MAR 141 DESCRIPTIVE GENERAL CHEMISTRY A TEXT BOOK FOR SHORT COURSE BY S. E.f TILLMAN Professor of Chemistry, Mineralogy and Geology United States Military Academy WEST POINT, N. Y. UNITKD STATKS MlIjTARY ACADEMY PRKSS 1897 'triwi Q« J566 COPYRIGHT, 1897, BY S. K. TUBMAN. i x PREFACE. This book has been prepared to meet the requirements of the very short course in General Chemistry taught to the Cadets of the Military Academy. The matter embraced is the result of more than sixty years' selection and sifting" made in the effort to secure that most essential and important for this course. The arrangement adopted is that which long experience and careful consideration have shown to accomplish the best results in the time available for the study of the subject. S. E. TILLMAN. West Point, N. Y., June 15, 1897. TABLE OK CONTENTS ESSENTIAL PRINCIPLES OF CHEMISTRY. PAGES. Introductory remarks, Table of Elements 5-7 Laws of fixed proportions and multiples 8-9 Atomic theory 9-11 Chemical notation and nomenclature 11-17 Chemical reactions and conditions affecting affinity 17-22 Radicals, bases, acids, and salts m. 22-27 Equivalent and atomic weights 27-32 Law of Avogadro and determination of molecular weights 32-35 Atomic weights from Avogadro's law 35-39 Number of atoms in molecules, isomorphous relations 39-42 Volume relations of elements and compounds 42-44 Relations between specific heats and atomic weights 44-47 Valency 47-51 Atomic weights and other properties of elements 51-52 Stochiometry '. 52-56 NON-METALS. Oxygen and ozone 57-62 Hydrogen 62-67 Nitrogen and atmospheric air 07-71 Water and hydrogen peroxide 71-82 Carbon and its different forms S3-90 Compounds of carbon and oxygen 90-97 Hydrocarbons (methane, acetylene, ethylene) 97-100 Combustion and flame 100-110 Silicon and boron 110-113 Compounds of hydrogen and nitrogen 113-117 Compounds of nitrogen and oxygen 117-122 Chlorine and hydrochloric acid 122-125 Bromine, iodine and fluorine 125-133 Sulphur 133-136 Hydrogen sulphide and oxides of sulphur 136-142 Sulphuric acid, sulphates and other sulphur acids 142-149 Selenium and tellurium 149-150 2 Phosphorus, oxides and oxy-aeids of phosphorus 151-155 Arsenic and its non-metallic compounds 155-158 Argon and helium 158 METALS. Potassium and its compounds 159-166 Sodium and its compounds 166-174 Ammonium and itscompounds 174-177 Barium and its compounds 177-178 Calcium and its compounds 178-184 Magnesium 184-185 Zinc and its compounds 186-190 Aluminum and its compounds 190-195 Iron, its reduction, metallurgy and important compounds 195-220 Cobalt, nickel, manganese, chromium 220-222 Molybdenum, tungsten, uranium, bismuth and antimony 223-224 Tantalum, niobium and vanadium 224 Tin and its reduction 224-227 Titanium, zirconium, thorium, germanium, cerium 227 Lead, its reduction and important compounds 227-237 Copper, its reduction and important compounds 237-245 Silver, its reduction and important compounds 245-252 Mercury, its reduction and important compounds 252-257 Platinum and other metals of the same group 257-260 Gold, its metallurgy and important compounds 260-266 ORGANIC CHEMISTRY. Chemistry of the carbon compounds 267-268 Classification of carbon compounds 268-270 Structural and rational formula? 270-271 Isomerism and polymerism 271 Saturated hy dr ocarb ons 272 Unsaturated hydrocarbons 275 Acetylene series 276 Benzene series 276 Terpenes 277 Camphors, resins, balsams 278 Caoutchouc, India rubber 279 Guttapercha 282 Alcohols 282 Acetic acid 289 Acetates... : 291 Vegetable acids 292 Ethers 295 Cyanogen and compounds 296 Phenols 297 Carbohydrates 298 Vegetable colors 305 Albuminous substances 306 Alkaloids 308 APPLICATIONS OF CHEMISTRY. Calorific value 311 Calorific intensity 312 Glass making 314 Pottery manufacture 318 Explosives 322 Manufacture of coal gas 337 Alcoholic beverages 343 Beer making 343 Wine making 345 Distilled liquors 348 Bread making 348 Fixed oils v 352 Manufacture of soap 353 Manufacture of leather 355 Preparation of cheese 359 ESSENTIAL PRINCIPLES OF CHEMISTRY. The science of chemistry has for its object the study of the nature and properties of all kinds of matter and endeav- ors to classify the changes which matter undergoes. Nearly all substances accessible to man are of a compound nature, and may be decomposed or separated into simpler forms of matter, these simpler forms being" generally very different from the original substances — thus, water is a compound sub- stance and may be separated into its constituents which are gaseous bodies, oxygen and hydrogen. Common salt is a compound, one of its constituents being a white solid and the other a yellowish colored gas. Those substances which thus far have not been separated into simpler forms of matter are called elementary substances or simply elements. The terms chemical affinity, chemical attraction and force of affinity, have been used to designate that force by virtue of which substances enter into combinations and form compounds. The compounds which are formed under the influence of affinity generally have properties entirely different from those of their constituents. The force of affinity must be clearly distinguished from other forces exerted between all descriptions of matter, such as cohesion, which binds together the individual particles of the same body, and adhesion which designates the attraction existing between the particles of different bodies, as the ad- hesion of a liquid to glass; other effects are also observed which come under the head of molecular actions. From all these, chemical attraction is distinguished by the complete change of character which follows its action; it might be defined as that property of matter by virtue of which new bodies are generated. This property of matter is concerned in all chemical changes, and chemistry may be defined as the science which investigates the relations ivliicli affinity estab- lishes betiveen bodies, determines the laivs governing its action, and examines the character and constitution of the substances which result from its operation. Chemical changes perma- nently affect the properties of bodies, and physical do not. There are at present recognized seventy-two elementary bodies bnt only sixty-two of this number have been obtained in the free state. The existence of the others is established from spectroscopic indications and from an examination of their compounds. Of the total number fifty-six are usually classed as metallic and the others as non-metallic. This divis- ion is in part arbitrary since the divisions graduate into each other. The accompanying table classifies the elements as above stated, the most important being distinguished by heavier type and italics. These substances present every variety of physical char- acter, state of aggregation, etc., some are solid, some liquid and some gaseous ; some are light, others heavy, some occur in the free state and others only in combination. About six- teen elements make up ninety-nine hundredths of all known matter. Table of Elementary Bodies, with Their Symbols and Atomic Weights. Metals, Isolated. NAME. SYMBOL. ATOMIC WEIGHT. NAME. SYMBOL. ATOMIC WEIGHT. Aluminium, Al. 27.0 Magnesium, Mg. 24.0 Antimony,* Sb. 120.0 Manganese, Mn. 54.0 Barium, Ba. 137.4 Mercury, Hg. 200.0 Bismuth,* Bi. 208.9 Molybdenum, Mo. 95.5 Cadmium, Cd. 112.0 Nickel, Ni. 58.0 Caesium, Cs. 132.6 Osmium, Os. 198.5 Calcium, Ca. 40.0 Palladium, Pd. 105.7 Cerium, Ce. 140.4 Platinum, Pt. 194.4 Chromium, Cr. 52.0 . Potassium, K. 39.1 Cobalt, Co. 58.9 Rhodium, Rh. 104.0 Columbium (orNio- Rubidium , Rb. 85.3 bium ) , Cb. 93.8 Ruthenium, Ru. 104.2 Copper, Cu. 63.2 Silver, Ag. 108.0 Didymium, Di. 145.4 Sodium, Na. 23.0 Gallium, Ga. 70.0 Strontium, Sr. 87.4 Glucinum (or Be- Thallium , Tl. 203.7 ryllium ) , Gl. 9.0 Thorium, Th. 233.4 Gold, Au. 196.2 Tin, Sn. 117.7 Indium, In. 113.4 Titanium, Ti. 48.0 Iridium, Ir. 192.7 Tungsten, W. 183.6 Iron, Fe. 56.0 Uranium, U. 239.8 Lanthanum, La. 138.5 Vanadium, V. 51.3 Lead, Pb. 206.9 Zinc, Zn. 65.0 Lithium, Li. 7.0 Zirconium, Zr. 89.4 Metals, not Isolated. Decipium, Dp. 159.0 Tantalum, f Ta. 182.0 Erbium, E. 166.0 Terbium, Tr. 148.8 Holmium, Ho. 162.0 Thulium, — 170.4 Samarium, Sm. 150.0 Ytterbium, Yb. 89.1 Scandium, Sc. 44.0 Yttrium, Y. 172.8 Non=Metals. Argon, 40.0 Iodine, I. 126.6 Arsenic, As. 75.0 Nitrogen, N. 14.0 Boron, B. 10.9 Oxygen, O. 16.0 Bromine, Br. 79.8 Phosphorus, P. 31.0 Carbon, C. 12.0 Selenium, Se. 78. S Chlorine, CI. 35.5 Silicon, Si. 28.2 Fluorine, F. 19.0 Sulphur, S. 32.0 Hydrogen, H. 1.0 Tellurium, Te. 128.0 *Because of their chemical properties Antimony and Bismuth might with propriety be classed as non-metals. fTlie existence of this body is beyond doubt, but its certain isola- tion has not been accomplished, though it is sometimes classed with the isolated metals. LAW OF FIXED OR DEFINITE PROPORTIONS. The relative weights of the constituent elements in any chemical compound are fixed— or, the same compound always contains the same elements in the same proportions by weight. This was the first general law governing chemical action discovered; it was recognized before but not fully estab- lished until the beginning of this century. Thus in 100 pounds of water, which is a compound of oxygen and hydro- gen, there are always 88.889 pounds of oxygen and 11.111 pounds of hydrogen. In 100 grains of lime which is a compound of calcium and oxygen there are always 28.571 grains of oxygen and 71.429 grains of calcium. The same fixity of proportions exists among the constituents of all compounds. It is the law of definite proportions which so clearly distinguishes true chemical compounds from mere mechan- ical mixtures ; in the first the constituents are always in fixed proportions, in the mixture they may be in any proportions; in a mixture the ingredients may generally be distinguished and separated by mechanical means alone, but such means are not alone sufficient to distinguish or separate the con- stituents of a chemical compound. Again, as has been stated, in a chemical compound the properties of the con- stituents have entirely disappeared, but in a mixture the properties of the ingredients exist in varying degrees depending upon the proportions of the ingredients them- selves. SOLUTIONS AND ALLOYS. Although these distinctions characterize true chemical compounds and mechanical mixtures there are classes of bodies such as solutions and alloys in which these distinc- tions do not so plainly exist. Bodies in these states appear 9 to be in less intimate condition than trne chemical union and more so than that of mechanical mixture. These bodies (solutions, alloys, etc.) graduate imperceptibly on the one hand into true chemical compounds and on the other into mere mixtures. The law governing" the formation of such bodies is not known. The word compound in the text is always used to indicate a true chemical compound — that is, one in which the proportions of the constituents are invar- iable and otherwise characterized as above stated. LAW OF MULTIPLES. The same elements generally unite in more than one pro- portion forming different compounds, in such cases the proportions of the elements produce simple ratios; the law may be more specifically stated as follows: when two todies, A and B unite in several proportions the different quantities of B which unite ivith a fixed quantity of A bear a simple ratio to each other, thus the several quantities of sulphur which unite with the same quantity of potassium are to each other as the numbers 1, 2, 3, 4 and 5 and the same numbers give the different amounts of oxygen which unite with the same quantity of nitrogen, as illustrated in the following tables : POTASSIUM. SULPHUR. NITROGEN. OXYGEN 2.438 1 1.75 1. 2.438 2 1.75 2. 2.438 3 1.75 3. 2.438 4 1.75 4. 2.438 5 1.75 5. This is the second general law governing chemical ; that was established m iction THE ATOMIC THEORY. The above law was discovered by Dalton of Manchester, and his writings show that lie had observed it as early as 1802. From his investigations during 1803 and 1804 he 10 gained a clear conception of the law and it is involved in the results at which he arrived, though it was not published until 1805. At about the same time, and largely by the consideration of the same data that established the Law of Multiples, Dalton was led to propose the Atomic Theory, which was first published in 1807. This theory, as conceived by Dalton, asserts that all simple bodies are composed of small indivis- ible particles, or atoms, the atoms of any element having all the same weight, which is different from the weight of the atoms of all other elements, and chemical compounds result from the combination of atoms of different substances. The law of definite proportions and the law that the quantities of one element which can unite with a constant quantity of another increase successively by well defined steps and not continuously, or the law of multiples, are both reasonably explained by this theory; in the first case it is only necessary to conceive that the substance always contains the same number of atoms of each of its elements, in the second case more than one compound between two elements can result only by the successive additions of one or more entire atoms. The weight of the particle of the new body formed by the union of atoms was by Dalton held to be equal to the sum of the weights of the atoms entering it. The above is the substance of Dalton' s Atomic Theory. In its essential points it has been strengthened by the subse- quent test of experimental research and in its expanded form is the basis of the developed chemistry of to-day. The atoms in Dalton's theory were assumed to be indivisible, but the chemistry of to-day merely asserts that they have not been divided and not that they cannot be. The particles of matter resulting from the combination of the same or different kinds of atoms are now termed molecules. The same kind of atoms combining form a mole- cule of an elementary substance, while different kinds form 11 a molecule of a compound substance. The chemical concep- tion of molecules is thus clear and defined : The molecule is the smallest mass of the substance which retains all and only the qualities of the substance itself. The body is but an aggregate of molecules, each of which has properties identical with those of the body itself If the molecule of a compound substance be resolved into its con- stituents the properties of the compound are destroyed. The atoms ,are the smallest individual masses yet known to enter the molecules. They do not ordinarily exist sepa- rately, but are combined with the same or different kinds of atoms, forming, in the first case, elementary and, in the second, compound molecules; compound molecules them- selves sometimes unite forming 1 molecules of still greater complexity, or molecules of the second order, or even higher orders. CHEMICAL NOTATION. Elements. The atomic theory is expressed in the nota- tion employed in chemistry. The symbols of the elements are given in the second column of the preceding table. The symbols employed are the first letters of the Latin names of the elements, a second letter being added when the names of more than one element begin with the same letter. These symbols represent atoms of their respec- tive elements, the different atoms of different substances having different weights as already stated. Several atoms of the same element are represented by placing a coefficient before the symbol or a numeral to the right and below, thus three atoms of hydrogen are represented by 3H or H 3 . Compounds. A molecule resulting from the combination of atoms of different kinds is represented by placing the symbols of the atoms in juxtaposition, thus, a molecule of common salt, a compound of sodium and chlorine, is repre- sented by NaCl. 12 If more than one atom of either element enters the molecule it is shown by placing" the corresponding" numeral to the right and below the symbol of the element, thus a molecule of water is a compound of one atom of oxygen and two of hydrogen and is represented by OH 2 . When it is desired to indicate several molecules the numeral is placed as a coefficient or the molecule is enclosed in brackets and the numeral placed to the right, thus, three molecules of water would be represented by, 30H 2 or (OH 2 ) 3 . A combination of molecules is sometimes indicated by their juxtaposition with a comma between, thus the combination of zinc oxide (ZnO) and sulphuric oxide (S0 3 ) is indicated by ZnO,S0 3 ; to indicate a group of such molecules they are enclosed in brackets and a coefficient placed to the left, thus 3(ZnO,S0 3 ). Combinations of molecules, however, are more generally indicated by grouping the symbols of the elements involved and placing the proper numerals to the right and below to show the number of atoms of each element which enter ; thus the compound above would be written ZnS0 4 . A molecule of water (OH 2 ) combining with a molecule of sulphuric oxide (S0 3 ) would form a molecule represented by S0 4 H 2 . Again, C0 2 combining with OH 2 would give C0 3 H 2 . These molecules are multiplied by placing a coefficient in front as, 2ZnS0 4 , 3S0 4 H 2 , 5C0 3 H 2 , etc. 13 NOMENCLATURE. The names of the elements correspond to no fixed rule. Some are named in allusion to a certain property, or to a cir- cumstance connected with their discovery or history. The names of the more recently discovered metals end in um and several of the more recent non-metals in ine, as sodium, potassium, platinum; chlorine, bromine, etc. Binary Compounds. Compounds are termed binary, ternary, quaternary, etc., according* as they contain two, three or four elements. Binary compounds of metallic and non-metallic elements are usually named by changing" the termination of the non-metallic element into ide — thus, compounds of oxygen, chlorine, sulphur, etc., with metals are called respectively oxides, chlorides, sulphides, etc., as potassium oxide, sodium chloride, lead sulphide, etc. The same method of naming holds in binary compounds of non- metallic elements; the termination of the more distinctly non-metallic element is changed into ide, thus a combination of S and O forms a sulphur oxide, of H and CI a hydrogen chloride, of C and O a carbon oxide, etc. Oxides. The oxides are very numerous and important and for convenience are divided into two principal classes. The first class contains all those oxides whose chemical properties are similar to those of the oxides of K, Na, Pb, etc., and are called basic oxides. The second class contains all those oxides whose chemical properties are similar to the oxides of S, C, P and N, etc., and are called acid oxides; generally the oxides of the metals are basic and of the non-metals acid. Some of the acid and basic oxides are capable of uniting directly and forming compounds called salts, thus when the oxide of sulphur (S0 3 ) in vapor, is passed over heated barium oxide (BaO), combination ensues and a salt called barium sulphate (BaS0 4 ) is formed. There is also an inter- mediate group of oxides designated as neutral oxides because 14 of their slight disposition to enter into combination; man- ganese dioxide (Mn0 2 ) is an example of this class. These neutral oxides may also be formed from non-metals ; water (H 2 0) and carbon monoxide (CO) are examples. These classes are not separated by distinct lines but graduate into each other; the same oxide may sometimes exhibit either acid or basic properties according to circumstances. Again, although the most characteristic basic oxides are oxides of the metals, yet some of the higher metallic oxides exhibit acid properties and some of the metals form only acid oxides. Oxy- Acids. Most of the acid oxides unite readily with water forming compounds called oxy-acids, which possess to a marked degree the properties termed acid, such as sour taste, corrosive action, the power of reddening certain blue vegetable colors and yet more important, the power of exchanging the hydrogen which they contain for a metal and forming salts. Thus the oxide of sulphur (S0 3 ) called sulphuric oxide, unites energetically with water (OH 2 ) form- ing sulphuric acid, the formula for which is SOJI 2 . Again the oxide of nitrogen (N2O5), called nitrogen pentoxide, will unite with water forming nitric acid (N 2 6 H 2 ) or 2N0 3 H. Carbon dioxide (C0 2 ) also unites with water forming (C0 3 H 2 ) carbonic acid. Sulphuric or nitric acid will act upon zinc and exchange its hydrogen for the metal and form a salt called zinc sulphate or zinc nitrate. The property of exchanging their hydrogen for a metal is the most character- istic property of acids and will be referred to again. It is now seen that salts may be formed in two ways, either by the direct union of basic and acid oxides or by the replacement of the hydrogen in an acid by a metal. Prefixes. Binary compounds of oxygen following the law of multiples are distinguished as mono, di, tri, etc., ac- cording to the degree of oxidation, a compound intermediate between a monoxide and a dioxide is called a sesquioxide, as 15 CrO, chromium monoxide; Cr0 2 , chromium dioxide; CrOs, chromium trioxide; Cr 2 3 , chromium sesquioxide; etc. Binary compounds of the other elements under the same law are designated in the same way, as, monosulphide, monochloride, disulphide, dichloride, etc. etc. Suffixes. When an element forms but two oxides they are also often distinguished by placing before the word oxide the name of the element with the termination ous for the lower, and ic for the higher oxide, thus Sulphurous oxide, S0 2 . Sulphuric oxide, S0 3 . Carbon dioxide, C0 2 . These same terminations are also used to specify the two more important oxides of an element even when it forms more than two oxides, thus, the basic salifiable (salt forming) oxides of iron are FeO, ferrous oxide, Fe 2 3 , ferric oxide. The salts which are formed from such oxides have the same terminations, as ferrous and ferric salts. It has been stated that the acid oxides unite with water, forming oxy-acids, and that these acids may form compounds called salts, by exchanging their hydrogen for a metal. If the name of the oxide terminates in ous the name of the acid formed by its union with water also terminates in ous, thus Sulphurous oxide unites with water and forms sulphurous acid; Nitrous oxide unites with water and forms nitrous acid; Phosphorous oxide unites with water and forms phos- phorous acid. 16 The salts which result from these acids by exchanging their hydrogen for a metal, have the termination ite — thus, salts from sulphurous acid are called sulphites, from nitrous acid, nitrites; as, lead sulphite, potassium nitrite, etc. If the oxide terminates in ic the acid formed by its union with water has the same termination — thus Sulphuric oxide unites with water, forming sulphuric acid; Nitric oxide unites with water, forming nitric acid; Phosphoric oxide unites with water, forming phosphoric acid; Carbon dioxide unites with water, forming carbonic acid, etc., etc. The salts which result from the oxy-acids ending in ic, by an exchange of hydrogen for a metal, have the termination ate, thus salts from the last named acids are sulphates, nitrates, phosphates, respectively — as lead sulphate, potas- sium nitrate, etc. In naming binary compounds, the Latin prefixes uni, bi, ter, etc., are sometimes used instead of the Greek, but the latter are more generally employed. Hydr acids. The acids above referred to are all oxy-acids and it was once supposed that all acids contained oxygen. We now know that there are bodies possessing all the properties of acids which do not contain oxygen, they all, however, contain hydrogen and they are capable of exchang- ing this hydrogen for a metal and forming salts. Some of the acids which contain no oxygen are composed of hydro- gen and one other element. There are only a few such examples, some of them are — hydrochloric acid (HG1), hydrobromic acid (HBr), hydrofluoric acid (HF), sulphydric acid (SH 2 ). The salts formed by replacing the hydrogen in the hydracids by a metal are named in accordance with the rule for binary compounds. Thus, when the hydrogen in hydrochloric acid is replaced by zinc, we have zinc chloride 17 — if potassium replace the hydrogen, in hydrobromic acid, we have potassium bromide, etc. The above system of nomenclature is the one most generally followed, but there are slight departures from it by certain chemists. The principle of the system is that the composition . of the compound shall be briefly expressed in its name. In addition to this, many substances have popular names which will be found in the text, or have been other- wise named as will be subsequently explained. CHEMICAL REACTIONS. Nearly all chemical changes result from the reciprocal action of chemical agents upon each other and are therefore called reactions. Those substances which differ most in chemical properties act most readily upon each other. From the definition of molecules it is evident that these changes take place among the molecules, and although these mole- cules are invisible it should be appreciated that whatever chemical changes occur in the bodies must come through an alteration of their molecules. By means of the symbols given we can represent the changes which occur. Reactions are usually represented by equations, in the first member of which are placed the symbols of the substances employed called reagents, and in the second member the symbols of the products obtained. Reactions consist either in the direct addition or separation of elements, or in the substitution of an atom of one element for one or more atoms of another element, or of a group of atoms of one molecule for a similar group of another. We thus have first, synthetical reactions in which a more complex body is formed by the union of simpler bodies; in this case the bodies should be opposed in properties. Thus— BaO+S03=BaS0 4 Pb+0=PbO. 2 18 Second, analytical reactions, as when calcium carbonate is heated it yields calcinm oxide and carbon dioxide, thus — CaC0 3 heated=CaO+C0 2 . In this class a more complex body is broken into simpler ones. Third, metathetical reactions, in which the transforma- tion of previously existing compounds is brought about either by simple substitution or double decomposition, thus — Zn+2HCl=ZnCl 2 +H 2 NaCl+AgN0 3 =AgCl+NaN0 3 . In the case of double decomposition, if the body desired be a salt, one of the reagents must contain the acid part and the other the basic part of the salt desired. These equations are but the expressions of observed facts, and their truth is known from observation, and not from deduction. They express only the known results from known premises and give no indication of the complex phenomenon of the reaction itself. They represent the distribution of weights before and after chemical change. In every reaction, since there is only a change, and not a loss or destruction of matter, the total weights of matter in the two members must be the same, as also must be the total number of atoms of each and all the elements. Some substances occur native, but the majority of them are obtained by one or the other of the above methods. The most common reactions are of the metathetical kind. Affinity has been defined as a property of matter by which new compounds are formed. It is frequently con- ceived to be the cause of chemical action and hence termed the force of affinity. It is essentially concerned with action between atoms but also extends to action between molecules. Without limiting the conception of affinity it is convenient to adhere to the practice of designating it as a force. There are conditions and circumstances under which reactions 19 occur more readily than others and the force of affinity may be said to vary with conditions, and except under entirely known conditions it is entirely impossible to predict the result of an experiment. As illustrating- the above state- ments we may refer to certain adventitious circumstances which influence chemical actions or their results. CONDITIONS AFFECTING AFFINITY. Insolubility. It is a rule almost without exception that when two soluble salts, containing the constituents of an insoluble, or sparingly soluble one, are brought together in solution the salts decompose each other and the less soluble salt is formed. This rule may be illustrated by bringing together in solution ammonium carbonate and calcium chloride, when the calcium carbonate will be formed and precipitated, as indicated by the reaction: (NH,) 2 C0 3 +CaCl 2 =CaC03+2NH 4 Cl. Volatility. In many instances when hvo salts, containing the constituents of a volatile one, are heated together the volatile one is produced and driven off. This is illustrated when calcium carbonate and ammonium chloride are heated together, ammonium carbonate is formed and volatilized. CaC03+2NH 4 Cl (heated) =CaCl 2 +(NH 4 ) 2 C0 3 . Again, certain acids or acid oxides which are volatile may be displaced by others of feebler attraction, but which are not volatile. Solution. The force of affinity acts only at insensible distances and whatever tends to prevent the closest prox- imity of the molecules tends to prevent action. Owing to cohesion in solids and the distance between the particles in the gaseous state, neither of these is most favorable to chemical action. In solution cohesion is slight, and the distance between particles is small, and this is the mosl favorable state for chemical action, consequently it is often 20 desirable to bring one or both of the bodies to a state of solution. Of the other causes which affect the force of affinity we may mention Temperature, for at one temperature mercury unites with oxygen, and at a different temperature the oxygen separates from it. Physical Surroundings. If the vapor of water be passed over heated iron filings it is decomposed and iron oxide is formed; on the other hand, if hydrogen gas be passed over heated iron oxide it reduces it to the metallic state, while the vapor of water is reformed. 3Fe+40H 2 =Fe 3 4 +H>. H 8 +Fe 3 4 =3Fe+40H 2 . Again, if sulphydric acid gas in excess be passed over acid potassium carbonate, slightly heated, carbon dioxide is liberated and potassium sulphide formed, whereas, if carbon dioxide be passed through a solution of potassium sulphide the acid carbonate is reformed and sulphydric acid gas passes off. The nascent state is one very favorable to chemical action ; this is the condition in which bodies exist when just liberated from some combination. Thus, if free hydrogen be passed into nitric acid there is no action, but if the acid act upon zinc immersed in it the hydrogen set free decomposes a portion of the acid. Catalytic Action. This refers to effects which are ap- parently brought about by the mere presence of a body. Thus, if potassium chlorate be heated with manganese dioxide it is decomposed more easily than when heated alone. The same effect is produced by the presence of other oxides, and is probably due to the fact that these oxides pass to a state of higher oxidation and then in turn are themselves reduced. Only oxides capable of higher oxidation produce the result. 21 Disposing Affinity. This term is used to embrace an extensive class of actions which are induced by the presence of certain bodies and which would not occur in their absence. It differs from the catalytic action in that the disposing body is found to be changed at the close of the operation, while the influencing body in catalysis is not. It should be understood that these so-called cases of modified chemical action are only the statements of facts invariably observed. These facts will soon undoubtedly be included under the more perfectly developed laws govern- ing chemical action. Many examples of this action will be observed as progress is made in the course. Influence of Pressure on Chemical Action. When a body is decomposed, in a confined space, by heat, some of the products being gaseous, the decomposition will go on until the liberated gas or vapor has attained a certain pres- sure, greater or less according to the temperature. No further decomposition will then take place nor will the elements or constituent gases recombine so long as the tem- perature remains fixed; but if the temperature be raised the decomposition will begin again and continue until the vapor reaches a tension definite for that temperature, when it will again cease; if on the other hand, the temperature is lowered, recombination ensues until the tension of the remaining gases is reduced to that corresponding to the lower temper- ature. Decomposition under these conditions has been designated by Deville by the term " Dissociation." The effect of pressure is also seen in the retarding - influence it exerts in the action of acids upon zinc. If the escape of the gas which is lib- erated is prevented the action is retarded. On the other hand, there are numerous reactions which are greatly promoted by increased pressure, such as those which depend on the solution of gases in Liquids, or on the prolonged contact of substances which under ordinary cir- cumstances would be volatilized by heat. 22 RADICALS, BASES, ACIDS, AND SALTS. We are now prepared to supplement the system of nom- enclature given, to a certain extent, and to explain the use of certain terms which have long been, and still are in nse in chemistry, and to more fully define others which we have already used. Radicals. In the metathetical reactions it was indicated that the elementary atoms not only change places with each other, atom for atom, but one atom with more than one of another kind, or one with a group of other kinds or groups of atoms of different kinds with each other. These inter- changing atoms or groups appear to bear the same relations to the molecules they enter as did the atom or atoms replaced. Thus, in the following reactions — AgN0 3 +NaCl=AgCl-hNaN0 3 , AgN0 3 +NH 4 Cl=NH 4 N03+AgCl, the atom of silver is replaced in the first by an atom of sodium, in the second by the group (NH 4 ). Such groups of atoms are called compound radicals, and it is assumed that in ordinary reactions they are transferred from molecule to molecule without loss of integrity. The elementary atoms which perform similar parts in different molecules may be called elementary radicals, so that the term radical is appli- cable to both elementary atoms and groups of atoms. Only a few of the compound radicals have been isolated. They are assumed to so exist because the same group, or, at least the same proportional amounts of the same elements enter several compounds. The symbol of every compound mole- cule may be formulated into possible radicals, but unless the radicals enter several compounds there is nothing gained by the assumption. Radicals are designated as acid or basic according as they fulfill the parts of acid or basic compounds. Of elementary radicals, generally the metallic atoms are basic, and the non-metallic atoms acid radicals. Thus, in 23 NaCl the sodium is the basic and the chlorine the acid radi- cal. In ternary combinations the compounds of oxygen with the metals are usually basic radicals and the compounds of oxygen with the non-metals acid radicals. Thus, in 3K 2 0, As 2 5 , the molecule K 2 is basic, the other the acid radical; in Na 2 S0 4 the Na 2 is the basic, and the S0 4 the acid radical. Compound radicals consisting" of carbon and hydrogen only, are usually basic, but those which contain oxygen also, are generally acid. The radical NH 4 is strongly basic. The basic radicals are also called electro-positive, and the acid electro-negative radicals. Bases. This term is more general than basic oxide (already-mentioned) and includes a class of bodies desig- nated basic hydrates, simply hydrates or better hydroxides These hydrates were formerly supposed to contain water as such, but now they are believed to contain oxygen and hydro- gen in the form of hydroxyl (OH) and not in the form of water (OH 2 ). They can usually be formed from water by replacing half its hydrogen by a metallic element. Thus, 20H 2 +K 2 =2KOH+H 2 20H 2 +Na 2 =2NaOH+H 2 . These hydroxides of potassium and sodium and also those of lithium, caesium and rubidium are very soluble in water and give solutions which corrode the skin and convert fats into soaps ; they differ from the hydroxides of all other metals (except that of barium) in that they are not decomposable by heat alone. Very similar to them in chemical properties is the hydroxide of ammonium formed by dissolving ammonia gas (NH 3 ) in water. All of the hydroxides just named are called alkalies. The great similarity of ammonium hydroxide to the others named gives grounds for the assumption that the radical NH 4 exists, and that amnionic hydroxide may be formulated, X 11 ,0 1 1 just as potassic hydroxide is : K01J . 24 The hydroxides of Ba, Ca, Sr and Mg are called alkaline earths. They are less soluble than the alkalies, less caustic, and, except that of Ba, can be decomposed by heat into a metallic oxide and water. Thus, Ca0 2 H 2 +heat=CaO+OH 2 . This process may be reversed, and the hydroxide obtained by mixing the metallic oxide with water. Thus, CaO+OH 2 =Ca0 2 H 2 = Calcic hydroxide. The hydroxides of this group can also be obtained by replac- ing half the hydrogen in water by the metallic atom, thus — Ca+20H 2 =Ca0 2 H 2 +H 2 , . Ba+20H 2 =Ba0 2 H 2 +H 2 . The hydroxides of many of the other metals are still more readily decomposed by heat, and can not as a rule be formed direct from the (jxides and water. They may be obtained by adding a solution of a soluble salt of the metal to one of the hydrates named above. Thus, ZnCl 2 +2KOH=2KCl+ZnO,H,>. The hydroxides may all be regarded as compounded of metallic atoms with the radical hydroxy! (OH). Thus, KOH. Ca(OH),. 0r 2 (OH) 6 . Metallic Oxides, Basic Anhydrides. Just as hydroxides are obtained by replacing half the hydrogen in water by a metallic atom or basic radical, so the metallic oxides or basic anhydrides may be considered as formed by a replacement of all the hydrogen in one or more molecules of water by metallic atoms. Thus, K 2 +OH 2 =K 2 0+H 2 . Ca+OH 2 =CaO+H 2 . The term base in inorganic chemistry is generally applied to both hydrates and basic anhydrides and also to certain compound radicals, all of which form salts with acids, but there is a tendency to limit the term to hydroxides. Acids. The general properties of acids have already been stated, the most characteristic of which is their capacity to 25 exchange a part or the whole of the hydrogen which they contain for metallic elements or basic radicals. Some of the acids contain only hydrogen and one other element, as hydrochloric acid (HC1), hydrobromic acid (HBr), sulphy- dric acid (SH 2 ), &c, but most acids consist of hydrogen and more than one other element, as H 2 S0 4 , sulphuric acid; HN0 3 , nitric acid; C0 3 H 2 , carbonic acid; &c. The hydrogen in all these acids may be replaced in several ways — by acting on the acid with either a metal, metallic oxide, hydroxide or a metallic salt. Thus, H 2 S0 4 +Na 2 =Na 2 S0 4 +H 2 . 