Prepare- the Insoluble Compounds. Among the 
 many salts of calcium there are several that are not solu- 
 ble in water, especially in water that contains ammonia, 
 and such can be obtained by precipitation. 
 
 JKr. 138. Place about 5 cc. of calcium chloride in a test- 
 
THE CALCIUM GROUP. 209 
 
 tube, add about as much water, and heat the mixture up to 
 boiling-point. Then add slowly a solution of ammonium 
 carbonate as long as it continues to produce the precipitate. 
 The time to stop may be known by letting the solid settle 
 a little, and then notice whether another drop of the ammo- 
 nium carbonate has any effect. The white precipitate is 
 calcium carbonate. Am Cl was also made, but stays dis- 
 solved in the clear liquid. Thus : 
 
 CaCl 2 + (NH 4 ) 2 CO 3 = CaCO 3 + 2NH 4 C1 
 
 A very valuable fact is shown in this experiment. Notice 
 that one carbonate precipitates another. We wanted to 
 make the insoluble CaCO 3 , and we did it by using the sol- 
 uble (N H 4 ) 2 C 3 . The fact is, that a soluble salt precipi- 
 tates an insoluble salt of the same class as itself. If we 
 want an insoluble hydrate we will use some soluble hydrate 
 to make it. Or, if we want an insoluble sulphide we will 
 use some soluble sulphide to produce it. There are a few 
 exceptions to this rule, but it is so generally true as to 
 be an excellent guide. 
 
 For example, we wish to make the insoluble calcium 
 sulphate. Let us select some soluble sulphate to do it 
 with. It may be potassium sulphate, K 2 S0 4 , or hydrogen 
 sulphate, H 2 S O 4 , or some other. 
 
 Ex. 139. Place about 5 cc. of water in a test-tube, and 
 add about as much solution of any soluble compound of 
 calcium, such as the chloride or nitrate, and then add, 
 little by little, a solution of K 2 S0 4 . 
 
 Repeat the operation, using H 2 S0 4 . 
 
 The precipitate is calcium sulphate in both cases. 
 
 Can you write the reactions ? 
 
 But the term insoluble is not applied to a substance, 
 because the fluid dissolves absolutely none of it; we call 
 a thing insoluble when a fluid dissolves only very little. 
 
210 THE CALCIUM (UIOUP. 
 
 Everything is soluble in some degree, but in many cases 
 the quantity, which will dissolve in the amount of fluid 
 used, is too small to be taken account of. Such are called 
 insoluble substances. 
 
 Now CaS0 4 is somewhat soluble in water. In fact, 
 400 cc. of water will dissolve about 1 g. of it, and if you 
 have, say 10 cc. of fluid in your test-tube (Ex. 139), there 
 must be about , 1 of a gram of the sulphate in solution ; 
 the rest of the sulphate is the precipitate. A precipitate 
 will always be seen whenever the fluid present cannot 
 dissolve all of the substance which the reagent makes, 
 but not otherwise. 
 
 To Prepare Soluble Compounds If, in any case, 
 
 the new compound made by a chemical reagent is soluble, 
 it may be obtained by evaporating the clear liquid, in 
 which it is dissolved, until crystals will form, or to dry- 
 ness if necessary. For practice, the student should pre- 
 pare some calcium nitrate, and calcium acetate, from the 
 pure carbonate, or from marble. 
 
 THE CALCIUM GROUP. 
 
 Two other metals, barium, Ba", and strontium, Sr", are 
 very much like calcium, and these three form the calcium 
 group of metals, or, as it is also called, the group of the 
 alkaline earths. 
 
 In general, these three metals combine with the same 
 substances and in the same proportions. Their attraction 
 for oxygen makes them tarnish quickly in air, and en- 
 ables them to decompose water when they touch it. The 
 hydroxides thus formed are strongly alkaline. In these 
 chemical actions barium is more energetic than strontium, 
 and strontium more than calcium. Now this is also the 
 order of their atomic weights, if we start with the largest. 
 
 Thus: 
 
 Ba = 137 Sr = 87:5 Ca = 40 
 
THE CALCIUM GROUP. 211 
 
 This is another illustration of the curious fact, noticed 
 among groups of the non-metals, that the properties of 
 elements seem to depend on their atomic weights. 
 
 The great resemblance of barium and strontium to cal- 
 cium will be seen if we make and compare some salts of 
 these three metals. Some differences will also be dis- 
 covered. 
 
 Ex. 140. Make the carbonates of barium and strontium 
 just as that of calcium was made in Ex. 138, and notice 
 how much alike these three carbonates appear. 
 
 Ex. 141- Arrange three test-tubes, each with 5 cc. of 
 water, and add to one 5 cc. of strong solution of Ba C1 2 , to 
 the second, as much strong solution of SrCl 2 , and to the 
 third, as much strong solution of CaCl 2 . Then add to each 
 a little solution of calcium sulphate. 
 
 Notice a precipitate at once in the Ba tube only. Heat 
 the other two to boiling, and notice then a precipitate in 
 the Sr tube, but none in the other. 
 
 The barium sulphate forms at once in the cold. 
 
 The strontium sulphate at once only when heated. 
 
 The calcium sulphate does not form at all. 
 
 This experiment will help us to decide, in any case, 
 which one of these three metals, if either, is present in a 
 given solution. But why is not the calcium sulphate pre- 
 cipitated here as it was in experiment 139 ? 
 
 Flame Colors. Ex. 142. A volatile compound of cal- 
 cium will tinge the flame yellow-red ; of strontium, brilliant 
 crimson ; of barium, green. Try these compounds, and ob- 
 serve the flames with the naked eye, and also through cobalt 
 glass. Mark well the difference between these and the 
 flame colors of potassium and sodium. 
 
METALS OF THE ZINC GROUP. 
 
 Magnesium. Mg". The metal magnesium is found 
 as a carbonate and as a silicate, these two being its most 
 important compounds in the rocks. Its sulphate, known 
 as Epsom salt, is its most important compound. It is 
 found in solution, and in some mineral springs it is a val- 
 uable constituent. What is commonly called magnesia is 
 the oxide of this metal, Mg"O. It is used in medicine. 
 The Epsom salt, Mg S O 4 + 7 H 2 0, is still more valuable 
 as a medicine ; but on the whole magnesium and its com- 
 pounds do not rank high among useful substances. 
 
 The chemical actions of magnesium compounds are a 
 little like those of the calcium group. Its carbonate is 
 insoluble in water. 
 
 Ex. 143. Precipitate Mg"CO 2 from its chloride just 
 as was done for CaCO 3 in Ex. 138. 
 
 Ex. 144- Put 5 cc. ammonium chloride in a test-tube, 
 and to this add 5 cc. of magnesium chloride. Then add 
 the ammonium carbonate. Does a precipitate form? If 
 not it shows that magnesium carbonate is soluble in 
 ammonium chloride. This is a fact. In this respect this 
 carbonate differs from those of the calcium group. In 
 general the compounds of this metal are more soluble than 
 those of that group. 
 
 ZINC. Zn". 
 
 The metal zinc is found in several minerals which occur 
 
 in considerable quantities in the rocks, such as " calamine," 
 
 which is the carbonate, "blende," which is the sulphide, 
 
 and " zincite", the oxide. These are its most valuable ores. 
 
 212 
 
METALS OF THE ZINC GROUP. 213 
 
 Zinc is a useful metal, and it is manufactured on a largo 
 scale from these native compounds. 
 
 Manufacture of Zinc. Suppose the metal is to be 
 taken out of the oxide, Zn 0. The problem is how to get 
 rid of the oxygen. Turn back to Ex. 72, and you recall 
 the strong attraction of carbon for oxygen, and how, on this 
 account, carbon reduced Cu to metallic copper. Now this 
 is the fact applied to get the zinc out of Zn on a large 
 scale. The oxide and charcoal are put into vessels of fire- 
 clay and heated in a furnace. What reaction occurs ? It 
 may be written : 
 
 Zn O + C = C O + Zn. 
 
 The zinc, in the form of vapor, is led out into cold 
 vessels, where it is condensed. 
 
 But suppose the zinc is to be taken out of one of the 
 other ores, say the sulphide, Zn S. The problem, then, is 
 to get rid of the sulphur. The problem is solved by first 
 changing the sulphide into the oxide, and then reducing 
 the oxide by carbon as before. And to change the sul- 
 phide to oxide it is simply heated in the air, when oxygen 
 of the air takes the place of sulphur in the ore. Thus : 
 
 Zn S + 3 O = Zn O + S O 2 
 
 This heating of an ore in the air is called roasting. The 
 object of it is to change the ore to an oxide. It is in many 
 cases, as in this one, the first step in the process of get- 
 ting a metal from its ores. 
 
 Uses of Zinc. The uses of zinc are quite numerous. 
 When heated to a temperature above that of boiling water 
 (125 -150) it can be rolled out into thin sheets. This 
 sheet-zinc is in familiar use. Zinc is brittle, and cannot 
 be rolled out at temperatures much higher or lower than 
 those given above. Zinc is also used as a covering for 
 
214 METALS OF THE ZINC GROUP. 
 
 sheet-iron; for this purpose sheets of iron are simply 
 dipped in melted zinc; it is then called galvanized iron. 
 Zinc and copper melted together form brass. Zinc, cop- 
 per, and nickel, melted together, form German silver. 
 Substances like these, which consist of two or more 
 metals together, are called alloys. These and other alloys 
 of zinc are useful. 
 
 Compounds of Zinc. Of the compounds of zinc we 
 may mention the following : zinc oxide, which is used as 
 a paint under the name of zinc -white, and is made for this 
 purpose by heating the carbonate. Zinc chloride, used by 
 tinners for cleaning the surface of metals for soldering, 
 and also as a disinfectant. Zinc sulphate, known as white 
 vitriol, a poisonous substance, but used in small quantities 
 in medicine. 
 
 Preparation of Insoluble Compounds. Among its 
 compounds which are insoluble in water are the carbon- 
 ate, the sulphide, and the hydroxide. To make these we 
 may start with zinc chloride. 
 
 Ex. 145. Make a solution of zinc chloride for use, by 
 putting bits of zinc in a bottle and pouring a few cubic cen- 
 timeters of H Cl on them. There should be zinc left in 
 the bottle when the action is over, for then the zinc chlo- 
 ride will be free from acid. 
 
 Ex. 146. Add a few drops of this solution of ZnCl 2 
 to 10 cc. of water, and then add (N H 4 ) 2 C0 3 . 
 Describe the result and write the reaction. 
 
 Ex. 147. To 10 cc. of water, with a few drops of Zn C1 2 
 add AnigS. 1 What is the white precipitate which falls? 
 
 1 This ammonium sulphide, and the hydrogen sulphide for the next 
 experiment, are made by passing H 2 S through dilute ammonia (half 
 water) for one and water for the other. Use the same apparatus as 
 in Ex. 107. 
 
METALS OF THE ZINC GROUP. 215 
 
 Write the reaction. What soluble compound is also 
 made in this reaction? 
 
 Ex. 148. To a few cubic centimeters of Zn C1 2 add a few 
 drops of hydrochloric acid, and then add a solution of 
 hydrogen sulphide, H 2 S. Do you get a precipitate? If 
 not, it shows that Zn S is soluble in this liquid. 
 
 We make the sulphide whether we use Am., S or H 2 S, 
 but the first is an alkaline substance, while the second is 
 an acid, and we find that the sulphide is not soluble in 
 the alkaline liquid, Ex. 147, while it is soluble in the 
 acid liquid, Ex. 148. 
 
 Ex. 149. To a few cubic centimeters of the Zn C1 2 with 
 an equal bulk of water add N H 4 H little by little, until 
 after shaking it, and then blowing the air out of the tube, 
 the strong odor of ammonia remains. 
 
 Describe the two changes which occurred. 
 
 The explanation is this: Ammonium hydroxide changes 
 the zinc chloride to zinc hydroxide, which takes the form 
 of a white precipitate because it is insoluble in water. But 
 it is soluble in ammonium hydroxide, and so just as soon as 
 there was added more than enough to make the precipitate, 
 the excess began to dissolve that which had been made. 
 Whenever, as in this case, a precipitate dissolves in the 
 reagent which makes it, it is said to be soluble in excess. 
 
 The Zinc Group Magnesium, zinc, and cadmium are 
 
 the members of this group. These elements are much 
 alike. They are all bluish-white metals. They have 
 many of the same properties, but in different degrees. 
 
 For example, cadmium melts- at a comparatively low 
 temperature, zinc at a higher ; 423 C., and magnesium at 
 one still higher. Cadmium becomes a vapor at a low red 
 heat, zinc if heated but little hotter, and magnesium at 
 a bright red heat. They take fire in the air, cadmium 
 
216 METALS OF THE ZINC GROUP. 
 
 burns less freely, zinc with a fine blue flame, and magne- 
 sium with a dazzling whiteness. They decompose dilute 
 acids, cadmium rather slowly, zinc more freely, and mag- 
 nesium very promptly. 
 
 This order of their properties is also the order of their 
 atomic weights, beginning with the largest. Thus : 
 
 Cd Zn Mg 
 112 65 24 
 
 SUGGESTION. Compare, by experiment, the action of H 2 S, and 
 of Am 2 S, on some soluble compounds of zinc, cadmium, and mag- 
 nesium, and note the different results. 
 
 Then take from the teacher or a friend, who knows what they 
 are, some specimens, and see if you can decide whether each is a 
 compound of either of these metals. 
 
THE IRON GROUP, 
 
 MANGANESE. MR". 
 
 As a metal, manganese need not detain us, since it 
 is rarely used in chemistry or the arts. In the form of 
 the "black oxide," MnO a , it is found in many parts of the 
 earth. This is its chief ore, although it occurs in other 
 minerals and rocks in some abundance. Jt unites with 
 oxygen in several proportions, reminding us, in this re- 
 spect, of nitrogen: there are five oxides of each. 
 
 Salts of Manganese. - - Two of these those which 
 contain least oxygen act with acids to produce salts: 
 they are basic, while one of them that which contains 
 most oxygen acts with bases to produce salts : it is acid. 
 The other two do not produce salts at all : they are neu- 
 tral. The student should think of the bearing of this fact 
 on our definition of metal, p. 192. 
 
 From the basic oxide, Mn 0, we may get manganous 
 chloride and manganous sulphate, which are the salts most 
 common in the laboratory, while from the acid oxide, 
 Mn 2 O-, we may get the potassium permanganate, which is a 
 beautiful salt, much used in the laboratory and out of it. 
 Its solution in water is intensely purple, but this fine color 
 is quickly lost in presence of anything which has an affinity 
 for oxygen. It parts with its oxygen so readily to other 
 things, that it is a most powerful oxidizing agent. In the 
 laboratory, it is used for this purpose, and out of it too ; for, 
 since bad odors and putrid organic matter are destroyed by 
 oxygen, the permanganate is a valuable disinfectant. 
 
 PREPARATION OF SOME INSOLUBLE SALTS. Among the 
 insoluble salts of manganese we may mention the niangan- 
 
 . 217 
 
218 THE IRON GROUT. 
 
 cms carbonate, sulphide, and hydrate. A study of these 
 will reveal some of the most characteristic reactions of this 
 metal. 
 
 Ex. 150. To make the carbonate, proceed exactly as in 
 Ex. 146 with zinc, using a solution of manganous sulphate 
 instead of the zinc compound. 
 
 What is the color of manganous carbonate ? 
 
 What is the color after some time in the air ? 
 
 To answer this last question, it is well to filter the liquid, 
 and leave the precipitate on the filter. The change you 
 will discover is caused by the oxygen of air, which changes 
 the manganoMs carbonate to the mangan/c hydrate. This 
 change does not occur in the case of zinc. 
 
 Ex. 151. To make the sulphide, proceed just as in 
 Ex. 147 with zinc, using manganous sulphate, and Am 2 S. 
 What is the color of the manganous sulphide ? 
 Write the reaction which took place. 
 What soluble compound is made at the same time ? 
 
 Ex. 152. Try to make the sulphide by using H 2 S. 
 Proceed exactly as in Ex. 148 with zinc. 
 What is the result, and why ? 
 
 Ex. 153. To make the hydrate, Mn H 2 2 , proceed just 
 as in Ex. 149 with zinc, using MnSO 4 . 
 
 What is the color of this manganous hydrate? 
 Is it, like the zinc hydrate, soluble in excess ? 
 What change happens if it is left in the air ? 
 
 The pure manganous hydrate is white, but it is changed 
 by oxygen into brown manganic hydrate. 
 
 Ex. 154. To a few cubic centimeters of the manganous 
 solution, add as much ammonium chloride, and then add 
 ammonia as before. 
 
THE IRON GROUP 210 
 
 Do you get the precipitate ? If not, it shows that man- 
 ganous hydrate is soluble in ammonium chloride. You 
 will get none of it, if enough of this chloride is present. 
 
 PREPARATION OF POTASSIUM MANGANATE. The man- 
 ganate is soluble in water, and of course it cannot be pre- 
 cipitated. But there is another way of making salts, and 
 that is by fusion, or, as it is often called, the "dry way." 
 
 Let us mix a little " black oxide " of manganese with 
 an equal weight of solid potassium hydroxide and half as 
 much potassium chlorate. This mixture should be strongly 
 heated. It may be done in a thin iron spoon, or the bottom 
 of a broken porcelain dish. When well fused, the mass will 
 turn green, and this green substance is potassium manga- 
 nate, K 2 Mn 4 . Let it cool and then put it into water, and 
 you shall find that the manganate dissolves, yielding a fine 
 green solution. 
 
 PREPARATION OF PERMANGANATE. If now you boil 
 some of this green solution, you shall see its color change 
 to a rich purple-red. The fact is, that the green manganate 
 is easily oxidized, and is thus changed into the red perman- 
 ganate, K 2 Mn 2 8 . This change takes place on boiling its 
 solution. The curious change of color, from green to red, 
 has given to the manganate the name "chameleon mineral.'' 
 The permanganate holds its oxygen very loosely, and will 
 therefore oxidize other bodies readily. By this action it 
 decomposes organic matter. When added to water contain- 
 ing organic matter, it becomes colorless or brown by giving 
 up its oxygen. 
 
 Nickel. Ni" Nickel is a white, hard metal, which is 
 
 much like iron, but does not rust as easily, and on this 
 account it is used as a plating on the surface of other 
 metals, such as steel, copper, and brass. 
 
 Nickel salts are generally green, but the description of 
 them need not detain us. 
 
220 THE IRON GROUP 
 
 Cobalt. Co" Cobalt is more rare than nickel. It 
 
 also is a hard, white metal, with a reddish tinge however, 
 and in other qualities it is much like nickel and iron. The 
 salts of cobalt are highly colored, and the color depends 
 on whether they contain water. Thus cobaltous sulphate, 
 when it contains water, CoS0 4 , 7H 2 0, is a beautiful red 
 salt, but once drive its water off by heat, and the sulphate, 
 CoS0 4 , is blue. The silicate is used to color glass; so is 
 the oxide. For this purpose no substance yields a richer 
 blue. The blue glass used in viewing colored flames is an 
 example. 
 
 The student should prepare some nickel and cobalt salts 
 and study them by making, with them, the same experi- 
 ments as have been already made with salts of zinc and 
 manganese. 
 
 IRON. Fe" or (Fe 2 ) vl . 
 
 While manganese, nickel, and cobalt are quite rare and 
 little used, iron is the most abundant and the most useful 
 of metals. 
 
 Occurrence in Nature. Iron is found in the rocks, 
 in the soil, in plants, and in the bodies of animals. There 
 is no metal more widely diffused than iron. 
 
 Native iron is sometimes found in the earth, and 
 "meteoric stones," which come from space outside the 
 earth, are little else than iron, with also some native nickel 
 and cobalt. 
 
 The sulphide, FeS 2 , "pyrites" is found almost every- 
 where, sometimes in yellow scales, sometimes in perfect 
 cubes, which are also yellow. It is so often mistaken by 
 the ignorant for a precious metal, that it is called " fool's 
 gold." 
 