2HCl+ZnO=ZnCl 2 +OH 2 . HBr+KOH=KBr+OH 2 . Ca0 2 H 2 +S0 4 H 2 =S0 4 Ca+20H 2 NH 4 OH+N0 3 H=NH 4 N0 3 +OH 2 HCl+AgN0 3 =AgCl+HN0 3 . It is thus seen that although salts are sometimes formed by the direct union of a basic and an acid oxide (see page 13) they are far more generally formed by the replacement of the hydrogen in an acid, in part or whole, by a basic radical either elementary or compound. The acids without oxygen are called hydrogen acids, or hydracids, and those containing it oxygen acids or oxy -acids. The oxygen acids like the hydrates may be regarded as compounds of hydroxyl with an acid radical instead of with a basic radical. Thus, Nitric acid, N0 3 H=N0 2 (OH) ; Sulphuric acid, S0 4 H 2 =S0 2 (OH) 2 . Basicity of Acids. When an acid contains but one atom of hydrogen in its molecule replaceable by a metal or basic radical it is said to be monobasic; when two, bibasic; when three, tribasic; &c. Monobasic acids can form but one class of salts, the metal replacing the whole of the hydrogen in one or more mole- cules of the acid. Thus, 26 HC1+K=KC1+H, 2HCl+Zn=ZnCl a +H 2 . A bibasic acid may form two classes of salts, viz.: — primary or acid salts in which only half the hydrogen in the molecule is replaced, and secondary salts in which the whole is replaced; in the latter case if the hydrogen is replaced by one metal the salt is called normal, and if by two metals double. Tims, KHSO4 is an acid salt, acid potassium sulphate. K2SO4 is a normal salt, normal * KNaS0 4 is a double salt, potassio-sodic Tribasic acio^s may form three classes of salts — primary, secondary or tertiary, including' normal, double and triple, in which the hydrogen is wholly or partially replaced by one or more metals. The following list contains the most important and common inorganic acids, arranged according to basicity: MONOBASIC ACIDS. BIBASIC ACIDS TRIBASIC ACIDS. Hydrochloric, HC1. Hydric (water) OH 2 . Orthophosphoric Hydrobromic, HBr. Sulphydric, SH 2 . H 3 PQ 4 Hydriodic, HI. Sulphuric, S0 4 H 2 . Hydrofluoric, HF. Carbonic, C0 3 H 2 . Nitrous, HN0 2 . Pyrosulphuric, H 2 S 2 7 . Nitric, HNO3. Chloric, HCIO3. Acid Anhydrides. The application of the term acid oxide has been already given (page 13). Many of these oxides can be obtained by abstracting the constituents of water from acids, and hence have also received the names of acid anhydrides or simply, anhydrides. As has been stated, most of these anhydrides display great readi- ness to unite with water, forming acids. Thus, S0 3 +H 2 0=H 2 S0 4 . In this respect they bear the same relation to acids that basic oxides do to hydrates. Salts. The formation of salts by the direct nnion of acid and basic oxides, and by the replacement of the hydrogen in an acid, by different methods, have been already referred to. Now it is evident that, in the reaction between acids and hydroxides, while we considered that the hydrogen of the acid 27 was replaced by a metallic atom or basic radical, we might, with equal propriety, have considered the hydrogen of the hydrate as replaced by an acid radical, thns : KOH+N0 2 OH=KNO,+H 2 0. From these considerations it is evident that the term salt is 'a descriptive one and cannot be defined in independent lan- guage. If only a part of the hydrogen in the hydroxide be replaced by the acid radical the salt is called basic. Basic salts are also defined as those formed by the union of a normal salt with a basic oxide or hydroxide, the base thus being in excess of that necessary to form a normal salt. On the other hand, a normal salt may combine with an acid oxide so that there is an excess of acid oxide over that necessary to form a normal salt: such a salt is called an anhydro salt. EQUIVALENT WEIGHTS OR EQUIVALENTS. It has already been stated that substances may replace each other in combination and that chemical actions generally consist of an interchange between the elements of different molecules. When HC1 acts upon Zn, the zinc replaces the hydrogen, which is envolved as a gas; when potassium is thrown upon water it replaces the hydrogen of the water forming KOH; if mercury be added to a solution of silver nitrate the silver is replaced by the mercury and itself deposited. The replacement of one element by another always takes place in fixed proportions. The relative quantities of the elements which thus replace each other in combination ((re called equivalent iveights or chemical equivalents. Equivalent weights are those quantities of the elements which possess the same chemical value and are capable of filling each other's places directly or indirectly. The chemical equivalent^ are made specific by defining thou as those weights which will combine with or displace, or ((re chemically equivalent to. one part by weight of hydrogen. 28 Strictly speaking, quantities of elements could only be said to be equivalent when they had actually replaced each other in combination, but quantities of elements which are equivalent to the same quantity of another element are assumed to be equivalent to each other, thus 35.5 parts of chlorine are known to unite with 1 part of hydrogen, 23 of sodium and 108 of silver, consequently the numbers 1, 23 and 108 are the equivalent weights of hydrogen, sodium and sil- ver. In a similar way the equivalents of all elements may be expressed. These equivalents are the result of direct experiment and are based on no hypothesis as regards the constitution of matter. But in addition to the fact that many of the equiv- alent weights have to be determined indirectly there is another difficulty which arises as soon as we consider those bodies which combine in more than one proportion, thus, tin forms two chlorides in one of which 58.5 parts of the metal are combined with 35.5 parts of chlorine and in the other 29.25 parts of tin are combined with the same amount of chlorine; which of these is to be taken as the equivalent weight of tin? The same difficulty is encountered in all cases in which combination occurs in more than one propor- tion between elements, and as most bodies combine in more than one proportion the idea of equivalent weights is not definite. ATOMIC WEIGHTS. The distinction between atoms and molecules has already been given and although 'the atom is the smallest mass of matter yet distinguished, the modern chemistry does not assert that the atom is beyond the limit of divisibility, it simply asserts that it has not yet been divided and that in all Jmown chemical processes the atomic masses act as units, and it matters not what may yet be accomplished in dividing atoms, their integrity is retained in all reactions with which we are at present familiar. 29 With the promulgation of the atomic theory the deter- mination of the relative weights of the elementary masses or the relative combining" numbers became an absorbing problem. These weights are the numerical constants of the science of Chemistry — they are the essential data in all quantitative analysis as well as in the application of Chemistry to the necessities of daily life. To make possible a clear understanding of the method of determining atomic weights the student must bear in mind that although we cannot isolate and operate upon a single molecule of a body, yet in transforming a body we but transform its individual molecules and whatever change the body undergoes is also undergone by each molecule thereof and whatever relation is found to exist among the constituents of a body also exists among the constituents of a single molecule. Determination of Atomic Weights by Analysis. By ac- curate analysis we can determine the proportions of the elements which enter many compounds and consequently the proportions of the elements which enter the molecules, and if we knew the number of atoms of each element in the molecule we could deduce the relative weights of the atoms. Thus, the analysis of water shows that oxygen and hydrogen enter the molecule in the proportion by weight of oxygen =8 and hydrogen =1. If there were an equal number of atoms of each element in the molecule the numbers 8 and 1 would represent the atomic weights. Now there is another compound of oxygen and hydrogen in which the proportions by weight are oxygen = 16 and hydrogen =1. Assuming from the first compound that the atomic weights are 8 and 1 we might in the second case conclude that the compound contained two atoms of oxygen; this would then account for the new proportion 1(> to 1, but if we, with equal propriety, assume that the second compound contains one atom of each of the elements then the relative atomic weights are 1(> and 1 and the first compound, water, necessarily contains two atoms of hydrogen. 30 Thus with nothing before ns except the results of simple analysis, the atomic weights would be uncertain, they might be correct or they might be multiples or sub-multiples of the correct ones, depending upon whether or not the number of atoms which enter the molecule was correctly assumed. Determination of Atomic Weights by Substitution. The method of substituting one element for another can often be made use of to assist in reaching a correct conclusion as to the number of atoms which enter the molecule. For example, if water be treated with metallic sodium it is acted upon in such a way as to produce a substance whose composition is Sodium, Hydrogen, Oxygen 23 1 16 and if this compound be evaporated to dryness and heated with more sodium the remaining portion of the hydrogen is driven out and replaced by the sodium and we have a com- pound of Sodium, Sodium and Oxygen. 23 23 16 It is thus evident that the hydrogen in the molecule of water has been replaced by halves and it follows from the concep- tion of atoms that there must have been at least two atoms in the molecule. Now if we could be certain that the molecule contained only one atom of oxygen we would again have the atomic weights of hydrogen and oxygen to be 1 and 16. With only the data yet before us we could not certainly conclude that the molecule of water has but one atom of oxygen and hence the atomic weights would still be un- certain. Again, if we take marsh gas, a compound of carbon and hydrogen, the hydrogen may be replaced by four separate substitutions, so that there must be at least four atoms of hydrogen in the molecule of marsh gas and if it be assumed 31 that they are combined with one atom of carbon we arrive directly at the atomic weights. But as in the preceding case 1 the number of atoms of each element is not determined by substitution alone and the atomic weights would remain uncertain. Determination of Atomic Weights by Decomposition. By the decomposition of certain bodies and the formation of others it is sometimes possible to compare the amounts of a certain element in the two and if the number of atoms of the element in either be known the number in the other is also determined. The above are the only purely chemical means for the deter- mination of atomic weights and it is seen that they leave a doubt as to the correct numbers. It should be borne in mind that by a combination of all the methods and by an examin- ation and comparison of various compounds of the same element the uncertainty is very small. Thus, in the case of carbon it is indisputable that the smallest increment or decre- ment which can be made in any compound is 12 times as great as the smallest weight of hydrogen that can be intro- duced or displaced and if we adhere to the smallest separable portion as the atom, the uncertainty as to the atomic weight is exceedingly slight in the case of this and many other elements. These purely chemical methods for the determination of atomic weights have been supplemented by means dependent upon physical considerations. The coincidences between the results obtained by these different means are so satisfactory as to dispel doubt as to the correct atomic weights of the great maiority of the elements except such doubt as is due to imperfection of process. We will now explain the method of determining the atomic weight by the introduction of physi- cal considerations. 32 PHYSICAL AND CHEMICAL RELATION OF ATOMIC WEIGHTS. Law of Ayogadro. From a consideration of the relations existing between the specific gravities and the determined atomic weights of certain elements, Avogadro, an Italian, in 1811 was led to propose the hypothesis that equal volumes of all gases under like conditions of temperature and pressure con- tain the same number of molecules. The hypothesis uses the word molecule in the sense already given and involves the idea that the elements in their inter- nal structures are analogous to compounds and that the molecules of elementary bodies may contain more than one atom, and it will later appear that there are good reasons for such belief. This hypothesis has become of fundamental importance in chemistry in determining- molecular weights and settling atomic weights ; it is supported by the results of all investigations made to determine the internal structure of gases, and upon the theory of molecular mechanics it affords a mathematical explanation of the laws of compression and temperature, and if the mechanical theory of gases be accepted the hypothesis of Avogadro follows as a mathe- matical necessity; from these considerations the hypothesis is to-day justly considered a law. Accepting the hypothesis as a physical law an important corollary follows directly — viz.: The molecular weights of substances are directly proportional to their specific gravities in the gaseous state, or the actual weights of the molecules of substances are to each other as the actual weights of equal vol- umes of the substances in the gaseous state, under like 'condi- tions of temperature and pressure. Determination of Molecular Weights. It is therefore plain that the weights of the molecules of different gases may be readily obtained in terms of the weight of the molecule of any gas assumed as a standard by simply determining their specific gravities, with reference to the standard gas. It 33 simplifies the comprehension of the subject here considered to adopt hydrogen as the standard for specific gravities. To illustrate the above method, let us suppose that a vol- ume of oxygen weighs sixteen times as much as an equal volume of hydrogen, then since these volumes contain the same number of molecules the molecule of oxygen will weigh sixteen times as much as the molecule of hydrogen; or if a given volume of hydrochloric acid weigh 18.25 times as much as an equal volume of hydrogen the molecule of HC1 will weigh 18.25 times as much as the molecule of H. Now if we also take the weight of the hydrogen molecule as the standard for molecular weights the molecular weights and specific gravities will be represented by the same num- bers, thus, the specific gravity of oxygen referred to hydrogen is 16, the molecule of oxygen weighs 16 times as much as the molecule of hydrogen and if the weight of the hydrogen molecule be taken as unity the weight of the oxygen molecule is 16; therefore when hydrogen is used as the standard for specific gravities and the weight of the hydrogen molecule as the standard for molecular weights the molecular weights and specific gravities are indicated by the same numbers. Now if we should use half the weight of the hydrogen molecule as the standard for molecular weights it is evident that the molecular weights would all be double what they were when we used the whole molecule as the standard and then instead of being indicated by the same numbers as specific gravities the molecular weights would be the doubles of the specific gravities. For reasons which will appear subsequently it is found convenient to use the weight of half of the hydrogen molecule as the standard for molecular weights. For convenience, we shall, following Prof. Cooke, call the weight of the half hydrogen molecule a microcrith and in writing it shall abbreviate it to m. c. Now bearing in mind 3 34 that the molecular weights of substances are the actual weights of their molecules in terms of some standard, we may say that the molecular weights of all gases may be obtained in m. c. by doubling their specific gravities referred to hydrogen as the standard; e.g., the specific gravity of HC1 is 18.25 the weight of its molecule in m. c. is therefore 36.5 — the specific gravity of XH 3 is 8.5 and the weight of its molecule is 17 m. c. In most cases by chemical analysis we can determine accurately the proportions of the constituents which obtain in any compound, thus, in the case of water, analysis shows that it is composed of one part by weight of hydrogen to eight of oxygen, but this proportion of 1 to 8 holds also with the numbers 2 and 16, 3 and 24, 4 and 32, &x?., and from the proportion alone we cannot tell which of the numbers (9, 18, 27, 36, &c.,) is the molecular weight of water vapor, but by finding the specific gravity of water vapor (which is 9) and doubling it, we are enabled to decide that 18 is the molecular weight— that is, a molecule of water vapor weighs 18 m. c. It should be observed that the determination of the specific gravity of a compound gas is a less accurate operation than the analysis of the gas. The analysis gives an accurate num- ber (the combining number of the gas or gases under consideration) and the specific gravity merely tells what multiple of that number to take. Thus from the law of Avogadro we are enabled very simply to decide whether a number is the molecular weight or a multiple or sub-multiple of it. This method of deter- mining molecular weights is clearly only applicable to volatile substances, the molecular weights of the non-volatile substances must be determined in other ways. OTHER METHODS OF DETERMINING MOLECULAR WEIGHTS. The determination of the molecular weights of substances from their gaseous specific gravities is the most important but not the only method of determining molecular weights. Several other methods have become available but thev can onlv be here mentioned. 35 Molecular Weights from Osmotic Pressure. The mixing of dis- similar substances, gases, liquids or solids in solution, through membranous diaphragms is in general termed osmose. Membranous bodies, such as rubber, parchment, &c, permit the passage of molecules of different substances with very unequal facility. If a solution of a substance be separated from a quantity of the pure solvent by a proper diaphragm or osmotic membrane, a certain pressure will be exerted on the membrane from the side of the dissolved substance. This pressure is called osmotic pressure. It has been found that the osmotic pressure is directly proportional to the weight of the dissolved substance in a unit of volume of the solvent and this pressure varies directly as the absolute temperature of the solution. From these and other considerations it seems highly probable that equal volumes of different solutions at the same tem- perature and osmotic pressure contain the same number of molecules of the dissolved substances. From this conclusion it is possible to determine molecular weights. A solution of a solid whose molecular weight is unknown may be prepared so that its osmotic pressure is the same as that of a solution containing a known weight of a solid whose molecular weight is known, the temperatures of the solutions being the same. Then the molecular weights of the solids will be to each other as the weights of equal volumes of the solutions. Molecular Weights by Depression of Freezing Point. It has been shown that when weights of substances proportional to molecular weights are dissolved in equal weights of the same solvent, they lower the freezing point of the solvent to the same extent. From this gen- eralization it is evident that the molecular weights may be determined. This method is called the cryoscopic method of determining molecular weights. Molecular Weights by Lowering Vapor Pressure. A precisely similar law holds with regard to the effects of a dissolved substance upon the vapor pressure of the solvent. When weights of substances propor- tional to molecular weights are dissolved in equal weights of the sol- vent they lower to the same extent the vapor pressure jof the solvent. This fact may also be used to determine molecular weights. Determination of Atomic Weights from Avogadro' s Law. From what has been said it is evident that the determina- tions of atomic weights by the methods thus far given were unsatisfactory because of our inability to decide as to the number of atoms entering the molecule. It will now be shown how we may obtain other information on this point. 36 Let its compare the gaseous compounds of the elements we are studying with each other. It is evident that a compound molecule must contain at least one atom of each constituent element, therefore, if we find the smallest weight of an element in any compound we shall have found its atomic weight. Take for example the compounds of hydrogen in Table I — in the first column are given the specific gravities, the doubles of these numbers in the second column give the molecular weights in microcriths, in the third column is given the per cent of hydrogen in the molecule, or the proportion which the weight of hydrogen, in the molecule bears to the whole weight of the molecule, in the fifth column this weight of hydrogen is given in m. c's. TAELE I. Specific gravi- Molecular •weight Proportion of hydrogen. Weight of H. in Symbols. ties. m m. c. m. c. Hydrochloric acid, 18.25 36.5 •0274=3^ 1 HC1 Hydro bromic acid. 40.5 81.0 •0123-.V 1 HBr Water vapor, 9.0 18.0 .1111=/* 2 OH, Sulphydric acid. 17.0 34.0 .0588=^ o SH, Ammonia, 8.5 17.0 .1765=tV 3 NH 3 Phosphorus tri-hydride. 17.0 34.0 .0882=^ 3 PH 3 Harsh gas, 8.0 16.0 .250 =& 4 CH 4 defiant gas, 14.0 28.0 .161 =^ 4 C 2 H 4 It is thus seen that the smallest weight of hydrogen in any of these compounds is one m. c, and this is the smallest weight yet found in any compound. It also appears from the table that the amounts found in the other compounds are multiples of this small weight. TABLE II. Specific Molecular gravi- weight - in m. c. 9 18.0 14 28 22 44 32 64 40 80 16 32 Proportion ™gM Symbols. Water vapor, Carbon monoxide, Carbon dioxide, Sulphur dioxide, Sulphur trioxide, Oxygen, .8889=11 .5714=M .7272=ff •50 =ff •60 =M l.oo =u 16 16 32 32 48 Q9 OH, CO co 2 so; so; o, 37 TABLE III. Specific gravi- Molecular weight Proportion of CI Weight of 01. Symbols. ties. in m. c. m m. c. Hydrochloric acid, 18.25 36.5 •9726= ||;| 35.5 HC1 Acetyl chloride, 39.2 78.5 • .452 = ff:f 35.5 C 2 H 3 OCl Carbonyle chloride, 49.5 99.0 .717 = U 71 COCl 2 Phosphorus tri=chloride, 68.7 137.5 77 4 — tor, 5 100.5 PClo Carbon tetrachloride, 77 154 .922 =#£ 1 142 cci, Chlorine, 35.5 71 1.000 =fi 71 CI 2 A similar comparison of the compounds of oxygen and chlorine in Tables II and III, shows that the smallest amounts of these elements which enter are respectively 16 and 35.5 microcriths, and no smaller weights have ever been found to enter; again, all larger amounts are multiples of these smaller weights. These facts lead irresistibly to the conclusion that these smallest weights are our chemical units or atoms, and the larger amounts are exact multiples because they contain two or more atoms. The law of Avogadro then gives us the means of deciding as to the molecular weights of gaseous substances and by a comparison of the various compounds we select the smallest weight of an element which enters any compound as the atomic weight. The number of times this weight is contained in the other molecules gives the number of atoms of the element which enter them. It can now be seen that had we not taken the weight of the half hydrogen molecule as the standard for molecular weights it would have been necessary to express the smallest amounts of hydrogen which enter certain compounds by %. Our standard m. c. is the smallest mass of matter which has yet been separated from any compound. It is the chemical atom, and since it is the half molecule, the molecule of hydro- gen -evidently contains two atoms. It should be remembered that the atomic weights depend upon the assumption that the same proportions which exist between the constituents of any compound, exist between the 38 constituents of the molecules of said compound. Such is the only rational assumption, and these atomic weights are the relative weights of the atoms or chemical units of dif- ferent substances, or the actual weights of the different atoms in terms of the weight of the hydrogen atom taken as unity. Compounds sometimes contain the elements in other pro- portions than that of atomic weights, but the variation from atomic proportions arises from the fact that molecules, as already stated, are formed by the union of an atom of one kind with one, two or three of another kind, or two of a kind with three of another, etc., etc. These different proportions are all combining or equivalent weights, and it is clear that they must be multiples or sub-multiples of the atomic weights. When elements unite in the proportion of one atom to one of another kind, the equivalent weights are the same as atomic weights, but they are different when the atoms unite in other proportions. The relations between specific gravities and adopted mole- cular weights are not usually so exact as is indicated in Tables I, II and III. The numbers here given (specific gravities) may be considered as corrected by the results of chemical analysis. From certain of their volatile compounds, by the applica- tion of Avogadro's law, the atomic weights of the following thirty-eight elements have been determined: Aluminum, antimony, arsenic, boron, bromine, bismuth, carbon, cadmium, chlorine, chromium, copper, fluorine, gallium, hydrogen, indium, iodine, iron, lead, mercury, molybdenum, nickel, nitrogen, osmium, oxygen, phosphorus, selenium, silicon, sulphur, tantalum, tellurium, thorium, titanium, tungsten, vanadium, zinc and zirconium. By this method alone four of the elements named (alum- inum, copper, gallium and iron) have atomic weights double those usually assigned them. 39 Number of Atoms in Elementary Molecules. When the atomic and molecular weights of an element are known it is evident that the quotient of the latter by the former gives the number of atoms in the molecule. The molecular weights of thirteen of the elements have been determined from their specific gravities in the gaseous state and thence the number of atoms in their molecules. The elements referred to are given in the subjoined table together with the relation between their atomic and molecular weights : Molecular Weight Elements. Atomic Weight Number of Atoms in Molecule. Cadmium, 1 Mercury, 1 Zinc, 1 Hydrogen, 2 Chlorine, 2 Nitrogen, 2 Tellurinm, 2 Oxygen, 2 *Bromine, 2 x Iodine, 2 x Selenium, 2 x SuIphur, 2 Phosphorus, 4 Arsenic, 4 It is thus seen that cadmium, mercury and zinc are monatomic and phosphorus and arsenic are tetratomic, the others were diatomic under the conditions of the experiments. Those elements marked with an asterisk varied in specific gravity with certain variations of tempera- ture. Thus, sulphur at a lower temperature had six atoms in a mole- cule and iodine at a higher temperature than that employed in the table had one atom in the molecule. Most of the elementary bodies thus appear to be diatomic. That this conclusion is involved in the law of Avogadro max also be seen from the following consideration. It is known that one volume of hydrogen combines with one volume of chlorine to form two volumes of PIC1 — from the law, each o\' the two volumes of HC1 contains as many molecules of 11(1 as each of the original volumes contained molecules of H 40 and CI respectively ; now snppose that the volumes of H and CI each contain n molecules of H and CI respectively, the two volumes of HC1 must each contain n molecules, and as each molecule of HC1 must contain at least one atom of H and one of CI, there must have been at least 2n atoms of each of these elements, and consequently two atoms to each of the n molecules. In the same manner by considering' the fact that one volume of oxygen combines with two volumes of hydrogen to form two volumes of water vapor, we arrive at the conclusion that the molecule of oxygen contains two atoms and by similar considerations of certain of their com- pounds the molecules of nitrogen and sulphur may be shown to contain two atoms. These are unavoidable conclusions from the law of Avogadro, but there is also some independent evidence that certain molecules of ele- ments contain two atoms. Thus it was found that carbon burned in the protoxide of nitrogen produces more heat than when burned in oxygen. A natural explanation of this fact is found in the supposition that it requires more heat to decompose the molecule of oxygen (it being composed of two atoms) than it does to decompose the molecule of the protoxide of nitrogen. Again, the nascent state which has been referred to as favorable to chemical action may be conceived to be due to the uncombined condition of the elementary atoms when just liber- ated from some previous combination. Thus, when hydrogen gas is passed through nitric acid it produces no chemical change. The molecules above referred to each have two atoms, but such is not the case with all elementary molecules. Again, the relations between the specific heats of gases at a constant volume and a constant pressure are not exactly what they should be from a consideration of the external work done ; it requires more heat to raise the temperature of a gas under constant volume than it should, in proportion to that required under constant pressure. Now it may be supposed that a portion of the heat is consumed in the first case in producing a motion among the particles of the molecules which does not appear as change of temperature, and if the supposition be correct then the discrepancy referred to should not be observed in a gas whose molecule contains one atom. The relation between the specific heat of mercury vapor at a constant pressure and constant volume was found to accord exactly with theory, which seems to be a physical proof that the mercury molecule has but one atom. 41 Isomorphous Relations. Bodies which crystallize in the same or in very similar forms are said to be isomorphous, and the fact that many compounds of similar chemical constitution do crystallize in the same form led some chemists to believe that the same crystalline form assured the same atomic constitution of the respective molecules of the substances, that an equal number of atoms arranged in the same way or united in the same way, gave the same crystalline form. It is now known that when the term isomorphism is used in the above sense the conclusion is not warranted. If in addition to the same crystalline form we impose the con- dition that the bodies under consideration must be capable of replacing each other in the same crystal without destroy- ing the form, the idea of isomorphism becomes much more restricted and the conclusions which result from its applica- tion in fixing atomic weights are generally satisfactory. Thus, it is known that aluminum and oxygen unite in only one proportion, 18.3 of aluminum to 16 of oxygen, but this same proportion exists in the numbers of aluminum and OXYGEN. 36.6 32 54.9 48 73.2 64 and the atomic weight assigned to Al will depend upon the constitution assigned to the oxide — if the oxide be a OXYGEN. ALUMINUM. monoxide we shall have Al O 16 18.3 dioxide we shall have Al 2 32 36.6 trioxide we shall have Al O a 48 54.9 sesquioxide we shall have Al 2 Oa 48 ] wi\ The numbers in the last column are the weights which must be assigned to the atom of aluminum according to the several modes of constitution indicated in the first column. 42 The constitution of the oxide alone does not enable us to deeide between the different formulas, but as the aluminum oxide is isomorphous with the sesquioxide of iron it is assumed to be a sesquioxide and its atomic weight thus becomes fixed as 27.4. The utility of this law is limited in application to groups of closely allied substances and its indications become more valuable when connected with conclusions from other physical laws. The law of isomorphism was first enunciated by Mitscherlich in 1819. Yolume Relations of Elements and Compounds. Under the law of Avogadro we have seen that when hydrogen is used as the standard for specific gravities and the half hydrogen molecule as the standard for molecular weights, the specific gravities of gases are the halves of their mole- cular weights. As most elementry gases are diatomic it follows that the atomic weights and specific gravities of elementary gases are given by the same numbers — one-half their molecular weights. Since specific gravities are given by the weights of equal volumes it follows that equal volumes of elementary gases contain atomic proportions by weight. Atomic proportions being the proportions which combine it likewise follows that the combining volumes of all diatomic elementary gases are equal, and if we conceive the smallest combining volumes of such gases to contain only one atom we reach the conclusion that the ultimate combining volumes of elementary gases occupy equal spaces, or atoms of elementary gases occupy equal spaces. From the above relations it is readily seen that the number of volumes of the diatomic elementary gases which combine to form a com- pound gas are indicated by the number of atoms of each element which enter the molecule of the compound gas. Thus, to form HCl there are required 1 vol. H and one vol. CI NH 3 there are required 1 vol. N and three vols. H OH 2 (water vapor) there are required 1 vol. O and two vols. H 43 Research widely extended has proven that with a few exceptions, which may yet disappear, the molecules of com- pound gaseous bodies occupy twice the space of the hydro- gen atom, no matter how many atoms of the elementary gases enter the compound molecule. Thus, each of the molecules HO, NH 3 , CH 4 , C 2 H 4 , CO, &c, occupies twice the space of the hydrogen atom. Since the same proportions exist between the quantities of the elements which form the whole body as do be- tween the quantities which form the molecule, it follows that no matter how many volumes of elementary gases com- bine to form a compound gas of the first order, they are all condensed to two volumes in the compound. All molecules, whether of the first or a higher order, occupy equal spaces, hence the same law of condensation holds in combinations of higher order than the first. This law of condensation is illustrated in the examples below. 2 vol. H +1 vol. O give 2 vol. water vapor = OH 2 2 vol. CI +1 vol. O give 2 vol. hypochlorous anhydride = C1 2 2 vol. N +1 vol. O give 2 vol. nitrogen protoxide = N 2 1 vol. CI + 1 vol. H give 2 vol. hydrochloric acid gas = HC1 1 vol. N +3 vol. H give 2 vol. ammonia = NH 3 2 vol. CO + 2 vol. Clgive 2 vol. carbonyl chloride = COCl 2 2 vol. C 2 H 4 + 1 vol. O give 2 vol. ethene oxide = C, H , O Apparent Exceptions to the Law of Volumes. — From the foregoing considerations it is seen that the molecules of gaseous bodies are believed to occupy equal spaces, twice the space occupied by the hydrogen atom, and that their vapor densities referred to hydrogen are the halves of their mole- cular weights. There are a few apparent exceptions to this law, but the exceptions are believed to be due to molecular changes which take place in the bodies under the influenceof heat during the determination of their vapor densities, and that there is no occasion as yet to doubt the validity of 44 Avogadro's law. Among the bodies which were first thought to be exceptions may be mentioned PCls, NLLC1 and C 2 H 4 2 . The quotient obtained by dividing the atomic weight of a simple body by its density is called the atomic volume, and that obtained by dividing the molecular weight of a body by its density is called the molecular volume. If matter were continuous these quotients would give the relative volumes of atoms and molecules. Specific Heats and Atomic Weights. The investigations of Pettit and Dulong in relation to the specific heats of the solid elements developed the fact that their specific heats are very nearly inversely proportional to their atomic weights, so that if atomic proportions, by weight, of these different elements be taken the quantity of heat to change the temper- ature of these proportions through equal intervals is the same in all. In the following table a number of the solid elements are arranged according to their determined specific heats, begin- ning with those having the greatest: — H A HX A Lithium, 0.941 7 6.6 Sodium, 0.293 23 6.7 Aluminum, 0.214 27.4 5.9 Potassium, 0.166 39 6.5 Iron, 0.114 56 6.4 Nickel, 0.109 59 0.4 Copper, 0.0952 63.4 6.0 Zinc, 0.0955 65.2 6.2 Silver, 0.0570 108 6.2 Tin, 0.0562 118 6.6 Gold, 0.0324 197 6.4 Platinum, 0.0324 197.4 6.4 Lead, 0.0307 207 6.4 In the 1st column are the specific heats, in the 2nd the atomic weights and in the third the product of these num- bers; water is taken as the standard of specific heats. This table exhibits the inverse relation existing between atomic 45 weights and specific heats and the products all fall between the numbers 5.4 and 6.9 — the mean value when all the solid elements are considered is usually given as 6.4. It is true that there are variations from this number but the variations are slight and are probably due to the causes which influence the thermal condition of bodies and render the exact determ- ination of specific heats uncertain. Since the announcement of Pettit and Dulong in 1819, that the atoms of all elements have the same capacity for heat, or the same specific heat, many facts have been accum- ulated in favor of the generalization and render it very probable that it is correct. This number (6.4) is frequently called the atomic heat of elements. This law gives us a ready means for the determination of the atomic weights of elements when their specific heats are known, it being only necessary to divide the number 6.4 by the specific heat. However, the difficulty of determining specific heats accurately, limits very much this method of arriving at atomic weights, but the law enables us to decide with certainty between two or more possible hypotheses. We have seen that analysis will give the proportions of the constituents of a compound with a great degree of accuracy and if we can decide as to the number of atoms of the respective elements in the compound the atomic weights become known, e. g.: analysis shows that silver chloride con- tains 108 parts of silver and 35.5 parts of chlorine — with only this fact we can not tell whether there be one or more atoms of silver, but by dividing 6.4 by the specific heat of silver (.057) we get 112 a number so nearly coinciding with the result of analysis as to show beyond doubt that there is but one atom. As the result of analysis is more reliable than the determination of specific heat we accept 108 as the weigh! of the atom of silver — the specific heat merely deciding us as to the number of atoms in the compound. 46 The specific heats of the elementary bodies have not been determined at any common temperature, so that the values found are not strictly comparable. The specific heats of the elements generally vary with the temperature, but there are certain temperature-intervals, different for the different elements, between the limits of which the specific heats are nearly constant. For this interval only is the law of Dulong and Pettit true. The following forty-nine solid elements have had their specific heats determined directly : Aluminum Cobalt Magnesium Selenium Antimony Copper Manganese Silicon Arsenic Didymium Mercury Silver Boron G-allium Molybdenum Sulphur Beryllium Gold Nickel Sodium Bismuth Indium Osmium Tellurium Bromine Iodine Palladium Thallium Carbon Iridium Phosphorus Thorium Cadmium Iron Platinum Tin Calcium Lanthanum Potassium Tungsten Cerium Lead Rubidium Uranium Chromium Lithium Ruthenium Zinc Zirconium With but few exceptions the product of the specific heat into the atomic weight is approximately equal to 6.4, all fall- ing between 6 and 7. The exceptions are boron, beryllium, carbon, gallium and silicon. The application of the law of equal atomic heats has been found in many instances to extend to chemical compounds in the case of bodies of similar atomic composition. In such cases the products of the specific heats into molecular weights are nearly constant and are equal to as many times 6.4 as there are atoms in the molecule. If the law were of general application to compounds it would give us obvious means for the determination of the number of atoms in a molecule and a method of general application in determining atomic weights. But the law is not of general application to compounds and can only be used to a limited extent in determining atomic weights. 47 In the case of the solid elements when their specific heats are deter- mined under specified conditions it may be considered that there arc no exceptions to the law of Pettit and Dulong, so closely do the products of the atomic weights and specific heats approximate to a common number. The difficulty of determining: how much of the heat trans- ferred to gases and compounds is consumed in performing internal and external work and how much in simply affecting temperature, renders it as yet impossible to bring them under the general law. It is a reasonable expectation that this will be done as our knowledge of molecular structure increases. VALENCY OR QUANTIVALENCE. We have already seen that the atomic and equivalent weights of some of the elements are the same, and in others that the atomic weight is some multiple of the equivalent weight. In other words that atoms of certain elements can only replace or combine with atoms of other elements in the proportion of one to one, in other cases this equivalency or substitution can occur in the proportion of one atom to two or more of another kind — thus, chlorine, bromine and iodine always combine with hydrogen in the proportion of one atom to one, oxygen and sulphur one atom to two of hydrogen, and when sodium acts on hydrochloric acid each atom of sodium replaces one of hydrogen, as Na+HCl=NaCl+H, with zinc under the same circumstances each atom replaces two of H, as Zn+2HCl=ZnCl 2 +H 2 . This difference of combining or replacing power has been called vale ncy, quantivalence and atomicity. The first term is deemed best and will be adhered to — the second may be used with pro- priety — but the third should not be used in this sense. If we select the hydrogen atom as the standard of refer- ence the valency of any other element is known by the number of hydrogen atoms that its atom is equivalent to in the sense just given. The elements have been classed according to degree of valency as univalent, bivalent, trival- ent, &c, and are also called monads, dyads, triads, tetrads, pentads, &c The elements of even valency are also called artiads and those of uneven valency perissads. The valency 48 is sometimes indicated by putting dashes or Roman numerals after the symbols of the elements, thns — O n , C IV , P v , &c. Another method of indicating the valencies of elements and the manner in which they are supposed to be satisfied in combination is by graphic formulae thns, water may be rep- resented by H— 0— H and carbon dioxide by o=c=o, marsh gas by H I H— C— H. I H These are called graphic or structural formulae and indicate nothing more than the degree of valency of the elements and the manner in which they may be supposed to be sat- isfied in combination. The valency of an atom as shown by its replacing power corresponds exactly with that shown by its combining power — that is, an atom capable of replacing a certain number of monad atoms is also capable of combining with the same number — thus the atom of zinc which is capable of replacing two atoms of hydrogen is also capable of combining with two atoms of CI, or Br — monad elements. This property of valence is inherent to radicals, already defined, as well as to elements, and is manifested when they change places in reactions with other radicals or elementary atoms; some radicals are capable of combining with or replacing one monad atom and others more than one. In the above graphic formulae it is seen that the units of valency of each atom are represented as satisfied by com- bination with units of valency of other atoms; such com- pounds are called normal or saturated compounds and in the molecule of such a saturated compound the sum of the perissad atoms is always an even number. This is the Law 49 of even numbers and it is of necessity true in saturated compounds, from the above definition of such compounds. To form a saturated molecule it is not however necessary that the units of valency of each atom shall combine with the units belonging to atoms of different elements, they sometimes combine with those of other atoms of the same element, thus — c — c c — c — c III III III . II III H3 H 3 H 3 H 2 H 3 which are saturated hydro-carbons.* By considering the above formulae it is evident that if an atom of any kind could be removed the balance of valency would be destroyed and a certain number of units of valency would be left unsatisfied — thus if from the saturated mole- cule CH 4 we remove one atom of H, we get the compound CH 3 , from S0 3 remove one atom of O and we get S0 2 . These unsaturated molecules constitute the compound radicals already referred to and the valency of a compound radical may generally be said to equal the valency of the atom or atoms which the saturated molecule may be considered to have lost. As already stated, it is only a few of these non- saturated molecules that exist in a free state, as CO, S0 2 , &c, in other cases two of the unsaturated molecules combine with each other, and then again they appear as transferable compounds in chemical reactions without isolation. The tendency of unsaturated radical molecules to combine with each other seems to be analogous to the action of the atoms of elementary bodies — since we have seen that these ele- mentary atoms seldom exist in the free state but are com- bined in pairs. It may also be stated that generally the combined radicals which exist separately have an even valency. *It is evident from this consideration that there is a lack of pre- cision in the definition of a "saturated molecule." Other definitions have been proposed but are upon the whole not more satisfactory. 4 50 Variable Valency. The valency of an element is not a fixed and unvarying property. Many of the elements exhibit varying" degrees of valency as is especially shown by their varying degrees of combining power — thus tin forms two compounds with CI — viz.: SnCl 2 and SnCh and phosphorus forms PC1 3 and PC1 5 , numerous other examples might be given. Compounds formed under these varying influences are often as different from each other as are the compounds of different elements and hence arises the difficulty of classifying the elements according to their valency. How- ever, of the different degrees of valency shown by the same element some one degree is generally more common and the compounds resulting from its action more permanent than any other and in several elements, as H and the alkaline metals, the valency has been found invariable. Of the multivalent elements the variation in valency usually takes place by a loss or gain of two units of valency, so that the possible conditions of the same element are usually all even or all odd, thus, CI may be univalent, trivalent, quinquivalent and septivalent. 8 may be bivalent, quadrivalent or sexvalent. It is at present impossible to account for these variations but as a general rule the compound in which the valency of a polygenic element is most completely satisfied is the most stable and the others tend to pass into this one. From these considerations it is evident that the valencies of most of the elements are not fixed and the conditions of the variations are not known. From a consideration of all the facts the most logical conclusion is that the valency is, like affinity, a relative property of the atoms, depending upon a variety of causes, among which may be classed the mutual influence of the atoms on each other, the relative quantities of the acting substances and the temperature. It may also be observed that the theory of valency reiterates the law of multiples, which is the simple statement of an experimental fact. Valency and Affinity. Valency and affinity are properties inherent in the atoms and as yet understood, are distinct and different properties. Affinity has reference to the force with which atoms or molecules attract each other and is approxi- 51 mately estimated by the thermal effects of their combina- tions. Valency has reference only to the saturating capacity in combination or replacement and irresistibly introduces the idea of arrangement of atoms in the molecule. The abstract idea of valency has reference only to the numerical capacity of saturation, but the concrete conception sees each body characterized by a particular order in combination and every molecule of a definite structure. The theory of valence then finds application in expressing the relations between the atoms of molecules and in allowing conception of the relative constitution of bodies. Again, from knowledge of the more common valency of elements the theory is of great importance in expressing all ordinary reactions, the results of the general laws of combination. RELATIONS BETWEEN THE ATOMIC WEIGHTS AND PROPERTIES OF THE ELEMENTS. Although atoms are hypothetical masses and are beyond direct observation, their relative weights, as has been stated, are the con- stants of chemistry and are indispensable to analysis and stochiome- trical research. It now seems possible that these numbers may become equally important in all branches of physical science, for recent investi- gations point to an interdependence, more or less complete between the atomic weights and physical properties of the elements. In 1815, Prout brought forward the view that the matter of which all elements are composed is hydrogen and that the atomic weights of all other elements are entire multiples of the atomic weight of hydrogen and this has been known as Prout's Law. The investigations of Stas of Brussels, undertaken for the purpose of testing Prout's Law are frequently held to invalidate it, but so large a majority of the atomic weights are so nearly exact multiples of that of hydrogen, that it can hardly be the result of chance, and Prout's view is still believed by many chemists to have a high degree of probability. It has also been long known that the atomic weights of many allied elements have certain simple numerical relations, but New- lands was the first to point out the fact that the elements, when arranged in numerical order of their atomic weights, exhibit a periodic recurrence of similar properties. This Law of Periodicity may be illustrated by a consideration of the first fourteen elements after hydro- gen, and is most evident if we consider the atomic volumes of the solid elements in connection Avith their atomic weights. The atomic volume, as already stated, is obtained by dividing the atomic weight by the density of the clement. The elements referred to are here arranged in order of their atomic weights and immediately beneath each is written its atomic volume, then its density. Li = 7 Gl = 9.0 Bo=n C=12 X=14 0=16 V =11.9 5.6 4.0 3.6 o o D = 0.59 1.64 2.6s 3.3 Na =23 Mg=24 Al =27.3 Si=2S P=31 S=32 V =24 14 10 11 16 16 52 Fl=19 o Cl=35.5 27 D =97 1.75 2.67 2.49 1.S4 2.06 1.38 The atomic volumes of the elements thus gradually decrease tow- ard the middle of the series and then increase. The densities of the elements increase toward the middle and then decrease. The volatili- ties of the elements also diminish toward the middle and then increase. The more common valencies of the elements increase toward the mid- dle of the series and then decrease. In addition to these properties others, as the malleability, fusibility, conductivity, refractive power and heat of combustion, also apjjear to be closely connected with their atomic weights. Mendelejeff and others have shown that the entire list of elements can be thus arranged in series and that the properties of the elements are in periodic relations with their atomic weights. The classification of the elements cannot be properly discussed without a fair knowledge of the subject matter of chemistry, and this discus- sion is accordingly not essential to that knowledge, but the proba- bilities in favor of the Periodic Law are great, and it promises, at no distant day, to furnish a new basis for physical investigation as well as for a classification of the elements. STOCHIOMETRY. That class of chemical computations which can be made from a consideration of the numerical relations of atomic weights and the volume relations of elements and compounds is called stochiometrical. From a knowledge of preceding principles many such computations are possible. It has already been stated that the symbols of the respective elements represent atoms and that the atoms of different elements have cliff erent weights — that the molecular weights of substances are the sums of the weights of the atoms in their respective molecules. In the most limited sense chem- ical symbols represent atomic weights of their respective elements in terms of the weight of the H atom, but in a more general sense, in all equations, reactions and formula^ they stand for quantities proportional to atomic weights and when the amount by weight of any one element in a formula or 53 equation is given the amounts of all the others become known. Percentage Composition. Thus, the formula for water is OH 2 and from the relations expressed in the formula if either the amount, of H or O is assumed the amount of the other element is also known. From the formula of a substance it is evident that we may also readily compute its percentage composition — thus, the formula of alcohol is C 2 H 6 — the molecular weight is 46, hence in 46 parts by weight of alcohol there are — 24 of C 6 of H 16 of O 46 hence in 100 parts we should have for C 46 : 24: :100 : x= 52.18 for H 46 : 6: :100 : y= 13.04 for O 46 : 16: : 100 : z= 34.78 100.00 Having given the percentage composition of a substance we can also readily determine the numerical relations exist- ing among the atoms but not necessarily the actual number of atoms in the molecule — thus the percentage composition of acetic acid is C = 40 H = 6.67 O = 53.33 100.00 since these numbers are the relative weights of the elements in the substance if we divide them by the atomic weights the quotients will express the relations existing among the num- bers of atoms of the different elements. Performing the division referred to we have for the numerical relation of atoms Kj-i.M 0.6.67 Os.33 54 which is evidently the same as Ci H 2 Oi. Empirical and Molecular Formulae. The simplest expres- sion for the numerical relations existing among atoms of a molecule of a substance is called its empirical formula; that is to say, when we express the numerical relation among the atoms by the smallest numbers possible ; thus above CiH 2 Oi is the empirical formula for acetic acid. The same relations exist among the numbers of atoms whether the formula be GH 2 Oi, C 2 H 4 2 , or C 3 H 6 3 , &e. The formula which gives the exact number of atoms of each of the elements which enters the molecule of a sub- stance is called the molecular formula. It can not be com- puted with certainty from the percentage composition alone, but if the molecular weight of the substance is known the problem admits of definite solution, for from the molecular weight we know the sum of the atomic weights and can decide which of the formulae expressing the numerical rela- tions among the atoms is the molecular formula. Thus, in the example above the molecular weight of the acetic acid is 60, hence it is evident that of the possible formulae C 2 H 4 2 is the molecular formula of the acid. The molecular formula is always the same as, or a multiple of, the empirical formula. Problems Inyolving Weights. Since, as has been said, in the most general sense the symbols represent quantities pro- portional to atomic weights and formulae represent quantities proportional to molecular weights it is easy to determine the amounts of the various substances indicated in any equation when the amount of any one is assumed. For this purpose it is only necessary to express the atomic and molecular weights of the different terms of the equation and simple proportions will solve the problem. Thus, in the equation Zn+2HCl=ZnCl 2 +H 2 . 55 expressing* the action of Zn upon HC1, suppose we assume that Zn stands for 10 ounces of zinc — then to determine how much HC1 is indicated we proceed as follows: the atomic weight of Zn=65.2 and the molecular weight of HC1=36.5. The reaction indicates that for the transformation of 65.2 parts of Zn there are required 2x36.5=73.0 parts of HC1 — hence the amount to transform 10 parts of Zn would be determined by the proportion 65.2 : 73 : : 10 : x. The amounts of the other substances involved in the reaction under the supposition that 10 ounces of zinc are employed would be determined in exactly the same manner. It matters not whether some of the terms of the equation are simple atoms or whether all the terms are composed of molecules. The molecular and atomic weights of the different terms express the relations existing between the amounts of the substances employed in the reaction and from these relations the amounts of all the substances indicated can be determined when the amount of any one is assumed. Problems Involving Volumes. All of the above solutions depend upon the numerical relations of atomic weights but a chemical equation expresses not only relative weights but also relative volumes of the reagents and products when in a state of gas. We have seen that all gaseous molecules occupy equal spaces and that gaseous atoms occupy one half the space of the molecule, coupling these facts with the principles of notation explained it is evident that the relative numbers of volumes in an equation of gaseous terms can be read off directly — thus 2CO+0 2 =2C0 2 and CH 4 +0 4 =C0 2 +2H 2 0. In the first equation, since molecules occupy equal spaces, it is seen that the number of volumes of CO a is the same as the number of volumes of CO and the number of volumes of O 56 involved is one half that of the other gases. — In the second equation the relative volumes are, one of CH 4 , two of O, one of C0 2 and two of OH 2 (vapor of water). It is often desirable to pass from volumes to weights or the reverse in the case of gaseous bodies. The problem is so simple as to require only the statement that in the first case we multiply the number of volumes by the weight of a unit of volume and in the second case we divide the weight by the weight of a unit of volume; volumes, of course, being always taken under standard conditions of temperature and pressure. CHEMISTRY OF THE NON-METALS AND THEIR COMPOUNDS. OXYGEN. Oxygen is the most abundant and widely distributed of the chemical elements. It exists in the uncombined state in atmospheric air forming" about one-fifth of its volume ; it is there mixed with nitrogen which constitutes nearly the entire bulk of the remaining four-fifths. In the free state oxygen is an essential to all forms of life. In the combined form it is an important constituent of most of the mineral and organic substances. In this form it constitutes eight-ninths, by weight, of water and about one- half, by weight, of silica and of the various silicates and limestones, which compose by far the greater portion of the earth's crust. Oxygen was discovered by Priestly in England in 1774 and called by him dephlogisticated air. In the folio wing- year it was independently discovered by Scheele in Sweden. It was named oxygen by Lavoisier. Physical Properties. Oxygen is a gas tasteless, odorless, colorless, and perfectly transparent. It is slightly soluble, water at 60° F. dissolving about .03 of its volume. By great pressure and low temperature it has been liquefied and by further cooling solidified. Its specific gravity referred to hydrogen is given by its atomic weight; it is thus seen to be slightly heavier than atmospheric air; when liquefied it is lighter than water. 58 Chemical Properties. Oxygen is remarkable for the wide range of its chemical action. With the exception of bromine it forms compounds with all other elements and with the exception of six elements it unites directly (that is without the intervention of a third substance). These combinations as already stated are called oxides and the process is termed oxidation. The combination of oxygen with the other bodies is always accompanied by the development of heat but if the oxidation is very slow the heat may not be perceptible. If the oxidation be sufficiently rapid to produce light and heat it becomes a case of combustion. Combustion in a general sense is any chemical action accompanied by heat and light ; all ordinary cases of com- bustion in air are processes of oxidation, the light and heat being the result of the chemical union of the oxygen with the body burned. In most cases an elevation of temperature is necessary to bring about the union of oxygen with other substances; with some bodies at ordinary temperature it unites slowly without sensible elevation of temperature, and with a few rapid oxidation takes place producing com- bustion. Action on Non-Metals. Among the non-metals phos- phorus is the only element that combines with oxygen at the ordinary temperature. In the air it gives off white fumes and emits a pale phosphorescent light. It is then under- going oxidation and if it be finely divided true combustion will result. This may readily be accomplished by dissolving a little phosphorus in carbon disulphide and pouring the solution on blotting paper; when the solvent evaporates, the finely divided phosphorus exposes a large surface to the action of the air, and the paper being a bad conductor the temperature rapidly rises and brilliant combustion results. In warm air a very slight elevation of temperature will cause phosphorus to burn and this is sometimes brought about by 59 the oxidation of the outside particles; phosphorus must accordingly be handled with great care. Phosphorus produces a bright light when burning in the air but the brilliancy is greatly increased when it is burned in pure oxygen due to the more rapid combustion and consequent higher temperature. All substances which burn in air burn far more readily in pure oxygen. By the combustion of phosphorus in air phos- phoric oxide is produced (P 2 5 ) which may be seen to rise in clouds from the burning phosphorus. This oxide is readily absorbed by water forming phosphoric acid. If a piece of wood charcoal be heated to redness at a single point and be plunged into a jar of oxygen brilliant combustion takes place, the oxygen combining with the car- bon producing carbon dioxide (C0 2 ) which is a colorless gas. Pure carbon has to be heated very highly before it will com- bine with oxygen and then the combustion is unattended with flame. Sulphur burns in air with a blue light when its tempera- ture is raised to about 500° F. In pure oxygen the brilliancy is much increased ; in each case the product of combustion is sulphur dioxide (S0 2 ) which readily unites with water form- ing sulphurous acid. Action on Metals. Several of the alkaline and alkaline earth metals (potassium, sodium, lithium, barium, calcium, and strontium) are readily oxidized in the air. Other of the common metals as iron, lead, and mercury are scarcely acted upon by dry air, and gold, silver, and platinum not at all. Under the influence of high temper- ature many of the metals burn readily. A magnesian ribbon will burn in air if the end of the ribbon be heated in a Bun- sen burner; the light is almost insupportable to the eye. The burning of iron is also easily accomplished and is best shown in a small way by wrapping one end of a softened steel watch spring spirally around a little cylinder of char- 60 coal and attaching the other end to a suitable holder, igniting the charcoal and plunging the whole into a jar of oxygen. It burns very brilliantly sending off a shower of sparks. The black oxide of iron Fe 3 4 is produced by the combus- tion. Zinc may be burned by a precisely similar arrangement giving (ZnO) zinc oxide. Iron can be prepared in such finely divided form that when exposed to air it will take fire spontaneously; it is then called pyrophoric iron. The preceding illustrations which might be extended indefinitely are all cases of oxidation, and it is seen that oxidation may or may not produce the phenomenon of com- bustion. All ordinary combustion in air is but the oxidation of the body burned, oxygen being the sustaining principle of such combustion and also of animal life. All bodies which burn in air burn with increased splendor in pure oxygen. It is well here to recall the important fact already stated that the oxides of the non-metals are generally acid oxides and of the metals basic oxides. The former when acted upon by water give the substances which we have defined as acids and the latter tend to neutralize these acids. So general is this tendency of the metallic oxides that any substance which forms a basic oxide may be defined as a metal, though it is not decided that every metal forms a basic oxide. Preparation of Oxygen. For laboratory and experimental purposes oxygen is most readily prepared from potassium chlorate (KC10 3 ) or manganese dioxide (Mn0 2 ). From either of the substances oxygen may be obtained by heating in suitable apparatus the results being indicated by the follow- ing reactions; KC10 3 (heated) =KCl+0 3 , 3Mn0 2 (heated) = MntOt+Oi. To accomplish these results a higher degree of heat is required than is convenient and it is customary and advisable to mix with the chlorate from one-fourth to one-fifth its F.G.I. Prepay P. F u „ fa. Bel 61 weight of the oxide when the liberation of oxygen takes place at a lower temperature than when either substance is used alone. The mixture of potassium chlorate and man- ganese dioxide may be heated in a glass retort or Florence flask, the retort or flask being closed by a perforated cork into which fits a short glass tube. A rubber tube connects with the glass tube and serves to convey the gas to a gas holder or to a jar filled with water standing on a bee-hive shelf. The manganese dioxide, or pyrolusite as it is called in mineralogy, is not changed in this operation. The action of the manganese dioxide comes under the term of catalytic action and is not thoroughly understoood but the oxide prob- ably passes to a higher state of oxidation and is then reduced. Oxygen may also be prepared by the decomposition of water (H 2 0) by electricity. In some laboratories both oxygen and hydrogen thus obtained are kept on hand in large holders, the electricity being supplied by dynamo- machines. Oxygen may be prepared on a large scale directly from the atmos- phere by passing a current of air over a mixture of caustic alkali and manganese dioxide ; alkaline manganates are thus formed. By passing steam over the heated manganates they are resolved into the original constituents with the liberation of oxygen. The operation can be made continuous. There are many other methods by which oxygen may be prepared. Priestly when he discovered oxygen obtained it from the red oxide of mercury. OZONE. Ozone was discovered by Schonbein in 1840. It appears to be a modified form of oxygen in which it is believed that there are three atoms in the molecule instead of two as in ordinary oxygen. Accord- ing to Avogadro's law it should be one and a hall' times as heavy as common oxygen and this has been determined to be the case by exper- iment. It exists in very small quantity in the atmosphere and is found in the purer air of the country or the seaside more than in thickly pop- ulated places. It has been estimated to constitute not more than one volume in a million volumes of air. 62 Physical Properties of Ozone. Under ordinary conditions ozone is a transparent gas showing a bine tinge when viewed along a glass tube a meter in length. The color deepens by pressure. The gas has a peculiar and distinct odor. It is more easily liquefied than pure oxygen and the liquid has a blue color. When heated to 300° F. ozone is converted into oxygen with an increase of half a volume. Chemical Properties. Ozone is chemically much more active than oxygen combining with many substances that oxygen will not affect. It will decompose potassium iodide liberating the iodine. In the pre- sence of alkalies it will unite with nitrogen and convert it into nitric acid. It will oxidize silver and also a solution of indigo, bleaching the latter; ordinary oxygen does not act upon these substances. Ozone acts upon many organic substances and it is to this fact that its bene- ficial effect in the air is attributed. In most cases of oxidation the remaining oxygen appears to be the same in volume as the original ozone. Air highly charged with ozone can not be breathed with im- punity, its action on the system resembling that of chlorine. Preparation of Ozone. Ozone is produced by the passage of electric sparks through the air or oxygen and is generally observed by its odor when a spark electric-machine is operated in the air. It is also pro- duced during the decomposition of water by electricity, by the slow oxidatioD of phosphorus and turpentine in the air. This latter fact has been suggested as an explanation of the acknowledged salubrity of pine regions. The presence of ozone may be detected by bringing into it a piece of paper moistened with a solution of starch and potassium iodide; the ozone liberates the iodine which gives a blue color with the starch. The test however does not insure the presence of ozone as certain other substances will have the same action, among these are chlorine, bromine, and nitrogen dioxide. HYDROGEN. Hydrogen rarely occurs in a free state under terrestrial conditions, though it has been found to a limited extent in certain volcanic emanations, in the gases given off by oil wells, and occluded in certain meteorites. The spectroscope has shown it to be present in the atmosphere of several of the heavenly bodies, especially the sun. Hydrogen was discovered by Cavendish in 1766 and called by him inflammable air; it was subsequently named hydrogen by Lavoisier. 63 Physical Properties. Hydrogen is a transparent gas, taste- less, colorless, and odorless. It is the lightest substance known. Water is 11160 times as heavy as hydrogen at G C. It is not poisonous though animals can not live in this gas alone, oxygen being necessary to life. Hydrogen being the lightest substance known it is conveniently taken as the standard for the specific gravity of gases — that is to say the standard to which other gases and vapors are referred. Owing to its great lightness hydrogen can be collected by downward displacement or poured upward from one vessel to another; on account of this property it is employed for filling balloons. Hydrogen is slightly soluble, water dissolving .02 of its volume at 0° C. and 30" barometric pressure. By great pressure and cold, hydrogen has been liquefied, giving^ a steel blue liquid. The conducting power of hydro- gen for heat is, according to Magnus, greater than that of any other gas. Another remarkable physical property is its great power of passing through animal and vegetable mem- branes and porous substances generally. This property is called diffusive power and it is a physical property common to all gases and vapors. The diffusive powers of gases are found to be inversely proportional to the square roots of the densities of the gases. Hydrogen accordingly diffuses far more rapidly than any other gas; because of this property hydrogen is more difficult to confine than any other gas. It will leak through a stop cock which will retain oxygen and nitrogen and it cannot be kept long in rubber bags, blad- ders, &c. The diffusive property of gases causes them to fill uniformly any space in which they may be placed. It also causes gases to mingle uniformly even against the force o\' gravity; thus if two vessels one containing oxygen the other hydrogen, be connected by a narrow tube with the oxygen below, in a short time they will be uniformly mixed. 64 The same result follows with any two gases that do not act chemically upon each other. The remarkable diffusive power of hydrogen may be shown by the following experiment — take an unglazed porous cup (a common bat- tery cup answers well) and close the open end with a cork through which extends a glass tube ; then invert this cup and insert the tube into a tightly sealed bottle arranged with a jet tube as shown in figure I. By placing a glass jar containing hydrogen over this cup the liquid may be forced out of the lower vessel in a jet several feet high. In this experiment the oxygen in the lower vessel passes out through the, porous pot into the hydrogen jar, but the hydrogen passes in much more rapidly and the pressure of the hydrogen added to that of the oxygen in the bottle drives out the water. The true diffusion of gases depends upon the motion of their molecules, but this diffusion is often complicated by the nature of the septa through which diffusion takes place. If the diaphragm exerts an adhesive or liquefying action on the gases, or if it is moistened with any liquid which exerts a solvent power on them, the simple diffusion passes into osmose or osmotic action. These processes are very important in nature; by true diffusion the uniform composition of the atmosphere is mainly maintained and the accumulation of noxious gases prevented, by osmose the function of respiration is per- formed and the aeration of the blood accomplished. Certain of the metals as platinum and palladium possess the power of absorbing and condensing within their pores large vol- umes of some of the gases. This action is called occlusion of gases. Certain meteorites have been found to contain a large amount of hydrogen indicating that they have come from regions where hydrogen exists at greater pressure than in our atmosphere. The terms osmose and diffusion are also applied to the processes by which substances dissolved in liquids pass into solutions of less density through diaphragms or against the force of gravity. Chemical Properties of Hydrogen. The chemical proper- ties of hydrogen cause it to combine readily with several of the non-metals but it shows little if any disposition to combine 65 with metals. The most evident chemical characteristic of hydrogen is its disposition to burn in oxygen. These gases may be mixed in any proportion and they will not act on each other at ordinary temperature, but if a jet of hydro- gen issuing into oxygen or air be touched with a flame it takes fire and burns producing great heat but very little light, the flame being barely visible. The result of the com- bination of hydrogen and oxygen is water as may readily be shown by holding a glass tube over the flame when moisture rapidly deposits on the side of the tube. Since hydrogen is inflammable and burns in the air it might be expected that it would not support the combustion of bodies which burn in oxygen. This may be proven by inserting a lighted taper into an inverted jar filled with hydrogen. The flame of the taper will be extinguished and the hydrogen will take fire and burn at the mouth of the jar. If a mixture of oxygen and hydrogen in certain propor- tion be raised to the temperature of ignition, which can be done by an electric spark or a flame, chemical union at once follows attended by violent explosion. This property of the gases makes great care necessary in experimenting with a mixture of them. Hydrogen weight for weight, produces more heat in burn- ing than any other substance. One pound of the gas in burning to water produces 34,462 units of heat. The explo- sion of the mixture of hydrogen and oxygen is of course due to the high temperature which results from the great heat of the chemical union, the heat expanding greatly the water vapor formed by the combination. The most violent explo- sion occurs when the gases are mixed in the proportion of two volumes of hydrogen to one of oxygen a fact shown by the formula of water. If air be used instead of oxygen the explosion will be less violent due to the presence of the inac- tive nitrogen. Owing to its tendency to combine with oxygen when 66 heated, hydrogen will take oxygen from many other bodies containing* it. This removal of oxygen is designated as a reducing or deoxidising process and the body accomplishing it is called a reducing or deoxidizing agent. Tims most of the metallic oxides are reduced at a red heat by hydrogen, which is one of the best reducing agents; for example CuO+H 2 =Cu+H 2 0. On the other hand a body which gives oxygen to another body is called an oxidizing agent. Preparation of Hydrogen. The process by which hydro- gen is usually prepared for laboratory purposes is to act upon dilute sulphuric acid with zinc. The zinc decomposes the acid with liberation of hydrogen and formation of zinc sulphate as indicated by the following reaction Zn+H 2 S0 4 = ZnSOd-H 2 . For this purpose the zinc is cut into small strips or granulated by pouring melted zinc into water from a moderate height ; a greater surface is thus exposed for con- tact with the acid. If the sulphuric acid is too strong the zinc sulphate formed does not readily dissolve off the zinc and the chemical action is retarded or stopped. On the other hand if the zinc be pure, it will scarcely act upon the acid; the action is generally facilitated by lead or other metal impurities which have an electrical effect not yet described. This method of preparing hydrogen can be followed in common Woullf bottles, shown at A in the figure. The zinc is put into the bottle and the acid added at B ; the hydrogen is passed out at the tube C and collected by displacement as described under oxygen. Hydrochloric acid may be used to replace the sulphuric in this process or iron may be used instead of the zinc, but the hydrogen from iron is generally less pme than that from zinc. Hydrogen may also be prepared by passing steam over iron turnings contained in a tube heated to redness. The !i 1 11 V Fia.3 *WWf to £w*fc. 67 oxygen of the steam combines with the iron and the hydro- gen passes on through the tube — 3Fe+4H 2 0=Fe304+4H 2 . It will be observed that the physical properties of hydro- gen place it with the non-metals while the chemical proper- ties ally it to the metals. NITROGEN. Nitrogen occurs free in the atmosphere of which it constitutes about four-fifths, oxygen constituting nearly the whole of the remaining one-fifth. It also occurs in the volcanic gases, in the atmosphere of the sun, and in certain nebulge, and has been found in meteorites. In the com- bined form it exists as nitrous and nitric acids, in the compounds of ammonia, and in the organisms of plants and animals. Nitrogen was discovered by Rutherford of Edinburgh in 1772. Physical Properties. Nitrogen is a colorless, transparent, odorless, and tasteless gas. Water at 60° F. dissolves less than .015 its volume. By great cold and pressure it has been liquefied and solidified. Chemical Properties. In its chemical deportment nitro- gen is very inert. It combines directly with