 The chief ores of iron are two oxides and a carbonate. 
 The richest of all is the " Magnetic oxide," Fe 3 O 4 , which is 
 so called because it is able to attract a magnet. It is very 
 
THE IRON GROUP. 221 
 
 abundant in this country. There are mountains of it in 
 Missouri, and vast beds of richest quality in New York. 
 It is black. 
 
 Haematite is the other oxide, Fe 2 3 . It is red or brown, 
 and sometimes, in the form of beautiful crystals, its color 
 is dark steel-gray. 
 
 The carbonate, Fe C O 3 , is still less rich in iron, and it is 
 generally mixed with clay and other earthy matters, which 
 make it poorer still. Such a carbonate is called "clay-iron 
 stone." 
 
 These ores are rarely pure ; they are largely mixed with 
 sulphides and earthy matter, and the red oxide contains 
 water; it is Fe 2 3 , 3H 2 0. All these facts have to be 
 taken into the account in the process of extracting the iron. 
 
 ROASTING THE ORES. In working other ores than the 
 best oxides, they are first roasted, p. 213. In this process 
 water is driven off, sulphur is burned into sulphurous 
 oxide, carbon dioxide is set free from the carbonate, and 
 the iron of the whole is changed into oxide, which re- 
 mains mixed with the earthy matters of the ore. 
 
 REDUCING THE OXIDE. The next thing to be done is 
 to decompose the oxide and liberate the iron. The power 
 of hot carbon to reduce an oxide, Ex. 72, is here applied. 
 
 The process is carried out in a blast-furnace, a furnace 
 in which the fire is driven by a blast of air. Such a fur- 
 nace is pictured in Fig. 64. It may be 50 or 100 feet high, 
 and at its widest place inside it may be 12 or 18 feet in 
 diameter. The furnace is fed from the top, and kept full 
 of fuel, crushed ore, and fragments of limestone, thrown 
 in together. 
 
 The fire is started at the bottom, and is urged to the 
 greatest intensity by a blast of air driven in by the power 
 of a steam-engine. 
 
 In this intense heat the earthy parts of the ore, and the 
 
222 
 
 THE IKOX GROUP. 
 
 limestone, melt together into a glassy substance, called the 
 "slag." The carbon of the fuel seizes the oxygen of the 
 
 ore and sets the iron 
 free. Kept melted by 
 the intense heat, the 
 iron runs to the bottom 
 of the furnace into a 
 sort of chamber made 
 to receive it, while the 
 lighter slag floats on 
 the surface of the melt- 
 ed metal. 
 
 In front of the fur- 
 nace is a large level bed 
 of sand, with one main 
 fin-row through its cen- 
 ter, and many branch 
 furrows on either side, 
 as shown in the cut. 
 
 At intervals of about 
 twelve hours the fur- 
 nace is opened at the 
 
 bottom for the metal to run out. It then flows down into 
 the furrows of the sand-bed, where it is allowed to grow 
 cold. 
 
 The iron thus made is called cast-iron, and, in the form 
 of the short bars made in the sand, it is called pig-iron. 
 
 But besides iron this cast-iron contains carbon, silicon, 
 sulphur, and phosphorus, in small quantities. These im- 
 purities make the metal weak, brittle, and fusible. Never- 
 theless, it is used for the manufacture of a great many 
 articles where great strength is not required. 
 
 In fact, pure iron is not found at all in commerce. The 
 very purest contains a little carbon. 
 
THE IRON GROUP. 
 
 223 
 
 The Three Forms of Iron. There are three forms 
 of iron, known as cast-iron, wrought-iron, and steel. 
 
 WROUGHT-IRON. This is the purest form of commercial 
 iron ; it is the toughest, strongest, and most malleable. It 
 is made from cast- 
 iron by robbing 
 it of its impuri- 
 ties, and this is 
 done by bringing 
 oxygen into con- 
 tact with all parts 
 of the melted 
 metal. The fur- 
 nace in which 
 this is done is 
 called a rever- 
 berator?/ furnace, 
 and by help of 
 the cut, Fig. 65, the operation may be understood. 
 
 The cast-iron is placed upon a large hearth, D ; the fire 
 is built in a separate part of the chamber. Flame and hot 
 gases from the fire strike against the arched roof of the 
 furnace, and the intense heat is thrown from the roof down 
 upon the cast-iron. In a little time the iron begins to 
 soften, and at length it becomes a pasty mass of half- 
 melted metal. Then the furnace-man unstops a hole, />, 
 thrusts a paddle through it into the pasty mass, and work- 
 ing this paddle about (puddling) he thoroughly stirs the 
 metal, so that all parts of it are slowly brought in contact 
 with the hot air at the surface. 
 
 The hot oxygen of the air seizes the impurities, one 
 after another. Some of the new compounds form a 
 liquid slag, which is drawn off out of the furnace at b, 
 while others are gases which pass up and out of the high 
 chimney. 
 
 Fig. 65. 
 
224 THE IROX GROUP. 
 
 The result is, that the iron is soon left almost free from 
 its impurities. A large part of its carbon has been burned 
 away, and has gone off as carbon dioxide. A large part 
 of the other impurities are also burned, but some of the 
 slag, thus made, is still mixed with the purified iron. 
 
 The furnace-man then lifts out a ball of this pasty iron, 
 weighing perhaps sixty pounds, or even more, and puts it 
 under the heavy blows of an immense hammer, or some- 
 times under the tremendous pressure of the squeezer. In 
 this way the impurities which are still mixed with the 
 iron are pounded or squeezed out, so that the iron is left 
 more pure and compact. 
 
 The mass of iron is then forced through grooves between 
 two strong rollers. The very great pressure of these 
 rollers lengthens the mass out into a slender rod or bar. 
 
 For the best quality of bar-iron, as this form is often 
 called, the bars, made by the first rolling, are cut into 
 short lengths and bound together in bundles, to be heated 
 over again and rolled into bars a second time. By re- 
 peating these efforts the purest and strongest iron to 
 be found in commerce is obtained. It is u'rouyht-iron, 
 also called malleable iron. 
 
 STEKL. Neither cast-iron nor wrouyht-iron has the 
 qualities which render iron useful in all the various ways 
 in which this metal is employed ; a third form, which is 
 better than either of these for many uses, is steel. 
 
 The difference between steel and the other two kinds of 
 iron is best shown by the action of fire and water. 
 
 Let wrought-iron be strongly heated and then suddenly 
 cooled by a plunge into cold water. Very little if any 
 change will be produced. 
 
 Let steel be treated in the same way, and it will be made 
 almost as hard as diamond, and so brittle that it will snap 
 before it will bend. Let this brittle steel be heated again 
 
THE IRON GROUP. 225 
 
 to a point below red-heat and then cooled, and it is softened 
 somewhat, and, what is more remarkable, it is made so 
 elastic that it will bend rather than break, and spring 
 back again when released from the force. 
 
 Cast-iron may be hardened as much as steel may be, but 
 it cannot be made elastic. 
 
 With this difference in properties we find a difference 
 in composition, for while each is composed of iron and 
 carbon, it is found that cast-iron contains the largest pro- 
 portion of carbon, wrought-iron the smallest, and steel a 
 proportion between the other two. 
 
 It would seem, then, that steel could be made in two 
 ways : 
 
 By taking away some carbon from cast-iron. 
 
 By adding some carbon to wrought-iron. And, in fact, 
 the steel so largely used in the arts, is made in both these 
 ways. Thus : 
 
 1. From two to six tons of cast-iron is melted and 
 then run into a large globe-shaped vessel made of a sub- 
 stance which will not melt at the highest heat to be 
 attained. In the bottom of this vessel there are many 
 holes, and a strong blast of air is driven through them. 
 The air bubbles up through the melted metal, and a most 
 furious burning begins. The oxygen attacks the silicon, 
 and the sulphur, and the carbon, and some of the iron also, 
 and burns them into compounds with itself. 
 
 In this way the iron is partly purified, but the chemical 
 action goes too far, and removes so much carbon that too 
 little is left. By adding some cast-iron to the purified 
 mass, enough carbon is given back to change the whole into 
 steel. 
 
 The globe-shaped vessel (converter) is then turned on its 
 pivots, and the melted steel is run out into a ladle, and 
 then poured into moulds. 
 
226 THE inox uvour. 
 
 Less than half an hour is time enough to change these 
 tons of cast-iron into steel. The process is called the 
 Bessemer process. 
 
 2. In the other way of making steel, bars of wrought- 
 iron are packed in charcoal, and the two are shut up to- 
 gether in air-tight boxes. They are then made red-hot, and 
 are kept so for several days. 
 
 During this heating, carbon finds its way into the solid 
 iron and changes the whole mass to steel. This product 
 is known as blistered steel, because the bars, on coming out 
 of their hot bed, are found to have a great many bubbles 
 or blisters on their surface. The steel is then melted and 
 run into moulds. This method of making steel is called 
 cementation. 
 
 Compounds of Iron. _ Some facts about the chemical 
 action of iron have been noticed already. The production 
 of ferrous sulphate in Ex. 120, and of ferrous chloride in 
 Ex. 94, showed the action of iron on acids, the most direct 
 way of making some salts of this metal. 
 
 Experiments 96 and 97 are still more instructive. They 
 should now be studied over again, because they prove that 
 there are two distinct chlorides of iron, the ferrous chlo- 
 ride, FeCl.,, and the ferric chloride, Fe 2 Cl a . And this 
 illustrates a most important fact, for iron forms not only 
 two chlorides, but also two sulphates, two nitrates, and, 
 in fact, two large classes of salts, the ferrot/ salts, such 
 as ferrous chloride, and the ferric salts, such as ferric 
 chloride. 
 
 COMPARE THE FERROUS AND FERRIC COMPOUNDS. These 
 two classes of iron compounds are unlike in appearance, 
 and quite different in their chemical behavior. These 
 differences are most distinctly shown by experiments. In 
 the first place 
 
 Ex. 155. Make some ferrous and some ferric chloride, 
 
THE IRON GROUP 227 
 
 to be used in the work which follows. To do this use clip- 
 pings of small iron wire, or small nails, and add them to 
 hydrochloric acid and aqua regia until these liquids will dis- 
 solve no more. For directions, see Ex. 96 and Ex. 97. The 
 hydrochloric acid yields solution of ferrous chloride. The 
 aqua regia yields solution of ferric chloride. 
 
 Note the colors of these solutions. 
 
 Ferrous salts are generally light green ; while ferric 
 salts are generally reddish yellow or brown. 
 
 Ex. 156. Prepare two test-tubes, each with about 10 cc. 
 of water, and add to one, 1 cc. of the ferrous chloride and 
 to the other, 1 cc. of the ferric chloride. Now add ammo- 
 nium hydroxide in drops to the first, and notice the precipi- 
 tate which forms. Afterward treat the second in the same 
 way. The ferrous chloride yields ferrous hydroxide, 
 Fe(HO) 2 . The ferric chloride yields ferric hydroxide, 
 Fe 2 (HO)(j. The color of the first is light green, of the 
 second brownish red. 
 
 Now filter the ferrous precipitate out, and leave it on the 
 paper in the air. You will find it turning red like the 
 other hydroxide. In fact, the moist ferrous hydroxide 
 actually changes into the ferric hydroxide. Thus: 
 
 2 Fe (H 0) 2 + H 2 O + O = Fe 2 (II O) 6 . 
 
 So it is also with other iron compounds of the ous class : 
 the air oxidizes them into the ic form. This illustrates 
 the rusting of iron in moist air: this same reddish hy- 
 droxide is made. We then call it iron-rust. 
 
 But the ous compounds become ic compounds by the 
 action of other oxidizing agents than air, such as nitric 
 acid. Thus : 
 
 Ex. 157. Put about 1 cc. of ferrous chloride with about 
 5 cc. of water in a tube, add 4 or 5 drops of strong H N 3 , 
 and then boil it gently for a minute. 
 
228 THE IKON GROUT. 
 
 Notice a change in the color of the solution. 
 
 What change in the substance does this color suggest ? 
 
 Now add ammonium hydroxide, and observe the precipi- 
 tate. Is it green or red, ferrous or ferric hydroxide ? 
 
 What change does this prove that the H N 3 made ? 
 
 The nitric acid will, in the same way, change other ous 
 iron compounds into the ic form. It is said to oxidize them, 
 and yet it does not change them into oxides. It changed 
 the Fe C1 2 into the Fe 2 C1 , and it would change Fe S O 4 into 
 Fe., (S 4 ) 3 . Whatever changes any compound from a lower 
 to a higher form of combination is called an oxidizing a gent. 
 
 Ex. 158. Put two or three drops of ferrous chloride 
 with about 5 cc. of water, and then add drops of a solution 
 of potassium ferrocyanide. 
 
 In another tube make the same experiment with ferric 
 chloride. Note the different results carefully. 
 
 A beautiful deep blue precipitate is always made by 
 potassium ferrocyanide in ferric salts: it is "Prussian 
 blue." The same reagent in ferrous salts yields a pale blue 
 precipitate, and this difference is so marked, that one can, 
 in this way, tell whether a given iron solution holds a 
 ferrous or a ferric salt. 
 
 COMPARE SOME COMPOUNDS OF IRON WITH THOSE OF 
 ZINC AND MANGANESE. Ex. 159. Put a few drops of 
 ferric chloride in water, and add ammonium hydroxide " in 
 excess," to see whether ferric hydroxide is soluble in 
 excess, like that of zinc, Ex. 149. 
 
 Ex. 160. Put a few drops of ferric chloride into a little 
 water, add considerable ammonium chloride, and then the 
 ammonium hydroxide, to see whether the ferric hydroxide 
 is soluble in Am Cl, like that of manganese, Ex. 154. 
 
 Ex. 161. To 10 cc. of water with 1 cc. of ferric chloride 
 add a few drops of ammonium sulphide, Am 2 S. 
 
THE IRON GROUP. 229 
 
 What is the name and the color of this precipitate ? 
 Compare it with the sulphides of zinc and manganese. 
 
 Ex. 162. To 1 cc. of ferric chloride add a drop or two 
 of hydrochloric acid, and then add a solution of hydrogen 
 sulphide. Does the color of this result agree with that of 
 any of the iron compounds seen before ? 
 
 Ferrous sulphide, Fe S, is a black substance which is 
 not soluble in alkaline liquids, but is soluble in acids. For 
 this reason it is made by Am 2 S, but not by H 2 S. In this 
 respect it is like the sulphides of zinc and manganese. The 
 whiteness of the liquid in Ex. 162 is due to sulphur. The 
 H 2 S is decomposed by the ferric chloride, and its sulphur 
 is set free. 
 
 Chromium. Cr. Chromium maybe made by heating 
 its chloride with potassium, it is then a dark gray powder, 
 which in air takes fire before it reaches a red heat. But if 
 the chloride is heated with sodium, instead of potassium, 
 the chromium is set free as hard and shining crystals. 
 While, if the metal is made from its oxide, by heating 
 it with charcoal, it has a steel-gray luster, is hard enough 
 to cut glass, and combines with oxygen slowly when heated 
 in the air. It is a curious fact that, if we make the same 
 substance in different ways, it sometimes comes out with 
 different properties, as in this case of chromium. 
 
 In its chemical actions, chromium is sometimes a metal 
 and sometimes not. With acids it forms salts, like other 
 metals, such as chromium sulphate, Cr^SO^. But with 
 bases it forms salts, like the non-metals, such as potassium 
 chromate, K 2 Cr() 4 . Is it nature, or only the chemist, 
 who divides the elements into metals and non-metals ? 
 
 The chief ore of this metal is chromite, a compound of 
 iron chromium and oxygen. It is not the metal itself 
 which is obtained from this chromic iron, but its more use- 
 ful compounds. 
 
230 THE IRON GROUT. 
 
 Let the chromite be heated with a mixture of potassium 
 carbonate and potassium nitrate, and the potassium will 
 take the place of the iron. In this way the ore, iron chro- 
 mite, is changed into potassium chromate, K a Cr0 4 . This 
 new chromate can then be washed out with water. The 
 solution is very yellow, and when evaporated yields a 
 highly-colored yellow salt. 
 
 Now let a solution of this K 2 Cr 4 be treated with nitric 
 acid. Its color will change from yellow to red (try it), and 
 its substance will change from potassium chromate to 
 potassium dichromate, K 2 Cr<jO 7 . By evaporating the 
 solution, fine orange-red crystals may be obtained. (Do 
 this.) 
 
 Compounds of Chromium. The chromates generally 
 are highly colored, and some of the insoluble ones are 
 used as paints. The lead chromate, or "chrome-yellow"' 
 as it is known in commerce, is a good example. 
 
 Ex. 163. Make a solution of either potassium dichro- 
 mate or chromate, in water, and add little by little some 
 solution of lead acetate. The bright yellow precipitate is 
 the pigment, chrome-yellow, PbCrO 4 . 
 
 Salts, such as chromium sulphate, in which the chro- 
 mium is basic, are sometimes violet-colored, sometimes 
 green. 
 
 Chrome alum is a quite common substance made of two 
 sulphates, the chromium and potassium sulphates. It has 
 a fine violet color. From this compound we can easily 
 get chromium hydroxide, which is green. Thus : 
 
 Kx. 164- To a solution of a little chrome alum in 
 water, add, little by little, some ammonium hydroxide. 
 Notice the bluish-green precipitate of Cr 2 (H 0) 6 . 
 
 Is this, like the zinc hydroxide, soluble in excess? 
 Is it, like the manganese hydroxide, soluble in Am Cl ? 
 
THE IRON GROUP. 231 
 
 Will it, like the ferrous hydroxide, turn red when ex- 
 posed to air ? 
 
 Can you get the same precipitate by K H instead of 
 NH 4 HO? 
 
 And if so, is it soluble in excess of K H ? 
 
 Ex. 165. To a solution of a little chrome alum in 
 water add Am 2 S, little by little, and compare this pre- 
 cipitate with that in the last experiment. It is the same 
 substance. 
 
 There is a chromium sulphide, Cr 2 S 3 , but it cannot be 
 made in the presence of water, like the sulphides of man- 
 ganese, zinc, and iron ; the hydroxide will come instead. 
 
 THE IRON GROUP. 
 
 The five metals iron, manganese, nickel, cobalt, and 
 chromium are closely related, and, together, form the 
 Iron Group. 
 
 The metals in this group are much alike in color, luster, 
 and hardness, and much alike in chemical behavior. For 
 example, they all unite with oxygen, and in more propor- 
 tions than one, making oxides which are sometimes basic 
 and sometimes acid. 
 
 But their affinity for oxygen is not equally strong, for 
 while chromium and manganese rust quickly when exposed 
 to moist air, iron does so much more slowly, while nickel 
 and cobalt will keep their luster unless heated. It is in- 
 teresting to note that this order of the metals, in their 
 behavior with oxygen, is also the order of their combin- 
 ing weights. Thus : 
 
 Cr Mn Fe Ni Co 
 
 52 55 56 58 59 
 
 Another fact is curious : these atomic weights are nearly 
 alike. In other groups we have not found it so. Look, for 
 example, at the potassium and the calcium groups. 
 
232 THE IRON GROUP. 
 
 SUGGESTIONS. If the student has made the experiment with 
 the ammonium sulphide, Am 2 S, he has seen how very different 
 are the sulphides of zinc, manganese, iron, and chromium. And 
 if he has used ammonium hydroxide, N H 4 H O, he has also seen 
 how very different are the hydroxides of these metals. Now, by 
 the experiment with these two reagents, he ought to be able to 
 tell with considerable certainty whether any substance which is 
 given him is a compound of one or another of these metals. 
 
 Let him try to do this by "taking specimens from the teacher or 
 a friend who knows what they are. Nickel and cobalt may also 
 be included in the list, if thought best. 
 