only a few elements among which may be mentioned silicon, boron, magnesium, carbon, oxygen, and hydrogen; with the last named it combines when one or both elements are in the nascent state to form ammonia (NIL). It has no positive poisonous properties but is incapable of supporting respiration or combustion, oxygen being essential to these processes. Its presence in the atmosphere moderates the action of pure oxygen. The slight affinity existing between nitrogen and the other elements gives a characteristic property to its com- pounds many of which are very unstable; thus the nitro- 68 genized principles of plants and animals are prone to decomposition and many artificial compounds of nitrogen are highly explosive. Preparation of Nitrogen. Nitrogen is generally obtained in small quantity by burning phosphorus in air confined over water. A porcelain capsule containing phosphorus is floated on the water, the phosphorus is ignited and the whole covered with a bell jar. The burning phosphorus unites with the oxygen forming phosphoric oxide (P 2 5 ) which after a time is absorbed by the water. In larger quantity it may be prepared by passing air over finely divided copper heated to redness in a porcelain tube. The oxygen is removed by the copper. One of the easiest methods of preparing pure nitrogen is to heat in a glass retort potassium nitrite and ammonium chloride — KNCU+NH 4 C1=KC1+2H 2 0+N 2 . ATMOSPHERIC AIR. The gaseous envelope surrounding the earth consists essentially of a mixture of nitrogen, oxygen and argon together with small but variable quantities of carbon diox- ide (C0 2 ), and water vapor with traces of other substances due to accidental or local causes ; among the latter may be mentioned ammonia (NH 3 ), marsh gas (CH 4 ), sulphuretted hydrogen (SH 2 , and sulphur dioxide (SO,), the last two may generally be detected near cities and towns. Argon has been only recently discovered and constitutes about one per cent, of the atmosphere. The thickness of the earth's envelope is estimated to be about forty-five miles measured from the earth's surface. The air probably extends beyond this height but is in an extremely rarefied condition. Physical Properties. The density of the air according to the law of Boyle rapidly diminishes with the height. Due to its weight the atmosphere exerts a pressure on all bodies. The assumed average pressure of the atmosphere at the sea 69 level has been generally adopted by engineers as the unit of pressure and this unit is named an atmosphere. The pres- sure is generally expressed in terms of the barometric col- umn, that is the height of the mercury column which the air will support. In British measure an atmosphere is equivalent to the pressure of 29.905 inches of the barometer at 32° F. at Lon- don and is very approximately 14.73 pounds on the square inch of surface. In the metric system the atmosphere is .00032 greater than in the British. For all ordinary chemical calculations it may be taken that water is 773 times as heavy as air, both taken at common standard temperature and pressure. Composition of the Atmosphere. We owe to Cavendish, 1781, the first accurate determination of the proportions of the essential constituents of the atmosphere (N and O). These gases are mixed in the air very approximately in the proportion of 21% of oxygen and 79% of nitrogen by volume and 23% of oxygen and 77% of nitrogen by weight. There is but very little variation in the proportions of these constit- uents from whatever source the air is obtained. The proportion of the oxygen and the nitrogen can be very approximately found by passing air over very finely divided copper contained in a glass tube, carefully weighed, and heated to redness ; the nitrogen is made to pass into an exhausted globe. The increase in weight of the tube gives the weight of the oxygen and of the globe the nitrogen. The other two all pervading constituents of the air are water vapor and carbon dioxide; these vary with conditions. Carbon Dioxide of the Air. The amount of carbon diox- ide (C0 2 ) in the air varies slightly with the locality and with the season, being greater nearer centres of population than in the country and greater in winter than in summer. In the country a greater amount has been found in the air at nigh.1 70 than during the day, the difference being due to the different action of plants during the day and night; this diurnal varia- tion is not observed at sea. The amount of carbon dioxide in normal air is from three to four volumes in 10000. In cities, in winter and especially, in heavy fogs which prevent diffusion, it may rise to six or seven volumes in 10000. The amount of carbon dioxide though relatively very small is actually very great. Upon this gas the vegetable kingdom is dependent for its existence; plants by the aid of sunlight decompose the carbon dioxide retaining the carbon and returning the oxygen to the air. On the other hand all animal respiration and all ordinary combustion take oxygen from the air and return to it carbon dioxide. Owing to this cyclic process the change in the proportion of these constituents in the atmos- phere must be very slow. The quantity of aqueous vapor in the air is far less constant than the carbon dioxide. This quantity varies primarily with the temperature of the air as already ex- plained in the subject of heat. The other important circum- stances which affect the quantity are the prevailing direction of the winds, the configuration of the land, and the nearness of the bodies of water. Upon the average the aqueous vapor is from 1 to 1.5 volumes to 100 of air. Other Gaseous Constituents of the Air. Ozone can nearly always be detected in normal air and its presence is more common in the purer air. Hydrogen dioxide is also very generally present in the air and its chemical actions are in many cases analogous to those of ozone and it is difficult to distinguish between the two. Ammonia or more gener- ally its carbonate is nearly always present in minute but variable quantity in the air. The ammonia results from the decomposition of tlie organic matter and in the presence of moisture combines with the carbon dioxide and other acids present in the air; the nitrates and nitrites of ammonium are sometimes from this source present in the atmosphere. Other gases occur locally in minute quantities in the air, the most common of which have already been mentioned as sulphuretted hydrogen, sulphur dioxide, and marsh gas. 71 Solid Constituents of the Air. In addition to its gaseous constituents, minute particles of solid matter are suspended in the air and generally termed dust. Atmospheric dust is made up both of inorganic and organic matter. The in- organic matter is composed of various mineral compounds. The organisms are the propagators of mould, mildew, fermentation and putrefaction, and it is probable that the last named are the agencies through which certain diseases are spread. COMPOUNDS OF HYDROGEN AND OXYGEN. WATEE. Water is the most important compound of hydrogen and oxygen. With the exception of the air no substance is so indispensably necessary to terrestrial life as water. Its distribution is only second to that of the air and its absolute amount is enormously greater. Water is the cause of many of the most striking physical phenomena in nature and its uses for economical and domestic purposes are innumerable. Besides the enormous quantities which are spread over the surface of the earth and distributed as vapor through the air, it is an important constituent of all living beings and of many minerals. The composition of water was first discovered by Cavendish in 1781. Physical Properties of Water. Many of the physical properties of water are well known, a few will be men- tioned here. Thick layers of water have a blue color. Water has greatest density at 4° C. or 39.4° F. In freezing water expands by .09 of its volume so that eleven volumes of water become twelve volumes of ice. The melting point of ice under constant pressure is constant (0° C.=32 c F.) but water may be cooled below this point and still remain liquid. Water evaporates at all temperatures, and ice at tem- peratures below 0° C. will give oft' vapor without melting. 7-2 The absolute boiling point of water or the temperature above which it can not exist as a liquid is about 1076 c F. (580°C). As already stated water at maximum density is taken as the standard for the specific gravities of bodies in general and it is also the standard for the specific heats of bodies in gen- eral. One volume of water at the boiling point and under the standard pressure yields 1696 volumes of vapor at the same temperature and pressure, the specific gravity of the vapor being 0.622 (air = l). Solvent Power of Water. This power of water is not thoroughly understood. It may be defined as the power of water to form a homogeneous liquid with another substance brought into it. Thus many substances, gases, liquids, or solids brought into water disappear and a homogeneous liquid results. The results of these actions are such that the constituents can not be separated by purely mechanical means. The substance thus mingled with the liquid is said to be dissolved by it or in solution in the water. As already stated these solutions differ from mere mechanical mixtures and also to a certain extent from true chemical compounds. If a very small amount of the substance be dissolved in the water the solution is said to be dilute: when a large amount is dissolved it is a concentrated solution; and when the water will dissolve no more of the substance it is a satu- rated solution. There is no limit to the extent to which every solution may be diluted but in the case of gases and solids and of most liquids there is a limit to the amount of the substance that may lie brought into solution: but some liquids dissolve each other in all proportions, for example water and alcohol. Solution of Solids. The quantity of a solid required to produce saturation generally varies with the temperature, most solids being more soluble in hot than in cold water. If a saturated solution of such a substance be made in hot 73 water and then the water be allowed to cool it will, in general, not be able to hold so much of the solid in solution and the excess separates or as it is usually called is deposited in the solid form, often as crystals. The hot saturated solutions of some bodies do not deposit any of the dissolved substance if the solution is perfectly quiet while cooling and excluded from the air ; such solutions are called supersaturated. Water of Crystallization. Many salts in crystallizing from their aqueous solutions retain in combination a greater or less amount of water called water of crystallization for to it the form of the crystal is due. The amount of this water varies with the conditions of crystallization but the water and the salt are always present in molecular proportions by weight. Some salts when exposed to dry air lose their water of crystallization and crumble to a dry powder, this process is termed efflorescence. Those salts which do not part with their water of crystallization in dry air at ordinary tempera- ture, do so at the boiling temperature or at a somewhat higher one. Salts generally lose their color as well as their crystalline form by the removal of their water of crystallization. Some sympathetic inks owe their use to this property of changing color. A solution of the salt is used as ink but is invisible until the paper used for the writing is warmed ; cobalt chlo- ride is such an ink. Some salts retain a portion of their combined water usually one molecule more tenaciously than their water of crystallization; this is called ivater of constitution. In some cases it can be replaced by a salt. From the investigations of Guthrie it seems probable that all solu- ble salts form compounds with water at some temperature. Those Knits which combine with water and are soluble only at temperatures below 0° C are called crvo-h.vd rates. Many salts which solidify without combined water may enclose some water mechanically; such salts when heated are 74 likely to fly to pieces with a small report and are said to decrepitate. Bodies which absorb moisture from the air and become damp and ultimately liquid, are said to deliquesce. The thermal effect of the solution of a solid when there is no chemical effect is cold. Solution of Liquids. Water dissolves many liquids, some in all proportions. In such event it is usual to say that the liquids mix in all proportions, though the solution may be accompanied by a decided chemical action with a develop- ment of heat; water and sulphuric acid are examples. In other cases the solution is confined to certain limiting pro- portions of the liquids. In case of the solution of solids and liquids a contraction takes place in the volume of the solu- tion, the volume being less than the sum of the volumes of the two bodies. Solution of Gases. Gases are very generally soluble in water to a greater or less extent and the thermal effect of such solution is opposite to that in the case of solids, heat being produced. The heat is very evident when the gas is very soluble as in the case of ammonia and hydrochloric acid. Grases in most cases are removed from solution by heating, when not thus liberated they form definite com- pounds with the liquid and distil over with it; the compounds of hydrogen with the halogen elements are examples of this last class of gases. From the facts stated in regard to solu- tions it will be observed that, like alloys, they differ both from what we have defined as true chemical compounds and also from mere mechanical mixtures; perhaps the most evident distinction is that they differ from true chemical compounds by having no invariable composition, and from mechanical mixtures by the fact that, except in a few cases, there is a limit to the proportions in which the constituents may be present. 75 Chemical Properties of Water. It has already been stated that oxygen and hydrogen combining to form water develop great heat ; we should therefore expect water to be a permanent and stable compound. Although this is a fact, water can be readily decomposed in several ways. The alkali and alkaline earth metals decompose water at the ordinary temperature; for example, K 2 +H 2 0=K 2 0+H 2 . Some other metals do so at higher temperature. It may also be decomposed by the electric current. At high tem- perature water is decomposed into its elements, the decompo- sition according to Deville, beginning about 1000° C. and continuing with the increase of temperature up to about 2500° C. when it is completed. After the decomposition has commenced any fall of temperature will cause a recombina- tion of the elements. This general decomposition of a substance with increas- ing temperature accompanied by a disposition of the con- stituents to combine and reproduce the substance by a reduction of temperature is called dissociation. In its action on vegetable colors, water is neither acid nor basic. It combines with both basic and acid oxides to form definite chemical compounds. Its combinations with the oxides of the alkali and alkaline earth metals develop much heat and result in the compounds called hydroxides; for example, K 2 0+H 2 0=2KOH, CaO+H 2 = Ca0 2 H 2 ; as already stated it is not believed that water as such exists in these compounds but the oxygen and the hydrogen are present in the form of hydroxyl. Water combines with the acid oxides to form acids; for example, H 2 0+S03=H 2 S0 4 . Composition of Water. The composition of water may be determined by analysis or by synthesis. The analysis or separation of water into its constituents, may be accom- plished by passing an electric current through it under proper conditions. With proper arrangements the con- 76 stituent gases may be collected and their volumes and weights determined. The composition by synthesis can be determined by causing oxygen and hydrogen to combine directly, as by the passage of the electric spark through a mixture of the gases under such conditions as give the volumes of the gases involved. From the volumes the weights can be computed from the relations of the specific gravities. The synthetic determination can be more accurately made by causing an unknown quantity of hydrogen to combine with a precisely determined weight of oxygen and then weighing the water produced. The difference between the weight of the water produced and the weight of oxygen employed gives the weight of hydrogen that has combined with the oxygen. This is designated as gravimetric syn- thesis and a convenient method often pursued is to pass pure dry hydrogen over a known weight of heated copper oxide and accurately weighing the water produced; the loss of weight in the copper oxide gives the weight of the oxygen ; the difference between this and the weight of the water produced gives the hydrogen; CuO-j-H2 = =H 2 + Cu. NATURAL WATERS. Pure water is seldom or never found in nature. The impurities result from the materials, solids, liquids, or gases with which it comes in contact and they may be either in suspension or in solution. Suspended impurities are merely finely divided particles of matter mechanically distributed in the water, and they may be gotten rid of by subsidence or filtration; water often contains no suspended matter. Soluble impurities must be separated by distillation or a combination of this with more purely chemical means. The natural waters may be classified according to their occurrence as rain, sea, river, spring and well waters. Rain Water. Rain is the purest form of natural water but even it contains gaseous and dust particles derived from 77 the atmosphere through which it passes. The gases dis- solved by falling rain are of course those present in the atmosphere. Rain water accordingly always contains oxygen and nitrogen and generally more or less ammonia and carbon dioxide and often traces of other gases the quantity depending upon local conditions. By boiling rain or other natural water the gases in solution are driven out and may be collected. It is thus found that the oxygen and nitrogen in solution in these waters are not in the same proportion as they exist in the air. This is one of the best proofs that air is a mixture of oxygen and nitrogen and not a chemical compound. Spring and Well Water. The rain and the water result- ing from the melting of snow, sleet, and hail flow over the surface of the earth on their way to the sea. When these waters sink below the surface and reappear, they constitute springs ; if their subterranean channels be tapped artificially we have wells. Spring and well waters, in addition to the impurities of rain water, dissolve many soluble substances encountered in their flow; the impurities in such water depending upon the rock material through which they pass. The most common and abundant impurities are the car- bonates and sulphates of the alkaline earth metals, the chlo- rides and sulphates of the alkali metals, silica (silicon oxide) , carbon dioxide, and hydrogen sulphide. Many other substances of less frequent occurrence and of less importance are found naturally in these waters. By contamination from artificial sources, as by city or town sew- age, etc., spring- and well, and even river waters may become very impure and entirely unfit for human consumption. It is believed thai zymotic diseases generally, and it is known that (wo i>\ them., cholera and typhoid fever, are frequently propagated by drinking-water. The infectious or zymotic matter is contained in the discharges of affected people and passes by defective drainage into sources of water supply. In cases of such artificial contamination the additional impurities in the water are salts of nitrons and nitric acids, ammonia, and chlorides. By chemical analysis and a consideration of the sources of a water 78 supply, its safety for drinking purposes can generally be determined, but any water contaminated by sewage should be classified as dan- gerous. Hard and Soft Water. Common waters have been roughly classified as hard and soft, a classification originally depend- ing upon their action upon soap. Soap when rubbed in soft water forms a lather much quicker than when hard water is used. With the latter white curdy flakes not observed with the soft water, make their appearance before a lather is formed; this action is due to chemical causes and will be presently explained. The hardness of water is mainly due to the presence in the water of the carbonates and sulphates of calcium and magnesium. The carbonates of the metals, except those of the alkalies, are not soluble in pure water but if the water contains carbon dioxide in solution, as natural waters generally do, they will dissolve the carbonates. Magnesium sulphate is readily soluble in water and cal- cium sulphate very slightly so. The hardness due to the carbonates in solution is termed temporary because it can be readily removed; that due to the sulphates is called permanent because of the difficulty of removing it. Since the temporary hardness brought about by the car- bonates in solution is due to the presence of carbon dioxide, if this be removed the carbonates will be precipitated. The carbon dioxide may be driven off by boiling, on account of its decreased solubility with increase of temperature, and the carbonates will deposit on the sides of the containing vessel. Calcium sulphate is very slightly soluble in cold water and less soluble at high temperature. By evaporation of the water and increase of temperature there would also be deposited some calcium sulphate, but the calcium sulphate can not be entirely removed by boiling alone. 79 These depositions explain the furring" of kettles and incrustations of boilers. These deposits are usually colored brown or red due to the presence of iron oxide and vegetable matter, the former resulting from the iron carbonate depos- ited from the water. The temporary hardness of the water may also be removed by adding to the water a solution of calcium hydrox- ide, which combines with the free carbon dioxide remov- ing it as calcium carbonate and causing the deposition of the dissolved carbonate, H 2 0+CaC0 3 +C0 2 +CaO a H 2 =2CaC0 3 + 2H 2 ; this is the principle of the Clark process for softening water. Both the temporary and permanent hardness are removed by the household process of adding an alkaline carbonate to the waters, 2Na 2 C03+H 2 0+CaC0 3 +C0 2 +CaS0 4 =Na 2 S0 4 +2NaHC0 3 +2CaC0 3 , but this is practicable only on a small scale. It is often desirable to prevent the incrustation in boilers and the most efficient means yet suggested is to add ammonium chloride to the waters employed — there are then formed ammonium carbonate and calcium chloride, the latter remains in solution in the water and the former volatilizes in the steam, 2NH 4 Cl+CaC0 3 =2(NH 4 ) 2 C0 3 +CaCl 2 . The incrustations formed in boilers fed with sea water are mainly due to calcium sulphate and magnesium chloride in sea water. Natural Deposits from Hard Water. The metallic car- bonates except those of the alkalies are insoluble or nearly so in pure water, but they dissolve in water containing carbon dioxide and the greater the amount of carbon dioxide the greater the amount of the carbonates dissolved. Subterranean waters are often heavily charged with 80 carbon dioxide and coming" in contact with limestone rocks they dissolve much calcium carbonate. When these waters come to the surface of the earth the carbon dioxide escapes, due to diminished pressure, and the dissolved carbonates are deposited. This explains the phenomena observed at the so-called petrifying' springs which are constantly depositing limestone, and will rapidly cover with it any body placed in their waters. This phenomenon is abundantly witnessed in the Yellowstone Park — the objects are merely coated and not petrified. Such waters trickling into caves often deposit their salts so as to form large columns, often of great beauty, called stalactites and stalagmites. Of course when waters containing salts in solution are evaporated, they then leave their salts behind, so that deposits may occur by evaporation of the water as well as by the removal of the carbon dioxide. It is possible that the solution of the carbonates generally by carbon dioxide in solution, may be due to the formation of acid carbonates of the metals, but the formation of these substances has not been proved and if they are formed they are easily decomposed, for as we have seen boiling" drives off the carbon dioxide; if this is the case the soluble carbonate of calcium is represented thus — CaC03+C0 2 +H 2 0=CaH 2 (C0 3 ) 2 . Action on Soap. To understand the action of hard water on soap it is necessary to know that soap is itself a metallic salt of an alkali metal and fatty acid and common soap may be represented by the formula NaFt in which Ft stands for the complex formula of the fatty acid radical. When these soaps are treated with hard waters the calcium and mag- nesium salts by double decomposition form the soaps of these metals which are insoluble and perceptible as curdy scum on the water. A true lather from the soap will not form until the salts to which the hardness is due are removed by the formation of these insoluble soaps. 81 River and Sea Waters. River water does not differ essentially from well and spring water. The quantity of both mineral and organic impurities being diminished by the conditions of continual motion and exposure to the air. Sea water contains the same salts as spring and river waters and in addition a large amount of common salt, about four-fifths of the saline constituents of sea water being sodium chloride. The compounds of bromine and iodine are also found in small quantities in sea water. A gallon of sea water usually contains about 2500 grains of mineral salts. Sea water has no point of maximum density above the freez- ing point and solidifies at — 2° C. Mineral Waters. Natural mineral waters are those spring waters which contain mineral substances in such quantity as to exert a medicinal effect on the animal system or as to ren- der them entirely unfit for drinking purposes. Mineral and medicinal springs are very widely distributed ; some of the common kinds are chalybeate springs, which contain some salt of iron in solution; saline springs which contain one or more of a large number of mineral salts ; carbonated springs which contain carbon dioxide in solution; hepatic springs which contain hydrogen sulphide in solution. The escape of the gaseous constituents often produce effervescence; the same spring often contains both solid and gaseous constit- uents. Purification of Water. Waters often become purer by natural processes. This is the case with running waters and especially when they are subjected to thorough agitation and exposure to the air; an unfit water may thus become fit for drinking in a purely natural manner. The purity of all turbid water is greatly increased by allowing it to stand in tanks or reservoirs, by which most of the suspended matter is depos- ited. After remaining for some time in storage reservoirs it is customary to filter all large water supplies. The most 82 common method adopted is to allow the water to flow through layers of sand of different degrees of coarseness. Sand filtration when properly carried on is very efficient in remov- ing all suspended impurities, but it has little influence on the dissolved matter. It is also claimed by Professors Koch and Frankland that sand filtration removes a very large per cent of microscopic organisms. Besides sand, filters of char- coal or of coke and sand have been employed for purification on a large scale. The Hyatt filter which is largely used in this country uses coke and sand, in this process a little alum is added to the water before filtration. Filters of finely divided iron have been used in Antwerp in case of very impure water ; these niters exert a chemical as well as a mechan- ical effect upon the water. There are many other methods of purifying drinking water on a small scale. For refined chemical purposes water is purified by distillation. Alum is frequently used to clarify water; the effect is probably mainly due to the fact that if there be any carbonates in solution in the water, the alumina is precipitated, which has a coagulating effect and carries suspended matter with it. HYDROGEN PEROXIDE — H 2 2 . This substance has the composition H 2 2 . It was discovered in 1818. It is a great oxydizing agent in the case of many substances, readily giving up half its oxygen and being converted into water; upon other substances it acts as a reducing agent, being itself con- verted into water and oxygen liberated; it thus acts upon ozone — 3 +H 2 2 =20 2 +H 2 0. Hydrogen peroxide is a colorless, transparent, syrupy liquid ; it is heavier than water, has a bitter taste, and mingles with water in all proportions. Its most useful applications in the arts are by virtue of its oxidiz- ing power. Paintings which have blackened due to the formation of lead sul- phide can be restored to their original color by washing with a dilute solution of hydrogen peroxide — the lead being converted into lead sulphate. It is very important to the student of chemical philosophy because of its chemical relations. 83 CARBON. Carbon occurs free in nature in three distinct allotropic forms — as diamond, graphite, and mineral coal. These three forms differ widely in appearance and physical proper- ties, but their chemical relations prove their identity. The first two are crystallized and very nearly pure carbon; the third is amorphous, uncrystallized and includes many vari- eties of coal differing greatly in purity — the three principal varieties are anthracite or hard coal, bituminous or soft coal, and lignite or brown coal. In combination carbon is widely distributed. It exists in combination with oxygen in the carbon dioxide of the air, is present in all mineral carbonates, and is a constituent of all organic substances. It is the element by virtue of which all organic substances turn black when heated with limited access of air. All forms of carbon are solid, insoluble in all ordinary solvents, fused iron being the only known solvent, non-volatile except at the high temperature of the electric arc. Diamond. This is one of the rarest of substances and one of the most precious gems. It is usually obtained from allu- vial washings and appears generally to have come from sandstone or quartzyte rock; nothing definite, however, is known as to its original formation. It crystallizes in forms derived from the octahedron and is the hardest substance known. For use in jewelry it is cut and polished so as to bring out the brilliancy of its faces. Besides its use in jewelry it is used for pointing drills for boring in hard rock, to cut glass, and its dust is used in polishing. If heated very highly out of contact with air, as by the electric arc, it is converted into a black mass resembling graphite, but without loss of weight. It can be burned in the air and then leaves a small quantity of ash. Recently diamond, or carbon crystallized with the lustre of diamond, 84 has been prepared artificially, but the crystals thus made were very small. Graphite. This is found in beds and veins in the oldest crystalline rocks, has a greyish black color and metallic lustre, and is so soft as to leave a mark when rubbed on paper. It is a very useful substance, being employed in making the so-called lead pencils, for covering iron to prevent rust, and for mixing with clay to make crucibles which are designed to stand high and sudden change of temperature. Graphite is often produced artificially in the cooling of molten cast iron. It is also used as a reducing agent in some metallurgic operations. AMORPHOUS CARBON. This term includes in addition to the native mineral coals all the common artificial forms of carbon. The mineral coals are fully described in mineralogy. The principal arti- ficial varieties of amorphous carbon are charcoal, lampblack, animal charcoal and coke. Lampblack is the form of car- bon which is often deposited upon cold objects by the flame of gas or burning oil. These combustible bodies are com- posed almost entirely of carbon and hydrogen, and if the flame could be cooled down or the supply of air limited, the carbon escapes combustion and is deposited in a finely divided state commonly called soot. Lamp-Black is manufactured by subjecting organic sub- stances rich in carbon to imperfect combustion; that is combustion with an insufficient supply of air. For this purpose oils, fats, resins, and tarry matters are burned with a limited supply of air and the products of combustion conducted through a flue into a large chamber, along the sides and from the ceiling of which are suspended large cloths upon which the unburned carbon is deposited. The lamp-black thus obtained usually contains resinous or oily ,;.',,, , . ^ fiat 4. 85 substances and other impurities depending* upon the organic body burned. It is however sufficiently pure for the pur- poses for which it is generally used; viz., printers' ink and black pigments. Charcoal. Charcoal is the form of carbon obtained by heating wood out of contact with air. If wood be heated in the air it is entirely consumed except a small quantity of ash which is composed of the incombustible mineral matter of the wood. The part that has disappeared, the sap and the woody fibre, are composed almost entirely of carbon, hydro- gen, and oxygen. The woody fibre (cellulose) which con- stitutes nearly the entire solid part of the wood is more than one half carbon the remainder being oxygen and hydrogen. If wood be heated to redness out of contact with the air, no combustion can occur, but under this temperature the constituent elements of the wood rearrange themselves into simpler and more stable compounds. In this change the carbon is mainly left, retaining the form of the wood, but largely diminished in volume and still more so in weight. This resolution of a complex substance into simpler and more stable forms under the influence of high temperature out of contact with air is termed destructive distillation. In the case of wood it is often called charring, coaling, or carbonizing. The earliest and still the most common way of preparing charcoal for fuel, is as follows: Preparation of Charcoal. Billets of wood are built into a mound or stock around an upright pole or bundle of brush- wood which is withdrawn after the stock is completed and leaves an opening called the chimney. The billets may be nearly vertical, or horizontal, or inclined at any angle. When completed the mound usually has a dome shape and may have a diameter varying from thirty to fifty feet and with a height from ten to fifteen feet. The finished heap is 86 covered with chips, leaves, soil and earth, and often the coal dnst of a previous burning" is used for this purpose. Numer- ous openings are left around the base of the mound for the admission of air and escape of the products of distillation. The kiln is kindled in the centre and after the fire is started the top is closed. More air is required in the early stages of the carbonization so that the openings at the bottom are gradually closed and the mound is left to smoulder and cool. By this process the weight of charcoal obtained never exceeds 25% of the wood used. In this country as in many other places kilns or charcoal ovens are often built of brick or masonry; they are generally rec- tangular with arched tops or of a bee-hive shape. In these ovens the destructive distillation is accomplished by the combustion of a certain portion of the wood of the heap. In this country there is claimed for such ovens an economy of time and a gain in the quantity and quality of the charcoal but these advantages are denied at other places — the ovens are sometimes arranged to collect the products of distillation. Charcoal is also made by the destructive distillation of the wood in cast iron retorts, the wood being placed in a perforated iron case within the retort. In this method the heat is obtained from other fuel than the wood itself, though sometimes the combustible products from the wood are led to and burned in the furnace beneath the retort. At other times these products are condensed and used in the prepara- tion of acetic acid, wood naphtha, and methyl-alcohol. Distillation in retorts yields a greater per cent of charcoal and of better quality than the methods first described. All forms of carbon thus obtained contain impurities due to the non-combustible and non-volatile mineral matter of the wood. Properties and Uses of Charcoal. The appearance of charcoal needs no mention. It is one of the most unchang- ing solids known under ordinary conditions. This property 87 of carbon has long* been recognized and is shown in the charring- of wood intended to withstand extended exposure. Oak staves planted in the bed of the Thames by the ancient Britons in their defensive works against Caesar were charred and thus have been perfectly preserved to the present day. Charred stakes for marking the limiting lines of estates are often used. Charcoal is very porous and due to this property exerts an absorbent action on many substances. Oxygen is ab- sorbed by it in considerable quantity and many other gases to a far greater degree. This is especially noticeable with those gases which can be readily liquefied. It absorbs under ordinary conditions fifty times its volume of hydrogen sulphide and twice that amount of ammonia. A gas thus absorbed if capable of oxidation will be acted upon by the oxygen also contained in the charcoal. This property of charcoal explains its frequent use in deodorizing offensive matter and in purifying offensive atmosphere. Ammonia and hydrogen sulphide are two of the most common products of putrefaction and both are readily absorbed by charcoal. The absorbing power of charcoal also extends to liquids and solids, it is accordingly used to make water filters. Water passed through a good charcoal filter is clear and odorless. It is especially efficient in removing coloring matter. The charcoal has to be periodically heated to retain its absorbent powers. Besides the above uses charcoal is largely employed as a fuel and in the manufacture of gun-powder. With a free supply of air it burns readily without flame, producing carbon dioxide and yielding about twice as much available heat as an equal weight of wood. One pound of carbon burned to carbon dioxide will produce 8080 units of heat, C. scale. Its use in the manufacture of gun-powder will be referred to under that subject. Animal Charcoal. This form of carbon is made by the destructive distillation of animal substances as bone, skin, blood, &c, commonly from the first named substance. Bones are composed approximately of one-third animal matter and two-thirds mineral matter, three-fourths of this mineral matter being calcium phosphate. The animal mat- ter is composed mainly of carbon, hydrogen, oxygen, and nitrogen. The result of the destructive distillation of bones is a charred mass consisting of about one-tenth carbon and nine-tenths mineral matter. The decolorizing power of this form of charcoal far ex- ceeds that of other forms and it has frequent technical application for this purpose and is used industrially in sugar refineries and distilleries. The products from the distillation of bones are often collected and used, and the mineral matter from the bone- black itself is eventually employed as a fertilizer. Coke. Common coke results from the destructive dis- tillation of soft or bituminous coal. This distillation is sometimes made by burning coal in heaps as in the conver- sion of wood into charcoal, but generally the coke is prepared in specially constructed ovens and of these there are many forms. They are constructed of suitable masonry lined with fire-brick. In some of these the heat for the distillation is obtained by burning part of the coal in the oven ; in others the heat is obtained without burning any of the coal in the oven. In the latter kind the combustible gases driven from the coke and other fuel are burned to supply heat. The forms of coke ovens are too numerous for description here, the object in all cases is to accomplish the distillation with as little consumption of fuel as possible. The ovens are also varied in construction, depending upon whether they are arranged to secure the tar and ammo- nia. In this country the coke is usually made in bee-hive ovens and the secondary products are not saved. In Europe 89 the retort-ovens are very generally employed, and, in certain localities, the by -products from the volatile constituents of the coal equal in value the coke produced. The coke con- tains in addition to the fixed carbon the incombustible ash of the coal. Coke is of a dark grey color with a slightly graphitic lustre ; it produces a much higher temperature than common coal and is much used in iron smelting and other metallurgic operations. Coke is always produced in the manufacture of coal gas, the coal in the operation being distilled in closed iron retorts. In this manipulation it often happens that some of the denser gases containing carbon and hydrogen driven from the coal are decomposed by the high temperature and the carbon deposited upon the sides of the retort and is known as gas-coke. It is used for plates in carbon batteries and also for the manufacture of carbon rods for electric arc lights. Chemical Properties of Carbon. Carbon at the ordinary temperature is an inactive element, not combining with any other element; at higher temperature it combines directly with sulphur, hydrogen, and oxygen and under proper con- ditions will combine with other elements; at elevated tem- perature it is especially active in combining with oxygen. Heated to redness it burns brilliantly in pure oxygen and by the aid of heat it abstracts oxygen from many oxides remov- ing and combining with the whole or a part of their oxygen. When burned with a full supply of air carbon always yields carbon dioxide ; with a limited supply, carbon monox- ide is produced. In case an oxide gives up its oxygen at a low temperature to carbon, carbon dioxide is formed, but if a high temperature is required carbon monoxide is produced; these actions are represented by the accompanying *e- ^tien^ 2CuO+C=2Cu+C0 2 ; 2ZnO+2C=2Zn+2CO. 90 This removal of oxygen from a body has already been de- fined as a reduction, hence carbon is a reducing agent. It is the most important reducing agent employed in the indus- trial arts and upon this property and its heat giving power depend its uses in metallurgic operations. COMPOUNDS OF CARBON AND OXYGEN. CAEBON DIOXIDE. There are known two compounds of carbon and oxygen, carbon monoxide and carbon dioxide, both of which are gaseous at ordinary temperature. The latter is the more important; it has already been stated that it is a constitu- ent of the atmosphere, being normally present in the propor- tion of from three to four volumes in 10000 of the air. Its constant occurrence in the air is readily understood from known considerations. It is the product of the combustion of any form of carbon or any compound of carbon in a full supply of air. As all common fuels are composed mainly of carbon or its com- pounds it may be said that carbon dioxide is an abundant product of all ordinary combustion. It is likewise, given on 2 in all animal respiration, the oxygen of the air which is inspired combining with the carbon of the system to form carbon dioxide which is exhaled. All living vegetation extracts carbon dioxide from the air, but when the plant dies the process of decomposition in the course of time restores the carbon dioxide to the air again. If the plant is devoured by animals or consumed for fuel its carbon eventually returns to the air as carbon dioxide. Carbon dioxide is also given off to the air during the processes of fermentation and putrefaction of organic sub- stances. It is present to a greater or less extent in all spring waters and in some places, especially in volcanic regions it 91 escapes rapidly from such waters when they come to the surface, giving effervescing springs. It often issues in considerable quantity from openings in the earth's crust. When coming from such openings or even from springs it sometimes accumulates in neighboring depressions in such quantity as to destroy the life of animals venturing into them. Such a poison depression has been found at the east side of the Yellowstone Park ; the poison valley of Java is another and the accumulation of gas around the soda springs (so called) in south eastern Idaho often causes the death of birds seeking water. The air which permeates soils is found to be richer in carbon dioxide than is atmospheric air. In the combined form carbon dioxide occurs as a con- stituent of all limestones and other carbonates and conse- quently exists in this form in enormous quantity. It constitutes over 96 per cent of oyster shells and egg shells. Physical Properties of Carbon Dioxide. Carbon dioxide at ordinary temperature is a colorless gas, and has a slightly acid taste and smell. Its formula shows it to be much heavier than air and its greater density explains its disposi- tion to seek the lower levels. At 14° C. water dissolves its own volume of carbon dioxide and the quantity dissolved is directly proportional to the pressure to which the gas is subjected. When the pressure is diminished or removed the amount dissolved is diminished and if there is much diminution of pressure the gas escapes with effervescence. Carbon dioxide can be liquefied without very great difficulty to a mobile colorless liquid which will not mix with water. Its boiling- point in the liquid state is —88° C. (much of the liquid carbon dioxide is now manufactured for use as a fire-extinguisher). By causing it to evaporate under an air pump its temperature is lowered to — 130° C. Like many other bodies which are liquefied only by very great pressure its coefficient of expansion is very great, being greater than the coefficient for gases. 92 Chemical Properties of Carbon Dioxide. Carbon dioxide is not combustible as it can not take up more oxygen. It will not support ordinary combustion and will extinguish flame ; a few bodies which have a great affinity for oxygen will burn in carbon dioxide. If potassium be ignited and then dipped into a jar of carbon dioxide it will continue to burn. Air which contains less than 3 per cent by volume of carbon dioxide will extinguish a taper — that is when the carbon dioxide is about one-eighth the volume of the oxygen. Carbon dioxide is not poisonous when taken into the stomach but it will not support respiration. It is not poisonous in this case, but merely suffocates by depriving of the necessary amount of oxygen and also prevents the escape of the carbon dioxide from the system. A taper burning in a confined space is extinguished as soon as the carbon dioxide reaches a certain amount and long before all the oxygen is exhausted. Similarly confined air becomes unfit to breathe long before the oxygen is exhausted. Any considerable amount of carbon dioxide above the normal in air to be respired is objectionable in that it diminishes the proportion of oxygen. The actual amount of pure carbon dioxide that must be present in the air to render it unfit for respiration is not definitely settled. It has been found that air containing as much as 5 per cent may be breathed without injury and recent experiments indi- cate that a much larger proportion of pure carbon dioxide may be breathed for several hours without ill effect. It has been shown that the bad effects experienced in poorly ventilated rooms are due to other waste products, than carbon dioxide, given off from the lungs during respira- tion. Besides the carbon dioxide, water vapor, nitrogen, and oxygen of the expired air, there are other organic sub- stances undergoing decomposition which have a poisonous action in the system and to these are to be largely attrib- uted the unwholesome conditions so rapidly developed in 93 overcrowded and poorly ventilated rooms. As carbon diox- ide is constantly given off in respiration along with other organic impurities the amonnt of the first in the air will indicate approximately the quantity of the latter and there- fore may be taken as a test of the fitness of the air for res- piration. Generally speaking it may be stated that when the volume of the carbon dioxide is over oVo the volume of the air it should not be breathed for any considerable time; when the volume of the carbon dioxide reaches 2017 the volume of the air, its effects soon become perceptible in lan- guor and disagreeable sensations and any amount above this is very deleterious ; when the amount has reached three per cent it has been known to produce death. A well, fermenting tun, or any confined space where this gas is suspected, should be tested before entering it. If a candle flame is made dim by the air the space should be con- sidered unsafe. When any person is quickly overcome by such an atmosphere another person can not safely go to the rescue without first increasing the proportion of oxygen to the carbon dioxide. This may often be quickly done by moving an open umbrella, a bundle of straw or of brush up and down through the space. The above described properties of carbon dioxide make evident the necessity for good ventilation. The amount of carbon dioxide given off from the lungs and skin amounts to about ro cubic feet per hour, an ordinary three-foot gas burner gives off about two and one-half times that amount. In order that the added carbon dioxide shall be distributed through the proper amount of air to fit it for respiration, it is evident that a large amount of fresh air must be intro- duced into constantly occupied rooms. It is of course easy to compute this amount under any given conditions. In general it may be stated that perfect ventilation should be prepared to supply one thousand cubic feet of air per man 94 per hour, though one half that amount is usually considered good ventilation. Preparation of Carbon Dioxide. Carbon dioxide is in- variably produced when carbon is burned in a full supply of oxygen; for example, C+0 2 =C0 2 ; from this source it always contains other substances. It is readily prepared for laboratory purposes by acting upon fragments of marble (CaC0 3 ) with dilute hydrochloric acid. The carbon dioxide escapes with effervescence and is usually collected by downward displacement as it is some- what soluble, in water. The apparatus described for making hydrogen may be used in this case. The action is repre- sented thus, CaC0 3 +2HCl=CaCl 2 +H 2 0-fC0 2 . Any of the other mineral acids will liberate carbon dioxide from a carbonate, so that it can be readily prepared in many ways. Carbon dioxide is largely used in the manufacture of artificial mineral waters. Carbonic Acid and Its Salts. An aqueous solution of carbon dioxide exhibits weak acid properties. It colors blue litmus red, but the blue color returns upon drying. The solution acts upon bases and forms the salts called car- bonates. The formulae of the carbonates indicate the ex- istence of an acid having the formula H 2 C0 3 though this substance has not been isolated. It is probable that the acid is formed whenever carbon dioxide is passed into aqueous solution, but it readily breaks up into carbon dioxide and water. On account of the similarity of the carbonates to other salts, they are universally considered as formed by the replacement of hydrogen in carbonic acid by metals and the acid is bibasic. The carbonates are a very important class of bodies and it may be well to repeat their properties. The carbonates are all decomposed by mineral acids, are all, with un- 95 important exceptions, insoluble in water except the car- bonates of the alkalies, and are all decomposed by heat except those of the alkalies. They are all soluble in water containing' carbon dioxide. CARBON MONOXIDE. Physical Properties. Carbon monoxide is a colorless, tasteless gas with a very faint smell; it is slightly lighter than air as may be seen from its formula. It is almost insoluble in water. Its critical temperature is about — 140° C. Chemical Properties. Carbon monoxide is an extremely poisonous gas. It acts upon the red corpuscles of the blood and deprives the blood of its power of distributing oxygen to the system. It forms am explosive mixture with one half its volume of oxygen. It burns in air with a pale blue flame producing carbon dioxide, but extinguishes ordinary flame. At high temperature it readily takes oxygen and forms carbon dioxide; for this reason it is a powerful reducing agent removing oxygen from many metallic oxides and reducing them to the metallic state. It is accordingly a very valuable agent in many metallurgic operations. Its union with oxygen gives out much heat; carbon monoxide burning to carbon dioxide gives more than two-thirds of all the heat produced by the complete combustion of the carbon to carbon dioxide. Production and Uses. Carbon monoxide is always pro- duced by the incomplete combustion of carbon or carbon- aceous substances, that is when these are burned with an incomplete supply of air. If carbon dioxide be passed over heated charcoal or other carbon it gives up one half its oxygen to the carbon, both being converted into carbon monoxide, as indicated by the reaction C0 2 +C=2CO. This action explains the phenomenon frequently observed in connection with an open anthracite coal fire when a pale 96 blue flame is seen to play over the top of the mass of coal ; the combustion of the coal in the lower part of the grate with full supply of oxygen produces carbon dioxide, this passing through the heated layers of coal above, is converted into carbon monoxide. This carbon monoxide upon reach- ing the upper surface of the coal comes in contact with the air and burns with the blue flame observed. This ready production of carbon monoxide is often made use of in metallurgic operations when it is desired to have a flame play over the surface of an ore placed on the hearth of a reverberatory furnace. Anthracite coal which burns with but little flame is frequently employed in such furnaces and it then becomes necessary to heap the coal in the grate so as to form a mass of considerable height. The carbon monoxide is produced precisely as described above in the grate and passes into the furnace chamber and when air is admitted the carbon monoxide burns with a flame. By properly regulating the supply of air a high temperature can be produced. The attraction which carbon monoxide has for oxygen at a high temperature enables it to remove this element from many of its compounds. Carbon monoxide is accordingly one of the most powerful reducing agents and, as will be subsequently seen, the property is generally turned to account in removing oxygen from the metallic oxides, reducing the oxides of the metals. Carbon monoxide is one of the essential elements of water- gas, hydrogen being the other; carbon dioxide and nitrogen are also present in limited quantities. This water gas is now largely used for illuminating and for other purposes. Water gas is prepared by passing steam over white-hot coke, the result is indicated by the reaction C+H 2 0=CO-f H 2 . Some carbon dioxide is also present for the reason that at lower temperature the action of steam on carbon is to pro- duce carbon dioxide ; at certain temperature steam also acts 97 slightly on carbon monoxide producing carbon dioxide. Water gas usually consists of about 30% of hydrogen and 40% of carbon monoxide the remainder being nitrogen and carbon dioxide. As both hydrogen and carbon monoxide burn with faintly luminous flames, the gas to be used as an illuminant must be enriched or carburetted. This is accomplished by ad- mitting naphtha or crude oil to the heated coke during the gas production or by passing the gas through naphtha or over liquefied naphthalene. Water gas is valuable as a heat producer and then does not need to be carburetted. Its flame is entirely free from smoke and comparatively so from sulphur compounds. It produces a high temperature and a clear heat and is very valuable in melting and welding metals and in porcelain and glass manufacture. For laboratory purposes carbon monoxide is readily obtained by heating* potassium ferrocyanide with dilute sulphuric acid. COMPOUNDS OF CAEBON AND HYDKOGEN. Carbon and hydrogen form a larger number of com- pounds than any other two elements. These compounds ar,e designated as hydrocarbons. They enter largely into the composition of nearly all combustible bodies and include many of the inflammable gases, naphtha, benzene, &c. It is probable that all hydrocarbons are primarily derived from the organic kingdom and the study of these compounds belongs to organic chemistry. Only three of the simple hydrocarbons will be mentioned here; they are all con- stituents of common coal gas. methane; marsh gas; ch 4 . Methane is the only hydrocarbon containing one atom of carbon. It is found abundantly in the free state in nature. It is frequently termed marsh gas from its occurrence in marshy places. The bubbles of gas which rise to the surface when the mud at the bottom of stagnant pools is disturbed, are in fact marsh gas. It is believed to be one of the products of the decomposition of vegetable matter during its conversion into coal, hence its frequent occurrence in coal mines, where it is known as fire-damp. It is probable that all the hydrocarbons of petroleum and similar oils generally are derived in the same way. Physical and Chemical Properties. Methane is a color- less, odorless, and tasteless gas. Its formula shows it to be much lighter than air, hence it diffuses and mixes rapidly with it. When mixed with oxygen or air in suitable pro- portions it explodes violently upon ignition. The most violent explosion is indicated by the reaction, CH 4 +04= C0 2 +2H 2 0, in which there is just enough oxygen to com- pletely oxidize the carbon and hydrogen. The relative volumes of marsh gas and oxygen for this action are shown in the equation to be two volumes of oxygen to one of marsh gas ; it would accordingly require ten volumes of air for the complete oxidation of one volume of marsh gas. It is marsh gas which so frequently gives rise to the fatal explosions in coal mines. It will be observed that the pro- ducts of the explosion are also irrespirable and constitute the after-damp of mine explosions. Marsh gas has not been prepared by the direct union of its elements but can be prepared artificially. Marsh gas does not unite with other bodies without decomposition; chlorine decomposes it in direct sunlight, atoms of chlorine successively replacing atoms of hydrogen. At a high tem- perature marsh gas is separated into carbon and hydrogen. acetylene; ethene; c 2 h 2 . Acetylene can be produced directly from its elements by highly heating carbon in an atmosphere of hydrogen. This may be accomplished by immersing the electrodes of a voltaic arc in an atmosphere of hydrogen. The operation 99 is of but little practical importance but it is of great theo- retical interest because it is the first step in the artificial production of a large number of organic compounds. Physical and Chemical Properties. Acetylene is a color- less gas having a faint odor of geranium. From an ordinary gas jet it burns with a smoky flame, but when the air and gas are properly apportioned its flame is brilliantly luminous. It inflames spontaneously when brought into contact with chlorine and when mingled with air gives a mixture that can be exploded by ignition. Preparation of Acetylene. Acetylene is now prepared on a large scale by heating lime with powdered coal or other carbon in an electric furnace, by which calcium carbide is prepared. The calcium carbide if immersed in water yields lime and acetylene by this reaction, CaC 2 +H 2 0=CaO+C 2 H 2 . This method of preparing acetylene promises to give it a brilliant future as an illuminant for which purpose it is admirably adapted because of its great light giving power in proportion to the heat and objectionable products resulting from combustion. OLEFIANT GAS; ETHYLENE; C 2 H 4 . Olefiant gas like the other two hydrocarbons just de- scribed is a product of the destructive distillation of coal. It may be obtained artificially by the action of sulphuric acid upon alcohol. It is a colorless gas with a somewhat ethereal odor. It burns with a luminous flame and for complete combustion one volume of the gas requires three volumes of oxygen, C 3 H 4 +0«=2CO s +2H 2 0. The mixture of olefiant gas and oxygen in this proportion explodes with violence when ignited. The gas unites with chlorine and bromine, forming oily liquids, hence the term olefiant (oil-making). This action may be applied to determine the amount of the ethylene in the coal gas. 100 When subjected to high temperature olefiant gas is decomposed with a deposit of carbon and a separation of hydrogen, mash gas, and acetylene. CUMBUSTION AND FLAME. Combustion. The hydrocarbons above described, either separately or together, are found in many of our common inflammable gases; combustion and the properties of flame are accordingly very naturally taken up here. Combustion in general may be defined as chemical action accompanied by heat and light. The term combustion ordi- narily applies to the chemical combination of the oxygen of the air with the body burned. The temperature to which a body must be raised in order that combustion may take place is called the igniting point. When a body is said to be combustible it is generally meant that it burns in air. It is also customary to regard one of the bodies taking part in the action as the combusti- ble and the other as the supporter of the combustion. The enveloping medium is usually taken as the supporter of combustion and the other as the combustible, so that in the ordinary cases air is the supporter of combustion. These limitations are without scientific basis and the supporter of combustion may be any medium in which the phenomenon will occur. The process with proper arrangements, when both the bodies taking part in the combustion are gases, is reversible so that the supporter of combustion may become the com- bustible and the reverse; — thus while we usually burn hydro- gen in oxygen, oxygen may be burned in hydrogen. Similarly air may be burned in coal gas and the reverse. Flame. When both substances taking part in the com- bustion are gases, the action results in flame, which may be defined as gaseous matter heated to a temperature at which it becomes visible. Solids which do not volatilize at the tern- 101 perature of combustion do not give flame; carbon and iron are familiar examples. Luminosity of Flame. This may be due either to the in- candescence of gaseous matter or of solid particles present in the flame. A high temperature is always essential to in- candescence and consequently to luminosity. In all ordi- nary flames the gaseous matter which is heated results from the flame-gases themselves; the solid matter may result from these gases or may consist of foreign matter introduced for the purpose. It has been found as a general rule that denser gases and vapors when heated give off light at lower temperature than the less dense, and heated solids emit light at lower temper- atures than gases. Luminosity without Solid Particles. Examples of com- bustible bodies which afford dense flames and bright light without solid particles are seen in the case of phosphorus, arsenic, and carbon disulphide, which when burned in oxy- gen produce highly luminous flames, though all the products of combustion are gases at the temperature. The luminosity of the flame does not depend entirely upon the vapor density of the constituent gases themselves, but are affected by the pressure to which these gases are subjected. The luminosity of flame may often be increased by in- creasing the pressure of the medium surrounding the flame. Thus the luminosity of the flame of carbon monoxide burning in oxygen at ordinary pressure is only moderately luminous, but may be greatly increased by doubling the pressure. The faintly luminous flame of hydrogen burning in oxygen may be greatly brightened by increasing the pres- sure of the oxygen. For this reason a candle burns more brightly at a low than a high elevation. Flame Containing Solid Matter. The light-giving power of many of the common illuminating gases is still further 102 increased by the presence of solid matter intentionally intro- duced into the flame or separated from the flame-gases during' the chemical action of combustion. The Welsbach burner, among common gas-burners, is an illustration of free foreign solid matter introduced into the flame. The great luminosity in this burner is due to the introduction into the flame of a gauze hood of certain infusible metallic oxides. In the candle, oil lamp, simple gas-flames, and common flames generally, the light is mainly produced by the incan- descence of solid carbon particles which are separated in a finely divided state from the flame-gases. There are also usually present or produced in these flames dense hydro- carbons which emit light. The influence of such solid parti- cles may be illustrated by blowing powdered charcoal across a hydrogen flame. The calcium or lime-light owes its luminosity to a frag- ment of lime very highly heated by the oxyhydrogen flame. It is seen from the above considerations that the most essential conditions for luminosity in a flame are — (1) high temperature and vapors which are of themselves dense or made dense under the conditions of burning, (2) highly heated solid particles; the influences of these conditions operate simultaneously in most common illuminating flames. Structure of Flame. The simple flame is one that results from the combustion of a substance that undergoes no decom- position, but combines directly with the supporter of the combustion — hydrogen and carbon monoxide burning in oxygen are illustrations. There is but a single product of combustion in such cases. All such flames when the gas issues from a circular jet consist of a conical sheath of flame surrounding a cone of the gas. The flame-cone is hollow, that is to say, the interior cone of the gas is not burning. This fact may be simply proved by quickly depressing a white sheet of paper into the flame, when the flame cone will 103 char an annular space while the interior circle will be unaffected. A live match may be suspended in the inner cone without ignition if not allowed to touch the sides of the flame-cone. The conical shape of the flame is due to the fact of the gas issuing from the jet in the form of a cylinder, and being under a little greater pressure than the air, assumes the form of a slightly diverging cone. The gas first issuing from the jet burns as a ring around the orifice, the next layer of gas must pass above this ring in order to reach the air for its combustion. Each successive ring must pass through the preceding to reach the air and as each burning ring diminishes the volume of unburned gas these rings must grow smaller and the converging cone is the only possible form. This explanation holds for the shape of the candle flame or other flame resulting from the issuance of gas from a cylindrical wick. Hydrocarbon Flames. It has already been stated that these bodies enter largely into the composition of all our com- mon illuminating oils and gases. These bodies undergo decomposition during the combustion and the products of combustion are produced at successive stages. They give rise to flames more complex in structure than those just described. The common flames under this head are those of gas, oil, and the candle, the last will be described as typical of all. In the first case the fuel is supplied at the burner in the gaseous state, the gas having been obtained from the destructive distillation of coal at a distance; in the sec- ond (oil) the fuel is liquid and is converted into gas at the lamp. In the candle the tallow or wax is solid, so that it must be melted and distilled during the operation of burning. Candle Flame. In the candle flame there are three eon- centric cones; the interior is dark and is composed of unburned gas resulting from the destructive distillation of 104 the tallow, the next and the largest part of the name, is brightly lnminons and the outer cone is thin and only faintly luminous. There is also a bright blue cup at the base of the cone. The flame-cone proper consists of the outside and faintly luminous cone, the next or luminous one, and the blue cup at the base; the interior dark cone consists of combustible gases to which air does not penetrate and is not part of the flame. In the luminous cone combustion is taking place, but the air supply is not sufficient for complete combustion. At the temperature of the cone there results a decomposition of some of the hydrocarbons with a separation of free carbon. This free carbon heated to whiteness by the burning hydro- gen and other gases confers the great luminosity upon this cone. In the outer cone where the air supply is sufficient, more complete combustion takes place with production of great heat but little light. The blue cup at the base is due to the perfect combustion of a thin layer of gas 'at that point and to the lower temper- ature due to the presence of an excess of air. The combustible gases of the inner cone may be readily extracted and burned at some distance from the flame by inserting one end of an open glass tube six or more inches long into the cone. The unburned carbon in the luminous cone can be shown by depressing upon it a white porcelain plate. Flame for Special Purposes. Lighting Flames. From the foregoing considerations of the nature, properties, and structure of flames, it is evident that several considerations must enter into the construction of burners for different purposes. The Argand gas-burner is one of the most widely used burners for gas-lighting. The gas in this burner issues from the annular space between two concentric cylinders; the gas-flame is a hollow cylinder which is surrounded by the chimney and air is supplied to the flame both from the inside 105 and outside of the cylinder. The chimney acts effectively both in producing a draught and thus giving a liberal supply of air, which in combination with the regulated flow of gas per- mits the proper adjustment of the two for the best light. If there be too great a proportion of the gas some of the carbon escapes unburned and the flame smokes and the temperature is not high enough to produce a brilliant light. By using two chimneys and causing the air that feeds the flame to pass down between them, there is less chilling effect on the flame and an equal light may be obtained with a less consumption of gas. The Argand burner may be converted into the Wels- bach, already referred to, by the insertion of a durable gauze cylinder into the flame and regulating the air and gas sup- plies so as to produce the highest temperature. Smokeless Flames. Since luminous flames in general contain unburned carbon, they deposit soot when the flames come in contact with solids. When bodies are to be heated by flame as in laboratories and in kitchens, it is therefore advantageous to have flames in which the combustion is as perfect as possible, producing a smokeless flame. Smokeless Flames. This result is accomplished by mix- ing the air and gas in certain proportions before combustion, so that the hydrocarbons are burned without the separation of carbon, this also causes the disappearance of the luminous part of the flame. By a proper adjustment of the air and gas the flame from the combustion of a given amount of gas is smaller and the temperature higher. The principle upon which smokeless burners are con- structed, is well shown in the Bunsen burner. This burner in its simplest form, consists of a cylindrical tube mounted on a substantial base. The gas is led in at the base and ascends the tube, near the bottom of which there are two holes for the admission of air. The flow of the gas draws air into the tube and the mixture is burned at the top of the tube. The holes for the admission of the air can be entirely 106 or partly closed. By entirely closing the air-holes the flanie is white and lnminons, by admitting the proper proportion of air the flame becomes smaller, of a bine color, and almost non-lnminons. This loss of color was formerly supposed to be almost entirely due to the complete combustion of the hydrocarbons without the separation of the carbon. It is now known that the effect can be brought about by admix- ture with the hydrocarbons of other gases than air, as nitrogen and carbon dioxide. The loss of luminosity in the case of air is due partly to the more perfect combustion, to the cooling effect of the nitrogen, and to the fact that in the presence of nitrogen a higher temperature is required to decompose the hydrocarbons. The cooling effect of the nitrogen prevents the separation of the carbon at certain parts of the flame, but the more perfect combustion makes the temperature at other parts higher than the corresponding parts of the luminous flame. The flame of the ordinary Bunsen burner consists of only two cones. The inner cone is a mixture of air and gas; combustion is taking place only in the outer one. That the flame does not travel inward is due to the rate of motion of the mixed gases ; in the outer cone this speed is diminished so that the gases can be raised to the point of ignition. If the rate of flow of the gases be diminished the flame will penetrate further and further inward and can be made to strike down the tube to the point of inflow of the gas and air. The absence of flame in the inner cone of the Bunsen burner may be shown in the manner already given for common flames. The Blow-pipe Flame. This flame is produced by forcing a stream of air across a common gas, candle, or lamp-flame. The mouth blow-pipe is an instrument of great utility. In its simplest form it consists of a bent tube terminating in a small end with an aperture. This flame shows three cones but they are peculiar in appearance being long and pointed. G.8. 107 The innermost cone is composed of a mixture of air and combustible gases not in the state of combustion ; the second cone is blue in color and consists of gases undergoing com- bustion but with an insufficient supply of air ; the outer cone is but very faintly luminous and the combustion is there complete. The space between the outer and middle cone is filled with hot combustible matter which displays great reducing or deoxidizing power, especially is this so at the point of the second cone; this flame is accordingly called the reducing flame. Nearly any metallic oxide placed just in the tip of this cone is deprived of its oxygen and reduced to the metallic state. The highly heated air just beyond the point of the outer cone oxidizes very readily, hence this outer cone is termed the oxidizing flame. In the mouth blow-pipe it must be understood that the air is not propelled from the lungs, but simply from the mouth by the muscles of the cheek. The current of air may be produced by a bellows or other mechanical means. Oxy hydrogen Flame. By forcing a stream of pure oxygen through a gas flame, a blow-pipe flame of very high temper- ature may be produced. A flame from a mixture of hydro- gen and oxygen in proper proportions gives the highest temperature obtainable by chemical means . In the production of the oxyhydrogen flame, the gases (hydrogen and oxygen) are usually led by tubes from separate holders to the jet or blow-pipe where they are burned and allowed to mix only just before burning. Special precautions are made in the blow-pipe so that the mixture can not there explode. Safety Lamps. The temperature to which a gas must be raised in order that combustion may take place has already been defined as its ignition point, commonly called the kind- ling point. Combustion can not take place until this tem- perature is reached and if the temperature of the burning gas be reduced below this point the flame will be extinguished. 108 This fact may be simply illustrated with the candle flame by coiling 1 a thin copper wire into a cylindrical spiral about one- half an inch long* and of such diameter as to coincide with the flame-cone. If the coil be placed over the candle the flame will be extinguished, but if the coil be first heated and then placed over the flame it will shoot above the coil and continue to burn. A copper wire-gauze of sufficiently fine meshes may be placed over a gas jet and the flame will not extend above the gauze, or if the gas be lighted above the gauze the flame will not pass below. In each of these cases the temperature of the burning gases is reduced below the kindling point and combustion ceases. Different substances have different ignition points and owing to this fact a wire-gauze through which a marsh gas flame will not pass readily, permits the passage of the hydro- gen flame. The above considerations make clear the principles of safety lamps. The most celebrated of these is Davy's miners' lamp. This is an oil lamp the flame of which is enclosed in a cage of wire gauze made double at the upper part where the heat of the flame is most felt. The gauze has 400 or 500 meshes to the square inch. The lamp is so arranged that the reservoir can be supplied with oil and the wick trimmed without unscrewing the cage and thereby exposing the flame of the lamp. In an explosive atmosphere of marsh gas and air, the fire- damp may burn within the cage but the flame will be extin- guished by the gauze and not ignite the mixture outside. The lamp thus serves to give indications of the state of the atmosphere in a mine and enables an examination to be made without risk to the inspector. This is the true use of the lamp and it is not intended to enable workmen to labor in an explosive atmosphere. 