 If the substance given will not dissolve in water, perhaps you 
 can change it into another compound, of the same metal, which 
 will. Ferrous sulphide is not soluble in water, but hydrochloric 
 acid will change it into ferrous chloride, which is. Now, sup- 
 pose you do not know that the specimen is ferrous sulphide, and 
 yet you wish to find out if it is a compound of iron or of some 
 other metal. You can treat it with a little hydrochloric acid and 
 get a solution of the chloride, and then you can use the Am 2 S 
 and the N H 4 H O. 
 
 If hydrochloric acid will not answer, you can use nitric acid, 
 or even aqua regia, to get the substance into solution. But in 
 all cases, just as little of these acids as possible should be used. 
 
AIitJMINXftf. Al". 
 
 ALUMINUM is a beautiful blue metal, with a luster like 
 silver. It can be hammered into thin sheets, or dra.wn 
 into fine wire, or cast into any desired form, like iron. It 
 is one of the light metals ; it is only 2.56 times heavier 
 than water. It does not easily tarnish in air, and it melts 
 only at a high temperature. 
 
 At the same time that it has all these valuable proper- 
 ties, aluminum is one of the most abundant metals. It 
 is found combined with silica in clay, and in all slate 
 rocks, which are little more than hardened clay. In fact, 
 about one-twelfth the weight of the solid parts of the 
 earth is aluminum. 
 
 But there is no cheap way to get this metal from its 
 ores, and it is, therefore, too costly to be used in the arts, 
 in place of silver and iron, for many purposes, as it would 
 otherwise be. Its use is limited to ornamental work, and 
 to small articles of apparatus where strength with light 
 ness are required. 
 
 ' Compounds of Aluminum. Alum is the most useful 
 compound of this metal. Alum is really a compound of 
 two sulphates and water, for it is potassium and alumi- 
 num sulphate with much " water of crystallization." Its 
 formula is K 2 A1 2 (SO 4 ) 4 + 24H 2 0. This is the common 
 alum, although " ammonium alum " is also much used in- 
 stead; it has ammonium in place of potassium. 
 
 Aluminum oxide, or alumina as it is usually called, is 
 found in the rocks in beautiful crystals, having different 
 colors and known by different names. The topaz and the 
 emerald are examples ; the first is yellow and the second 
 green, but both are alumina. So are the oriental amethyst, 
 
234 
 
 which is purple, the sapphire, which is blue, and the ruby, 
 which is red. 
 
 Some compounds of aluminum are largely used in oper- 
 ations of calico printing and dyeing. This is true of the 
 sulphate and the hydroxide. 
 
 The following experiments will reveal some of the chemi- 
 cal characters of the aluminum compounds. 
 
 Ex. 166. Make a dilute solution of alum, and add, little 
 by little, NH 4 H O. The white gelatine-like precipitate is 
 aluminum hydroxide, A1 2 (HO) 6 . 
 
 Is this A1 2 (HO) 6 soluble in excess? 
 
 Can you get it by means of K H O instead of N H 4 H ? 
 
 And if so, is it soluble in excess of K H ? 
 
 Ex. 167. Make a dilute solution of alum as before, and 
 color it just distinctly red with a solution of cochineal. 
 Then add N H 4 H O. The aluminum hydroxide now com- 
 bines with the coloring-matter of the cochineal. It is red, 
 while the liquid is left colorless. 
 
 The color cannot be washed out of the hydroxide. Now, 
 it is this fact which makes the aluminum salt useful in 
 dyeing. For if cloth is first soaked in a solution of alum 
 and coloring-matter, and then plunged into a solution of 
 ammonia, the same reaction will take place in the filers 
 of the fabric, from which the color cannot afterward be 
 washed out by water. 
 
 Ex. 168. To a dilute solution of alum add a few drops 
 of Am 2 S, and compare the precipitate with that in Ex. 167. 
 It is the same substance. 
 
 There is a sulphide of aluminum, A1 2 S S , but water 
 decomposes it at once, changing it to the hydroxide. On 
 this account the sulphide cannot be made in solutions. In 
 this respect aluminum is like chromium. 
 
THE ANTIMONY GROUP. 
 
 Antimony. Sb"' Tins metal is now and then found 
 
 native, but it is oftener found in combination with sulphur 
 or oxygen. The chief ore is the antimony sulphide, Sb 2 S 3 . 
 
 The metal has a silvery appearance, quite brilliant, 
 but, unlike silver, it is very brittle. Its alloys are more 
 important than itself. We only need to mention type- 
 metal, which is far the most important of all alloys, since 
 the art of printing depends upon it. Antimony, tin, and 
 lead are melted together to make this alloy, from which 
 all types for printing are cast. 
 
 There are three oxides of antimony, and these are all 
 inclined to form acids rather than bases. This shows that 
 antimony is more like the non-metals than any other metal 
 which has yet been described. Another evidence of this is 
 the fact that antimony combines with hydrogen, just as do 
 nitrogen and phosphorus. The compound is called stibine, 
 and its formula is H 3 Sb. Stibine may be made and burned 
 just like arsine, Ex. 123, and it then yields a stain of anti- 
 mony on porcelain by Marsh's test, p. 181. 
 
 Bismuth. Bi'". This metal is crystalline, brittle, and 
 bright, with a reddish color. Bismuth, like antimony, forms 
 an alloy with lead and tin. This alloy is called fusible 
 metal, and it merits this title because it melts at a tem- 
 perature of only 94 C. The separate metals must be 
 heated much higher: tin melts at 228, bismuth at 267, 
 and lead at 325, but this alloy at 94. Such is very 
 generally the case with alloys : they melt more easily 
 than any one of the metals of which they are made. 
 
 235 
 
236 THE ANTIMONY (1ROUP. 
 
 Fusible metal, like type-metal, expands when it becomes 
 solid, and on this account it is used for taking casts 
 from medals. When cast in a mold it expands into every 
 line, and makes a most beautiful and faithful copy. 
 
 Bismuth, like a true metal, forms bases, and, like a non- 
 metal also, it forms acids. But its metallic nature is much 
 more distinct than that of antimony, since it is less likely 
 to form acids. This is also shown by the fact that it has 
 no compound with hydrogen. 
 
 The Group. Bismuth and antimony are much alike, 
 and, as we have just seen, both have the properties of 
 non-metals. In fact, they agree closely with the nitrogen 
 group. In bismuth the metalMc properties are very clear, 
 in antimony not so clear, in arsenic quite obscure, in phos- 
 phorus and nitrogen altogether wanting. From bismuth to 
 nitrogen, the transition from metal to non-metal is gradual 
 and perfect. 
 
 No better proof is needed that it is the chemist, and 
 not nature, who divides the elements into these two great 
 classes. 
 
 Such a division, however, is convenient. But chemists 
 do not all agree as to just where the line shall be drawn. 
 Some have put arsenic among the metals ; others have put 
 arsenic, and antimony too, among the non-metals. 
 
 In this book the line has been drawn between arsenic 
 and antimony. Because, then, we have on one side, all the 
 elements whose compounds with oxygen and hydrogen are 
 acids, and on the other, all those whose compounds with 
 oxygen and hydrogen are ever bases. The oxides of arsenic 
 are always acid, while one of the oxides of antimony is 
 basic, feebly so to be sure, but truly basic. 
 
 COMPARE THEIR REACTIONS. Some of the chemical 
 actions of bismuth, antimony, and arsenic will be a useful 
 study by experiment. 
 
THE ANTIMONY GROUP. 237 
 
 Ex. 169. Arrange three tubes each with about 10 cc, 
 of water. Into one put a few grains of arsenous oxide ; 
 shake it well, and if it does not dissolve, heat it. It 
 dissolves to a clear solution. 
 
 Into a second tube put a few grains of bismuth nitrate ; 
 shake it well : you find the liquid changed to a milky 
 whiteness, instead of a clear solution. To this then add 
 strong hydrochloric acid, drop by drop, and it will soon 
 become perfectly clear. 
 
 Into the third tube put a few drops of antimony chlo- 
 ride ; this liquid also at once becomes white. But add 
 hydrochloric acid as before, and it becomes clear. 
 
 The compounds of bismuth and antimony are decom- 
 posed by water, but of arsenic not. This effect of water is 
 not common. The white solids, precipitated by water, are 
 soluble in hydrochloric acid. 
 
 These three clear solutions may be used in the follow- 
 ing experiments. We will first study the sulphides, as 
 follows : 
 
 Ex. 170. Fit up the apparatus for hydrogen sulphide, 
 Ex. 107. Put an arsenic solution enough to cover the 
 end of the glass tube into flask a, and add a few drops 
 of HC1. Put an antimony solution, made clear by H CJ, 
 into flask b, and a bismuth solution, also made clear by 
 H Cl, into flask c, and then pass the H 2 S gas through 
 them all. 
 
 Observe that the sulphides of all three metals are 
 produced, and notice their different colors. 
 
 These are the first sulphides which we have found to be 
 insoluble in acid water. And of these, one, the orange-red 
 antimony sulphide, is soluble if much H Cl is present. 
 
 Ex. 171. Let the sulphides settle, and then pour off 
 the liquid ; add considerable water to each. Let the 
 
238 THE ANTIMONY GROUP. 
 
 sulphides settle, and decant the liquid again. We repeat 
 this work in order to wash the sulphides clean : do it once 
 more. Now pour yellow ammonium sulphide, (X H 4 ) 2 S, 
 upon each, and gently warm it. The question is, whether 
 the sulphides are soluble in this liquid. The bismuth 
 sulphide will remain unchanged, but the other two should 
 disappear ; they are soluble in yellow ammonium sulphide. 
 
 Ex. 172. Next compare the" hydroxides. For this pur- 
 pose make three clear solutions, as in Ex. 169, only be 
 more careful to not use more HC1 than just enough to 
 dissolve the white precipitates. Then add N H 4 H O, little 
 by little, to each. Observe the difference between the 
 arsenic and the other two solutions. 
 
 QUERIES. By what experiments could you decide whether a 
 given substance is a compound of aluminum or of chromium? 
 
 By what experiments could you decide whether a given sub- 
 stance is a compound of aluminum or of iron? 
 
 If a^ given substance is a compound of aluminum, or else of a 
 metal in the antimony group, by what experiment could you 
 decide which it is? 
 
 SUGGESTIONS. Take one or more specimens from the teacher 
 or a friend who knows what they are, and decide, by experiments, 
 whether each is, or is not, a compound of aluminum. 
 
 Take specimens, which may be compounds of any one of the 
 metals in the antimony group, and, by experiments, decide which. 
 
TIN AXD I/EAD. 
 
 Tin. Sn". Tin seems to have been known since the 
 earliest periods of history. 
 
 It was called Jupiter by the old alchemists, and stan 1 by 
 the people of Phoenicia. The people, just named, dis- 
 covered tin in Britain more than a thousand years before 
 the Christain era. 
 
 Tin is found in the form of tinstone. Tinstone is a 
 compound of tin and oxygen, Sn 2 ; it is the chief ore 
 of the metal. 
 
 The ore of tin is found in Cornwall, England, which 
 has been noted for its tin-mines for many hundred years. 
 Bohemia, Saxony, and Malacca and Banca, in India, also 
 yield the ore of this metal. In this country it seems to 
 be very rare, but it has been found in New Hampshire and 
 California. 
 
 EXTRACTION OP THE METAL. To obtain tin from this 
 ore would be a simple thing if the ore were pure ; for it 
 is an oxide which can be reduced by carbon. But the ore 
 is mixed with other matters, which make the process more 
 difficult. 
 
 To get rid of the rocky and earthy parts, the ore is 
 stamped to powder under wooden stampers shod with iron, 
 and then washed with water. To get rid of sulphur and 
 arsenic, the ore is roasted and washed, perhaps twice. And 
 then, to take away the oxygen, the roasted ore is melted 
 with charcoal and lime. 
 
 PROPERTIES OF THE METAL. Tin is a silver-white 
 metal with a fine luster, and somewhat harder than lead. 
 It can be hammered into sheets so thin that a thousand 
 
 1 The symbol for tin, Sn, comes from its old name Stan, or Stannum. 
 
240 TIN AND LEAD. 
 
 or more would be needed to make an inch in thickness. 
 It does not tarnish readily in air, showing that its attrac- 
 tion for oxygen is slight, but when heated, tin and oxygen 
 combine at once. 
 
 Because tin is so malleable it is much used in thin 
 sheets, called tin-foil. But the tin-foil of commerce usually 
 contains some lead, and sometimes a large proportion of 
 that metal. 
 
 Because air does not readily tarnish it, tin is used for 
 coating iron to keep it from rusting. The u tin " of which 
 common tin-ware is made is sheet-iron with a thin coat- 
 ing of tin. 
 
 Compounds of Tin. There are two compounds of 
 oxygen and tin ; one is called stannous oxide, Sn" O, the 
 other is the stannic oxide, Sn""0 2 . There are also two 
 chlorides, two sulphates, in fact, there are two classes 
 of tin compounds, the ous and the ic forms. 
 
 Starting with the metal itself we can make several of 
 the tin compounds and study by experiment their chemi- 
 cal behavior. We will first study the chlorides. 
 
 Ex. 173. Place 5 cc. strong hydrochloric acid in a test- 
 tube and drop into it a piece of granulated tin. Then heat 
 until the effervescence is brisk ; after which keep the tube 
 warm by holding it above the flame of the lamp until, 
 when taken away from the heat, the bubbling nearly or 
 quite stops. If, before this occurs, the tin is used up, 
 another piece must be added. When the effervescence is 
 brisk, a match-flame, brought to the mouth of the tube, will 
 cause a slight explosion. 
 
 What gas is set free by the action? 
 
 Into what compound is the tin changed ? 
 
 Sn" -f 2HC1 = Sn"Cl 2 + 2H. 
 The Sn Cl* is stannous chloride. 
 
TIN AND LEAD. 241 
 
 It is easy to change this ous chloride into the ic form 
 just as ferrous was changed into ferric chloride, Ex. 157. 
 
 Ex. 174- Pour about 2 cc. of the SnCl 2 solution into 
 another tube, add four or five drops of strong nitric acid, 
 and boil the mixture a minute. 
 
 Is there any evidence of a chemical change ? 
 
 But we may go further and prove that stannous chloride 
 is no longer present, in this way : 
 
 Ex. 175. Prepare two clean tubes with 10 cc. of water 
 in each, and add to one about a cubic centimeter of the 
 solution of stannous chloride of Ex. 173, and to the other 
 about as much of the solution just now made. Next add, 
 drop by drop, a solution of mercuric chloride to the first. 
 
 What is the color of the precipitate by the first drop ? 
 
 What change occurs when more and more are added? 
 
 These are the changes which this reagent always makes 
 in stannous chloride. Now add, to the other solution, 
 some drops of mercuric chloride in the same way. No such 
 changes should take place. Then it is plain that stannous 
 chloride is not present. 
 
 The fact is that the stannous chloride took' the chlorine 
 from the mercuric chloride, and so became stannic chloride. 
 The white precipitate at first, was mercurous chloride, and 
 the gray at last, was mercury itself. Thus : 
 
 1. 2HgCl 2 + SnCl 2 = SnCl 4 + Hg 2 Cl 2 
 
 Mercuric Stannous Stannic Mercurous 
 
 chloride chloride chloride chloride 
 
 2. Hg 2 Cl 2 + SnCl 2 = SnCl 4 + Hg 
 
 In this way mercuric chloride will always tell one 
 whether a given solution of a compound of tin is stan- 
 nous or stannic chloride. 
 
 We will next study the sulphides. The two sulphides 
 may be made by hydrogen sulphide. Thus : 
 
242 TIN AND LEAD. 
 
 Ex. 176. To 10 cc. of water arid cc. of the stannous 
 chloride of Ex. 173. And again, to 10 cc. of water add 
 cc. of the stannic chloride of Ex. 174. Then pass hydro- 
 gen sulphide through both. 
 
 The first gives stannous sulphide, SnS, brown. 
 
 The second gives stanic sulphide, SnS 2 , lemon yellow. 
 
 It is plain that tin must be added to the list of metals 
 whose sulphides are insoluble in acid water. 
 
 Now try these sulphides with yellow Am 2 S. Are they 
 soluble in it ? 
 
 Refer back to antimony, arsenic, and bismuth, to see 
 which of these have sulphides, which behave in the same 
 way, with Am 2 S. 
 
 LEAD. PW. 
 
 The lead ores of Spain and of England were worked by 
 the ancient Romans, and still farther back, even before the 
 sacred books of Exodus and Job were written, this metal 
 was known and used. 
 
 The ores of lead are many ; but for the most part they 
 are not abundant. One of them, however, is found in 
 immense beds and veins in the rocks. This ore is called 
 galena. It is a compound of lead and sulphur, PbS. 1 
 
 Illinois, Iowa, and Missouri, to say nothing of several 
 other of our States, have an abundance of galena stored 
 away in their rocks. 
 
 Extraction of Lead from its Ores To obtain the 
 
 metal, the ore is roasted, on the floor of a furnace, with 
 plenty of air. The hot oxygen changes a part of the sul- 
 phide into sulphate and another part into oxide, while a 
 third part remains as it was, sulphide. 
 
 The furnace is then shut tight, and the fire driven to a 
 
 1 The symbol for lead, Pb, is from the Latin name of the metal, 
 Plumbum. Lead is bivalent, Pb . 
 
TIN AND LEAD. 243 
 
 greater heat. The new compounds, just mentioned, then 
 attack and decompose each other, and all three of them 
 give up their metallic lead. The way in which these 
 three compounds reduce each other may be seen by writ- 
 ing the reactions. The three substances made by roasting 
 are PbS0 4 , Pb 0, and Pb S. 
 
 Then Pb S O 4 with Pb S become 2 Pb and 2 S <) 2 
 and2PbO " PbS 3 Pb SO, 
 
 The sulphurous oxide is carried away by the draught, 
 while the melted lead remains covered with the earthy 
 impurities of the ore, a melted slag, from under which it 
 may be drawn off. 
 
 BY IRON. There is another way of getting the lead 
 from galena, based on quite another principle. In fact it 
 may be given to illustrate another method of metallurgy, 
 p. 194. In this method one metal is used to liberate 
 another. This is called the precipitation process. 
 
 Some lead may be easily obtained by "precipitation," 
 and the experiment will illustrate the fact that one metal 
 may displace another from its compounds. Thus: 
 
 Ex. 177. Dissolve 8 g. or 10 g. of lead acetate, com 
 monly called " sugar of lead," in about 500 cc., a pint of 
 water, and if the solution is cloudy add a little 
 acetic acid to clear it. Put this into a white 
 glass bottle, and then hang in it a strip of 
 clean sheet zinc (Fig. 66), and let it stand 
 undisturbed. It will not be long before bril- 
 liant crystals of lead may be seen on the sur- 
 face of the zinc, but it should be left until 
 to-morrow, that we may witness the beautiful 
 growth of crystals, which has long been called the lead-tree. 
 
 Lead acetate and zinc, become zinc acetate and lead. 
 This shows the precipitation of a metal " in the wet way." 
 
244 TIN AND LEAD. 
 
 But in the case of lead ores, iron, instead of zinc, is 
 used to liberate the lead, and the change is brought about 
 by heat instead of in solution. The ore and scraps of iron 
 are heated together in a blast-furnace, when the iron takes 
 the sulphur away from the lead, thus : 
 
 Pb S + Fe = Fe S + Pb 
 
 This is the "precipitation" of a metal "by heat." 
 
 Properties of Lead Lead is so soft as to be easily 
 cut with a knife. Its freshly-cut surface shows that the 
 metal has a light-blue color and a line luster, which may be 
 seen, in the crystals, in Ex. 177. It is a heavy metal, being 
 11.4 times heavier than the same bulk of water. 
 
 Its attraction for moist oxygen is quite strong, even at 
 common temperatures, so that its surface is never bright 
 except when freshly cleaned. But why say " moist " oxy- 
 gen ? Because it is found that in perfectly dry air lead 
 does not tarnish, and also that in water which contains 
 no air it stays bright, which shows that both air and 
 moisture are required. 
 
 Lead Oxides. Lead combines with oxygen to make 
 three oxides. When heated in air the metal is changed to 
 lead oxide, PbO, a yellow powder known as litharye, 
 which is used in making flint-glass, p. 185. 
 
 There is also the lead dioxide, Pb0 2 , which is a brown 
 powder, and then another oxide, Pb 3 4 , called minium, or 
 red lead, whicli is used as a paint. 
 
 Many of the lead-salts are insoluble ; in fact, the nitrate 
 and the acetate are the only two, at all common, which 
 will dissolve in water. From these two, the student can 
 make other compounds of lead, and by so doing become 
 acquainted with the chemical actions of this metal. 
 
 Ex. 178. To make the carbonate. First make a dilute 
 solution of lead acetate, and make it clear by acetic acid 
 
TIN AND LEAD. 245 
 
 if need be, but use just as little acid as will answer this 
 purpose. Then add some ammonium carbonate. The 
 white solid obtained is "lead carbonate." 
 
 But it is found that this lead carbonate is not a pure 
 carbonate ; it contains lead hydroxide also. It is often 
 called the basic carbonate. This basic carbonate is the 
 " white lead " which is so much used as a paint. 
 
 Salts which contain an hydroxide are called basic salts. 
 
 Ex. 179. To a dilute solution of lead nitrate * add 
 ammonium hydroxide. The white precipitate is not a 
 pure hydroxide : it contains lead nitrate also. It is an- 
 other basic salt, called the basic nitrate. 
 
 Of what other metals are the hydroxides white ? 
 
 Is this lead precipitate soluble or insoluble in excess ? 
 
 What other hydroxides are like it in this respect? 
 
 Ex. 180. To a dilute solution of lead acetate add drops 
 of hydrochloric acid. No precipitate should appear. But 
 now use hydrogen sulphide. The black precipitate which 
 falls is lead sulphide, PbS. 
 
 What other metals have given sulphides by H 2 S in acid ? 
 
 Which of these other sulphides does this lead sulphide 
 resemble in color ? 
 
 Will Am 2 S dissolve this lead sulphide? 
 
 Ex. 181. To a strong solution of lead acetate add drops 
 of hydrochloric acid. A white precipitate appears : it is 
 lead chloride, Pb C1 2 . Now heat the mixture, and observe 
 that the chloride disappears. Let it cool again, and see 
 that the chloride returns in the form of needle-shaped 
 crystals. Why did not drops of HOI make a precipitate 
 of this chloride in Ex. 180, as well as in this one ? 
 
 All this proves that lead chloride is somewhat soluble 
 
 1 Make the lead nitrate by adding drops of HNO 8 to the basic 
 carbonate of Ex. 178, until the white substance is dissolved. 
 
246 TIN AND LEAD. 
 
 in cold water (Ex. 180), but not freely (Ex. 181), while in 
 hot water it dissolves largely (Ex. 181). 
 
 Have we found any other metal, so far, whose chloride is 
 insoluble ? 
 
 If a solution contains either Bi or Pb, can you tell which 
 by Ex. 181? 
 
 If a solution contains Bi or Pb, can you tell which by 
 Ex. 180? 
 
 Ex. 182. To a moderately strong solution of lead 
 nitrate add drops of potassium iodide. The bright yellow 
 precipitate is lead iodide, which is very sparingly soluble 
 in the cold. 
 
 But heat the mixture and the iodide disappears. If 
 there is water enough it will become perfectly clear. Now 
 let the tube and contents cool, and watch it. 
 
 Describe the iodide as it now appears. 
 
 Why does the iodide reappear? 
 
 Lead is the only metal whose compounds yield, in this 
 way, such a brilliant and crystalline iodide. Hence this 
 experiment is an excellent test for lead. The appearance 
 of rich yellow lead chromate, by the use of potassium 
 chromate (Ex. 163), is another excellent test for lead. 
 
 QUERY. By what experiments could you decide whether a 
 given compound is, or is not, a compound of tin or lead? 
 Try it. 
 
THE COPPER GROUP. 
 
 COPPER. Cn". 
 
 COPPER is often found in nature in the metallic state. 
 This is the case in the noted copper-mines of Cornwall and 
 Devon, in England. Some of the finest native copper in 
 the world is found in the region of Lake Superior, where 
 it occurs in great abundance. One single mass, of Lake 
 Superior native copper, weighed over 400 tons. 
 
 Native copper is crystalline. The separate crystals are 
 usually little cubes, but in some cases the 
 cubes are grown together in vast numbers 
 making up quite large masses, and these 
 masses often show most singular branch- 
 like forms, sometimes rudely resembling 
 the form of some growing plant. Fig. 67 
 is the picture of a specimen. 
 
 But copper, as native metal, is much less 
 abundant in nature than are its ores. 
 
 Copper pyrites, made of copper, 1 iron and 
 sulphur, CuFeS 2 , is the ore which is most 
 common. It is crystallized in cubes of per- 
 fect form, having the color and luster of 
 brass. Besides this there are other sulphides, such as 
 Cu 2 S and Cu S, also found in considerable quantity. 
 
 Malachite is a rich ore of copper, less common than 
 pyrites. It is a green stone, which takes a fine polish, and 
 is often used for ornamental purposes. In composition it 
 
 1 The symbol for copper is Cu, from the Latin name of the metal, 
 Cuprum. 
 
 247 
 
248 THE COPPER GROUP. 
 
 is a basic carbonate, for it contains both the carbonate and 
 the hydroxide of copper, CuC 3 , Cu (H 0) 2 . 
 
 Other ores of copper are widely distributed. Some are 
 blue, some are red, some are purple, some are gray, but we 
 need not stop to describe them. 
 
 Extraction of Copper. The metal is extracted from 
 its sulphide by roasting and reducing it in air. The ore 
 is first roasted and then melted, and then roasted again ; 
 this changes a part of the sulphide into copper oxide, Cu 0. 
 This roasted ore is then mixed with sand and heated in 
 a reverberatory furnace. The copper goes back into the 
 form of sulphide while the iron of the ore takes oxygen, 
 and, with the sand, becomes a liquid silicate. At the end 
 of this repeated roasting the copper is still combined with 
 sulphur, but it is rid of the iron. 
 
 The rest of the operation is like that of getting lead. 
 The sulphide is again roasted ; a part of it is changed to 
 oxide, while the rest remains as sulphide, and then, by 
 heating them strongly, these two compounds attack each 
 other, and the copper of both is set free. Thus : 
 Cu,S + 2CuO = 4Cu + S0 2 
 
 Properties. This metal has a peculiar deep red color, 
 not to be seen in any other. It is rather soft, easily bent, 
 very ductile, and very strong. It is one of the very best 
 conductors, and this makes copper, more than any other 
 metal, useful in all the applications of electricity. 
 
 ^jloys. The alloys of copper are many and important. 
 Brass is an alloy of copper and zinc ; German silver, of cop- 
 per, zinc, and nickel ; while bronze, and bell-metal, and gun- 
 metal, are made of different proportions of copper and tin. 
 
 Copper Compounds. Copper, when long exposed to 
 moist air, turns green ; the green coating is a carbonate. 
 The metal does not unite with oxygen at common temper- 
 atures of the air, but when heatecj. it does, and if intensely 
 
THE COPPER GROUP. 249 
 
 heated, it slowly burns, giving a fine green color to the flame 
 which heats it. This may be easily shown by holding a 
 small copper wire for some time in the edge of the Bunsen 
 flame. There are two oxides of copper : one is the cuprous 
 oxide, Ciu 0, which is red ; the other is the cupric oxide, 
 Cu 0, which is black. So there are also two chlorides, two 
 iodides, two sulphides, and, in fact, two classes of copper 
 compounds, the cuprozs and the cupr/c. 
 
 Cupric Sulphate. The cupric sulphate is the most 
 common salt of this metal. It is usually called copper 
 sulphate. It comes in the form of blue crystals, Cu S 4 + 
 5 H 2 0. The blue color depends upon the water of crystal- 
 lization, for when the water, 5 M 2 0, is driven off by heat, 
 as it may be very easily, the substance is white. This 
 salt goes under the common name of "blue vitriol," just 
 as the ferrous sulphate is called "green vitriol," and as the 
 zinc sulphate is called "white vitriol." 
 
 Study of Some Reactions of Copper. Starting with 
 the copper sulphate the student can produce several of the 
 compounds of copper, and in this way become acquainted 
 with some of the chemical peculiarities of this metal. 
 
 Ex. 183. Reduce a little copper sulphate to powder 
 and dissolve it in water little by little. First see how little 
 will be needed to give a perceptible blue color to, say 10 cc. 
 of cold water in a tube. Then add more and more until 
 it no longer disappears when shaken. 
 
 Many other copper compounds in solution have the same 
 color as this one. Indeed, when this blue color is seen in 
 a liquid it is a sign of the presence of some copper corn-- 
 pound, not a proof, but a sign. This solution may be used 
 for the experiments which follow. 
 
 Ex. 184- Add a cubic centimeter of the copper sulphate 
 solution to 10 cc. of water. Into this put slowly, one, two, 
 
250 THE COPPER GROUP. 
 
 three drops of ammonium hydroxide, arid shake it well. 
 The precipitate, which is deep blue when just enough of 
 the reagent is used, is copper hydroxide, Cu (H O) 2 . With 
 too little reagent the precipitate is pale blue. 
 
 Is this hydroxide soluble in excess ? 
 Compare this result with the effect of ammonia on 
 zinc, nickel, and cobalt, hydroxides. 
 
 Compare it also with lead and bismuth hydroxides. 
 
 Ex. 185. Add a cubic centimeter of the copper sulphate 
 solution to 10 cc. of water, and a few drops of hydrochloric 
 acid. 
 
 Note the evidence that copper chloride is soluble. 
 Then add hydrogen sulphide : black Cu S is made. 
 
 What other metals have given sulphides in acid water ? 
 Which of those others does this Cu S most resemble ? 
 Find out whether it is soluble or insoluble in Am 2 S. 
 
 The same brown-black sulphide is made when Am 2 S is 
 added directly to the original solution of cupric sulphate : 
 
 CuS0 4 + (NH 4 ) a S = CuS + (NH 4 ),S0 4 
 
 and ammonium sulphate (XH 4 ) 2 S0 4 is also made, which 
 remains dissolved. 
 
 Ex. 186. Place a bright piece of iron wire, or a knife- 
 blade, in a dilute solution of copper sulphate in water: 
 it is soon coated with red metallic copper. Leave it in 
 until the blue color is all gone from the liquid. Then try 
 a fresh piece of bright iron. It will need some time, but 
 the iron will take every particle of copper out, so that 
 this fresh piece will not be coated at all. 
 
 Cu S O 4 + Fe = Cu + Fe S O 4 
 Now by this reaction we see that, besides the metallic 
 
THE COPPER GROUP. 251 
 
 copper, Cu, some ferrous sulphate, l\ j S0 4 ,.must be made 
 at the same time. 
 
 Does the color of the liquid suggest the presence of an 
 iron compound ? See Ex. 155. 
 
 Can you prove, by experiment, that it does contain iron ? 
 
 MERCURY. Hg". 
 
 Mercury l is sometimes found in the earth as native 
 metal, but oftener in combination with sulphur. The sul- 
 phide, Hg S, is its chief ore, and it is called cinnabar. The 
 color of this ore is dark red, and in some specimens it is 
 almost as rich and brilliant as vermilion. Indeed, these 
 two things have the same composition ; cinnabar is the 
 native sulphide, vermilion is the artificial sulphide. The 
 ore is found in many countries; Spain, Austria, China, 
 and California are examples. 
 
 Extraction of the Metal Mercury is easily obtained 
 
 from cinnabar. The ore only needs to be roasted, when 
 this reaction will occur : 
 
 HgS-f 20 = Hg + S0 2 
 
 The ore is decomposed by the hot air ; its sulphur burns 
 off as sulphurous oxide, while its mercury is left free. 
 The metal is then in the form of vapor, which is led into 
 cold vessels, where it becomes liquid. 
 
 PROPERTIES. Mercury is a liquid, the only liquid 
 metal. It is tin-white, with a splendid luster. It is very 
 heavy, thirteen and a half times heavier than the same 
 volume of water. When cooled down to 39.5 C. it freezes 
 to a white lustrous solid ; when heated to 350 C. it boils. 
 
 With some other metals it makes alloys, but the alloys 
 of mercury are generally called amalgams. Zinc, copper, 
 
 1 The symbol for mercury, Hg, is taken from the Latin Hydrar- 
 gyrum, 
 
252 THE COPPER GROUP. 
 
 silver, and gold are changed into amalgams at once by 
 contact with mercury. 
 
 Compounds of Mercury Mercury does not tarnish 
 
 in air unless heated, but if kept at almost boiling heat, 
 it is changed into mercuric oxide, HgO, known as the 
 " red oxide, " Ex. 5. This metal also forms two series of 
 compounds, the -lc and the ous. Thus we find mercuric 
 chloride and mercurous chloride, mercuric and mercurous 
 sulphates. 
 
 Mercuric chloride, Hg C1 2 , is the virulent poison, known 
 under the name of corrosive sublimate. 
 
 Mercurous chloride, Hg. 2 Cl 2 , is the medicine known 
 under the name of calomel. 
 
 Both of these are white solids, and when seen in powder 
 are alike in appearance, but the poison is soluble in water, 
 while the medicine is insoluble. 
 
 MERCUROUS COMPOUNDS. The metal mercury is soluble 
 in nitric acid, which, if dilute, changes it to mercurous 
 nitrate. 
 
 Ex. 187. Put a small globule of mercury into a tube, 
 and add a cubic centimeter of dilute nitric acid. Then 
 heat it. The mercury will slowly waste away, and, if need 
 be, let more acid be added, but not too much, so that 
 the metal shall be completely dissolved. 
 
 This solution of mercurous nitrate may be used as 
 follows : 
 
 Ex. 188. Add a few drops of it to 5 cc. of water, and 
 then add drops of hydrochloric acid. The white solid 
 obtained is mercurous chloride, or calomel, Hg 2 Cl 2 . 
 
 What other metal yields a precipitate with H Cl? 
 
 Is this chloride, like that one, soluble by boiling ? 
 
 Now add to the white chloride a little ammonium 
 hydroxide and note the marked change in color. This is 
 
THE COPPER CROUP. 253 
 
 the only white chloride which will turn black when 
 treated with ammonia. 
 
 Ex. 189. Add a few drops of the nitrate to 5 cc. water, 
 and then add ammonium hydroxide. The same black 
 precipitate is made at once. 
 
 Mercurous compounds are the only ones which yield 
 black precipitates with ammonia. 
 
 MERCURIC COMPOUNDS. A solution of corrosive subli- 
 mate, mercuric chloride, may be the starting-point in our 
 study of the chemical actions of mercuric compounds. 
 
 Ex. 190. Add a cubic centimeter of mercuric chloride 
 to 5cc. of water. Add also drops of hydrochloric acid. 
 No precipitate will appear. 
 
 Can you explain the fact that H Cl can make no precipi- 
 tate in any mercuric compound ? 
 
 Finally add hydrogen sulphide, and notice any changes 
 of color which may occur. At first the precipitate may 
 be white, but with more and more H 2 S it 'will become 
 yellow, brown, and at last black. The mercuric sulphide, 
 HgS, when well formed is black. 
 
 What other metals have given black sulphides by H 2 S ? 
 
 Ex. 191. Add a cubic centimeter of Hg C1 2 to 5 cc. of 
 water, and then use NH 4 HO, little by little, to excess. 
 
 What is the difference between the actions of 1ST H 4 H 
 on the mercurous and the mercuric compounds? 
 
 Ex. 192. To another dilute solution of the HgCl 2 add 
 one drop of hydrochloric acid, and then put into it a 
 piece of bright copper wire. 
 
 Notice the coating which soon gathers on the wire. 
 
 What is it ? Its appearance, especially when rubbed, 
 will be likely to inform you. So will the reaction if it 
 Ire written, thus: 
 
 Hg. 
 
254 THE COPPER GROUP. 
 
 SILVER. AS*. 
 
 Silver is sometimes found in the native state. Such 
 specimens are often very beautiful, looking like metallic 
 twigs and branches. But this metal is more abundant in 
 combination, sometimes with chlorine, but oftener with 
 sulphur. The sulphide of silver is sometimes found alone, 
 but, in most cases, it is in company with the sulphides of 
 other metals, such as lead and copper. These mixed 
 sulphides of silver and other metals are the chief ores of 
 silver. 
 
 Silver is almost always present in galena, and much 
 silver is obtained from that ore. 
 
 Extraction of the Metal. There are different 'ways 
 of taking silver from its ores. We will study two of 
 these. 
 
 First suppose the silver is to be taken from its sulphide, 
 which contains the sulphides of other metals, as it usually 
 does. Can the ore be treated the same as the ores of 
 zinc or lead, that is, changed to an oxide by roasting 
 in air ? No, because silver, unlike those metals, has very 
 little attraction for oxygen. But it has a very strong 
 attraction for chlorine, and this fact is made use of to 
 get the metal away from the sulphur in its ore. 
 
 For this purpose, the ore is well stamped, to crush it 
 to powder, and then mixed with a little about one 
 tenth its weight, common salt sodium chloride. The 
 mixture is then heated, and, to make sure that the work 
 is well done, the ore is mixed with more salt and heated 
 again. In this operation, the chlorine of the salt seizes 
 the silver of the ore, and holds it in the form of silver 
 chloride. 
 
 The next thing is to take the chlorine away, and iron 
 is used for this purpose because chlorine has a stronger 
 
THE COPPER GROUP. 255 
 
 attraction for iron than for silver. The chloride of silver 
 is put into strong oaken casks, with a little water and 
 fragments of iron. This mixture is violently shaken by 
 turning the casks rapidly, and, under this treatment, the 
 iron robs the silver of its chlorine. The silver is thus 
 left free, but it is in very fine particles scattered through 
 the mixture in the casks. How shall it be collected? 
 
 Just at this point the use of mercury comes in. Mercury 
 is poured into the casks, which are then set rotating again 
 faster than before. This brings the silver and mercury 
 together, and they at once combine to form an amalgam, 
 p. 251, and the next thing is to get the silver out of this 
 amalgam. 
 
 To do this it is only necessary to heat the amalgam, 
 when the mercury will pass off as vapor while the silver 
 will be left behind. 
 
 But the metal is still mixed with such other metals, 
 copper, iron, and antimony, as were in the ore. These must 
 be removed, and so the metal is mixed with lead, and again 
 melted while a current of air is driven over its surface. 
 The oxygen seizes the lead and other metals, but not the 
 silver, which is thus left pure. 
 
 SILVER FROM GALEXA. But much of the silver now 
 in use comes from the lead ore, galena. When the lead 
 is obtained from this ore by the method described, p. 242, 
 the silver comes with it, and then the problem is, how to 
 get the small quantity of silver out of the large mass of 
 lead. 
 
 The lead is melted, and then allowed to slowly become 
 cold. When it cools, crystals begin to form, and these 
 crystals are pure lead. These crystals of lead are taken 
 out with a strainer. They are melted over again, and 
 again cooled; another crop of pure lead crystals is then 
 taken out, and this heating, and cooling, and dipping out 
 
256 THE COPPER GROUP. 
 
 pure lead is continued, the silver every time remaining in 
 the molten mass, until what is left behind is quite rich 
 in the precious metal. 
 
 And then oxygen is called upon to take away the lead 
 that remains. The rich alloy is melted on a bed of bone- 
 ash, and hot air is driven over it. The hot oxygen seizes 
 the lead, but does not combine with the silver. The lead 
 oxide soaks into the porous bone-ash and leaves the pure 
 silver behind. This method of separating silver from lead 
 is called cupellation. 
 
 Properties of Silver. Silver is the whitest of metals. 
 It is ten and a half times as heavy as water. It is much 
 harder than gold, and very malleable and ductile. 
 
 Oxygen does not attack it even when hot ; but its surface 
 will quickly blacken in the presence of hydrogen sulphide 
 because silver and sulphur strongly attract each other. 
 