109 Stephenson' 's Lamp. Stephenson's original safety lamp was constructed upon the principle that the explosive mix- ture could be carried by the flame so rapidly that there would not be time for the mixture to be raised to the igniting" point. This rapid flow of the gases was accomplished by a tall chimney producing a powerful draught. If the velocity of the gases be greater than the rate of propagation of combustion in the mixture the flame will not spread. This principle has already been referred to in explaining the hollow structure of the Bunsen flame. The explosions which have so often proved disastrously fatal in coal mines and which the safety lamp is intended to help prevent, have in most cases been due to explosive mixtures of marsh gas, other hydrocarbons, and hydrogen with the air. Fine coal dust in the air of the mine increases the liability to explosion and in some cases this dust has been the sole cause of explosion. Explosions have occurred in flour mills through the general diffusion of flour dust throughout the building. Any readily combustible substance thickly distributed as fine dust through the air will burn with explosive effect. Slow and Flameless Combustion. There are several sub- stances which possess the power of causing the slow combustion of certain gases. Finely divided platinum or even platinum foil will bring about the combination of hydrogen and oxygen. A clean thin strip of platinum foil put into a jar containing a mixture of hydrogen and oxygen, will immediately cause their combination to begin, and if the foil be very thin its temperature may rise to redness and cause the explosion of the remaining mixture. If the platinum be reduced to the state of minute division as is the case of platinum black or its surface greatly extended as in spongy platinum, it immediately becomes red hot in a mixture of hydrogen and oxygen. Eydrogen falling upon platinum black in air is immediately ignited. Upon 110 this principle lamps for m^Gsteigous^ light have been constructed. If a thin piece of platinnm foil be heated but not suffi- ciently to emit light, and held in a jet of gas escaping from a Bunsen burner, its temperature will rise to redness and it will continue to glow as long as the mixed gases impinge upon it. This is a case of nameless combustion. The same result may be brought about in vapor of alcohol and ether. Although platinum possesses this property to a marked degree, it is not limited to this metal; palladium and gold display it to a less degree while glass and certain stones show it to a still lower degree. A full explanation can not be given of these results, but they are due to the property which the solids possess of con- densing gases upon their surfaces or of absorbing them and bringing them under the temporarily changed conditions within their sphere of mutual action. When the ignition point of a substance is lower than the temperature produced by its combustion, it will burn when once ignited ; but when the reverse is the case there will be required a continual application of external heat to keep up the combustion. SILICON. In many of its chemical relations silicon resembles carbon, but while the latter is the characteristic element of the organic kingdom the former is one of the most abun- dant elements of the mineral world. Silicon is not known to occur in the uncombined state, but in combination it is next to oxygen the most abundant and widely distributed element. In combination with oxygen, as silicon dioxide (silica), it occurs in sand and the various forms of quartz, which are among the most common and abundant forms of natural minerals. It also exists very widely in the silicates which result from the combination of silica with various metallic oxides. These silicates form the Ill great mass of the rocks which make up the earth's crust. Silicon oxide is also found in certain species of the vegetable kingdom. The element silicon is of no practical importance; it has been obtained both in the amorphous and crystalline forms, being in the first a dark brown powder and in the second of a metallic lustre resem- bling graphite. The powder burns vividly in oxygen until covered by a coating of silica; the graphitic form is incombustible. The amor- phous form readily attacks platinum when heated with it. It is claimed by some that there is a third form of silicon corresponding to the dia- mond form of carbon. Preparation of Silicon. Silicon may be prepared by decomposing potassium silico-fluoride at high temperature by potassium as indica- ted by the reaction, K 2 SiF e +K 4 — Si+6KF. After cooling the potas- sium fluoride is dissolved out by water. SILICA; Si0 2 . The only oxide of silicon, silica (Si0 2 ), is a very import- ant compound. Alone or in combination it forms a very large proportion of the earth's crust. The purest natural form of silica is rock crystal, a clear transparent variety of quartz. The dense white varieties of sand are nearly pure silica ; in a less pure form silica and the silicates constitute the greater part of nearly all soils. Its action in soils seems to be mainly mechanical as silica takes but little part in the direct sustenance of plants. It serves as a receptacle or basis through which the other ingredients of the soil are dis- tributed. Its chemical and physical stability admirably fit it for this purpose. Silica is found in the outer sheaths of cer- tain grasses and reeds and as tabasheer in the joints of the bamboo. This fact proves its solubility to a certain extent otherwise it could not be taken up by plants. Many hot springs and geysers also dissolve it. It is deposited in large quantities by the springs and geysers of the Yellowstone Park. The natural varieties of silica are insoluble in pure water but hot alkaline solutions readily dissolve the amorphous 112 varieties and under high temperature and pressure also dis- solve many of the crystallized forms. Silica is essentially an acid oxide forming salts with many metallic oxides. Owing to its non- volatility, it decomposes all salts of volatile acids when highly heated with them. It thus replaces acids which at a lower temperature displace it. When heated with bases, silica generally unites with them forming silicates. The silicates are the most common and abundant of minerals. As feldspars and micas the silicates enter largely into the composition of granitic rocks and the different varieties of clay are hydrous silicates of aluminum. Common glass is a mixture of several silicates. The silicates as a class are all insoluble except certain alkaline silicates in which there is a large proportion of the base. Silicic acid is generally represented as tetra-basic and the formula written H 4 Si0 4 , or Si0 2 with 2H 2 0, but the formulas of many of the silicates indicate their derivation from silica combined with more or less than two molecules of water. A compound consisting of silicon and carbon (SiC) can be prepared by heating silica with carbon in an electric furnace. The compound is called carborundum and has come into considerable prominence lately as an abrasive. It is made in large quantity at Niagara Falls. BORON. This element has not been found in the free state. In combination it is almost entirely confined to the mineral kingdom though its pre- sence has been detected in grape Tines and a few other plants. It is the basis of boric acid in which combination it is found in certain volcanic waters and forming many borates of the metals, one of the most important and common of which is sodium borate or tincal. The element may be obtained by heating boron trioxide with potassium. B 2 3 +3K 2 — B 2 -f 3K 2 0. In this manner boron is obtained as a dark brown powder. Boric Oxide and Acid. Boron forms but one oxide the formula of which is B 2 3 . This oxide forms three oxy-acids. The native acid found in volcanic regions is tribasic represented by the formula 3H 2 0, B 2 O s or H3BO3, but is converted into other forms by the action of heat; at red heat all the water is driven off. 113 The acid is an antiseptic and is sometimes used alone or with glycer- ine to preserve meats and other food. The solution of the acid in alcohol imparts a green color to the flame of the vapor. It will give color to steam issuing- from a boiling solution of the acid if a flame be held in the steam. Borates. At high temperature boric oxide combines with many metallic oxides giving glassy borates which often have characteristic colors — upon this property depends the main use of boric acid in the arts. The formulae of most of the borates do not indicate their deriva- tion from a tribasic acid. Borax or sodium borate is one of the most important of this class of salts. Borax occurs native in tincal. It is readily prepared by the action of boric acid on sodium carbonate. It will be further mentioned under sodium. COMPOUNDS OF HYDROGEN AND NITROGEN. Ammonia (NH 3 ). This is a compound of hydrogen and nitrogen indicated by the formula NH 3 . It is primarily of organic origin and results from the putrefaction of organic matter, from the destructive distillation of coal, bones, and other organic matter. It is constantly removed from the air through absorption by rain and by the soil. It has been found in the emanations of volcanoes. In the com- bined form it is frequently present in beds of guano (the excrement of sea fowls) and as the chloride and sulphate in certain volcanic regions. It is also present in small quantity as carbonate, nitrites, and nitrates in soils and water where, in the last named forms, it becomes available for plant food. Animals during life, and both plants and animals after death return to the air in the form of ammonia the nitrogen which existed in their organisms and possibly some of it is returned as free nitrogen. They thus return to the air the ammonia which was taken from it. The manner in which the nitrogen of the air was originally made available for food and started upon its endless circuit has been difficult to determine and even now is not thoroughly understood. It has lately 1 uvn found that certain species of bacteria exist which are capable of oxidizing the nitrogen of the air and thus starting it upon the cycle of plant service. One form of these 8 114 bacteria is found to ply its vocation in connection with the growth of leguminous plants having" their homes in the roots of the plants. It is also found that bacteria are instrumental in transforming the nitrogen of dead organic matter into available shape for plant use again. Physical Properties of Ammonia. Ammonia is a color- less gas, having a strong, pungent odor which excites to tears. It has a caustic, burning taste. Its specific gravity is eight and one half referred to hydrogen. It is liquefied by a temperature of — 40° C. at atmospheric pressure, or by a pressure of six and one half atmospheres at 10° C. In the liquid state it is a colorless mobile liquid which at 0° C. has a specific gravity .62. Its boiling point is — 33. 7° C. under atmospheric pressure. During the evaporation of liquid ammonia great reduction of temperature takes place and it has for this reason been frequently used in the artificial production of cold for freezing, or other purposes. Gaseous ammonia is more readily soluble than any other gas, water at 15° C. dissolving over 750 times its volume, the volume of the solution being something more than one and one half times that of the water. During the solution of the gas more heat is evolved than corresponds to the liquefaction of the gas, which can only be attributed to chemical action. The gas however can be entirely removed from the water and no definite compound of the two is known. The solubility of the gas increases as the temperature of the water diminishes. The great solu- bility of ammonia in water may be strikingly illustrated by filling a bottle with ammonia by displacement over mercury, making the mouth of the bottle air-tight and transferring to a vessel of water; when the stopper is removed the water immediately fills the bottle and if the water be admitted by a tube through the cork it will play as a fountain. In Carre's freezing apparatus for ice, liquid ammonia is 115 allowed to evaporate from a strong" iron receiver which sur- rounds the water to be frozen. The vapor of the ammonia is absorbed by water contained in another receptacle, so as to increase the rapidity of evaporation from the receiver. The ammonia can then be driven ont of the water in the second vessel by heat and condensed by its own pressure in the receiver and the operation repeated. The boiler is of course allowed to cool before evaporation from the receiver begins. Chemical Properties of Ammonia. Ammonia is alkaline to a very high degree ; it has the alkaline action on vege- table coloring matter and combines with acids, neutralizing them completely. It can be kindled in the air, but will not continue to burn when the external source of heat is removed. In an atmosphere of pure oxygen the ammonia burns with a continuous flame. It is decomposed into its elements by passage through a red hot tube, two volumes of ammonia producing one volume of nitrogen and three volumes of hydrogen. Ammonia escaping into an atmosphere of chlorine takes fire and burns producing ammonium chloride. Its solution is largely used in the arts and as a reagent in the chemical laboratory. By neutralizing the solution of ammonia with the mineral acids, salts are obtained bearing- strong resemblance to the corresponding salts of sodium and potassium. This taken in connection with the other strong- alkaline characters, has given rise to the suggestion that the solution of ammonia contains an alkaline hydroxide (XH 4 OH) similar to KOH and NaOH, in which NH 4 performs the same function as potassium and sodium. This hypothetical radical (NH 4 ) is called ammonium. The salts from the solution of ammonia may be considered as formed either by the direct union of ammonia with the acids or by the replacement of the hydrogen of the acid by ammonium; in the latter case ammonium acts similarly to 116 the metals in forming" salts. The salts of ammonium will be more fully described in connection with the metallic salts. Ammonia is easily expelled from its salts by heating with slaked lime or a solution of potash or soda. On account of its striking* odor this gives a ready test for such a salt. Preparation of Ammonia. There are many sources from which ammonia may be obtained, but the chief source is the ammoniacal liquor of the gas-works. The manufacture of gas will be described later, at present it is sufficient to know that ammoniacal liquor results from the destructive distillation of coal in the manu- facture of gas. This liquor contains several compounds of ammonia, two of the most important of which are the carbonate and hydro srilphide (NH 4 ) 2 C0 3 , and NH 4 HS. The liquor containing these substances is heated with lime in a still, the lime displaces the ammonia from combination and it is conducted into a tank containing sulphuric or hydrochloric acid. The acid combines with the ammonia forming ammonium sulphate or chloride, depending upon the acid used. There is always some hydrogen sulphide driven on 2 in the operation, but this escapes from the receiv- ing tank and is burned. The sulphate of ammonia is the form in which the ammonia is generally sold for fertilizing. The chloride after purification by heating and sublimation is used for various purposes and is the form generally used to give pure ammonia. From the chloride, ammonia is readily obtained by heating it with powdered lime as indicated by the reaction, 2NH 4 Cl+CaO=CaCl 2 +H 2 0+2NH 3 . The gas may be conducted into a vessel of water until a solution of the required strength is obtained. By this means liquor ammonia is prepared as an article of commerce. The most convenient way of obtaining ammonia for labo- ratory purposes is to gently heat liquor ammonia; the gas passes from the solution Very readily and may be collected 117 by downward displacement or over mercury. The gas may be readily prepared for laboratory nse directly from the chloride as above indicated if the liquor ammonia be not on hand. In the above method of separating the ammonia from the ammoniacal liquor of the gas-works, the ammonia was dis- placed from its combination by another base, lime being used. It is possible (and sometimes done) to treat the ammoniacal liquor with an acid (sulphuric or hydrochloric) which combines with the ammonia and liberates carbon dioxide and hydrogen sulphide. But the sulphate or chloride thus produced is mixed with many other constituents of the liquid and is more difficult to purify. Other sources for the commercial preparation of ammonia are the blast furnaces and coke ovens ; the ammonia in these cases also resulting from the destructive distillation of coal. Although the direct combination of nitrogen and hydro- gen is only acconfplished with difficulty, this compound is sometimes produced when nitrogen is brought into contact with nascent hydrogen. Hydrozine or Hydrozoic Acid. There are two other compounds of nitrogen and hydrogen hydrozine (N 2 H 4 ) and hydrozoic acid (N 3 H), but they have up to the present time received no useful application. COMPOUNDS OF NITROGEN AND OXYGEN. These elements under ordinary conditions show no dispo- sition to enter into combination, however there are rive distinct compounds of them known; viz., N 2 0, NO, N 2 O b >, N0 2 =N 2 4 , and N 2 5 . These formulae show that the quanti- ties of oxygen that unite with a given quantity of nitrogen are to each other as 1:2:3:4:5. There are three oxy-acids of nitrogen corresponding to the first, third and fifth of these oxides. The compositions of these acids and their relations to the corres- ponding oxides will be seen from the following formulae; 118 N N ^O Hyponitrous anhydride. |tO Hyponitrous acid. ^ T qO Nitrous anhydride. ^ O Nitrous acid. ^q 2 Nitric anhydride. h° 2 ° Nltric acid - The first two acids have not been obtained in a free or pure state and are known from their salts. The third is the most important of these acids and is the one from which all the compounds of nitrogen and oxygen are obtained directly or indirectly. NITRIC ACID. Preparation. The combination of oxygen and nitrogen can be brought about directly by artificial means, and in the presence of water nitric acid results but the acid is always prepared from natural nitrates. The manufacture of nitric acid is a commercial process and is accomplished by heating sodium nitrate with sul- phuric acid in suitable retorts, usually in cast iron cylinders. The proportion of the reagents and the final reaction are indicated by the equation, 2NaN03+H 2 S0 4 =Na 2 S0 4 +2HN0 3 . The nitric acid vapor produced is conducted from the retorts into stoneware or other suitable receivers in which it is condensed, the receivers being cooled by water. During the operation some of the vapor of the nitric acid is decomposed thus, 2HN0 3 =H 2 0+0+2N0 2 , the last product being a red vapor which in the solution of the condensed acid gives it a yellowish-red color. Pure nitric acid is colorless, but if exposed to sun-light the above reaction takes place with the resulting color. The oxygen thus liberated exerts a pressure on the acid in the bottle and may result in ejecting some of the liquid when the stopper is withdrawn. The strongest acid in the com- mercial manufacture is obtained by using pure reagents and collecting the middle portion of the distillate separately. For the most concentrated colorless acid some other precau- 119 tions are necessary. The strength of the acid is indicated by the specific gravity ; the strongest has the specific gravity 1.53, common aquafortis has the specific gravity of 1.30 and contains less than 50 per cent of acid. On a small scale in the laboratory the acid may be made from either potassium nitrate or sodium nitrate by heating the salt with sulphuric acid in a glass retort and condensing the acid in a flask cooled by a wet cloth. In the laboratory method it is better to use the reagents in the proportions indicated by the following reaction, KN03+H 2 S0 4 =KHS0 4 + HN0 3 , for this reaction requires lower temperature and the acid salt is more easily dissolved out of the retort than would be the normal sulphate, which would be formed were double the amount of nitrate used. A given quantity of Chili saltpetre will produce more acid than the same weight of common nitre. In India and other dry countries potassium nitrate occurs in certain places as an efflorescence on the surface of the soil. This is the principal source of nitre. Sodium nitrate or Chilian saltpetre occurs as immense beds along the northern coast of Bolivia and Peru. Properties of Nitric Acid. Nitric acid when pure is a colorless liquid which fumes strongly in the air owing to condensation of the acid vapor by the aqueous vapor of the air. It has a very choking, suffocating smell. It is very corrosive, the strongest acid produces painful sores when brought into contact with the skin, and the dilute acid turns the skin and other organic matter yellow. A drop of sul- phuric or hydrochloric acid will stain cloth red and the color may be partially or wholly restored by prompt application of ammonia while the stain of nitric acid is intensified by ammonia though the corrosive action is prevented. Under ordinary conditions strong nitric acid is weakened and weak nitric acid strengthened by boiling, until an acid of 6*8 per cent is reached when the whole distils over without 120 any change. If the pressure nnder which the distillation occurs be varied the strength of the distillate will also vary. Nitric acid is a powerful oxidizing agent, very few substances being able to withstand its action. Phosphorus dropped into a dish containing strong nitric acid is oxidized, often with such energy as to give name, P 2 5 being pro- duced. Sulphur is oxidized by hot nitric acid to sulphur trioxide S0 3 . Finely divided carbon or sawdust may be set on fire by strong nitric acid. Nitric acid acts upon some organic substances so readily as to inflame them. A small quantity of oil of turpentine poured upon strong nitric acid in an open capsule ignites with some violence. Hair or silk may be made to take fire by holding it in the vapor of boiling nitric acid. Nitric acid acts upon all the common metals except gold, platinum and aluminum. It generally forms nitrates but sometimes only oxidizes the metals. Owing to its strong oxidizing power hydrogen is never evolved by the action of this acid upon the metals. The hydrogen displaced by the metal is oxidized by the remaining acid present. It has been shown that if nitric acid is entirely free from nitrous acid it acts very slowly if at all upon many metals. In addition to the actions above named, nitric acid acts upon a variety of organic compounds, one or more atoms of the hydrogen of the organic compound being replaced by one or more molecules of N0 2 . The resulting compounds are nitro-substitution compounds and will be referred to again. Nitric acid is mono-basic. Uses. Nitric acid is of great importance in the arts; among its most important uses may be mentioned the manu- facture of coal-tar colors, the preparation of nitro-com- pounds which include nearly all the high explosives, of many nitrates used in the arts, and the refining of gold and silver. An alloy of copper with gold is readily detected by 121 touching" it with nitric acid when the copper present will give the green nitrate. It is remarkable that the dilute acid generally acts more readily than the concentrated. Nitrates. The nitrates constitute a very important class of salts. They are all decomposed by heat and are soluble in water (with unimportant exceptions). They are, like 'the acid, oxidizing agents. Powdered lead nitrate and charcoal may be exploded by a blow. Common nitre is used in gun- powder because of its oxidizing power and several other nitrates are employed in other explosives. The negative chemical properties of nitrogen, its little disposition to combine with other elements and its character as a permanent gas are probably at the basis of the insta- bility of its compounds, to which we shall have frequent occasion to refer. The nitrates being generally soluble the acid can not be precipitated and it is not so easily detected in solution as the other common mineral acids. The easiest test is as follows — add to the suspected solution in a test tube, a solution of iron sulphate ; then introduce below the mixed liquids concentrated sulphuric acid if there be present any nitrate, the sulphuric acid will liberate the nitric acid and the ferrous sulphate reduces it to N0 2 which colors the two liquids at the surface of their junction. Nitrous Oxide, Laughing Gas, N 2 0. This gas may be obtained by heating ammonium nitrate in a Florence flask fitted with cork and delivery tube. It may be collected by displacement over warm water or mercury. The nitrate should be heated gently or nitric oxide will be produced. Properties. N 2 is a colorless transparent gas with a slight odor and sweetish taste. It is more soluble than oxygen, water dissolving its own volume at 10° C. It sup- ports ordinary combustion like oxygen; the combustion is due to the oxygen, the nitrogen monoxide being decomposed and the nitrogen set free. Carbon burned to carbon dioxide in nitrogen monoxide produces more heat than when burned 122 ill oxygen which shows that heat is evolved in the decompo- sition of nitrous oxide and must have been consumed in its production. A substance which absorbs heat in its produc- tion is called endotliermic, one which gives it out exothermic. Laughing gas is used as an anaesthetic in dental surgery. It may be drawn into a test tube in the liquid state from the holder. The liquid supports combustion. It may be dis- tinguished from oxygen by its greater solubility and sweetish taste. Nitric Oxide, NO. This oxide is readily obtained by the action of dilute nitric acid npon copper. The metal is oxidized and the acid deoxidized with the separation of nitric oxide, the oxide formed is acted upon by another portion of the acid and copper nitrate is formed. The nitric oxide is a colorless transparent gas, but in con- tact with oxygen it unites with it, giving the nitrous oxide if the oxygen be in excess, otherwise some trioxide is formed, giving a very characteristic reddish brown vapor. The presence of oxygen may be readily detected by the addition of this gas. It will support combus- tion if the temperature of the burning body is high enough to decom- pose the gas. OTHER OXIDES OF NITROGEN. Nitrous Anhydride, N 2 3 . There is still some uncertainty as to the existence of this compound. The substance generally assumed to be X 2 3 is very probably a mixture of nitrous and nitric oxides. A solu- tion of the substance is believed to contain nitrous acid, though the acid has not been isolated. Nitrogen Tetroxide. This substance is the main result of the action of oxygen upon the nitric oxide. This gas possesses the property of combining directly with certain metals forming nitro-metals. The tetroxide will support combustion if the temperature of the burning body be high enough to decompose the gas. Nitrogen Pentoxide, N 2 5 . The pentoxide may be obtained by dehydrating nitric acid with phosphorus. It is a white crystalline sub- stance. It is very unstable and when suddenly heated explodes with violence. It dissolves in water forming nitric acid. CHLORINE; CI. Chlorine has not been found in the uncombined state in nature. It is a member of an important natural group including iodine, br online, and fluorine. On account of the 123 occurrence of the first three in the salts of sea water, the group has been called the halogens, and their compounds the haloid compounds. In combination with the metals, chlorine is of abundant occurrence, the most common chloride being" sodium chloride, common salt. In the Stassfurth deposits potassium chloride is also an abundant constituent. Many other chlorides occur native. The chlorides of sodium and potassium, especially the latter, are found in animal secretions. Chlorine is also found in combination with hydrogen as hydrochloric acid, in the gases issuing from certain volcanoes. Preparation of Chlorine. Chlorine may be extracted from common salt by heating a mixture of the salt and man- ganese dioxide with dilute sulphuric acid. The reaction is indicated by the equation 2NaCl+Mn0 2 +2H 2 S0 4 =Na 2 S04+ MnS(X+2H 2 0+Cl 2 . Chlorine may also be obtained from hydrochloric acid by gently heating manganese dioxide with it, as indicated by the equation, Mn0 2 +4HCl=MnCl 2 +2H 2 0+ Cl 2 . This gas is a very offensive one to deal with and special precautions and care should be taken in obtaining and manipulating it. On the manufacturing scale chlorine is obtained by the second method. Chlorine is now prepared on the manufacturing scale in Europe by the electrolysis of common salt. The same process is employed in this country to prepare sodium hydroxide but the chlorine, so far as can be learned, is wasted. Physical and Chemical Properties. Chlorine is a greenish yellow gas, with a specific gravity of 35.5 referred to hydro- gen. It has a disagreeable suffocating odor and is easily liquefied. At ordinary temperature water dissolves about two volumes of the gas. For experimentation chlorine is collected by displacement, or over tepid water; it acts upon mercury and there is considerable loss in collecting it over 124 # cold water. A strong brine solution dissolves it much less readily than water. Chlorine has powerful affinities and unites with a great number of the other elements even at ordinary temperature. Its affinities do not extend to oxygen but are strongly exerted towards hydrogen and the metals. Its affinity for hydrogen is its most distinguishing characteristic. It combines directly with hydrogen, bromine, iodine, sulphur, arsenic and phosphorus. Phosphorus finely divided or a well dried piece, will take fire in chlorine; powdered arsenic dropped into the gas inflames. It combines directly and at ordinary temperature with nearly all the metals. Powdered antimony and several other metals in the form of thin leaf take fire when dropped into the gas. On account of its affinity for hydrogen a lighted wax taper plunged into the gas will continue to burn with a smoky flame, the hydrogen of the taper burning, the carbon being separated. For the same reason many of the hydrocarbons will take fire spontaneously ; a strip of bibulous paper wetted with oil of turpentine and plunged into the gas bursts into flame with a copious liberation of soot — a mixture of chlorine and acetylene explodes violently when exposed to light. Chlorine is not capable of direct combination with carbon, which fact accounts for the separation of the carbon in the cases just cited. On account of its attraction for hydrogen it will decom- pose water if the solution be exposed to light. A mixture of hydrogen and chlorine can be kept in the dark, but if exposed to diffused daylight they combine quietly, if to direct sunlight, they combine suddenly with explosion. Uses. The most useful applications of chlorine depend upon its affinity for hydrogen. Its most valuable property from an industrial point of view is its bleaching power. 125 Chlorine poured into a solution of indigo or other vegetable coloring matter will rapidly discharge the color. The same action is observed if cloth dyed with vegetable colors be dipped in a solution of chlorine. Colored flowers are bleached when dipped into a jar of the gas. For bleaching it is essential that water be present, as per- fectly dry chlorine does not even affect litmus. The chem- istry of the process seems to be due to the action of the chlorine upon the water, liberating the oxygen, which in connection with the chlorine converts the coloring matter into oxidized or chlorinized products, which are colorless or nearly so. Chlorine is largely used in the arts for bleaching linen and cotton goods and rags for the manufacture of paper. Silken and woolen goods would be injured by chlorine and are bleached with sulphurous acid gas. For bleaching pur- poses neither the gas nor its solution is so convenient as the combined form, hence it is generally employed in the form of bleaching powder called chloride of lime, from which the gas is easily liberated as desired. Chlorine is also one of the best deodorizers ; by virtue of its affinity for hydrogen it breaks up and removes from the air hydrogen sulphide and ammonia both of which result from the putrefaction of organic matter and are very ob- jectionable. Chlorine is also used as a disinfectant; its affinity for hydrogen and its oxidizing power enable it to destroy certain micro-organisms which are injurious to health. Liquid chlorine is now an article of commerce ; it is put up and transported in iron bottles lined with lead; it is used in the extraction of gold from its ores. HYDROCHLORIC ACID; HCI. Occurrence. It occurs in nature in the gases omitted from volcanoes and has also been found in the spring waters of volcanic districts. 126 Preparation. Hydrochloric acid may be produced by the direct union of the elements but for use it is always prepared by acting upon sodium chloride with sulphuric acid as indicated by the following reaction, NaCl+H 2 S04=NaHS0 4 -fHCl; the gas may be collected by displacement or over mercury. By using the proper proportion of the ingredients and a higher temperature the reaction for the production of the acid can be made to take the form, 2NaCl+H 2 S0 4 = Na 2 S0 4 +2HCl. Hydrochloric acid was formerly obtained in enormous quantities as a bye-product in the Leblanc process of manufacturing sodium carbonate, the first step in the operation being indicated by the above reaction. The manufacturer of the alkali was compelled to prevent the escape of the liberated acid into the air because of its destructive action upon vegetation. Owing to changes in the methods of making alkali the hydrochloric acid is now a principal product in the Leblanc method. The acid vapors resulting from the action of the sulphuric acid upon the salt, are thoroughly cooled and then brought into contact with a large surface of water by which the acid is absorbed. Properties. Hydrochloric acid is a colorless gas with choking pungent odor. It fumes strongly in the air by con- densing the moisture there present. Its formula shows it to be heavier than air. It is very soluble in water, one volume of water at ordinary pressure and 0° C. dissolves 500 volumes of the gas. As is generally the case the solubility decreases as the temperature rises. The solubility of the gas may be illustrated in the same manner as with ammonia. The common liquid designated as hydrochloric acid is a solution of the gas in water, the strongest solution at 8° C. and ordinary pressure contains 43.8 per cent of the acid and has a specific gravity of 1.22. The strength of the acid may be inferred from its specific gravity. 127 If a weak solution of the acid be boiled, it loses water and becomes stronger; if a strong solution be boiled it loses acid and becpmes weaker until in each case the solution contains 30 per cent of the acid when this solution distils over at a temperature of 110° C. This would seem to indicate a definite compound between the water and acid in the proportion named, but this proportion changes with the pressure. Commercial hydrochloric acid is usually yellow from impurities. It is very likely to contain some chlorine, some sulphuric acid, some arsenic, and some iron chloride. Mix- tures of snow or powdered ice and hydrochloric acid make very convenient refrigerants. Hydrochloric acid is readily liquefied by cold and pres- sure. The liquid acid is colorless, with a specific gravity of .9. The liquid acid is almost without action upon most of the metals which are readily attacked by the aqueous solu- tion. The liquid acid does not act upon lime. Dry hydro- chloric acid gas does not act upon calcium carbonate. Action of Hydrochloric Acid upon the Metals and Metal- lic Oxides. All the metals which decompose water will more readily act upon hydrochloric acid liberating hydrogen and forming a chloride. Sodium, potassium, zinc, iron, and tin are examples. Hydrochloric acid does not readily act upon aluminum and when boiling to a slight extent upon silver. The acid acts upon metallic oxides, forming a chloride and water, two atoms of chlorine replacing one atom of oxygen. Those oxides to which there are no corresponding chlorides (the less basic oxides) frequently evolve chlorine from the acid. Thus while the lower oxide of manganese forms manganese chloride (MnCl 2 ), Mn0 2 evolves chlorine; MnO+2HCl=MnCl 2 +H 2 0; MnO 2 +4HCl = Mn01 2 + 211-0+01,.. Of the common metals the dichlorides are soluble in water except the dichloride of lead, the monochlorides are soluble except those of silver and mercury. Any soluble chloride in solution gives upon the addition of silver nitrate a white 128 curdy precipitate of silver chloride, which blackens upon exposure to light and is readily soluble in ammonia. This is a very characteristic test for a chloride in solution. AQUA REGIA ; NITRO=MURIATIC ACID. This is a name given to a mixture of three volumes of hydrochloric acid and one of nitric acid. The mixture will dissolve gold or platinum while neither of the acids singly will do it. A chloride of the metal is formed and the power of the mixture depends upon the chlorine liberated. HN0 3 + 3HC1=2H 2 0+N0C1+C1 2 . COMPOUNDS OF CHLORINE AND OXYGEN. Chlorine and oxygen have not been made to combine directly but there are known two oxides of chlorine and four oxy-acids ; the oxides are C10 2 and C1 2 0. The oxides are very unstable bodies and dangerous to handle because of their explosive character. The oxy-acids of chlorine are hypochlorous (HCIO), chlorous ( HCIO 2 ), chloric ( HCIO 3 ), and perchloric (HCIOJ. The salts of the first and third are of considerable importance. Some of the metallic hypo- chlorites are useful in bleaching and potassium chlorate is of practical importance as an oxidizing agent ; these salts will be referred to under the metals from which they are formed. COMPOUNDS OF CHLORINE WITH CARBON, SILICON, BORON, AND NITROGEN. Although chlorine does not combine directly with carbon, several chlorides of carbon can be obtained by indirect means as by the action of chlorine upon the hydrocarbons one atom of chlorine removing and combining with one atom of hydrogen and another atom of chlorine taking the place of the removed atom of hydrogen. This mode of sub- stitution is called metalepsis. Chlorine combines directly with silicon and boron. With nitrogen it forms a very explosive compound indica- ted by the formula NC1 3 . This compound is formed by the action of chlorine upon ammonium chloride and is very dangerous to handle. BROMINE; Br. Occurrence. Bromine is not found free in nature. It occurs mainly in combination with potassium, sodium, and magnesium in small quantities in sea water; more abun- dantly in certain mineral waters as at Kissingen and in the 129 mother liquor of the salt works at Stassfurth, Germany, and of several of the salt works of the United States. Most of the bromine consumed in the United States comes from the mother liquor of the salt works in the United States and some from Stassfurth. It is obtained in greater quantity from the Ohio brine wells, and some from those of Pennsyl- vania, West Virginia and Michigan. Preparation. After the less soluble salts are separated from the mother liquor by evaporation and crystallization, the liquor is intro- duced into a still and acted upon by chlorine. The chlorine liberates the bromine which is distilled off by passing steam into the still. The chlorine may be produced in the same still or introduced from a separ- ate retort. Properties. Bromine is the only non-metallic element which is liquid under ordinary conditions ; it has a distinct red color; at 15° C. it has a specific gravity of 3. It emits an orange reddish acrid vapor which is very irritating and dis- agreeable, more so than that of chlorine. Three parts dis- solve in 100 parts of water by weight. In its chemical attributes it resembles chlorine; it combines directly with many metals and non-metals and bleaches like chlorine. Little use has been made of bromine since chlorine can generally be used for the same purposes and is much more abundant. It has, however, been used as a disinfectant, in the manufacture of coal tar dyes, and in analytical chemistry; for the last it is much more convenient than chlorine, being a liquid. For disinfecting the liquid is absorbed by cakes or sticks of kieselguhr or other porous earth made plastic by molasses. These sticks absorb a large amount of bromine and are kept in tightly stopped bottles. Several bromides are employed in medicine and in photo- graphy. Bromine is soluble in carbon disulphide and ether. Hydrobromic Acid; HBr. Bromine combines directly with hydro- gen forming hydrobromic acid (HBr). corresponding to hydrochloric acid (HG1). Oxy=Acids of Bromine. No oxides of bromine have boon obtained but there are two oxy-acids similar to the corresponding chlorine acids. Hypobromons acid (HOBr) and bromic acid (HBrO s ). 