 Articles of silver-ware and silver coin are well known. 
 But we must remember that none of these are made of pure 
 silver. The pure metal is quite too soft to be able to stand 
 the wear which these things receive. To harden the silver, 
 small portions of other metals are mixed with it. 
 
 For silver coin, some copper is added to harden the 
 precious metal. In this country the standard coin metal is 
 made of silver 90 parts and copper 10 parts. In England 
 the proportion of copper is less (7.5), in Germany it is 
 more (12.5). 
 
 Compounds of Silver The most important com- 
 pound of silver 1 is the nitrate, AgNO 3 , and this is made 
 by the action of nitric acid on the metal. This action 
 begins instantly on putting the two together, and goes 
 on vigorously until one or the other is exhausted. 
 
 1. Ag + HN0 8 = AgN0 8 + H 
 
 2. H + HN0 8 = H 2 + NO, 
 
 1 The symbol for silver is Ag, from the Latin name Argenlum. 
 
THE COPPER GROUP. 257 
 
 The silver takes the place of hydrogen in the acid, 
 making the silver nitrate, Ag N 3 , and setting the hydro- 
 gen free, but this hydrogen instantly attacks another por- 
 tion of nitric acid, and forms water and nitrogen dioxide. 
 The liquid left is a solution of silver nitrate. By evapo- 
 rating this liquid, transparent crystals of the silver nitrate 
 may be obtained. 
 
 Ex. 193. To 10 cc. of water add 4 or 5 drops of silver 
 nitrate, and then add drops of hydrochloric acid. A white 
 precipitate forms at once : what is it ? 
 
 Boil this precipitate, as lead chloride was boiled in Ex. 
 181. Is it soluble in hot water, like lead chloride ? 
 
 Add ammonium hydroxide to it, as was done with the 
 Hiercuro^s chloride, Ex. 189. 
 
 Does it blacken by ammonia, as the mercurous chloride 
 did ? What is the effect of the ammonia on it ? 
 
 By these differences, we can easily distinguish these 
 three chlorides, one from another. 
 
 Ex. 194. To 10 cc. water add drops of silver nitrate, 
 and then hydrochloric acid, or a solution of common salt, 
 which will have the same effect. Place the tube with this 
 white silver chloride in sunlight, and notice its change 
 of color. 
 
 Other silver salts are also very sensitive to the action 
 of light. On this account the compounds of silver are 
 much used in the art of photography. 
 
 Separation of Silver and Copper. We have seen 
 that silver coin is an alloy of silver and copper. The two 
 metals have been melted together : can we get them apart 
 again, or prove that they are in the coin? The student 
 is now able to do this, and the work is an interesting and 
 instructive exercise. 
 
 Ex. 195. Put a ten-cent piece in an evaporating-dish 
 and cover it with a mixture of strong nitric acid and water, 
 
258 THE COPPER GROUP. 
 
 half and half. Then heat gently, until chemical action 
 begins. Describe the action, thus : 
 
 What gas is set free? What color does the liquid 
 become ? 
 
 What compound of silver is made ? What compound of 
 copper ? 
 
 When the chemical action is over, or nearly so, pour 
 about 1 cc. of the blue liquid into about 5 cc. of water, and 
 then add drops of hydrochloric acid, or, better, of solution 
 of common salt, NaCl, until a drop no longer makes a 
 precipitate. Let the precipitate settle, and then pour the 
 liquid off into another tube. 
 
 Wash the precipitate by pouring water upon it, shaking, 
 and then, when it is settled again, pouring the 'water off 
 into the waste. Do this a second time. 
 
 Now you have the copper of the coin in the blue liquid, 
 and the silver of the coin in the white precipitate. 
 
 Prove that the blue liquid contains copper, by the use of 
 iron, Ex. 186. 
 
 Prove that the white precipitate is silver chloride by 
 treating a part of it with hot water, another part with 
 ammonia, and exposing another part to the sunlight. 
 
 SUGGESTION. Take specimens from the teacher or a friend 
 who knows what they are, and, by experiment, decide whether 
 each one is, or is not, a compound of lead, of silver, or of mer- 
 cury. If it prove to be a compound of mercury, then decide 
 whether it is a mercuric or mercurous compound. 
 
GOLD AND PLATINUM. 
 
 GOLD. Au" r . 
 
 GOLD is almost always found in the native state. Unlike 
 the metals described before, this precious metal is very 
 rarely found in combination with other elements : it is 
 found as native metal. Yet this native gold is not pure ; 
 it is mixed with silver, and sometimes, too, with copper, 
 and often with other baser metals. Native gold is found 
 in fine grains among the sands of certain rivers, and also 
 in solid quartz rocks. Now and then a nugget of consid- 
 erable size occurs. 
 
 Extraction of Gold. Gold is obtained from sands and 
 other loose materials by the process called "washing." 
 The material is put into a shallow pan and well stirred up 
 with water. Gold is so heavy that the grains will quickly 
 settle to the bottom, and then the earthy matter may be 
 poured off from above it. Sometimes the gold-bearing 
 deposit is washed by rocking it in a cradle through which 
 a stream of water is slowly running. The lighter earth 
 or sand is then washed away, while the heavy gold dust 
 lags behind, and is caught in grooves in the bottom of 
 the cradle. The precious metal is then dissolved in mer- 
 cury, and afterward separated by heat. 
 
 Gold is obtained from quartz rock by " amalgamation." 
 The quartz rocks are crushed to the finest powder and 
 then mixed with mercury. The mercury dissolves the 
 gold and leaves the quartz. The amalgam of gold is then 
 distilled, and the mercury goes away as vapor while the 
 gold is left behind. 
 
 PROPERTIES. Gold is remarkable for its fine yellow 
 color and beautiful luster. It is among the heaviest of 
 
 259 
 
2 GO GOLD AND PLATINUM. 
 
 metals, about nineteen times (19.33) heavier than water. 
 It is the most malleable of metals ; it is said that leaves 
 have been beaten so thin that 280,000 would be needed 
 to make an inch in thickness ! There is a curious fact 
 about the color of gold-leaf ; it is this : looked at in the 
 usual way it is yellow, but let a leaf be spread upon glass, 
 so that it may be held up between the eye and a window, 
 or the sky, and it will be green. 
 
 At a temperature of about 2000 F. (1102 C.) this pre- 
 cious metal melts into a greenish-colored liquid. The 
 highest heat of a furnace can scarcely change it into 
 vapor, but the furious flame of the oxyhydrogen blowpipe 
 can; its vapor has a purple hue. 
 
 Few chemicals, even of the most corrosive character, 
 <3an harm this noble metal. Oxygen cannot rust it ; 
 sulphur cannot tarnish it ; nor can the strongest acids 
 corrode it. For one element, however, it has a strong 
 attraction; this is chlorine. On this account it dissolves 
 readily in aqua regia ; in fact this liquid received its 
 name, which means royal water, because it was found to 
 dissolve gold, the "king of metals." It changes the 
 gold to gold chloride, AuClg. 1 
 
 Gold is used for ornament and as money. But when 
 pure it is almost as soft as lead, and hence unfit for 
 either use. To make it harder a little copper or silver 
 is added. The alloy used for coin in this country must 
 be made of nine parts of gold to one part of copper. 
 
 PLATINUM. Pt. 
 
 Platinum is a still rarer metal than gold. In small 
 quantities gold is very widely distributed in the earth, 
 but platinum is found in few places. It is found in 
 largest quantity on the slopes of the Ural mountains, and 
 
 1 The symbol for gold is Au, from the Latin Aurum. 
 
GOLD AND PLATINUM. 261 
 
 in Brazil arid Peru. It is always found in the native state, 
 but mixed with other metals, several of which, like osmium 
 and iridium, are still rarer metals than itself. 
 
 Pure platinum is silver-white. Oxygen cannot attack 
 it at any temperature, and only the intense heat of the 
 blowpipe can melt it. On these accounts platinum vessels 
 are much used in the laboratory. Aqua regia and the 
 caustic alkalies will dissolve platinum, and many other 
 metals will form alloys with it, which melt more easily 
 than the metal itself and are attacked by acids. 
 
 The Platinum Group There are five very rare metals 
 which are much like platinum in many of their properties. 
 They are palladium, iridium, osmium, ruthenium, and 
 rhodium. Palladium is remarkable for its action on hy- 
 drogen. When heated to redness it absorbs this gas, and 
 forms what seems to be a true alloy. And this fact would 
 indicate that hydrogen is itself a metal. Accordingly it is 
 sometimes called hydrogenium. 
 
 Osmium is remarkable for its great weight ; it is the 
 heaviest substance known, having a specific gravity of 
 22.477. An alloy of osmium and iridium is found some- 
 times in the sands with gold ; it is harder than steel, and 
 is used for the tips of gold pens. 
 
CLASSIFICATION OF THE METALS. 
 
 How Classes are made. We have seen that some 
 elements combine with oxygen and hydrogen to produce 
 acids while others combine with oxygen and hydrogen to 
 produce bases. If we put all those which produce acids 
 together, and all those which produce bases together, we 
 have all the elements in two large groups, the non- 
 metals and the metals. 
 
 Now this illustrates the way in which classes are made. 
 If the chemist has a large number of substances, he may 
 find, by studying them separately, that several are alike 
 in some important character; these he can put together 
 to form a class or group. Others in the list will not agree 
 with these, but while unlike them they will be like one 
 another, and these he can put together to form a second 
 class or group. And in this way he may at length have 
 the entire list divided into groups, each group holding 
 only those individuals which are alike in the leading char- 
 acter, however much they may differ in other particulars. 
 
 THE CLASSES OF NON-METALS. We have seen that 
 the non-metals are placed in four groups, known as the 
 chlorine group, the sulphur group, the nitrogen group, 
 and the carbon group. The leading character, or, we may 
 say, the foundation of this grouping, is valence. All uni- 
 valent non-metals are put into one group, all bivalent 
 non-metals into another, all trivalent non-metals into a 
 third, and the quadrivalent non-metals into a fourth. 
 
 THE METALS NOT CLASSED IN THE SAME WAY. Now 
 the classification of the metals is also sometimes founded 
 on valence. Then, all univalent metals go together into 
 one group, all bivalent into another, and so on. But in 
 
 262 
 
CLASSIFICATION. 263 
 
 this book, the metals have not been grouped in this way, 
 and the reason is, simply, that such groups of the metals 
 would not best suit our particular purpose in the study of 
 these elements. What we have wanted to do is to become 
 acquainted with the general properties and behavior of the 
 metals, and if they are grouped by their valence, metals 
 quite different in properties and actions will sometimes 
 be thrown together. As, for instance, silver is univalent, 
 so are potassium and sodium, and all these will be in the 
 univalent group if our classes are made by valence. 
 But silver has few properties like the others. If we are 
 studying the properties of the metals, it is better to put 
 those together which are most nearly alike, and then silver 
 will go with copper and mercury, instead of with potassium 
 and sodium. 
 
 MORE THAN ONE WAY TO GROUP THEM. In fact, the 
 classes of metals in this book are founded on likeness of 
 properties, and not on valence. Thus we have the potas- 
 sium group, because there are several metals which are 
 all very much like potassium, soft, light, alkaline ; and 
 the calcium group, because there are several metals like 
 calcium ; and the iron group, because the properties of 
 iron are much the same as those of the other members. 
 This is the most helpful way of grouping the metals 
 when our object is to study their properties. 
 
 But there must be some reason why some elements are 
 so much alike and others so different. There must be 
 some reason why some are univalent, others bivalent, and 
 others with still different degrees of valence. If we could 
 only get at this cause of their differences, the elements 
 would fall into natural groups. We could then know the 
 place of every one of them in the true system of nature. 
 But the chemist does not yet know this cause. He knows 
 the facts only. On this account the true system of the 
 
264 CLA.^.^lFK ATIOX. 
 
 elements in nature is still beyond his reach. And until 
 he reaches it, the elements will be classified in different 
 ways, as different leading facts are chosen on which the 
 classes may be founded. 
 
 FOUR WAYS TO CLASSIFY THE METALS. There are, in 
 fact, four important ways of classifying the metals. One 
 way is founded on valence; a second way is founded on 
 likeness of pi^erties ; a third way is founded on atomic 
 weights ; a fourth way is founded on the solubility of com- 
 
 We need not stop longer with the first two of these; 
 the third and fourth are yet to be described. The third 
 is important because it includes all elements, metals and 
 non-metals alike, in one system, and comes nearer than 
 any other to being the " natural " system. The fourth 
 is important because it is used in chemical analysis. 
 
 THE NATURAL SYSTEM. 
 
 Classification by Atomic Weights We have seen 
 that the elements chlorine, bromine, iodine, and fluorine 
 are very much alike in properties. They also combine with 
 the same elements and in the same proportions. But while 
 they have many of the same properties they have them in 
 different degrees. Fluorine is the most active, chlorine 
 next, then bromine, and finally iodine is least active of 
 all. Their properties vary in this order. .And we have 
 also noticed the fact that their atomic weights vary in the 
 same order. The same fact has been noticed in our study 
 of other groups. 
 
 NEWLAXD'S DISCOVERY. Such facts led Mr. Newland 
 in 1863 to arrange many of the elements in the order of 
 their atomic weights, beginning with the one whose atomic 
 weight is least, and then, on looking over the list, he dis- 
 covered that the elements with, like properties were scat- 
 tered at about equal distances apart. 
 
CLASSIFICATION. 265 
 
 Let us leave out hydrogen and begin with lithium, whose 
 atomic weight is next larger than that of hydrogen, and 
 put the atomic weights under the symbols of the elements 
 in the order of value, and we have 
 
 Li Be B C N O F Na 
 
 7 9 11 12 14 16 19 23 
 
 But sodium, Na, is like lithium, Li. Both are metals of 
 the alkalies, and univalent. Now begin with sodium and 
 go on: 
 
 Na Mg Al Si P S Cl K 
 
 23 24 27 28 31 32 35.5 39 
 
 But potassium, K, is like sodium and lithium, alkaline 
 and univalent. These properties are found in every 
 seventh metal in the list so far, and not in any between. 
 
 Let us write the list, of the first twenty-one, in lines 
 of seven. Thus: 
 
 Li = 7 Be= 9 B =11 C = 12 N=14 O = 16 F =19 
 Na = 23 Mg = 24 Al = 27 Si = 28 P = 3l S =32 Cl =35.5 
 K =39 Ca=40 Sc=44 Ti = 48 V = 51 Cr = 52 Mn = 55 
 
 And we find that the elements which are most alike fall 
 together, under one another, as lithium, sodium, and potas- 
 sium in the first column, and fluorine and chlorine in the 
 last. 
 
 It is a curious fact that if we add 16 to the atomic 
 weight of lithium, we get that of sodium, with the same 
 properties. Add 16 again, and we get the atomic weight 
 of potassium, another element with the same properties. 
 Add about 16 to the atomic weight of any one arid we get 
 the atomic weight of another which has similar proper- 
 ties. This is true until we reach phosphorus, when we 
 must begin to add 20 instead of 16. 
 
266 CLA SSI PICA TION. 
 
 MENDELEJEFF'S TABLE. Now the Russian chemist, 
 Mendelejeff, went so far as to make a table of all the 
 known elements in the order of their atomic weights, 
 and he found that all those elements, which are most 
 alike, then fell into the same column. The horizontal 
 lines of elements in this table are called "series" and 
 the columns are called " yroups." In all there are 12 
 series and 8 groups. Three of these series are given on 
 p. 265, and in them are the tirst three members of seven 
 groups. The fact is that 
 
 If all the elements are placed in the order of their atomic 
 weights those which are most alike will be found at regular 
 distances apart. As the atomic weights increase, the same 
 properties appear, again and again, at regular intervals. 
 This is known as the periodic law. 
 
 The Spiral of Elements. The table of elements has 
 been made in many shapes. The spiral form, 1 Fig. 68, 
 shows the main point very clearly, which is, that the 
 elements fall naturally into groups as their atomic weights 
 vary by regular additions. 
 
 We begin with lithium at the center, and wind our way 
 around the spiral, to the left, until we come out at the 
 cirpumference. Along the way we pass by elements with 
 larger and larger atomic weights in regular order. The 
 spiral is divided into eight sections by lines from the 
 center, and the elements which are alike in properties 
 are found together in these sections. In fact, this con- 
 tinuous spiral of atomic weights throws all the elements 
 into eight natural groups. 
 
 Take, for example, our chlorine group, p. 147, whose mem- 
 bers have been found to be so much alike. We find them 
 
 1 First given by Baumhauer in 1870, then modified by Huth in 
 1884, and adopted by Carnelly in 1885. Chemical News, Vol. 63, 
 p. 184. 
 
CLASSIFICATION. 
 
 267 
 
 all in the seventh group of the spiral, brought there by the 
 order of their atomic weights. We find all the members of 
 the oxygen group in the sixth, all of the nitrogen group 
 in the fifth, and all of the calcium group in the second. 
 
 Fig. 68. 
 
 But in each of these "natural groups" in the spiral 
 we find some elements which have not before been put 
 together. In the first, for example, we find all the metals 
 of the potassium class, and with them, copper and silver. 
 Now many of the leading properties of copper and silver 
 are not like those of sodium and potassium. They do not 
 
268 CLASSIFICA TION. 
 
 agree with these in being soft, light, and combustible on 
 water. Yet in some things they do agree quite closely. 
 For example: 
 
 Potassium forms the oxide K 2 O 
 Copper " " Cu 2 O 
 
 Silver " " Ag 2 O 
 
 In these compounds the atoms of potassium, copper, and 
 silver hold the same relation to oxygen. And the order 
 of their atomic weights brings them together in the same 
 group in the spiral. 
 
 THE VACANT PLACES. There are many vacant places 
 in the spiral : what is the meaning of these gaps ? They 
 lead us to think that the elements are not yet all 
 discovered. 
 
 When the table was first made there was a vacant place 
 where gallium, Ga, now stands in the third group. Men- 
 delejeff said that there ought to be an element whose 
 "atomic weight is about 69, its specific gravity about 6, 
 and its atomic volume about 11.5," to fill this gap. After- 
 ward gallium was discovered. Its atomic weight proved to 
 be 69.8, its specific gravity 5.9, and its atomic volume 11.8. 
 From its vacant place in the table, Mendelejeff was able 
 to give the properties of this metal before it had been 
 discovered. He did the same thing for the element scan- 
 dium, Sc, also in the third group. Possibly other elements 
 are yet to be discovered by which other gaps will be 
 filled. 
 
 THE ANALYTICAL SYSTEM. 
 
 Classification Founded on Solubility. We have 
 found that hydrochloric acid will give a precipitate if 
 mixed with a solution of a compound of silver, Ex. 193, 
 but none if mixed with a solution of a compound of copper, 
 Ex. 185. This is because silver chloride is insoluble in 
 the liquid used, while copper chloride is soluble. 
 
CLASSIFICA TION. 
 
 269 
 
 Now all metals whose chlorides are insoluble, like that 
 of silver, can be put with silver to form one group. Such 
 differences in solubility throw the metals together into 
 classes called the analytical groups. 
 
 But we have found, by experiment, what many of the 
 insoluble compounds of the metals are, and we can see, 
 from our experiments, which are alike and which not 
 alike. Indeed, if we will just gather up the facts which are 
 scattered among our experiments, we shall find the metals 
 falling into the analytical groups. If the student has 
 made the experiments he will find it an interesting and 
 profitable exercise to deduce this classification from them. 
 
 To do this make a t^ble, with six columns, like the 
 blank form below, and then fill the blank spaces opposite 
 the numbers in each column, by consulting the record of 
 the results obtained by the experiments with the metals, 
 thus : 
 
 CHLORIDES 
 
 insoluble in 
 acid water. 
 
 SULPHIDES 
 
 insoluble in 
 acid water. 
 
 HYDROXIDES 
 
 insoluble in 
 NH 4 HO, 
 andNH 4 Cl. 
 
 SULPHIDES 
 
 insoluble in 
 NH 4 HO. 
 
 CARBONATES 
 
 insoluble in 
 N H 4 H O, 
 and N H 4 Cl. 
 
 ALL SALTS 
 
 soluble. 
 
 \ 
 
 \ 
 
 \ 
 
 1 
 
 1 
 
 1 
 
 2 
 
 o 
 
 2 
 
 9 
 
 9 
 
 9 
 
 3 
 
 3 
 
 3 
 
 3 
 
 3 
 
 3 
 
 
 4 
 
 
 4 
 
 
 4 
 
 
 5 
 
 
 
 
 
 
 6 
 
 
 
 
 
 
 7 
 
 
 
 
 
 Group I. 
 precipitated 
 by H Cl. 
 
 Group II. 
 precipitated 
 byH 2 S. 
 
 Group III. 
 precipitated 
 by NH 4 HO. 
 
 Group IV. 
 precipitated 
 
 by(NH 4 ) 2 S. 
 
 Group V. 
 precipitated 
 
 by (NH 4 ) 2 
 C O 3 . 
 
 Group VI. 
 not precipi- 
 tated. 
 
 Place in the first column a list of all the metals which 
 will give a precipitate with hydrochloric acid: you find 
 their names by looking back over the experiments under 
 
270 CLA SSIFICA TION. 
 
 each metal. This list will contain the metals whose 
 chlorides are insoluble in acid water. These metals make 
 up Group I. 
 
 Place in the second column a list of all the other metals 
 whose sulphides are insoluble in acid water. These will 
 make Group II. 
 
 Place in the third, a list of all metals not found in 
 the first and second columns whose hydroxides are not 
 soluble in N H 4 H 0, or N H 4 Cl. In this way we make 
 out Group III. 
 
 Place in the fourth, a list of all the metals not found 
 in the first three columns, whose sulphides are insoluble 
 in N H 4 H 0. These are the metals of Group IV. 
 
 Place in the fifth, all the remaining metals whose 
 carbonates are insoluble in N H 4 H 0, or N H 4 Cl. These 
 are the metals in Group V. 
 
 Place in the sixth, all the remaining metals whose 
 chlorides, sulphides, hydroxides, and carbonates are all 
 soluble. These are the metals in Group VI. 
 
 We now find that our study of the metals, by experi- 
 ment, has not only given us the facts about them and 
 their compounds, but that it has also given us a way to 
 detect their presence in substances whose composition is 
 unknown to us. In fact, we are now prepared to analyze 
 a salt, thus : 
 
 To find out what Metal a Salt contains. If the 
 salt is in the solid form we begin by making a solution 
 of it. Then, 
 
 1. Taking a small quantity of the solution in a 
 tube, we add hydrochloric acid drop by drop. If a pre- 
 cipitate is made in this way, it shows that the metal of 
 the salt is one or another of the three in Group I. And 
 then, to learn which one of these it is, we may try, with 
 the solution, the experiments which are given under the 
 
CLASSIFICATION. 271 
 
 head of each of these particular metals, in our previous 
 study of them. 
 
 But if the hydrochloric acid yields no precipitate, we 
 may say that the salt is not a compound of any one of 
 these three metals, and may seek further, to find whether 
 it is one of the seven metals of Group II. 
 
 2. The question is, whether its sulphide is insoluble 
 in acid water. And to answer it, we take a little of the 
 solution, make it acid by adding a drop or two of hydro- 
 chloric acid, and then add hydrogen sulphide, H 2 S. If 
 a precipitate is made in this way, our salt is a com- 
 pound of one of the seven metals of Group II., but if 
 none, it is not. 
 
 Now the sulphides of three of these seven metals can 
 be dissolved by ammonium sulphide (N H 4 ) 2 S, while those 
 of the other four cannot. So we may take a little of 
 our precipitate, and warm it with ammonium sulphide, 
 and, if it proves to be soluble, we may say that the metal 
 in our salt is one of these three, but if insoluble, we say 
 that it is one of the other four. 
 
 In either case we may find out which particular one 
 of the metals is present, by making the experiments given 
 in this book in the description of each of them. 
 
 But if hydrogen sulphide has given no precipitate, we 
 say that our salt is not a compound of any one of these 
 seven metals, and go on to learn whether it is of one of 
 the three in Group III. 
 
 3. The question now is, whether its hydroxide is 
 insoluble in ammonia and ammonium chloride. And to 
 answer this, we take a little of our first solution, put into 
 it, first a considerable quantity of ammonium chloride, 
 N H 4 Cl, and then add ammonia, N H 4 H 0, until the liquid 
 smells strongly of this substance. It must be well shaken 
 and the air blown out of the tube, then the odor of ammo- 
 
272 CLASSIFICATION. 
 
 ma will show when enough has been added. If a precipi- 
 tate is made in this way, we may say that our salt is a 
 compound of one of the three metals in Group III. And 
 then, to know which one, we note the color of our precipi- 
 tate and also make the experiments already described in 
 the study of these three metals. 
 
 But if we get no precipitate, we say that our salt cannot 
 be a compound of any one of these metals. 
 
 4. The next question is, whether the sulphide of the 
 metal we are after is insoluble in ammonia water. And 
 to answer this, we take a little of our first solution, and put 
 a little ammonia with it, then add ammonium sulphide 
 drop by drop. A precipitate now shows that our salt is 
 a compound of one of the four metals in Group IV. We 
 then decide which one of the four, by noting the color of 
 the sulphide, and also making the experiments given in 
 our description of these metals. 
 
 No precipitate here, with ammonium sulphide, proves 
 that no one of these four metals is present in our salt. 
 
 5. We next ask, whether the carbonate of our metal 
 is insoluble in ammonia and ammonium chloride, for if 
 it is, then our metal is one of the four in Group V. 
 
 To a little of the solution of our salt we add consid- 
 erable ammonium chloride, N H 4 Cl, and then add ammo- 
 nium carbonate (NH 4 ) 2 CO 3 . If we get a precipitate, we 
 next decide which one of the four metals of Group V. is 
 present in our salt, by the experiments already given in 
 the study of these metals. 
 
 But if no precipitate is made, these four metals are 
 thrown out of the question, and our salt must then be a 
 compound of one of the metals in Group VI. 
 
 6. Which one of these four is it ? This is the final 
 question. To answer it, we may make the experiments 
 which are given in the descriptions of these metals, and 
 see with which of the four our results agree. 
 
CLASSIFICA TION. 273 
 
 By following the order of the groups in this regular 
 way, one can bring out the metal of almost any simple 
 salt, with certainty and very quickly. 
 
 The student may do this with a few simple salts whose 
 names he does not know. The teacher will select them 
 and keep a record of their names, and at the end of 
 his work the student should report his work and the 
 result of it. He should write down, in a short way, 
 every experiment he makes, and what the result of it 
 is, and what it proves; and he should do this for each 
 experiment, at the time he makes it, and not wait until 
 others are made. 
 
 On page 275 is a copy of one report of an "analysis," 
 which shows a form of the notes to be kept in each case. 
 Notice that, below the heading, which is the name of 
 the student, date of the work, and number of the sub- 
 stance, the sheet is divided into three columns. In one, 
 is put a brief description of all the experiments made. 
 In the second, the result of each is written, and in the 
 third, the fact which it proves. 
 
 To find out what Acid the Salt contains. But 
 when we have found the metal in a salt, we do not 
 yet know the name of the salt. It may be a nitrate, a 
 chloride, or some other compound. The next step is to 
 identify the acid part of it. This is done by making 
 the tests which were described in our study of the non- 
 metals, or the experiments described in the Exercises. 
 Thus a test for sulphuric acid is given on p. 167, and 
 the use of it, to show whether a substance is a sulphate, 
 is illustrated in Ex. 122. See also the Exercises, p. 173. 
 Hydrochloric acid, or its salts, the chlorides, may be 
 identified by the test on p. 147. See also the exercises on 
 p. 151. Nitric acid, and the nitrates also, may be detected 
 by the " Copperas Test," p. 100. If a salt is a carbonate 
 
274 ( 'L. 1 SSIFICA TION. 
 
 it will effervesce , when treated with dilute acid, and the 
 gas which is set free will whiten lime-water. 
 
 In this work for the acid, as in that for the metal, 
 brief notes of all the experiments should be made, and re- 
 ported. 
 
 To Name the Salt. Having found what metal a salt 
 contains, and also what the acid part of *it is, you can de- 
 clare the name of the salt which was given you for analysis 
 (p. 136). For example, having found strontium and nitric 
 acid, the substance itself must be strontium nitrate. 
 
 In this way, a "simple" salt, that is, a salt which 
 contains only one acid and one metal, may be analyzed. 
 The work is a most valuable exercise for the student at 
 this stage of his progress, and, with a good reference book 
 at hand, it should be carried as far as time will permit. 
 
 Hint as to further Work. Even "complex" sub- 
 stances, that is, substances which contain more than one 
 metal or acid, may be analyzed by very natural additions to 
 the foregoing work. If, for example, we have a mixture 
 of, say, silver and copper nitrates, we can detect both the 
 silver and the copper. For we can separate them by using 
 H Cl, as was done in Ex. 195. 
 
 If our mixture should contain one metal of every group, 
 still every one of them could be "separated," and then 
 " identified," by just such work. In such a case we could 
 use the group reagents (see bottom of table, p. 269) one 
 after another, in regular order. H Cl would take out all 
 of the metal of Group I., and leave all the others in solu- 
 tion. Every group reagent in its order would precipitate 
 all of the metal of its group, and leave all those of groups 
 that come after in solution. In this way we should get 
 each metal alone, and could then identify it. Of course, 
 if a group reagent gives no precipitate, all metals of its 
 group must be absent. 
 
CLASSIFICA TION. 
 REPORT OF AN ANALYSIS. 
 
 Name Date. 
 
 Substance No._. 
 
 275 
 
 EXPERIMENTS. 
 
 RESULTS. 
 
 INFERENCES. 
 
 I. Add drops of HC1. 
 
 No precipitate made 
 
 Absence of Group I. 
 Ag, Hg (ous), and 
 Pb. 
 
 II. To I. addH 2 S. 
 
 No precipitate made 
 
 Absence of Group II. 
 Hg(ic), Bi,Cu,Cd, 
 As, Sb, Sn. 
 
 III. To the original 
 solution add NH 4 C1 
 and N H 4 H O. 
 
 No precipitate made 
 
 Absence of Group 
 III. Fe, Al, Cr, 
 
 IV. To III. add 
 (NH 4 ) 2 S. 
 
 No precipitate made 
 
 Absence of Group 
 IV. Mn, Zn, Ni, 
 Co. 
 
 V. To original solu- 
 tion add NH 4 C1 
 and(NH 4 ) 2 C0 3 . 
 
 A white precipitate 
 
 Presence of Group V. 
 Ba, Sr, or Ca. 
 
 VI. To the original 
 solution add solu- 
 
 No precipitate made 
 in the cold 
 
 Absence of Ba. 
 
 tion of Ca S 4 . 
 
 
 
 VII. Heat VI. to boil- 
 
 A white precipitate 
 
 Presence of Sr. 
 
 ing. 
 
 
 
 Vllt. Flame-test. 
 
 Brilliant crimson 
 
 Confirms presence 
 of Sr. 
 
 Hence substance No is a compound of strontium. 
 
APPENDIX. 
 
THE APPARATUS. 
 
 THE following list contains the pieces in a single set of ap- 
 paratus for the course of experiments described in this book. 
 The full set is shown in the cut, Fig. 69. It is designed for 
 the use of beginners, unused to manipulation, and of teachers 
 who are oftentimes so pressed by other duties that little time 
 remains for the preparation of experiments. Selected from the 
 standard articles in the outfit of the chemist, they are neat 
 in appearance, efficient in action, easily put together, and 
 comparatively cheap. The forms shown in the cut are of the 
 pieces which have been actually used in devising and testing 
 the experiments described. 
 
 Fragile articles, such as test-'aibe3 rj.d flasks, should be 
 bought in quantity, to allow for breakage. One balance will 
 serve several workers. The same is true of the thermometer, 
 where economy must be practiced, and a single graduated 
 cylinder for each will do very well, although in that case all 
 cannot, at one time, make Ex. 37. 
 
 The pieces are here described in the order of their numbers 
 in the cut. 
 
 1. Graduated Cylinder. A tall and narrow glass 
 cylinder on foot, about $ inches in diameter, 25 cc. graduated 
 to halves. 
 
 Number required in single set 2 
 
 2. Test-tubes and Rack. Tubes 6 inches long by f 
 inch in diameter. They should be bought by the gross. The 
 rack to support the tubes can be made by any carpenter. Its 
 form is shown in the cuts. 
 
 Number required in single set 12 
 
 279 
 
280 APPENDIX. 
 
 3. Side-neck tube. Of German or soft glass, and of 
 Bohemian or hard glass, 6 x inches. They may be bought 
 by the dozen, and kept in stock. 
 
 Number required in single set, of soft glass . . 1 
 
 " hard "... 1 
 
 4. Mortar and Pestle. Of glass or porcelain, glazed 
 inside and outside, 3 inches diameter. 
 
 5. Support with Ring and Clamp. The support is 
 of iron. It is the so-called retort-stand. We select the small 
 size, usually provided with two rings. Only one ring is called 
 for, but the second will be found useful. These rings should 
 be arranged, as shown, to be taken off at the side of the rod. 
 The clamp is "small size " with " universal movement," to hold 
 a tube or flask in horizontal or vertical or oblique position. 
 
 6. Side-neck Flask. A round bottom flask with a side 
 neck attached to the stem. 
 
 Number required for each student's set, 150 cc. . 1 
 
 " the teacher's set, 150 cc. . 1 
 
 and 250 cc. . 1 
 
 7. Conical Flasks. The so-called Erlenmeyer flasks, 
 or Beaker flasks. These are thin and rather fragile, but with 
 care will last a long time. Their freedom from color, perfect 
 transparency, uniformity in shape and size, render them 
 peculiarly well fitted for the examination of gases and liquids. 
 Flasks of the usual form, or bottles, may be used instead of 
 these, and, if made of white glass, and have mouths of uniform 
 size, to be perfectly closed by the stoppers, bottles are very good 
 and more durable. The mouth should be f to 1 inch in diam- 
 eter, taking a No. 4 or No. 5 E. & A. soft rubber stopper. 
 
 The use of these flasks and bottles, as described, for collect- 
 ing and examining gases, dispenses with the pneumatic cistern, 
 and the unpleasant wetness which goes with it. This method 
 also enables one to dispose of noxious substances with gratify- 
 ing success. 
 
 For each student 200 cc. or 6 oz. flasks 4 
 
 For the teacher, 200 cc. or 6 oz. flasks 2 
 
 500 cc. or 16 oz. flasks ... 4 
 
UII71RSIT7 
 
 8,9. Rubber stoppers. Success in managing gases 
 by this method demands that all joints in the apparatus shall 
 be air-tight. Such joints are easily made by means of rubber 
 stoppers No. 9, arranged with glass tubes No. 8. Each flask or 
 bottle is to be supplied with this arrangement, and they are then 
 to be joined together by rubber tubing. The first cost of rubber 
 stoppers is larger than of cork, but their durability is a compen- 
 sation. They should be of the "best soft rubber," and of such 
 sizes as to fit the mouths of the flasks and tubes in use. Their 
 sizes are described by numbers, but the same number, used 
 by different makers, does not always describe the same size or 
 quality. To be definite, we now refer to those stamped " E. 
 & A." (Eimer and Amend). 
 
 No. 3 will fit a f- inch tube or flask or bottle. 
 No. 4 " " J " flask or bottle. 
 No. 5 " " 1 " " bottle. 
 
 One " solid " will be needed, to close the side-neck tube or 
 flask ; one " with two holes," to close each flask or bottle in 
 use. 
 
 1C. Bunsen Burner. In laboratories not supplied 
 with gas, the alcohol lamp is the best substitute. 
 
 11. Glass Funnel. The best German make, with long 
 thin stem. Diameter 2 inches. 
 
 12. Wide-mouth Bottles. Flint glass, tall style. 
 
 Bottles should be bought by the dozen, or in larger labora- 
 tories by the gross. 
 
 Needed for each set, wide-mouth, 200 cc. or 8 oz. . 1 
 
 extra wide-mouth, 200 cc. " " . 1 
 
 wide-mouth, 400 cc. " 16 oz. 1 
 
 13. Forceps. Steel, plain, 4 inches. 
 
 14. Glass tubing. Made of the best German or soft 
 glass. It should be of such size as to fit the holes in the rubber 
 stoppers used, about & inch outside diameter for those de- 
 scribed above. It may be cut into pieces, of any length desired, 
 by first drawing across it the edge of a sharp three-cornered 
 
282 APPENDIX. 
 
 file, once, making a distinct scratch, and then pulling the tube, 
 almost but not quite lengthwise. The sharp cut edges may 
 be rounded by heating them until red in the lamp-flame. 
 Glass tubing is to be bought by the pound. 
 
 15. Porcelain Dish. So-called " evaporating dish." 
 The R. B. porcelain is best. Diameter 3 inches. 
 
 These may be bought by the dozen. 
 
 Needed for each set 1 or 2 
 
 16. Drying Tube. The so-called "chloride of calcium 
 tube," with one bulb, length 5 inches. 
 
 17. Pinch-cock. Mohr's, small size, strong. 
 
 18. The Balance. A balance of good quality is the 
 most costly piece in the outfit for laboratory work. In quali- 
 tative chemistry, such as the foregoing course, it is not abso- 
 lutely indispensable, because something can be done by means 
 of cheap substitutes, even by such as an ingenious student 
 can make. 
 
 The balance shown in the cut is a Becker's balance, listed 
 in " Becker Brothers" catalogue as No. 14, at $11.00. With a 
 glass case, which is very desirable to protect the instrument 
 from dirt and corrosion, it is listed as No. 16, at $ 22.00. It is 
 neat, accurate, sensitive to 2 ing., and durable. 
 
 The weights for this balance should be a set of 50 g. to 1 g. 
 in brass, and 500 mg. to 1 mg. in platinum or aluminum 
 with forceps, all in a lined and covered box. Such a set is 
 listed by Becker Brothers at $9.00, and by Eimer and Amend 
 at $5.50. 
 
 From parties (John Wanamaker, Philadelphia) who import 
 from Becker's Sons of Rotterdam, the balance and weights 
 just described, or their equivalent, can be obtained by schools, 
 free of duty, at much less cost. 
 
 19. The Water Pan. A pan about 8 inches diameter, 
 and 3 or 4 inches deep, with flat bottom and straight walls. 
 It may be of glass a so-called crystallizing dish, as shown in 
 the cut, or it may be of agate-iron ware, which is likely to be 
 more durable, but less shapely. 
 
APPENDIX. 283 
 
 20. A common Plate. A small size china plate. 
 
 21. Rubber Tubing. To connect the Bunsen Burner 
 with the gas supply, white rubber, thick, inch diameter inside, 
 may be used. Red rubber is better, and a little more costly. 
 
 For joining parts of the gas-apparatus the black or red 
 tubing, of usual thickness, is to be preferred. The size should 
 correspond with that of the glass tubing, which it must fit. 
 Rubber tubing is bought by the foot. In pieces of 12 feet it 
 comes a little cheaper. 
 
 22. A Chemical Thermometer. A Centigrade ther- 
 mometer, graduated from about 20 to +200. The best in- 
 strument has its scale on the glass stem itself. A cheaper and 
 very good instrument has a paper scale enclosed in a glass 
 tube, which protects the stem. 
 
THE CHEMICALS. 
 
 IN the following list may be found the names and formulas 
 of all the substances required to make the experiments de- 
 scribed in this book. Chemicals, to be used in the study of 
 chemistry, should be of the best quality. Many of those fur- 
 nished by the shops are impure, and often lead to wrong and 
 troublesome results. It is better to buy chemicals, as you buy 
 apparatus, from well-known dealers in laboratory supplies. 
 