9 130 IODINE; I. Iodine has not been fonnd in a free state; in nature it occurs in combination, principally with potassium, sodium, magnesium, and calcium as iodides or together with these metals and oxygen as iodates. Iodine is found in sea water, in many mineral waters, and as sodium iodate (NaI0 3 ) in the Chilian nitre beds. Preparation. The two principal sources of iodine are kelp (the ashes of sea weed) and the native Chilian saltpetre or "Caliche," the latter source now furnishes the greater pro- portion of iodine. Many varieties of sea-weed extract the iodine from sea water as a necessary portion of their food ; when these weeds are burned the iodine is left in the ashes or "kelp," together with a large number of other salts. The iodine is mainly in the form of iodides of sodium and potassium. These iodides are separated from the other salts as per- fectly as possible and then the iodine is liberated by the combined action of sulphuric acid and manganese dioxide exactly as chlorine is liberated from common salt. In the "Caliche " the iodine is in the form of sodium iodate (XaI0 3 j from which it is precipitated by the action of acid sodium sulphite. Properties. Iodine is a crystalline solid of a bluish black color resembling graphite. In the solid state its specific gravity is nearly 5. It volatilizes sensibly at ordinary tem- perature diffusing an odor resembling that of chlorine. It fuses at 114° C. and gives a beautiful violet vapor which is one of the heaviest known gases being nearly nine times as heavy as air. At a higher temperature the color of the vapor changes and its density becomes less. It is slightly soluble in water, readily soluble in carbon disulphide, benzene, petroleum spirit, and solution of potas- sium iodide and alcohol. In chemical properties it resembles chlorine and bromine but is less energetic being displaced from its compounds by these elements. It combines directly with many elements both metallic and non-metallic. Phosphorus placed in con- tact with powdered iodine at once takes fire, as also does 131 powdered antimony when dropped into iodine vapor. In the presence of water it attacks gold. When brought into con- tact with starch it gives a sky blue color; this is a very delicate test for free iodine and will reveal the presence of a millionth part in any liquid ; iodine in combination will not affect the starch. Uses. Iodine is largely used in the manufacture of aniline colors but the bulk of its compounds is used in medicine. A small quantity is also used in photography — the iodides of silver, potassium, ammonium, and cadmium being used for this purpose. The tincture of iodine is a mixture of iodine and potas- sium iodide dissolved in alcohol. Iodine dissolved in carbon disulphide gives a solution opaque to light but transparent to heat. To give the starch test the iodine must be in the free state and as it nearly always exists in combination, it is necessary to add to the liquid under examination some agent to liberate the iodine. The test is usually made by adding to the suspected liquid a little starch paste then a little chlorine water, the chlorine will liberate the iodine if present in the form of an iodide. Iodine is of course an equally delicate test for starch. Iodine can be combined directly with hydrogen to form hydrogen iodide or hydriodic acid ; this acid is very similar to hydrochloric and hydrobromic acids. Oxides and Oxy=Acids of Iodine. Iodine can be directly oxidized by ozone but the only oxide definitely known is I 2 O r> . Iodic acid (HI() 3 ) has been isolated. The periodic acid (HIC) 4 ) has not been isolated, but salts corresponding to the acid are known. Other Compounds of Iodine. Iodine combines with carbon, nitro- gen and boron forming compounds similar to the chlorine compounds of the same elements. Considering the chemical resemblance of chlorine, bromine, and iodine it is very remarkable that the elements all combine with each other. FLUORINE; F. Occurrence. Fluorine occurs in combined form as fluor-spar (CaF, ) — sometimes called Derbyshire spar on account of its abundant occur- 132 rence in Derbyshire. It is also present in the mineral cryolite a double fluoride of aluminum and sodium. In a small quantity it is present in a number of other minerals, in the bones, and in the enamel of teeth. Fluor-spar is the most abundant compound containing it. This mineral crystallizes in cubes or octahedrons with varying shades of color, some of which are very delicate and beautiful. Preparation and Properties. Fluorine was not isolated until 1SS6. It was then obtained by decomposing hydrofluoric acid i HF i by elec- tricity. It is a colorless gas and the most chemically active element known. On account of its intense disposition to combine with other elements, it resisted until recently all attempts to isolate it. It decom- poses water instantly and combines readily with mercury. It explodes with hydrogen even in the dark, and combines with combustion with many non-metals, attacks the metals, and even attacks glass. No com- pound with oxygen is known. Hydrogen Fluoride; HF. This is the most important compound of fluorine. The pure acid can be obtained by heating acid potassium fluoride in a platinum retort with platinum tube and condensing arrangement cooled by a freezing mixture. The acid thus obtained is a colorless liquid a little lighter than water. It has a strong affinity for water and produces a hissing noise when brought into contact with it. A solution of hydrofluoric acid in water is obtained by heating pow- dered calcium fluoride i GaF 2 1 with sulphuric acid.. CaF 2 +H 2 S0 4 = 0aSO 4 +2HF. This operation is performed in a leaden retort with tube and condenser of the same metal, the condenser being cooled by a freezing mixture. This solution possesses powerfully acid properties and the vapor escapes rapidly from the water as the temperature rises. The dilute acid dissolves all ordinary metals except platinum, gold, silver, mercury, and lead. It also readily attacks glass if the least moisture be present, though it has been found that the anhydrous acid does not affect glass. Uses. The principal use of hydrofluoric acid depends upon its power of acting upon silica and the silicates. Powdered sand maybe dissolved in the aqueous solution of the acid and if the solution be evaporated the silica will volatilize as silicon fluoride (SiF 4 1. If a sili- cate be digested and heated with the acid a fluoride of the base will be left. The action of the acid upon glass is explained by its power of attacking silica, for glass is a mixture of two or more silicates. A design may be etched or engraved upon glass as follows : let the plate be coated with wax or etching-ground and the design drawn with a pointed instrument cutting through the wax. The plate is then placed with the waxed side down over a shallow leaden dish which contains calcium fluoride and sulphuric acid. Upon the application of a little heat the acid is disengaged and speedily makes the impression 133 upon the glass. If the engraving- is done with the vapor of the acid, the design is dull or opaque ; if the liquid acid is employed the lines are transparent. The gaseous acid does not produce an uniform opacity and is there- fore not generally suitable for the purpose. For opaque etchings a solution of the acid fluorides of the alkalies is used, usually one contain- ing some potassium or ammonium sulphate. SULPHUR; S. Occurrence. This is an elementary body of great import- ance. It occnrs abundantly in the free state and also as a constituent in many combined forms. In the uncombined form it is usually though not invariably found in volcanic- regions. In some localities sulphur is being deposited from chemical actions now taking place. These are called "living- sulphur beds" and occur in the regions of geysers, hot springs, fumaroles, and other evidence of recent volcanic- activity. The free sulphur is also found disseminated through stratified deposits alternating with beds of clay or other minerals. Sicily produces the greatest amount of native sulphur. It is also found in our own country in California, Nevada, Wyoming, Arizona, and Utah. The mines at Cove Creek, Utah, supply a considerable amount of sulphur. It occurs in many other places throughout the world. In the combined form it occurs as the sulphide of many metals, the most important being iron pyrites, FeS 2 ; copper pyrites, CuFeS 2 ; galena, PbS; zinc blende, ZnS; and cinna- bar, HgS. It occurs in sulphates and in hydrogen sulphide in many mineral waters. It occurs in many natural sulphates, the most important being those of calcium, lead, strontium, magnesium, and sodium. Extraction of Sulphur from Native Sulphur. Liffnatiou Process. All native sulphur must be separated from the mineral impurities which accompany it. This is usually 134 done by the lignation process or melting out the sulphur and there are several ways of accomplishing this. The sulphur ore is sometimes made into a kiln and the sulphur is melted out by smothered combustion, a portion of the sulphur itself being consumed to furnish the heat. This method though wasteful as regards sulphur is cheap in other respects and is employed to a large extent. The heat for driving out the sulphur may be obtained from extraneous fuel. High pres- sure steam has also been employed for melting sulphur out of its ores; in this case the ores are subjected to the action of the steam in closed iron vessels. A solution of calcium chloride in water with boiling point at 120° C. is sometimes used for furnishing the heat to melt out the sulphur. Distillation Process. The ores of sulphur are sometimes enclosed in retorts and subjected to distillation, the sulphur being condensed in the liquid state. Purification of the Crude Sulphur. Sulphur obtained by any of the above processes usually contains a few per cent of earthy impurities from which it is freed by distillation. If the vapor of the sulphur is condensed in a chamber below the melting point, it gives a pale yellow powder known as sublimed or flowers of sulphur. When the tem- perature of the chamber rises sufficiently high the flowers melt and are run out into sticks giving the roll sulphur or brimstone. If the vapor of sulphur be conducted directly into a condenser kept cool, the sulphur is deposited in a liquid state giving brimstone which is said to differ slightly from that first named. Extraction of Sulphur from the Sulphides. Sulphur was formerly obtained in considerable quantity from iron sul- phide (FeS 2 ) by heating it in the absence of air. At a very high temperature nearly one-half the sulphur can be separated, but at ordinary furnace heat only about one- fourth is separated. This method of preparing sulphur has 135 practically ceased as a manufacturing industry, the pyrites being used for making sulphuric acid. Sulphur can also be obtained from copper pyrites by roasting with proper precautions. This is sometimes done in the process of roasting the ore preliminary to the extrac- tion of the copper. The sulphur from the pyrites is generally found to contain impurities associated with those minerals and is purified by subsequent treatment. Sulphur from Other Sources. Sulphur is obtained in some quan- tity from the waste products of the gas works and in still greater amount from the waste products of the alkali works. Its presence in these products will be explained subsequently. Physical Properties of Sulphur. As ordinarily seen sul- phur is a lemon yellow, brittle, crystalline solid, insoluble in water but soluble in carbon disulphide. It exhibits several allotropic modifications the two most characteristic of which are marked by their action with the same solvent — one form being soluble in carbon disulphide the other form not. The soluble varieties of sulphur show two distinct crystalline forms ; one the native form of sulphur is the rhombic octahedron, the same form which results when it crystallizes from solution ; the other is the oblique prismatic which results when it cools after melting. The distinction between these crystalline forms extends to their fusing points and their specific gravities, the first having the higher specific gravity but lower fusing point. The insoluble form of sulphur shows several uncrystalline varieties, the most important of which are the ductile and the amorphous. The ductile sulphur results when boiling sulphur is poured in a thin stream into water; it is soft and elastic like rubber. The amorphous sulphur is always formed when the flowers of sulphur are deposited and will be left undissolved if the flowers be treated with carbon disulphide. Milk of sulphur is a soluble amorphous form of sulphur obtained by pre- cipitation by the addition of an acid to an alkaline solution of sulphur. This form is white and milky in appearance and is a medicinal preparation. If a solution of sulphur dioxide 4 be decomposed by electricity sulphur appears at. the negative pole as an Insoluble amorphous variety, while if a solution of hydrogen sulphide be electrolysed the sulphur appears at the positive pole as a soluble amorphous variety. For this reason the soluble varieties have been classed as electronegative and the insoluble as electropositive. 136 Chemical Properties. Sulphur possesses energetic affini- ties combining directly with a large number of elements. Many of the sulphides in atomic constitution correspond with the oxides of the same elements. Any modification of sulphur heated in the air or oxygen takes fire and burns with a pale blue flame producing sulphur dioxide. Finely divided sulphur, especially flowers of sulphur, is slowly oxidized in moist air yielding sulphuric acid. Sulphur in a finely divided state will combine with some of the metals at ordinary temperature and at a high temper- ature it will combine with nearly all the metals and with all the non-metals except nitrogen. It can very readily be made to display electrical properties as may be shown by friction or by powdering in a dry mortar. COMPOUNDS OF SULPHUR AND HYDROGEN. There are at least two compounds of hydrogen and sulphur. The most important, hydrogen sulphide, is analogous in composition to water haying the formula H 2 S. The other, hydrogen persulphide, contains a larger proportion of sulphur. Its formula has not been definitely determined but is thought to be H 2 S 2 though it may contain a larger proportion of sulphur. There are reasons for thinking that still more complex compounds exist. HYDROGEN SULPHIDE; H 2 S. Occurrence. This gas is present in the waters of many springs, which has caused them to be called sulphur springs and such mineral water sulphur water. It is found in large quantity among the gases issuing from volcanoes. It is very generally present among the products which result from the putrefaction of organic matter containing sulphur, both animal and vegetable. The offensive odor of rotten eggs is mainly due to it and it generally contributes to the unpleas- ant odors from sewers and drains. The gas is also found among the products of the destructive distillation of coal and other organic substances containing sulphur. 137 Properties of Sulphuretted Hydrogen. It is a colorless gas with the odor of putrid eggs and faintly sweetish taste. It is liquefied by a pressure of seventeen atmospheres. Water at ordinary temperature dissolves about three times its volume. The aqueous solution is acid to test paper and has the taste and smell of the gas. The gas is readily com- bustible giving the blue flame of sulphur. When the supply of oxygen is abundant the products of the combustion are water vapor and sulphur dioxide — 1128+03=1120+802 — and when mixed with oxygen in the proportions indicated, and ignited, the mixture explodes. If the supply of oxygen be limited some of the sulphur will be deposited. In the presence of moisture and oxygen the gas is decomposed with the deposition of sulphur hence the solu- tion of the gas in water can not be kept for a great while ; light produces the decomposition. The gas acts as a poison if inhaled in large quantities and even when much diluted with air it gives rise to disagreeable symptoms. Hydrogen sulphide is decomposed into its elements at a temperature a little above 400° C. Chlorine and bromine decompose it at ordinary temperature, removing the hydro- gen and depositing the sulphur. On account of its ready decomposability hydrogen sulphide acts as a reducing agent, thus when heated with concentrated nitric or sulphuric acid the hydrogen is oxidized and the sulphur deposited. Action with the Metals and Metallic Oxides. Many of the metals and metallic oxides act upon sulphuretted hydrogen in a manner resembling the action of the other hydrogen acids. With some of the metals as mercury, silver, and lead, this action takes place at ordinary temperature. When heated in the gas several other metals decompose it. It is because of its action upon silver that silver plate and other articles of silver often tarnish; silver egg spoons are blackened by the sulphur present in the eggs. Hydrogen sulphide acts upon many metallic oxides form- 138 nig metallic sulphides and water according to the general formula, MO+H 2 S=MS-fH 2 0. Action of Hydrogen Sulphide with Metallic Salts. Hydro- gen sulphide is one of the most valuable reagents in the chemical laboratory because of its disposition to act upon solutions of metallic salts. When hydrogen sulphide is brought into contact with solutions of metallic salts, charac- teristic precipitates are often formed. These precipitates are insoluble sulphides produced by the mutual decomposition of the dissolved salt and the hydrogen sulphide, some acid being produced at the same time due to the combination of the acid radical of the salt with the hydrogen liberated from the hydrogen sulphide. This action may be repre- sented by the general equation, 2MR-f H 2 S=2HR+M 2 S. All metals are thus precipitated from their solutions provided their sulphides are insoluble in the products of the reactions — water and dilute acid. Those metallic sulphides which are soluble in or decomposed by dilute acid would of course not be precipitated by the reaction above indicated. Any metals whose sulphides are soluble in acid solu- tions, may be precipitated from the solutions of their salts by the use of an alkaline sulphide instead of hydrogen sulphide. The alkaline sulphide generally used for the purpose is ammonium sulphide (NH 4 ) 2 S and the action is indicated thus, 2MR+(NHJ 2 S=M 2 S+2NH 4 R. From this reaction it will be seen that no acid is liberated and if the metallic sulphide represented in the second member is insoluble in the products of the reaction, it will be pre- cipitated. The metals may accordingly be divided into three classes — 1. Those whose sulphides are soluble in water; 2. Those whose sulphides are insoluble in water and dilute acid ; 3. Those whose sulphides are solu- ble in dilute acids but insoluble in water and dilute alkaline solutions. The first class is not affected by hydrogen sulphide ; the members of the second class are precipitated from a solution of their salts by hydrogen sulphide and those of the third by the addition of ammonium sulphide. 139 The sulphides of the different metals often have very characteristic colors, which taken in connection with reac- tions when treated with certain reagents, give the means of distinguishing and thus determining the metal present in a given solution. The action of hydrogen sulphide with the oxides and salts of lead explains the discoloration of lead paint which so fre- quently occurs. Any paint in which lead is an ingredient is liable to discoloration by hydrogen sulphide due to the forma- tion of lead sulphide. Paintings so discolored are sometimes partially restored by continued exposure to light and air, the lead sulphide being converted into lead sulphate. The presence of hydrogen sulphide in gas may be detected by moistening a paper with a solution of lead nitrate or lead acetate and exposing it to the action of the gas. The paper is blackened if a trace of hydrogen sulphide be present; if the gas be in solution it will immediately blacken upon the addition of a soluble salt of lead. In each case the dark color is due to the formation of lead sulphide. The converse of course holds, and the presence of lead in solution may be detected by the addition of hydrogen sulphide or any soluble sulphide. Preparation of Hydrogen Sulphide. It may be prepared by the direct union of its elements but for laboratory pur- poses it is generally obtained by the action of sulphuric or hydrochloric acid upon iron monosulphide, 2HCl+FeS=FeCl 2 +H 2 S; H 2 S0 4 +FeS=FeSO,-fH 2 S. The gas is given off without the application of heat. Obtained in this way the hydrogen sulphide nearly always contains hydrogen due to the presence of free iron in the iron sulphide. The pure gas may be prepared by heating antimony sul- phide with hydrochloric acid, Sb 2 S3+6HCl=2SbCl s +3H a S; in this method hydrochloric acid must be used for dilute sulphuric acid scarcely acts upon the antimony sulphide and 140 the concentrated decomposes the hydrogen sulphide liber- ated. The salts of hydrogen sulphide form an important class of ores of the useful metals and their properties will be sub- sequently described. COMPOUNDS OF SULPHUR AND OXYGEN. Four oxides of sulphur are known — the dioxide, S0 2 ; the sesquiox- ide, S 2 3 ; the trioxide, S0 3 ; and the persulphuric oxide, S 2 7 . The first two are important, the last two are scarcely known in the sep- arate state and will not be described. SULPHUR DIOXIDE; S0 2 . Occurrence. Sulphur dioxide occurs in the gaseous eman- ations from volcanoes and has been detected in the waters of certain volcanic springs. It is sometimes present in the air of towns or in the neighborhood of manufacturing works, in these cases resulting from the combustion of the sulphur of the fuel or by liberation in some chemical process. It has already been stated that sulphur dioxide is always the pro- duct of the combustion of sulphur in air or oxygen. It is removed from the air by oxidation and converted into sul- phuric acid. Physical and Chemical Properties of Sulphur Dioxide. It is liquefied at ordinary temperature under two atmospheres of pressure. Its boiling point is- -8° C. and it produces great cold by its evaporation. Water dissolves about 40 times its volume at ordinary temperature and the solution is believed to contain sulphurous acid but the acid has not been obtained in the separate state. Its formula shows it to be over twice as heavy as air. It extinguishes flame and is sometimes used to extinguish burning soot in a chimney, the sulphur being burned in the fire-place. It is a stable compound and not readily decomposed; at a high temperature it will combine with oxygen passing to sulphur trioxide. It is poisonous, causing death very quickly when breathed in a pure state and being injurious in even small quantity. 141 Preparation and Uses. In the laboratory sulphur dioxide is generally prepared by deoxidizing" sulphuric acid by heat- ing" with copper or carbon, 2H 2 S04+Cu=CuS0 4 +2H 2 0+S0 2 ; 2H 2 S0 4 +C = C0 2 +2H 2 -f2S0 2 ; the first is the more convenient method for all ordinary illustration. As a general rule it may be stated that those metals which act upon sulphuric acid at common temperature liberate hydrogen while those which act only by elevating the tem- perature liberate sulphur dioxide. Owing to its great specific gravity the gas may be collected by displacement or may be collected over mercury. USES OF SULPHUK DIOXIDE. Sulphur dioxide is extensively used as a bleaching agent for wool and straw goods which would be injured by chlorine. The presence of water is necessary for the action conse- quently the goods are usually moistened and subjected to the action of the gas. The sulphurous acid in bleaching often appears not to destroy the coloring matter but to form color- less compounds with it, for the original color frequently returns after the lapse of time. In other cases the action appears to be due to the abstraction of oxygen from the dye leaving it colorless. The solution of the gas in water is found to possess great deoxidizing power and it is thought to be due to the reaction between the sulphur dioxide and water by which hydrogen is liberated, the liberated hydrogen then abstracting the oxygen from the other body. Sulphur dioxide still further resembles chlorine in that it is used as a disinfectant. Clothes and buildings are often fumigated by burning sulphur but its action in this respect has been over-estimated. It has also been used as an anti- septic or preservative as it prevents and stop* fermentation. Wine and beer casks are sometimes treated with it to prevent 142 change in the fresh liquor introduced, and certain salts of sulphurous acid may be used for the same purpose. Sulphurous Acid and Sulphites. The solution of sulphur dioxide in water is believed to contain sulphurous acid H 2 S0 3 . This compound is not known in a free state but a large number of salts is known which can be obtained by treating the gaseous solution in water with bases. This fact justifies the conclusion that the acid exists and its salts indicate the formula H 2 S0 3 . The acid characters of the com- pound are not strong and it is very unstable, soon passing to sul- phuric acid. The salts are of course called sulphites and as the acid is bibasic there are two kinds. Sodium sulphite is largely used in the manufacture of paper, to destroy the excess of chjorine used in the bleaching. Sulphur Trioxide, Sulphuric Oxide, Sulphuric Anhydride, S0 3 . The compound may be formed by the direct union of sulphur dioxide and oxygen, by passing a mixture of the gases through a tube containing finely divided platinum. It may also be obtained by gently heating fuming sulphuric acid as indicated by the equation, H 2 S 2 7 (heated)= H 2 S0 4 +S0 3 . Pure sulphur trioxide is a liquid at ordinary temperature. It crystallizes when cooled in long transparent prisms which melt at 14.8° C. It fumes in the air and the solid form soon deliquesces. The oxide combines violently with water forming sulphuric acid. A piece of the solid oxide dropped into water hisses similarly to a red-hot iron. It is decomposed by heat into sulphur dioxide and oxygen. SULPHURIC ACID; H 2 S0 4 . Sulphuric acid is of fundamental importance both in the arts and sciences and, in fact, is the most important and useful acid known. It is a principal agent in the preparation of inorganic acids described already and of nearly all other acids. In a great majority of the arts and trades, sulphuric acid finds a greater or less application. The variety and extent of the demand for this acid makes its manufacture one of the most extensive and important of modern indus- tries. Owing to the above facts theory and practice combine to perfect the process of its manufacture which has now reached a high state of perfection. The other important inorganic acids are obtained from their salts but this one is mainly made from its elements — 143 built up from its constituents. The constituent raw materials most abundantly required in the manufacture are sulphur, oxygen, and water vapor the last two being" essentially without cost. The Leaden Chamber Process. The principal process employed depends upon the fact that sulphur dioxide in the presence of water vapor and certain oxides of nitrogen and the oxygen of the air, is converted into sulphuric acid. The fundamental reaction results may be expressed as follows — 3S0 2 +2HN03+2H 2 0=3H 2 S0 4 H-2NO; 2NO+0 2 =2N0 2 ; 2N0 2 +2S0 2 +2H 2 0=2H 2 S0 4 +2NO— the last two operations are continually repeated. It appears that the nitric oxide acts as a carrier of oxygen taking it from the air and becoming nitric peroxide. By transfer of oxygen to the sulphuric acid the peroxide is reduced to nitric oxide and the operation is repeated con- tinuously. If no loss of the nitrogen oxides occurred, a given quantity of nitric oxide would suffice to convert an indefinite amount of sulphurous acid gas into sulphuric acid but owing to unavoidable loss, it is necessary to constantly replenish this compound. This is usually done by generat- ing a small quantity of nitric acid by the action of sulphuric acid upon sodium nitrate and the nitric oxide is produced as in the first of the above reactions. The process of manufacture is as follows — Sulphur or metallic sulphides are burned in the air to produce sulphur dioxide. A small amount of the vapor of nitric acid is produced by the action of sulphuric acid upon sodium nitrate which vapor is caused to mingle with the sulphur dioxide and the oxygen of the air. To this mixture of gases in suitable apartments is added the proper amount of steam, when the reactions above indicated take place. The plant employed in the process consists of 1st. The burner, in which tho sulphur or sulphides are burned for the production of the sulphur dioxide. Through those burners is also admitted the air to 144 supply the oxygen required for the formation of the vitriol. 2nd, The arrangments employed for the production and introduction of the nitric acid vapor. These differ but that most generally used consists of a series of earthen ware or iron pots which are placed in the "nitre oven " ; these pots receive the charge of sulphuric acid and nitre for the production of nitric acid. The " nitre oven" is usually a sort of receptacle in some part of the burner or its flues so that the heat from the burner promotes the evolution of the nitric acid and the vapor of the acid is carried along with the air and sulphur dioxide. 3rd, The chambers which are immense rooms completely lined with sheet lead. They vary in number and size, usually however there are three or four with a capacity of from 40000 to 80000 cubic feet each. Into these chambers the gases from the burners are introduced and at various points jets of steam are projected into them. The floors of the chambers are soon covered with a solution of sulphuric acid. 4th, In addition to the above mentioned parts of the plant there are supplementary appliances generally used, the most important of which are two towers. One sit- uated between the burners and the chambers and the other at the exit end of the last chamber. The tower at the exit end of the chambers is to prevent the waste of the oxides of nitrogen, while the nitrogen of the air which takes no part in the chemical action in the chambers, is being removed therefrom. This exit called Gay Lussac's tower, is a tall chamber filled with porous material over which oil of vitriol is allowed to flow. The useless nitrogen escapes from the tower by a flue leading from the top of the tower to the chimney stack of the works but the oxides of nitrogen are absorbed by the oil of vitriol. The acid from this tower is pumped ufj and caused to descend over acid proof brick in another toAver (Glover's), which is placed between the burners and the chambers. The hot gases from the burners also pass through Glover's tower and in so doing they take up the oxides of nitrogen from the "nitrous" vitriol and return them to the chamber. The hot gases from the burners in passing through Glover's tower also carry back steam into the chambers and thus save fuel in steam raising. In the Glover towers the production of sulphuric acid takes place to a greater extent than in any other part of the chambers of the same cubical contents. The towers are not in universal use but they accom- plish great economy in the manufacture. When a Glover tower is used the whole of the chamber acid, as well as that from the Gay-Lussac tower, may be passed through it; the chamber acid is thus concen- trated by the heat of the gases from the burners and the gases are themselves cooled to the required temperature. If the chamber acid is passed through the Glover tower it has a specific gravity about 1.72 and is strong enough for many rough chemi- cal manufactures. If the chamber acid is not sent through the Glover tower, it is taken from the chambers when it reaches the specific 145 gravity about 1.60, for it then begins to absorb the oxides of nitrogen. This acid is strong enough for some applications but is usually further- strengthened by heating in leaden pans until it reaches a specific gravity about 1.72. The concentration can not be carried further in leaden pans because of the action of the acid upon the lead. The acid of specific gravity of 1.72 contains about 80 parts of sul- phuric acid and for greater strength the evaporation is carried on in glass, platinum or iron stills and this is the most expensive part of the operation. The concentrated acid of commerce thus obtained contains 98 parts of sulphuric acid and has a specific gravity of 1.84. The com- mercial acid generally contains some impurities, the most common of which are iron sulphate, lead sulphate, oxides of nitrogen, and arsenic. The last two may be removed by proper treatment and the first two by the actual distillation of the acid. At a distance from the factories the cost of the acid is largely increased because of the risk involved in the transportation. In case of breakage or leakage in transportation it is a very difficult body to manage. Pyrites now supplies the sulphur for much the larger pro- portion of sulphuric acid. In America the greater portion of the sulphur is from native sulphur, but the pyrites industry is constantly growing. The United States now pro- duces annually about 750,000 tons of sulphuric acid. The greatest uses of the acid in this country are in the phos- phate industries and in the refining of petroleum and manu- facture of high explosives.* *Mr. W.K. Quinan, Superintendent of the California Powder Works, informs the writer that certain advantageous improvements have recently been introduced in this country in acid manufacture. When pyrites is used as a source of sulphur it is almost impossible to obtain a perfectly clear acid, but by the improvements just referred to certain works have succeeded in producing a "sales" acid of 96 per cent strength in the Glover tower. This is done by lining the tower with very refractory material and greatly raising the temperature of the tower by conserving the heat from the burners. From the same authority it is learned that certain of the American works have succeeded in producing an artificial draught through the chambers by means of rotating fans placed in the flue at the end of the chamber system. This plan was first tried in Germany, but did not succeed then. This permits the production of a much greater amount of acid in the same chamber space. The acid chambers attached to the works above referred to yield three pounds of concentrated B 2 S0 4 to each pound of sulphur burned. 