 Reagents, which are to be used by students, should be kept 
 upon their tables in small bottles : liquids in glass-stoppered 
 bottles holding about 125 cc. or four oz., and solids in salt-mouth 
 bottles holding 2 oz. If substances are to be used by the 
 teacher they may, for the most part, be kept in the bottles in 
 which they are bought. Every bottle should be distinctly and 
 permanently labelled. 
 
 Unless economy must be rigidly practiced, the supply will not 
 be limited to the substances in this list; specimens, in great 
 variety, are very desirable. 
 
 The author will gladly give any information he can in regard 
 to the purchase or use of apparatus and chemicals. 
 
 Acetic acid, pure .... . HC 2 H 3 O 2 
 
 Alcohol . . . , . C 2 H 6 
 
 Alum . ..... K 2 A1 2 (S0 4 ) 4 + 24H 2 
 
 Ammonium carbonate, C. P. . (N H 4 ) 2 C O 3 
 chloride, C. P. . . NH 4 C1 
 
 hydrate . . . NH 4 HO 
 nitrate, cryst. . . NH 4 NO 3 
 
 Antimony chloride, sol. C. P. . Sb C1 8 
 
 Arsenous oxide . ' . - As a O, 
 
 Barium chloride, C. P. . . *. Bad, 
 
 284 
 
APPENDIX. 285 
 
 Bismuth nitrate, cryst. C. P. . Bi (N 3 ) 3 
 
 Bone-black C 
 
 Bromine Br 
 
 Calcium chloride, crude . . Ca C1 2 
 
 cryst. C. P. . 
 
 " oxide (quicklime) . . Ca O 
 
 Carbon pencil C 
 
 Chrome alum .... K 2 Cr 2 (S 4 ) 4 + 24 H 2 
 
 Cobalt nitrate, C. P. . .... Co(N0 3 ) 2 
 
 Cochineal . . , ;'.i . . 
 
 Copper, thin sheet . . . . Cu 
 
 chloride . . . . . Cu C1 2 
 
 sulphate, C. P. . . . Cu S 4 
 
 Dutch metal (imitation gold-leaf) Cu Zn 
 
 Ferrous sulphate, pure . . . Fe S O 4 
 
 " sulphide (sticks) . . Fe S 
 
 Hydrochloric acid, pure . . H Cl 
 
 Iodine I 
 
 Lead acetate . . '. - . . Pb (C 2 H 3 O 2 ) 2 
 Litmus (blocks) . . . 
 Logwood . ' . . . . *-' 
 
 Magnesium (ribbon) . . . Mg 
 
 chloride, cryst. . . Mg C1 2 
 
 sulphate, C. P. . . Mg S O 4 
 
 Manganese dioxide, powder . . Mn 2 
 
 sulphate . . - . MnSO 4 
 
 Marble CaC0 3 
 
 Mercury, redistilled . . . Hg 
 
 Mercuric chloride (cor. sub.) . . Hg C1 2 
 
 oxide . . . . HgO 
 
 Nickel chloride M C1 2 
 
 Nitric acid, pure . , , - H N 8 
 
 Oxalic acid, C. P H 2 C 2 O 4 
 
 Paraffine . . , . . C n H 2n 2 
 
 Phosphorus P 
 
 Potassium K 
 
 bromide, C. P. . . . K Br 
 
 " carbonate, C. P. . . K 2 C O s 
 
286 APPENDIX. 
 
 Potassium chlorate, cryst. . . K Cl O 3 
 
 chroma te ... K 2 Or O 4 
 
 dichromate . . . K 2 Cr 2 O 7 
 
 ferrocyanide . . K 4 Fe Cy 6 
 
 " hydrate, pure . . . K H O 
 
 iodide, C. P. . .... K I 
 
 nitrate, cryst. . . . K N O 8 
 
 " sulphate, cryst. . . K 2 SO 4 
 
 Platinum foil Pt 
 
 " wire .... Pt 
 
 Pyrogallic acid . . . C 6 H 3 (H O) 3 
 
 Silver nitrate, cryst. . . * . AgN0 3 
 
 Sodium . ^.^4.' . . . Na 
 
 biborate (borax) . ; ^ / Na 2 B 4 O 7 + 10 II 2 O 
 
 carbonate, C. P. . . . . Na 2 C O 3 
 
 hydrate, C. P. . . ... . Na H O 
 
 " nitrate . . ;. . . . NaNO 3 
 
 " sulphate .... Nn,SO 4 
 
 Strontium chloride . . . . Sr C1 2 
 
 nitrate, C. P. . . Sr (N 3 ) 2 
 
 Sulphur, flowers . S 
 
 roll . . .,v ... S 
 
 Sulphuric acid, pure . . . . . H 2 S O 4 
 
 Tartaric acid, cryst. . C 4 IF 6 8 
 
 Tin (granulated) . * .;.-. . . Sn 
 
 Zinc (sheet) . . . - . - * . , Zn 
 
 " (granulated) . . . . Zn 
 
 Sugar (granulated) >. ! -' . . , C 12 H 22 O^ 
 
 Salt . . * Jv^;t- . NaCl 
 
 Charcoal . . . . . . C 
 
 METRIC AND ENGLISH MEASURES. 
 
 Measures of Weight. 
 
 10 milligrams, mg. = 1 centigram, eg. = 0.154 grains. 
 10 centigrams, eg. = 1 decigram, dg. = 1.543 grains. 
 10 decigrams, dg. = 1 GRAM, g. = 15.432 grains. 
 
 10 grams = 1 decagram = 154.323 grains. 
 
 10 decagrams = 1 hectogram = 3.527 oz. avoir. 
 10 hectograms = 1 kilogram = 2.204 Ib. avoir. 
 
APPENDIX. 287 
 
 1 grain = 0.0648 g. or 04.799 mg. 
 
 1 oz. Troy = 31.1035 g. 1 oz. avoir. = 28.349 g. 
 
 1 Ib. Troy = 5760 grains. 1 Ib. avoir. = 7000 grains. 
 
 Measures of Volume. 
 
 10 cubic centimeters, cc. = 1 centiliter, cl = 0.338 fld. oz. 
 10 centiliters = 1 deciliter = 0.845 gill. 
 
 10 deciliters = 1 LITER, 1. = 1.057 quart. 
 
 10 liters = 1 decaliter = 2.642 gal. 
 
 10 decaliters = 1 hectoliters, hi. = 26.417 gal. 
 
 10 hectoliters = 1 kiloliter = 264.18 gal. 
 
 1 cu. in. = 16.386 cc. 1U, S. quart = 0.9469 1. 
 
 1 liter = 61.027 cu. in. 1 U. S. gal. = 3.785 1. 
 
 1 U. S. gal. = 231 cu. in. 1 Imp. gal. = 277.25 cu. in. 
 
 Measures of Length. 
 
 10 millimeters, mm. 1 centimeter, cm. 0.3937 in. 
 10 centimeters = 1 decimeter 3.937 in. 
 
 10 decimeters 1 METER, m. = 39.37 in. 
 
 10 meters = 1 decameter = 32.8 ft. 
 
 10 decameters = 1 hectometer = 328.08 ft. 
 
 10 hectometers = 1 kilometer, km. = 0.62137 mile. 
 
 1 inch = 2.534 cm. 1 millimeter - 0.0393 in. 
 
 1 yard = 0.9144 m. 1 meter = 1.0936 yd. 
 
 1 mile = 1.6093 km. 1 kilometer = about f mile. 
 
 Measures of Temperature. 
 
 Freezing-point of water = Centigrade, C. or 32 Fahrenheit, F. 
 Boiling-point of water = 100 " or 212 " 
 
 1 C. = f, or 1.8 F. 1 F. = f, or 0.555 C. 
 
 To change a Centigrade temperature to its equivalent Fahren- 
 heit temperature : Multiply by f and add 32 to the product. 
 
 To change a Fahrenheit temperature to its equivalent Centi- 
 grade temperature: Subtract 32 and multiply the remainder 
 by f. 
 
INDEX. 
 
 THE NUMBERS REFER TO PAGES. 
 
 ABSORPTION, analysis by, 70, 82. 
 
 of gases by charcoal, 106. 
 
 of gases by water, 59, 86, 146. 
 
 of hydrogen by palladium, 261. 
 Acid-forming elements, 192, 236. 
 Acids, 129. 
 
 action of, on bases, 133. 
 
 action of, on metals, 134. 
 
 chief characteristic, 130. 
 
 classes of, 130. 
 
 dibasic, 172. 
 
 monobasic, 173. 
 
 names of, 135. 
 Acid salts, 173. 
 Agate, 184. 
 Air spoiled by breathing, 79. 
 
 analysis of, 69-74. 
 
 in water, 59. 
 Alkalies, metals of, 204. 
 Allotropism, 39. 
 Alloys, 214. 
 
 of antimony, 235. 
 
 of bismuth, 235. 
 
 of copper, 248. 
 
 of gold, 260. 
 
 of mercury, 251. 
 
 of osmium, 261. 
 
 of silver, 256. 
 Alum, 233. 
 
 ammonium, 233. 
 
 chrome, 230. 
 
 Alumina, 233. 
 Alluminum, 233. 
 
 compounds of, 233. 
 
 compounds in dyeing, 234. 
 
 hydroxide, 234. 
 
 oxide, 233. 
 
 reactions of, 234. 
 
 sulphide, 234. 
 Amalgams, 251. 
 Amalgamated zinc, 26. 
 Amalgamation in metallurgy, 255, 
 
 259. 
 Amethyst, oriental, 233. 
 
 quartz, 183. 
 Amine, 182. 
 Ammonia, 84-90. 
 
 absorbed by charcoal, 106. 
 
 absorbed by water, 86, 88. 
 
 composition of, 90. 
 
 in food of plants, 102. 
 
 in air, 69, 85. 
 
 Nessler's test for, 99. 
 
 preparation of, 85. 
 
 solubility of, 88. 
 
 sources of, 84, 85. 
 Ammonium, 201-204. 
 
 alum, 233. 
 
 a metal, 202. 
 
 chloride, 19. 
 
 disulphide, 203. 
 
 hydrate, 87. 
 
290 
 
 INDEX. 
 
 Ammonium, hydrosulphide, 203. 
 
 reactions of, 203. 
 
 salts, 88, 202. 
 
 sulphides, 160, 203. 
 Analysis, defined, 24, 50. 
 
 by absorption, 70, 82. 
 
 by electricity, 51. 
 
 grouping for, 269. 
 
 notes of work in, 273, 275. 
 
 of air, 69-74. 
 
 of a metallic salt, 270-275. 
 
 of a complex salt, 274. 
 
 of a simple salt, 274. 
 
 of unknown substances, 270. 
 
 of water, 50-55. 
 
 report of an, 275. 
 
 systematic, 268. 
 Anhydride, defined, 165. 
 
 arsenic, 180. 
 
 arsenous, 179. 
 
 carbonic, 184. 
 
 phosphoric, 177. 
 
 phosphorus, 177. 
 
 silicic, 184. 
 
 sulphuric, 169. 
 
 sulphurous, 166. 
 Animal charcoal, 108. 
 Antimonetted hydrogen (stibine), 
 
 235. 
 Antimony, 235. 
 
 alloys of, 235. 
 
 compound with hydrogen, 235. 
 
 group, 236. 
 
 ores of, 235. 
 
 reactions of, 237. 
 
 related to non-metals, 235. 
 
 sulphide, 237. 
 
 Apparatus for this course, 279. 
 Aqua regia, 92, 143, 260. 
 Arsenuretted hydrogen (arsine), 
 180. 
 
 Arsenic, 178-182. 
 
 acid, 180. 
 
 Marsh's test for, 181. 
 
 native, 179. 
 
 oxides, 179, 180. 
 
 reactions of, 237. 
 
 related to metals, 236. 
 
 sulphide, 237. 
 
 white, 179. 
 Arsenous oxide, 179. 
 Arsenical pyrites, 179. 
 Arsenites, 180. 
 Arsine, 182. 
 Atmosphere, chemistry of, 65-83. 
 
 a mixture, 74. 
 
 analysis of, 69. 
 
 composition of, 73, 75. 
 
 constituents in, 69. 
 Atomic theory, 123. 
 
 weights, 118, 124. 
 Atomic weights and properties, 
 
 facts from the Cl. group, 151. 
 
 facts from the S. group, 162. 
 
 facts from the N. group, 182. 
 
 facts from the Ca. group, 210. 
 
 facts from the Zn. group, 216. 
 
 facts from the Fe. group, 231. 
 
 Newland's discovery, 264. 
 
 Mendelejeff 's system, 266. 
 
 shown in spiral form, 267. 
 
 suggests new elements, 268. 
 Atoms, 122. 
 Avogadro's law, 122. 
 
 BAKING POWDERS, 200. 
 Baking soda, 40, 200. 
 Barium, 210. 
 
 reactions of, 211. 
 Base-forming elements, 192. 
 Bases, defined, 133. 
 
 action on acids, 133. 
 
IXDEX. 
 
 291 
 
 Bases, names of, 130. 
 
 Basic salts, 245. 
 
 Battery, voltaic, 51. 
 
 Bell-metal, 248. 
 
 Bessemer process for steel, 226. 
 
 Bismuth, 235. 
 
 reactions of, 237. 
 
 related to non-metals, 236. 
 
 sulphide, 237. 
 Black-ash, 200. 
 Black-lead, 110. 
 
 Black oxide of manganese, 217. 
 Blast-furnace, 221. 
 Bleaching, by chlorine, 140. 
 
 by sulphurous oxide, 165, 166. 
 
 powder, 141, 208. 
 Blende zinc, 212. 
 Blistered steel, 226. 
 Bloodstone, 183. 
 Boiling-point, 61. 
 Bone-ash, 178. 
 Borax, 185. 
 Boric acid, 186. 
 Boron, 185. 
 
 valence of, 190. 
 Brass, 214, 248. 
 Brimstone, 155. 
 Bromides, 148. 
 
 reactions of, 151. 
 Bromine, 148. 
 Bronze, 248. 
 Bunsen burner, 10, 47. 
 
 CADMIUM, 215. 
 Caesium, 204. 
 Calamine, 212. 
 Calcium, 206-211. 
 
 carbonate, 206-208. 
 
 chloride, 86, 207. 
 
 flame color of, 211. 
 
 group, 210. 
 
 Calcium hydroxide (slaked lime), 
 207. 
 
 hypochlorite, 208. 
 
 insoluble compounds of, 208. 
 
 occurrence, 206. 
 
 oxide (quick-lime), 206. 
 
 phosphate, 178. 
 
 reactions of, 211. 
 
 soluble compounds of, 210. 
 
 sulphate, 208, 210. 
 Calcium carbonate, 1 13, 206. 
 
 decomposed by acids, 207. 
 
 decomposed by heat, 206. 
 
 dissolved by water, 208. 
 
 precipitated, 113. 
 Calomel, 252. 
 Calorie, 32. 
 Carbon, 103-112. 
 
 allotropic forms of, 111. 
 
 compounds with hydrogen, 
 115. 
 
 constituent of plants, 101. 
 
 diamond, 109. 
 
 dioxide, 112. 
 
 from sugar, 12. 
 
 graphite, 110. 
 
 group, 184. 
 
 lamp-black, 105. 
 
 manufacture of charcoal, 104. 
 
 monoxide, 115. 
 
 source of, in plants, 103. 
 Carbonates, 184. 
 
 basic, 245, 248. 
 Carbon dioxide, 112-114. 
 
 absorbed by plants, 81. 
 
 a constituent of air, 74. 
 
 by burning charcoal, 18. 
 
 preparation of, 112. 
 
 properties of, 113. 
 
 product of combustion, 42. 
 
 product of respiration, 78. 
 
292 
 
 INDEX. 
 
 Carbon, synthesis of, 36. 
 
 test for, 17, 36, 113. 
 Carbon monoxide, 82, 115. 
 Carbonic acid, 184. 
 
 anhydride, 184. 
 Carnelian, 184. 
 Cast-iron, 222. 
 Catalysis, 35. 
 Caustic potash, 197. 
 Caustic soda, 200. 
 Cementation, 226. 
 Chalcedony, 184. 
 Changes, of two kinds, 14. 
 Charcoal, 105. 
 
 action of, on colors, 108. 
 
 action of, on gases, 106. 
 
 action of, on oxides, 109. 
 
 a disinfectant, 107. 
 
 animal, 108. 
 
 combustion of, 36. 
 Chemical change, 13-40. 
 
 a change in molecules, 122. 
 
 agents to produce, 28. 
 
 a source of electricity, 25. 
 
 a source of heat, 25. 
 
 a source of light, 27. 
 
 combination, 17. 
 
 decomposition, 14. 
 
 double decomposition, 21. 
 
 exercises in, 39. 
 
 substitution, 19. 
 Chemical calculations, 127. 
 Chemical names, 135. 
 Chemicals for this course, 284. 
 Chemistry, how to study, 9, 12. 
 Chilian saltpetre, 90. 
 Chlorides, 141-147. 
 
 hydrogen-chloride, 145. 
 
 preparation of, by aqua regia, 
 92. 
 
 preparation of, by chlorine gas, 
 141. 
 
 Chlorides, preparation of, by chlo- 
 rine water, 142. 
 
 preparation of, by hydrochloric 
 acid, 142. 
 
 reactions of, 151. 
 
 test for, 147. 
 
 two, of one metal, 144. 
 Chlorine, 138-147. 
 
 action of, on metals, 140, 141. 
 
 a disinfectant, 140. 
 
 bleaching by, 140. 
 
 group, 147. 
 
 preparation of, 138. 
 
 properties of, 139. 
 
 test for, 147. 
 Chlorine group, 147-153. 
 
 general behavior, 151. 
 
 hydrogen compounds of, 150. 
 
 members of, described, 148, 149. 
 
 properties and atomic weights 
 of, 151. 
 
 reactions of, 151-153. 
 Choke-damp, 114. 
 Chrome alum, 230. 
 
 yellow, 230. 
 
 Chromic iron (chromite), 229. 
 Chromite, 229. 
 Chromium, 229. 
 
 compounds of, 230. 
 
 reactions of, 230. 
 Chrysoprase, 183. 
 Cinnabar, 251. 
 Classes, how made, 262. 
 Classification, 262-275. 
 
 analytical, of metals, 268. 
 
 a natural system, 264. 
 
 in a spiral form, 266. 
 
 Mendelejeff's table, 266. 
 
 metals and non-metals, 236, 262. 
 
 of metals, 262. 
 
 of non-metals, 261. 
 Clay, 233. 
 
INDEX. 
 
 293 
 
 Clay-iron stone, 221. 
 Coal, 105. 
 Cobalt, 220. 
 
 "fly-poison," 178. 
 Coin, analysis of, 257. 
 
 gold, 260. 
 
 silver, 256. 
 Combination, 17. 
 
 by volume, 55, 146, 147. 
 
 law of, by volume, 147. 
 
 law of constant proportions, 
 57. 
 
 law of multiple proportions, 
 
 97, 123. 
 
 C6mbining weights, 98. 
 Combustion, 37, 41-49. 
 
 a mutual action, 42. 
 
 imperfect, 42. 
 
 of hydrogen and oxygen, 43. 
 
 produces heat, 43. 
 
 produces light, 46, 49. 
 
 produces compounds, 42. 
 Complex salts, 274. 
 Compounds defined, 24. 
 
 differ from elements, 122. 
 
 formulas of, 124. 
 
 neutral, 134. 
 Constituent, 24. 
 Copper, 247-251. 
 
 alloys of, 248. 
 
 arsenite, 180. 
 
 carbonate, 248. 
 
 chloride, 141, 250. 
 
 compounds of, 248. 
 
 extraction of, 248. 
 
 hydroxide, 250. 
 
 native, 247. 
 
 ores of, 247. 
 
 oxides, 249. 
 
 pyrites, 247. 
 
 reactions of, 249. 
 
 Copper sulphate, 171, 249. 
 
 sulphide, 157, 250. 
 Copperas, 100. 
 Cork-borers, 31. 
 Corrosive sublimate, 252. 
 Cupellation, 255, 256. 
 Cupric compounds, 249. 
 Cuprous compounds, 249. 
 
 DECOMPOSITION, 14. 
 Definite proportions, law of, 57. 
 Deliquescence, 197. 
 Diamond, 109. 
 Dibasic acids, 172. 
 Diffusion of gases, 75. 
 Dimorphism, 157. 
 Disinfectants, 107, 140, 214, 217. 
 Distillation, 60. 
 
 fractional, 64. 
 Drinking-water, 59. 
 Dutch metal, 139, 141. 
 
 EFFERVESCENCE, 207. 
 
 Electricity and chemical action, 25. 
 
 decomposition by, 26, 51-54. 
 
 produces ozone, 38. 
 Element defined, 24. 
 
 differs from compound, 122. 
 Elements, ancient, 41. 
 
 atomic weights of, 118, 123, 
 124. 
 
 classification of, 262. 
 
 number of, 117. 
 
 symbols of, 118, 123. 
 
 table of, 118. 
 Emerald, 233. 
 
 English and French measures, 286. 
 Epsom salt, 212. 
 Equations, chemical, 127. 
 Etching glass, 150. 
 Evaporation, 20. 
 
294 
 
 INDEX. 
 
 Exercises in investigation, 39, 6:3, 
 
 82, 98. 
 
 Experiment, defined, 10. 
 value in chemistry, 12. 
 
 FERRIC CHLORIDE, 144. 
 
 Ferrous chloride, 144. 
 
 Ferrous and ferric compounds, 226. 
 
 Filter, 20. 
 
 Filtration, 20. 
 
 Fire, 41. 
 
 Fire-damp, 116. 
 
 Flame, due to gas, 45. 
 
 effect of cooling, 49. 
 
 oxyhydrogen, 43. 
 
 smoke of, 42. 
 
 source of the light, 47. 
 
 structure of, 48. 
 
 tests, 198, 201, 211. 
 Flame color, to produce, 198. 
 Flint, 183. 
 
 Flowers of sulphur, 155. 
 Fluorine, 149. 
 Fluor spar, 150. 
 Fly powder, 178. 
 Fool's gold, 154. 
 Formulas of compounds, 124. 
 Fractional distillation, 64. 
 Freezing-point, 63. 
 Fuel, 42. 
 
 Furnace, 221, 223. 
 Fusible metal, 235. 
 
 GALENA, 154, 242. 
 Gallium, 268. 
 Galvanized iron, 214. 
 Gas, illuminating, 85. 
 Gases, analysis of, 70, 82. 
 
 burn with flame, 45. 
 
 diffusion of, 75. 
 
 expansion of, 121. 
 
 Gases, measurement of, 71. 
 
 method of drying, 31. 
 
 method of collecting, 29, 33. 
 
 solubility of, 59. 
 German silver, 214, 248. 
 Glass, 185, 208. 
 
 blue, 220. 
 
 hard and soft, 14. 
 Gold, 259. 
 
 coin, 260. 
 
 extraction by washing, 259. 
 
 extraction by amalgamation, 
 259. 
 
 properties of, 259. 
 Graphite, 110. 
 Green vitriol, 249. 
 Groups, 262. 
 
 analytical, 269. 
 
 natural, 266, 267. 
 
 of non-metals, 147, 161, 182, 184. 
 
 of metals, 262-264. 
 Grouping by atomic weights, 264. 
 
 by likeness of properties, 263. 
 
 by solubility of compounds, 
 264, 268. 
 
 by valence, 262. 
 
 for analysis, 269. 
 Gypsum, 208. 
 
 HEMATITE, 221. v 
 
 Heat, agent in chemical change, 28. 
 
 a product of chemical change, 
 19, 25, 28. 
 
 intensity of, 44. 
 
 quantity of, 44. 
 
 unit of, 32. 
 Hydrates, 133. 
 Hydrocarbons, 115. 
 Hydrochloric acid, 145. 
 
 composition of, 146. 
 
 constant composition, 56. 
 
INDEX. 
 
 295 
 
 Hydrochloric acid, preparation of, 
 145. 
 
 properties of, 146. 
 
 solubility of, 58, 59, 146. 
 Hydrofluoric acid, 150. 
 Hydrogen, 28-32. 
 
 antimonide (stibine), 235. 
 
 arsenide (arsine), 180. 
 
 chloride, 145. 
 
 diffusion, 75. 
 
 explosibility, 30. 
 
 in nature, 32. 
 
 nitride (ammonia), 84-88. 
 
 phosphide (phosphine), 182. 
 
 preparation of, 19, 28. 
 
 properties of, 29-32. 
 
 set free by electricity, 26. 
 
 solubility of, 59. 
 
 sulphide, 158. 
 
 weight of a liter, 32. 
 Hydrogen sulphide, 158. 
 
 preparation of, 159. 
 
 properties of, 160. 
 
 use of, 160. 
 Hydroxides, 131. 
 
 names of, 137. 
 Hypophosphorus acid, 177. 
 
 ICE, 63. 
 
 Ignition tubes, 14. 
 Illuminating gas, 85. 
 Investigation of some chemical ac- 
 tions, 39. 
 
 in study of nitric acid, 92. 
 
 of sulphuric acid on iron, 40. 
 
 of H 2 S O 4 on oxalic acid, 82. 
 
 other examples of, 30, 63, 99, 
 
 173. 
 Iodides, 149. 
 
 reactions of, 161. 
 Iodine, 148. 
 
 Iodine, test for, 149. 
 
 tincture, of, 149. 
 Iridium, 261. 
 Iron, 220-232. 
 
 chlorides, 144. 
 
 combustion of, 36. 
 
 compounds of, 226. 
 
 extraction of, 221. 
 
 galvanized, 214. 
 
 group of metals, 217, 231. 
 
 hydroxides, 137. 
 
 manufacture of cast, 222. 
 
 manufacture of steel, 225. 
 
 manufacture of wrought, 223. 
 
 occurrence of, 220. 
 
 ores of, 220. 
 
 reactions of, 226-229. 
 
 sulphate, 170. 
 
 sulphides.. 158, 220. 
 
 two classes of salts of, 226. 
 
 JASPER, 183. 
 KINDLING-POINT, 44. 
 
 LABORATORY SUPPLIES, 279-284. 
 Lamp-black, 105. 
 Laughing-gas, 96. 
 Lavoisier's experiment, 65. 
 Law, 119. 
 
 Avogadro's, 122. 
 
 of constant proportions, 57. 
 
 of multiple proportions, 97, 123. 
 
 the periodic, 266. 
 
 the "two volume," 147. 
 Lead, 242-246. 
 
 carbonate, 244. 
 
 chloride, 245. 
 
 chromate, 230. 
 
 extraction of, 242, 243. 
 
 iodide, 246. 
 
 nitrate, 245. 
 
296 
 
 INDEX. 
 
 Lead, ores Of, 242. 
 
 oxides, 244. 
 
 properties of, 244. 
 
 reactions of, 245. 
 
 sulphide, 245. 
 
 symbol of, 242. 
 Lead-tree, 243. 
 Light, and chemical action, 27. 
 
 of flames, 46. 
 
 on nitric acid, 91. 
 
 oxyhydrogen, 46. 
 Lime, 206. 
 Lime-light, 46. 
 Limestone, 206. 
 Lime-water, 207. 
 
 a test for C0 2l 17. 
 Litharge, 244. 
 Lithium, 204, 265. 
 Lucifer match, 165. 
 
 MAGNESIA, 212. 
 Magnesium, 212. 
 
 carbonate, 212. 
 
 combustibility of, 13. 
 
 oxide, 212. 
 
 reactions of, 212. 
 
 sulphate, 212. 
 Magnetic oxide, 220. 
 Malachite, 247. 
 Malleable iron, 224. 
 Manganese, 217. 
 
 reactions of, 218. 
 Marble, 206. 
 Marsh-gas, 116, 184. 
 Matches, 165, 176. 
 Melting-point, 63. 
 Mendelejeff s system, 266. 
 Metal, denned, 192. 
 Metals, 192. 
 
 and non-metals, 193, 236. 
 
 analytical groups of, 269. 
 
 Metals, classification of, 262, 264. 
 
 native, 193. 
 
 number of, 193. 
 
 occurrence of, 193. 
 
 of the alkalies, 204. 
 
 of the alkaline earths, 210. 
 
 the calcium group, 210. 
 
 the copper group, 247. 
 
 the iron group, 231. 
 
 the platinum group, 261. 
 
 the potassium group, 204. 
 
 the zinc group, 215. 
 Metallurgy, 194. 
 
 amalgamation in, 255, 259. 
 
 cupellatioii in, 255, 256. 
 
 precipitation in, 243. 
 
 reducing ores, 213. 
 
 roasting ores, 213. 
 
 washing of gold, 259. 
 Meteoric stones, 220. 
 Methane, 116, 184. 
 Metric measures, 286. 
 Mercury, 251-253. 
 
 alloys of, 251. 
 
 chlorides, 252. 
 
 compounds of, 252, 253. 
 
 extraction of, 251. 
 
 ore of, 251. 
 
 oxide, 14, 252. 
 
 reactions of, 252. 
 
 sulphide, 253. 
 Mineral waters, 59. 
 Mining, 194. 
 Minium, 244. 
 Mispickel, 179. 
 Mixture defined, 24. 
 Molecular weights, 125. 
 Molecules, 121. 
 Monobasic acids, 173. 
 Mortar, 207. 
 Multiple proportions, 97. 
 
INDEX. 
 
 297 
 
 Multiple proportions, law of, 97, 
 123. 
 
 NASCENT STATE, 85. 
 Nessler's reagent, 98. 
 Neutral compounds, 134. 
 Neutral salts, 173. 
 Neutralization, 133. 
 Newland's discovery, 264. 
 Nickel, 219. 
 Nitrates, 92, 
 
 tests for, 100. 
 Nitre, 196. 
 Nitric acid, 90-95. 
 
 decomposition of, 91, 92. 
 
 preparation of, 91. 
 
 properties of, 91. 
 
 test for, 100. 
 Nitric oxide, 95. 
 Nitrogen,. 6<L , 
 
 compounds, 84. 
 
 group, 182. ^ 
 
 in plants, 102. *" 
 
 oxides, 92-96. 
 
 properties of, 69. 
 Non-metals, V& 
 
 classification of, 189, 262. 
 
 the carbon group, 184. 
 
 the chlorine group, 147. 
 
 the nitrogen group, 182. 
 
 the sulphur group, 161. 
 Nomenclature, 135. 
 Normal salts, 173. 
 
 OBSERVATION, 9. 
 Oil of vitriol, 166. 
 Onyx, 184. 
 Opal, 183. 
 Ores, 194. 
 Osmium, 261. 
 Oxidation, 37. 
 slow, 175. 
 
 Oxides, 37. 
 
 nitrogen, 96. 
 
 reduction of, 109. 
 Oxidizing agent, 217, 228. 
 Oxygen, 33-39. 
 
 allotropism of, 38. 
 
 in nature, 37. 
 
 preparation of, 14, 16, 33. 
 
 solubility of, 59. 
 
 test for, 34. 
 Oxyhydrogen flame, 43. 
 
 blowpipe, 43. 
 Ozone, 38. 
 
 PARIS GREEN, 180. 
 Percentage composition, 55. 
 Periodic law, 266. 
 Phosphates, 178. 
 Phosphine, 182. 
 Phosphoric acid, 177. 
 Phosphorous acid, 177. 
 Phosphorus, 175-178. 
 
 acids, 177. 
 
 action on air, 83. 
 
 allotropic forms, 176. 
 
 burning of, 67, 68. 
 
 manufacture of, 178. 
 
 oxides, 177. 
 
 properties of, 175. 
 
 red, 175. 
 
 salts of, 178. 
 Phosphuretted hydrogen (pho< 
 
 phine), 182. 
 Photography, 173, 257. 
 Pig-iron, 222. 
 Plants, composition of, 101. 
 
 food of, 102. 
 
 respiration of, 81. 
 Plaster of Paris, 208. 
 Platinum, 260. 
 
 group of metals, 261. 
 
298 
 
 INDEX. 
 
 Plumbago, 110. 
 Potash, 196. 
 Potassium, 195-198. 
 
 action on water, 195. 
 
 alum, 233. 
 
 carbonate, 196. 
 
 chlorate, 16, 35. 
 
 chloride, 197. 
 
 group of metals, 204. 
 
 hydroxide, 196. 
 
 manganate, 219. 
 
 nitrate, 196, 197. 
 
 occurrence of, 195. 
 
 permanganate, 217,219. 
 
 reactions of, 197. 
 
 tartrate, 197. 
 Precipitate, 23, 198. 
 
 when one will fall, 210. 
 Precipitation in metallurgy, 243. 
 Prussian blue, 228. 
 Puddling, 223. 
 Pyrites, arsenical, 179. 
 
 copper, 247. 
 
 iron, 154, 158, 220. 
 
 QUARTZ, 183. 
 Quick-lime, 206. 
 
 REACTIONS, 126. 
 
 numerical, 127. 
 
 way to write, 127, 190. 
 Red-lead, 244. 
 Red phosphorus, 175. 
 Report of analysis, 275, 
 Respiration, 77. 
 
 effect an air, 79. 
 
 of plants, 81. 
 
 products of, 78. 
 Reverberatory furnace, 223. 
 Rhodium, 261. 
 Roasting of ores, 179, 213, 
 
 Rock crystal, 183. 
 Roll brimstone, 155. 
 Rubidicein, 204. 
 Ruby, 234. 
 Ruthenium, 261. 
 
 SALT, defined, 131. 
 common, 56. 
 Salt-cake, 199. 
 Saltpetre, 90, 196. 
 Salts, 131. 
 
 acid, 173. 
 
 analysis of, 270-274. 
 
 basic, 245. 
 
 complex, 274. 
 
 names of, 136, 274. 
 
 preparation of, 131. 
 
 preparation by fusion, 219. 
 
 preparation by evaporation, 
 210. 
 
 preparation by precipitation, 
 
 208. 
 Sandstone, 183. 
 
 simple, 274. 
 Sapphire, 234. 
 Selenides, 161. 
 Selenium, 161. 
 Silica, 183. 
 Silicates, 184. 
 Silicic acid, 184. 
 Silicon, 183. 
 
 hydride, 184. 
 
 oxide, 183. 
 Simple salts, 274. 
 Silver, 254-258. 
 
 chloride, 22, 27, 257. 
 
 coin, 256. 
 
 compounds of, 256. 
 
 extraction from the sulphide, 
 254. 
 
 extraction from galena, 255. 
 
INDEX. 
 
 299 
 
 Silver, nitrate, 256. 
 
 ores of, 254. 
 
 properties of, 256. 
 
 reactions of, 257. 
 
 separation from copper, 257. 
 
 ware, 256. 
 Slag, 222. 
 Slaked lime, 207. 
 Slate rocks, 185. 
 Smoke, 42. 
 Snow-flakes, 63. 
 Soaps, 200. 
 Soda-ash, 200. 
 Soda-water, 114, 200. 
 Sodium, 199-201. 
 
 carbonate, 199. 
 
 chloride, 199. 
 
 hydroxide, 200. 
 
 reactions of, 201. 
 
 theosulphate, 173. 
 Solubility, 210. 
 Solution, 58, 59. 
 Spiral of elements, 266, 
 Stalactite, 208. 
 Stalagmite, 208. 
 Starch-test, 149, 152. 
 Steel, 224. 
 Stibine, 235. 
 Strontium, 210. 
 
 reactions of, 211. 
 Sublimation, 204. 
 Substitution, 19. 
 
 governed by valence, 189. 
 Sugar, solubility of, 10. 
 
 action with sulphuric acid, 11. 
 Sulphates, 170. 
 
 ways to make the, 172. 
 Sulphides, 154. 
 
 artificial, 157. 
 Sulphur, 154-163. 
 
 combustion of, 18, 67, 68. 
 
 Sulphur, crystals of, 156. 
 
 dioxide, 18, 163. 
 
 effect of heat on, 155. 
 
 flowers of, 155. 
 
 group, 161. 
 
 native, 154. 
 
 preparation of, 154. 
 
 roll, 155. 
 
 Sulphuretted hydrogen, 159. 
 Sulphuric acid, 166-170. 
 
 action on copper, 163, 171. 
 
 action on iron, 40. 
 
 action on oxalic acid, 82. 
 
 action on sugar, 11. 
 
 action on water, 25. 
 
 action on zinc, 170. 
 
 manufacture of, 168. 
 
 properties of, 166. 
 
 test for, 167. 
 
 uses of, 167. 
 Sulphurous acid, 165. 
 Sulphurous oxide, 163. 
 Sulphur springs, 159. 
 Supplies, chemical, 284. 
 Symbols, 123. 
 Synthesis, 24, 50. 
 
 TABLE, blank, for the analytical 
 
 groups, 269. 
 of symbols and atomic weights, 
 
 118. 
 
 of French and English meas- 
 ures, 286. 
 of the periodic system in a 
 
 spiral, 267. 
 
 Temperature, rule to change Cen- 
 tigrade to Fahrenheit degrees, 
 
 287. 
 rule to change Fahrenheit to 
 
 Centigrade degrees, 287. 
 Theory, 120. 
 
300 
 
 INDEX. 
 
 Theory, atomic, 123. 
 
 Avogadro's, 122. 
 
 distinguished from facts, 121. 
 
 of matter, 121. 
 Tin, 239-242. 
 
 chlorides, 240. 
 
 compounds of, 240. 
 
 extraction of, 239. 
 
 foil, 240. 
 
 ore of, 239. 
 
 properties of, 239. 
 
 reactions of, 241. 
 
 sulphides, 241. 
 
 ware, 240. 
 
 Tincture of iodine, 149. 
 Tin-foil, 240. 
 Tinstone, 239. 
 Tin-ware, 240. 
 Topaz, 233. { 
 
 Type-metal, 235. 
 
 UNIT of heat, 32. 
 
 VALENCE, 188-191. 
 
 a property of atoms, 188. 
 
 denned, 189. 
 
 described, 189. 
 
 measured, 189. 
 
 represented, 189. 
 
 governs substitution, 189. 
 
 governs reactions, 190. 
 
 in classification, 189, 262. 
 
 of boron, 190. 
 
 variation in, 191. 
 Ventilation, 80. 
 Vermilion, 251. 
 Vitriols, 166, 249. 
 Volume, changed by heat, 71, 121 
 
 changed by pressure, 71, 121. 
 
 composition by, 147. 
 
 of ammonia, 90. 
 
 of hydrochloric acid, 146. 
 
 
 Volume, of nitrogen oxides, 147. 
 of water, 56. 
 the law deduced, 147. 
 
 WATER, 50-64. 
 
 analysis of, 61. 
 
 a product of combustion, 41. 
 
 a product of respiration. 78. 
 
 as a solvent, 58. 
 
 boiling-point of, 61. 
 
 composition of, 55, 56. 
 
 distillation of, 60. 
 
 drinking, 59. 
 
 freezing-point of, 63. 
 
 greatest density of, 62. 
 
 hard and soft, 59. 
 
 in Ahe air, 74. 
 
 in nature, 57. 
 
 mineral, 69. 
 
 of crystallization, 186. 
 
 synthesis of, 31, 36. 
 Weights, atomic, 118, 124. 
 
 combining, 98. 
 
 metric and English, 286. 
 
 molecular, 125. 
 White lead, 245. 
 White vitriol, 214. 
 Wrought-iron, 223. 
 
 ZINC, 212-216. 
 
 amalgamated, 26. 
 
 chloride, 21, 214. 
 
 compounds of, 214. 
 
 group of metals, 216. 
 
 manufacture of, 213. 
 
 ores of, 212. 
 
 reactions of, 214. 
 
 sulphate, 170. 
 
 sulphide, 161, 215. 
 
 uses 
 
 Zincite, ! 
 Ztnc \thlte, 214 
 
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