10 146 Physical and Chemical Properties of the Acid. The concentrated acid obtained by the processes described always contains from one to two per cent of water. All the weaker acids by evaporation finally attain this composi- tion and then distil over unchanged at the temperature of 338° C. The vapor evolved during the distillation is not that of sulphuric acid but is a mixture of sulphur trioxide and water vapor which pass over and condense together in the receiver. If pure, the acid is a colorless, heavy, oily liquid. The acid has a powerful affinity for water and readily absorbs moisture from the atmosphere ; for this reason it is often used as a dessicating agent. It is thus employed in the laboratory for drying without heat. The objects to be dried are placed over a dish of sulphuric acid in a closed vessel and the operation is greatly facilitated by exhausting the air from the vessel. The acid is also frequently used to dry gases, the gases being made to pass over a surface of the acid. Pumice stone soaked in the acid is admirably adapted to exposing the gases to the action. The acid combines energetically with water, so that caution is always necessary in mixing them — the acid should always be poured into the water and not the reverse. The temperature produced by mixing the acid and water often exceeds that of boiling water. If four parts of the acid be added to one of powdered ice or snow there is an elevation of temperature, but if the proportions be reversed there is a reduction of temperature. Owing to its affinity for water it decomposes many organic compounds containing hydrogen and oxygen, remov- ing from the bodies these elements in the proportions to form water; it thus acts upon alcohol and oxalic acid. In a similar manner it acts upon paper, wood and sugar, remov- ing the oxygen and the hydrogen in the proportion to form water and leaving the carbon in excess, with the result of charring the body. This action is finely illustrated in the 147 case of sugar as follows: Dissolve some crystalline cane sugar in three-fourths its weight of warm water and allow it to partially cool; then add a volume of concentrated acid equal to two-thirds of the volume of the water used, the liquid blackens and froths up as a spongy mass of carbon. Even when much diluted the acid corrodes and destroys textile fabrics. Under the influence of heat it decomposes the salts of all acids more volatile than itself. On this account the acid is often said to be the strongest of the mineral acids, but this ability to decompose the salts of other acids is not alone the test of the strength of an acid as has already been pointed out. At a red heat the vapor of the acid is decomposed accord- ing to the following reaction, H 2 S0 4 (heated) = S0 2 +H 2 0-fO. Acids corresponding to the formula H 2 S0 4 of 100 per cent purity can be obtained by adding to the concentrated acid the exact amount of sulphur trioxide to combine with the water there present. When the concentrated acid containing 97 or 98 per cent of sulphuric acid is cooled to — 10° C. or below that point, the pure acid crystallizes and may be separated in the pure state; the latter process is now carried on upon a manufacturing scale. In combining with water the acid forms several definite compounds the best known of which are the combinations resulting from the union of one molecule of acid with one or two molecules of water which may be respectively represented by the formula? H 2 S0 4 ,H 2 and H 2 S0 4 , 2H 2 0. SULPHATES. Sulphuric acid acts readily upon metallic oxides and carbonates converting them into sulphates in the latter case with the evolution of carbon dioxide. Sulphuric acid cold or hot, dissolves all the metals except gold and platinum. The boiling acid attacks silver forming the sulphate with evolu- tion of sulphur dioxide. Under the same conditions it also acts slightly upon platinum. The very strong acid does not act upon cast iron. This metal can therefore be used for concentrating the acid after it reaches the strength which 148 attacks platinum. Before it reaches this strength it acts more readily upon iron than platinum. In the California powder works the last concentration takes place in iron retort, and Mr. Quinan states that chilled cast iron offers a high degree of resistance even to weaker acid. Gold is not acted upon hence the acid is often used in separating gold and silver or parting these metals. Generally speaking those metals which are acted upon at ordinary temperature by dilute acid liberate hydrogen, but when the concentrated acid or elevated temperature is required the corresponding sulphate is usually formed with the liberation of sulphur dioxide. This latter result is probably due to the decom- position of the strong acid by the liberated hydrogen, especially at high temperature. The sulphates are an important class of compounds many of them being extensively employed in the arts. They are insoluble in alcohol; as a class they are soluble in water except those of lead and of the alkaline earth metals (calcium, strontium, and barium), and these are slightly soluble except that of barium which is absolutely insoluble in water and only slightly so in acids. The normal sulphates are decomposed by heat except those of the alkali and alkaline earth metals and of magnesium, the latter only partially decomposing at very high temperature. The insolubility of the barium sulphate gives a ready preliminary test for the detection of any sulphate in solution — which is to add to the suspected solution any soluble salt of barium and if any sulphate be present a white precipitate will be formed insoluble in water and dilute acid. Pyro-sulphuric Acid or Di-sulphuric Acid. This acid is also called fuming sulphuric acid, Nordhausen oil of vitriol. Its formula is H2S2O7 (H 2 S0 4 , S0 3 ). It may be considered as consisting of a molecule of sulphuric acid and one of sulphur trioxide or two molecules of sulphuric acid less one of water. It is now made on a manufacturing scale by dissolving- 149 sulphur trioxide in sulphuric acid. This acid was originally manufactured at Nordhausen in Saxony, a fact which ex- plains one of its names. The original method consisted in distilling the basic ferric sulphate of iron by which sulphur trioxide was evolved and condensed in a solution of sul- phuric acid. The basic salt being obtained by oxidizing ferrous sulphate by exposing it to a moderate heat in air. This acid fumes in the air when the bottle containing it is open, due to the escape of sulphur trioxide. It is heavier than the common acid, its specific gravity being 1.9. It has important application in the preparation of indigo dyes and in the colors obtained from coal tar. This acid was obtained by the last of the above processes as early as the fifteenth century. Thiosulphuric Acid; H 2 S 2 3 . It was formerly called hyposulphuric acid. This acid has not been obtained in a free state being very unstable. Its salts however are stable and numerous, by far the most import- ant being the sodium thiosulphate. This salt is simply prepared by digesting powdered roll sulphur with solution of sodium sulphite (Na 2 S0 3 ). The latter salt combines with an atom of sulphur forming the thiosulphate (Na, 2 S 2 3 ) which maybe crystallized from the solu- tion. This is the salt so largely used in photography and commonly called hyposulphite or "hypo." It is also used as a substitute for sodium sulphite as an antichlore. The acid may be regarded as obtained from sulphuric acid by replacing one atom of oxygen by an atom of sulphur— hence the old term hyposulphurous is not strictly applicable. Hyposulphurous Acid; (H 2 S 2 4 ). The solution of this acid has been obtained but it rapidly decomposes. Its salts are more stable than the acid. The sodium salt is the most important and is obtained by the action of zinc filings upon a concentrated solution of the acid sodium sulphite. This salt is used by the dyer and the calico printer and its formula appears to be Na 2 S 2 4 . There are several other oxy-acids of sulphur whose names and formulae are here given, dithionic, H 2 S 2 6 ; trithionic, H 2 S 3 0, ; ; tetrath- ionic, H 2 S 4 6 ; pentathionic, H 2 S 5 6 ; very little is known of these and they are of little practical importance. SELENIUn AND TELLURIUH. Selenium. It is a rare element and much resembles sulphur in its mode of occurrence, physical and chemical properties. It lias been found in the free state but in very small quantity associated with sul- phur. It usually occurs as selenides of the metals together with the 150 sulphides. Selenium has been obtained in several allotropic forms the most distinct of which are the varieties which are soluble and insoluble in carbon disulphide. The crystalline form of selenium is a conductor of electricity and this power is much greater in light than in darkness. This alteration of conducting power with variation of light intensity has been made use of in constructing the photophone but the instrument has not yet proved of practical value. The name Selenium is from the Greek word (Sefarjvri) for moon, the closely resembling element having been called tellurium from tellus the earth. Tellurium. Tellurium is even less common than selenium. It has been found native in some gold ores, and in combination with gold and some other metals. It has recently been found in masses of 20 pounds weight in Colorado. It has the external appearance and lustre of bismuth and in its physical properties more closely resembles the metals than non-metals. In its chemical relations it is closely related to selen- ium and both these elements are connected by strong analogies with sulphur. Both tellurium and selenium form oxides and oxy-acids analogous to sulphurous and sulphuric oxides and the corresponding acids. They also form hydracids analogous to hydrogen sulphide, each of the above elements replacing sulphur in the respective com- pounds. Tellurium and selenium likewise combine with the chlorine group and notwithstanding their similarity to sulphur they both form sulphides. PHOSPHORUS; P. Occurrence. Phosphorus is very widely though not abundantly distributed in its compounds, but it never occurs in a free state. It is an essential constituent of all fertile soils. It is necessary to the growth of certain parts of the vegetable structures, especially of fruits and seeds. From plants used as food the compounds of phosphorus pass into the animal body and are essential constituents of the juices of the animal tissue, and more especially of the bony skel- etons of animals which contain nearly three-fifths their weight of calcium phosphate. Its compounds are found in all sea water, generally in river water, and in many springs. It has also been found in meteoric stones. Phos- phorus accordingly ranks with carbon, hydrogen, oxygen, and nitrogen as one of the elements essential to organic life. This element was discovered by Brand in 1668 ; he obtained 151 it from urine. Between 1670 and 1680 it is said to have been exhibited to several crowned heads of Europe as one of the wonders of nature. (Roscoe and Schorlemme, Treatise on Chemistry, vol. 1.) Preparation of Phosphorus. Formerly phosphorus was entirely obtained from bone-ash, but now the greater cheap- ness of many of the phosphates of mineral origin has led to their use for the manufacture of phosphorus. Other things being equal bone-ash is still the most desirable raw material for obtaining phosphorus; the ash is tricalcic diphosphate Ca 3 (P0 4 ),. The essential chemical principles involved in the prepara- tion of phosphorus may be stated as follows: The calcic phosphate is treated with sulphuric acid, which liberates the tribasic phosphoric acid with production of calcium sulphate. The tribasic acid under the application of heat loses water and becomes the monobasic acid. This acid is deoxi- dized by carbon with the liberation of phosphorus and formation of carbon monoxide. The changes are indicated by the reactions, Ca 3 (P0 4 )2+3H 2 S0 4 =3CaS0 4 +2H 3 P(V, by drying at low red heat, HsPO^HPOs+IiO; 2HP0 3 +6C= 6CO+H 2 +P 2 . The mechanical steps of manufacture may be outlined as follows — finely powdered bone-ash or other tricalcic phosphate is treated with sulphuric acid; the calcium sulphate thus produced is separated by filtration from the acid liquor, which contains orthophosphoric acid. This liquor is concentrated by evaporation in leaden pans. It is then absorbed by powdered charcoal, coke, or sawdust and heated to a dull red heat, by which action the orthophosphoric acid (H 3 P0 4 ) is con- verted into meta-phosphoric acid (HP0 3 ). The mixture of meta- phosphoric acid and carbon is now distilled in clay retorts, when the phosphorus is separated and condensed under water which soon becomes warm and in which the melted phosphorus is conveyed to certain points from which it is removed. Note.— By some authorities it is held that all the calcium is not removed by the sulphuric acid from the tricalcic phosphate but that the acid phosphate CaH 4 (P0 4 ) 2 is formed which is dissolved in the acid. liquid and converted into the metaphosphate of calcium by heat- 152 ing with carbon. This inetaphosphate then liberates phosphorus when distilled with carbon. The crude phosphorus thus obtained is purified by fusion and solidification and finally cast into sticks or wedges the entire operation being conducted beneath the surface of warm water. With unimportant exceptions the entire supply of the world's phosphorus is made at two places, Birmingham, England, and Lyons, France. To a small extent phosphorus has been produced in Philadelphia, Sweden and Russia. Properties of Ordinary Phosphorus. Ordinary phospho- rus when freshly made as above described is a translucent almost colorless wax-like solid. At ordinary temperature it is somewhat harder than wax, is flexible and sectile; at 5.5° C. and below, it becomes hard and brittle. Even in the dark it soon loses its translucency and becomes coated with an opaque white film. This action is hastened by the light, and by the action of direct sunlight it becomes red due to the con- version into the allotropic red phosphorus. It melts at 44° C. It is insoluble in water and usually kept immersed in that liquid. It is soluble in naphtha and carbon disulphide. It crystallizes when deposited from solution in carbon disul- phide. Its specific gravity is 1.83 at 10° C. Exposed to the air phosphorus gives off fumes and glows with a faint greenish light; both these phenomena are believed to be due to the oxidation of the phosphorus, but are not thoroughly understood. It inflames in the air when heated above its melting tem- perature and burns with a brilliant white flame evolving white clouds of P 2 5 . In pure oxygen this combustion is immensely luminous. The low temperature of the ignition of phosphorus renders great care necessary in handling it to avoid accident. It should generally be manipulated under water. Ordinary phosphorus is very poisonous when taken internally. The 153 vapor is also poisonous when inhaled. Persons engaged in manufactures requiring the manipulation of phosphorus are often affected by phosphorus poison, very frequently result- ing in the decay of the bones, especially those of the jaws and nose. Phosphorus when moist will combine with oxygen, chlo- rine, bromine, iodine, sulphur, and with many of the metals. Amorphous or Red Phosphorus. This is the principal allotropic form of ordinary phosphorus. When ordinary phosphorus is heated for 49 or 50 hours to 230°, or 240° C. in ovens, or in an atmosphere that does not act upon it, it is converted into a red opaque mass, which is widely different from common phosphorus. It is infusible at temperatures below red heat, is insoluble in carbon disulphide, is not poisonous, emits no vapor, and does not phosphoresce. It can not be inflamed by friction and does not even ignite in the air when heated to 260° C. at which temperature it is reconverted into ordinary phosphorus. The red phosphorus is much less chemically active than the ordinary phosphorus. This difference of action can be strikingly shown by placing the two varieties in contact with iodine when the red is unaf- fected and the common phosphorus unites with the iodine producing combustion. In the allotropic transformation there is no change of weight though the two varieties differ in specific gravity. The specific gravity of ordinary phos- phorus is about 1.83, that of the red phosphorus is 2.14. There are known other modifications of phosphorus. One form known as crystallized or metallic phosphorus can be obtained by heat- ing- red phosphorus in a sealed tube to 530° C. or common phosphorus may be heated to redness in a closed tube with lead for several hours. On cooling- the melted lead the phosphorus crystallizes out in black scaly crystals. This form is more inactive than the red phosphorus. Professor Ilemsen describes a snow-white phosphorus obtained in the form of powder by cooling- the vapor of phosphorus by ice- water in an atmosphere of hydrogen. The vapor density of phosphorus is i\-2 so that its molecule contains four atoms. At very high temperature the vapor density diminishes showing- a tendency to correspond to the ordinary law of volumes. 154 Uses of Phosphorus. The principal use of phosphorus is in the manufacture of matches. It is also used to a small extent in the preparation of certain vermin poisons. The lucifer matches are made by tipping the splints with sulphur, wax, or paramne, to surely convey the flame to the wood. The match composition consists of phosphorus and some oxidizing agent; those most commonly used being potassium chlorate, red lead, and lead nitrate. This mixture is usually bound together and attached to the wood by glue or gum. The safety matches which can not readily be ignited by ordinary friction have no phosphorus on the match but are coated with a mixture of antimony sulphide and one or more oxidizing agents. For ignition the matches have to be rubbed on a prepared surface (usually the side of the box which is covered with a mixture containing red phosphorus ; the red phosphorus mixed with fine sand or powdered glass) . Oxides and Oxyacids of Phosphorus. Four oxides of phosphorus are known the formulae of which are — P 2 4 , P 2 5 , P 4 6 , and P 4 0. The most important of these is the P 2 5 phosphoric oxide. Phosphoric Oxide. This oxide is prepared by burning phosphorus in dry air. It constitutes the white fumes which are seen when phos- phorus burns with flame in dry air. It has a great affinity for water and soon deliquesces if left exposed to the air. It is sometimes used as a dehydrating agent in the laboratory. It will even extract water from oil of vitriol. Orthophosphoric Acid; H 3 P0 4 . This is the compound usually designated as phosphoric acid. It is the acid whose salts are usually met with in nature as phosphates. The phosphates are indispensable to the growth and sustenance of plants and animals. In these com- pounds phosphorus is widely distributed. The acid is the final product of the oxidation of phosphorus in the presence of water. It may be prepared by boiling phosphorus with nitric acid. It can also be prepared from the native phosphates. The acid is tribasic. It was formerly used to a considerable extent in calico printing. There are several other oxy-acids of phosphorus whose names and formulae are given in the following table — Hypo-phosphoric acid, H 3 P0 2 ; Phosphorous acid, H 3 P0 3 ; Meta-phosphoric acid, HP0 3 ; Pyro-phosphoric acid, H 4 P 2 7 . 155 Other Compounds of Phosphorus. Phosphorus does not combine directly with hydrogen but there are three compounds of these two elements known. The most important of these is the gaseous phos- phuretted hydrogen, phosphine H 3 P. This gas can be prepared in several ways and will generally take fire spontaneously when exposed to the air but this action appears to be due to the presence of the liquid phosphide H 4 P 2 which is spontaneously inflammable. The other phosphide H 2 P 4 is a yellow solid. Phosphorus combines with the halogens forming two analogous compounds of each of the elements, chlorine, bromine, and fluorine. It also forms two compounds with iodine, but one of these is without an analogue among the other halogen compounds. ARSENIC; As. Occurrence. Arsenic occurs widely distributed but in small quan- tity, and resembles sulphur in its mode of occurrence. It is found native but more generally as the sulphides (realgar and orpiment) and the arsenides of the metals. It frequently occurs combined with the sulphides of the metals. Arsenic is used only to a small extent economically. Preparation. It is generally prepared in one of two ways. 1. By heating arsenical pyrites out of contact with air, the arsenic is distilled off and condensed by suitable arrangements. 2. By heating arsenious oxide with charcoal, the oxide is reduced and the arsenic is volatilized and condensed. Properties. In its appearance arsenic resembles a metal. It has a steel grey metallic lustre and is a conductor of heat and electricity. Its specific gravity is between 5 and 6. It volatilizes without fusing. In dry air at ordinary temperature it remains unchanged, but in finely divided form it oxidizes in moist air. At a temperature over 70° C. it oxidizes in the air and gives off fumes of arsenious oxide accompanied by a very penetrating and characteristic odor suggestive of garlic. When heated to a red heat in the air it burns with a bluish white flame, in oxygen its flame is very brilliant. It is insoluble in water. Pure arsenic does not appear to be poisonous but it may be oxidized after it is taken internally and then become a poison. In its chemical proper- ties it is closely allied to phosphorus. Arsenic forms no base with oxygen and hence differs from the elements classed as metals. It is used in small quantities to form alloys which possess characteristic proper- ties; it is thus used in the manufacture of shot, in bronzing brass and in other alloys. OXIDES. Arsenic forms two oxides, As 4 O e and As,0 5 . Arsenious Oxide; As.,0 (; . This compound is prepared on a com- mercial scale by roasting arseniferous minerals in suitable furnaces or 156 ovens when arsenious oxide is the principal product ; arsenical pyrites is usually the ore from which it is obtained. The sulphur and arsenic are thus oxidized the former escaping as sulphur dioxide. The arsenious oxide generally designated as " arsenical soot" is conducted into cham- bers which expose a large condensing surface. The oxide is here con- densed to a dark grey powder. The workmen employed to clear the chambers are clad in leather garments with glazed apertures for the eyes and they breathe through wet cloths. The powder is purified by resublimation and then obtained as a white, glistening, crystalline powder. If the crystalline arsenic be sublimed under slight pressure at high temperature white, amorphous, vitreous arsenic is obtained. Arsenious oxide is obtained in large quantity as a bye product in working up certain volatile ores, mainly those of cobalt, nickel, silver, and tin. It is obtained in large quantities in connection with the tin furnaces of Cornwall and Devon. The substance commonly known as arsenic in the shops is this oxide. It is usually sold in the form of a white powder resembling flour in appearance but much heavier its specific gravity being 3.7. It volatilizes without fusing. It may be distinguished from any resem- bling substance by the garlic odor emitted when dropped upon glow- ing coal. This odor is thought to be due to a lower oxide. Arsenious oxide is a powerful poison, less than three grains have proven fatal. The habitual use of it in continually increasing quan- tities will enable the system to withstand much larger doses. The best antidote for arsenic poison as given in the U. S. pharma- copoeia, is a mixture of dilute solution of ferric sulphate and magnesia. Carbonate of soda may replace the magnesia and a solution of the perchloride of iron may replace the sulphate. Emetics should also be used as promptly as possible. This antidote was discovered by Bunsen in 1834. It was a deduction from known chemical facts. Previ- ous to that time no antidote for this poison was known. Arsenious oxide has many applications some of which will be men- tioned. Uses. It is used medicinally to a certain extent. It is sometimes administered to horses to render their coats smoother. It is used in calico printing and in the preparation of certain colors, arsenic being present in many pigments. It is used in the preparation of aniline, in glass making, as a constituent of white fire in pyrotechnics, as a preservative of skins, and in the preparation of various kinds of vermin poison. Arsenious Acid. The acid has not been obtained in a free state. The solution of arsenious oxide in water, however, yields precipitates with certain metallic salts which indicate that the acid is tribasic, H 3 As0 3 . The brilliant Scheele's green is the arsenite of copper 157 (CiiHAs0 3 ). The arsenites are insoluble or difficultly soluble in water, except those of the alkalies. The formulae of the alkaline arsenites indicate that they are derived from HAs0 2 . Fowler's solution used in medicine is the arsenite of potassium. Arsenic Oxide and Acid. This oxide can be obtained by heating 1 arsenic acid. The acid is prepared by oxidizing As 2 3 with nitric acid under proper precautions. This acid is largely used as a substitute for tartaric acid in calico printing and in the preparation from aniline of rosaniline or the mag- nificent magenta dye. Arsenetted Hydrogen ; H 3 As. This is the only compound of arsenic and hydrogen known. It is always formed when nascent hydro- gen and arsenious oxide are brought together in acid solutions. It is of importance because its production affords a means of detecting the presence of a very minute quantity of arsenious oxide. Marsh's test for detecting arsenic in cases of poisoning depends upon the pro- duction of the gas. The gas itself is exceedingly poisonous and any experiment with it should be undertaken with very great care. The chemist Gehlen lost his life by inhaling the gas. Sulphides of Arsenic. There are known three sulphides of arsenic, the disulphide As 2 S 2 , the trisulphide As 2 S 3 , and the penta-sulphide As 2 S 5 . The two first named occur native. As 2 S 2 , Realgar. This compound occurs native crystallized in red rhombic prisms. It may be prepared by heating arsenic with sulphur, or arsenious oxide with sulphur. The. form which occurs in nature under the name of realgar, red orpiment, is usually prepared by distilling iron pyrites and arsenical pyrites together when the realgar distils over. It is used in the manufacture of the Bengal signal lights and Indian fire. In the air it burns with a blue flame ; with nitre it gives a brilliant white light. The Bengal lights are composed of a mixture of 24 parts of potas- sium nitrate, 7 of sulphur, and 2 of realgar. As 2 S 3 , Yellow Orpiment. This compound occurs native crystallized in yellow rhombic prisms. It may be prepared by heating arsenic with the proper amount of sulphur. The paint known as King's yellow is a mixture of yellow orpiment and arsenious acid and is of course poisonous. The penta-sulphide is of less importance than the other two. Compounds of Arsenic with the Halogens. Arsenic forms but one chloride, the trichloride AsCl 3 . It forms analogous compounds with bromine, iodine, and fluorine. It also forms a dicarbide. 158 ARGON AND HELIUfl. Argon. This body was very recently discovered. Lord Rayleigh had found that the specific gravity of chemically pure nitrogen was not the same as that of the nitrogen of the atmosphere. This led to the examination of the atmosphere and to the discovery that it contained a substance not previously recognized, amounting to nearly one per cent. By the combined efforts of Lord Rayleigh and Professor Ramsey the substance was isolated in 1894. The new body was named Argon (signifying without work) in allusion to its chemical inactivity. The investigations up to this time indicate that Argon is an element with density of 20, referred to hydrogen. It appears to be mon-atomic and hence its atomic weight would be 40. It has been liquefied and solidified by great cold and pressure. It has, up to this time, resisted all attempts to cause it to combine with other bodies. As there have been very extended efforts to form a compound with Argon, with neg- ative results, Professor Ramsey thinks that it may be non-valent or incapable of forming compounds. Helium. The existence of this body has been inferred for a consid- erable time, through the existence of a bright line in the solar spec- trum, not attributed to any known body. In seeking for a combined form of argon, Professor Ramsey for the first time in 1895 identified Helium among terrestrial bodies. It has not yet been definitely decided whether the body is an element, or a compound, or a mixture. The body is gaseous and has resisted all attempts to liquefy it although it has been subjected to enormous pressure and to the greatest attain- able cold. Its boiling point under atmospheric pressure, according to Olszewski, must be below —264° C. Helium, like argon, has resisted all attempts to form from it a compound with other elements. CHEMISTRY OF THE METALS AND THEIR COMPOUNDS. THE ALKALI METALS. The most important elements of this group are sodium and potassium. The other members are lithium, rubidium, and caesium. The first two are abundant in nature and widely distributed. Lithium is widely distributed, but only in small quantity. The last two members of this group are still more rare. These elements are highly electro-positive and as already stated their hydroxides are powerfully alka- line and their salts are generally soluble. The elements are soft, silvery white metals all of which decompose water and the two last of the group take fire in the air. POTASSIUM; K; 39.1. Occurrence. Potassium is not found in a pure state in nature but it occurs abundantly as a chloride in combination with other chlorides forming immense deposits. In combi- nation with silicon and aluminum, it is a common constitu- ent of the igneous and metamorphic rocks. From these rocks, by disintegration, it passes into the soil and finally into the plants, of which it is an essential food ingredient. From plants the salts of potassium pass into the organ- isms of animals. In plants it is mainly present as salts of vegetable acids. Preparation. Potassium was first isolated by Davy in 1807, by decomposing the hydroxide by electricity, the potas- sium appearing at the negative pole. 160 The method of Davy for preparing" potassium has long since been superseded. It is now prepared by deoxidizing potassium carbonate with charcoal. For a good yield the ingredients should be thoroughly mixed. An intimate mix- ture of potassium carbonate and charcoal is obtained by cal- cining potassium tartrate (C 4 H 5 6 K) in a covered crucible and this method is generally followed in preparing the car- bonate for deoxidation. The mixture of potassium carbonate and carbon is dis- tilled in iron retorts from which a short iron pipe leads to a receiver containing petroleum and kept cool by ice water. When the retort is heated to a high temperature the potas- sium distils over and condenses under the petroleum. The reaction occurring is indicated by the following equation, K 2 C03+C2=K 2 +3CO. The metal thus obtained is not pure and has to be redistilled or subjected to other treatment to perfectly purify it. Metallic sodium is now again being manufactured by elec- trolysis and it is probable that Davy's method for obtaining potassium by electrolysis may be reintroduced. Properties and Uses. Potassium is a silver white metal, specific gravity of .865 and rapidly tarnishes when exposed to the air. It floats on water and takes fire when placed upon water or even upon ice. More properly speaking the potassium decomposes the water and the liberated hydrogen takes fire, at the same time volatilizing some of the potas- sium, which burns with a violet color. Potassium melts below the boiling point of water. The greater difficulty attending the preparation of potassium and the fact that sodium can replace it in industrial operations has almost entirely limited its application to laboratory purposes. It will be seen from the relative atomic weights of potassium and sodium, that for equal weights, the latter element can do more chemical work. 161 Potassium Carbonate; K 2 C0 3 . This important salt is obtained on a commercial scale by several different processes. Formerly most of the potash or crude carbonate was obtained from wood-ashes, but this source has greatly decreased in importance and now only parts of the United States, Canada, Russia, Hungary, and Galicia supply it from this source. The amount of the carbonate however from wood-ashes is greater than that from any other single source. Potassium Carbonate from Wood- Ashes. It has already been stated that potassium exists in plants as the salts of organic acids. When the wood is incinerated the organic salts are decomposed and the potassium is left in the form of the carbonate. Of course the ashes contain other mineral substances resulting from other salts present in the plants. By lixiviation with water the more soluble salts are separated from the less soluble ; the former consists mainly of potas- sium carbonate with considerable portions of potassium sulphate and chloride ; the former consist mainly of potassium sulphate and chloride. By evaporation a considerable por- tion of the sulphate may be removed as it is less soluble than the carbonate. The residue then evaporated to dryness and calcined gives the crude potash of commerce which contains much potassium chloride and some sulphate. When greater care is observed in the process the product is purer and known under the name of pearlash. Potassium Carbonate from Beet-Boot Molasses. In making sugar from the beet-root there is left a syrup which can not be made to crystallize; this syrup is rich in mineral salts especially those of potassium. The syrup is first fermented for the production of alcohol. The liquor left behind is, in France, called "vinasse" and in G-erman " schlempe." This liquor evaporated to dryness, calcined and the cinder lixivia- ted furnishes a high percentage of potash salts, lv>CO :; , K2SO4, and KOI. This industry has obtained great develop- ment in Germany and France, 11 162 Potassium Carbonate from the Chloride. A large amount of potassium carbonate is made from the native chloride by a process similar to that employed in the manufacture of sodium carbonate from common salt, yet to be described. Potassium Carbonate from Sheep Wool. The washing from sheep wool is called " suint" and contains a considerable quantity of potassium mainly combined with animal acids. By evaporating the liquid to dryness and burning the residue the organic salts are decomposed and the carbonate of potas- sium left. This is separated by lixiviation from the ash. The potassium carbonate is obtained from other sources in small quantity but not on a commercial scale. Properties and Uses of Potassium Carbonate. The nor- mal potassium carbonate is a white solid extremely deli- quescent and soluble in less than its own weight of water, yielding a strongly alkaline solution. It is insoluble in alcohol. This substance is an important compound being used in the manufacture of soap and glass. In many States of America the country population make their own soap obtaining the potash "from the ashes of the wood used as fuel. The Acid Carbonate or Bicarbonate of Potassium. It can be prepared by passing carbon dioxide through moist potas- sium carbonate or through a solution of potassium carbonate. The salt is less soluble and less alkaline than the normal salt. It is converted into the normal carbonate by heat, 2KHC0 3 (heated) =K 2 C0 3 +H 2 0+C0 2 . It is used to a small extent in medicine. Caustic Potash ; KOH. This substance may be prepared by adding a solution of slaked lime to a boiling dilute solution of potassium carbonate, K 2 C0 3 +Ba6®s=CaC0 3 + Q^oh), 2KOH ; the reaction will not take place if the solution of the carbonate be too strong. The solution decanted from the insoluble calcium carbonate and evaporated, leaves a clear 163 oily liquid which solidifies to a clear white mass on cooling. It is often fused and cast into slabs or sticks. The hydroxide is a white solid, can be melted and volatilized, but is not decomposable by heat. It is deliques- cent and readily absorbs carbon dioxide forming the carbon- ate, and is frequently used for removing carbon dioxide from gases. It is very soluble in water and evolves much heat in dissolving. It is powerfully alkaline being the most power- ful alkali in general use. It softens and destroys the skin and on this account is used as a cautery. It is one of the most useful agents in the laboratory. Near Stayspor t in Germany, caustic potassa is now produced in large quantity by decomposing a solution of potassium chloride by elec- tricity. The works are primarily for the production of chlorine and the hydroxide is a valuable by-product. Potassium Chloride; KC1. This salt was formerly ob- tained as a secondary product in the manufacture of bromine from sea water and of iodine from the ash of sea weed, and of sugar from beet-roots. It is now almost exclusively obtained from the mineral carnallite, which is a double chloride of potassium and magnesium, KC1, MgCl 2 , 6H 2 0. Carnallite is found in vast quantities overlying the Stassfurth salt beds. The chloride is now an important raw material for manufacturing potassium carbonate and nitrate. Potassium Iodide and Potassium Bromide; KI and KBr. These compounds are used to a considerable extent in photography, in medi- cine, and in the laboratory. They are formed in the same way, by passing bromine or iodine into a solution of potassium hydroxide. Nitre; Saltpetre; KN0 3 . This important salt is often found as an efflorescence upon the surface of the soil in hot dry climates. It results from the oxidation of nitrogenous organic matter in the presence of potash in the soil. The formation of nitre under these circumstances is duo to the presence of specific microbes and the nitrification docs 164 not take place without them. Nearly all of the native salt- petre in commerce comes from the East Indies, one of the districts of Bengal supplying the greater portion. It is chiefly found in the neighborhood of villages where the animal refuse supplies an abundance of organic nitrogen. The surface of the soil which shows the white efflorescence is scraped off and lixiviated with water. This solution evapo- rated to crystallization furnishes "crude nitre" in which form it comes into market. This native process has been imitated artificially in the nitre beds or "saltpetre plantations." In Sweden formerly every land owner was obliged to furnish the government with a certain quantity of nitre. In France during the Rev- olution the artificial production of nitre was compulsory. In the artificial process animal and vegetable refuse of various kinds are mixed with wood-ashes, calcareous earthy material, old mortar, bones, &c. This mass is occasionally moistened with stable drainings. After the lapse of the proper time watering is discontinued and salts soon effloresce on the surface of the heap. The surface layer to the depth of a few inches is then removed and the soluble salts dis- solved out. The nitrates found in the solution are those of potassium, calcium, magnesium, and ammonium; the last three of which may be transformed into potassium nitrate by the addition of potassium car- bonate to the solution. In this process the basic parts of the nitrates except that of the ammonium nitrate, are derived from the earthy matters. The acid parts are believed to be formed by the oxidation of the ammonia resulting from the decomposition of the organic matter under the action of the "nitrifying" microbes. The presence of the bases is very favorable to the action. Nitre from Chili Saltpetre. By far the greater portion of the nitre which now comes into the market, is made from sodium nitrate, NaN0 3 , by treatment with potassium chloride. Double decomposition ensues in accordance with the reac- tion, NaN0 3 +KCl=NaCl+KN0 3 . The reaction is accom- plished by boiling together equivalent quantities of strong solutions of the two salts. In accordance with the law of insolubility the least soluble salt at the boiling temperature (NaCl) is formed and precipitated. The crystallized sodium 165 chloride is removed from the hot solution and the liquid allowed to cool; during the cooling" the salt least soluble in cold water crystallizes out (KN0 3 ). The solubility of the sodium chloride is about the same at boiling and common temperatures, so that there is no additional separation of it by cooling, while the solubility of the potassium nitrate is decreased more than six times by the reduction of the tem- perature. Properties of Potassium Nitrate. Potassium nitrate crys- tallizes in six-sided rhombic prisms surmounted by six-sided pyramids. It has a cooling and slightly bitter saline taste. Heated above its fusing point it evolves oxygen and is reduced to the nitrite; at a still higher temperature the nitrite is decomposed with evolution of nitrogen and oxygen, leaving the oxide of the metal. The salt is soluble in less than four times its weight of water at 18° C, the solubility increasing very rapidly with the temperature; at 100° C. water dissolves nearly two and one-half times its weight of the salt. Potassium nitrate, like the nitrates generally, is a power- ful oxidizing agent. Its formula shows it to contain very nearly one-half of its weight of oxygen, five-sixths of which are available for the oxidation of the combustible body. It is chiefly used in the manufacture of gun-powder and pyro- techny. Potassium Chlorate ; KC10 3 . This salt is a white crystal- line solid and like the nitrate is an oxidizing agent. It parts with its oxygen more readily than does the nitrate. At a high temperature it acts violently upon combustible bodies. If a jet of hydrogen or coal gas be placed upon the melted salt, ignition ensues and the gas burns brilliantly. The chlorate is much used in pyrotechny. The common friction primers for firing cannon contain a mixture of the chlorate, sulphur and antimony sulphide 166 made into a paste with dissolved shellac. A pull on the lan- yard withdraws a little rasp inserted in the primer and thus explodes the mixture, which ignites the powder in the lower part of the tube, and this communicates the name to the charge in the gun. The fact that a mixture of it and sulphur explodes by friction prevents its use in the manufacture of gun-powder. Its use as an oxidizing agent in matches has already been referred to. By heat it is eventually decom- posed into potassium chloride and oxygen, 2KC10 3 (heated) =KCl+KC10 4 +0 2 ; KC104=KCl+0 4 ; for this reason it is the most convenient source for obtaining oxygen in the labora- tory, as has already been stated. The chlorate may be prepared by the action of chlorine upon the hydroxide. Potassium Sulphates. The normal sulphate occurs native asso- ciated with the sulphate and chloride of magnesium in the mineral karnite from which it may be readily separated. It is also produced as a bye product in several industrial operations. Karnite is used as a fertilizer and potassium sulphate is used in the manufacture of alum. The bisulphate KHS0 4 , can be prepared by the action of sulphuric acid upon nitre. It finds use in chemical operations for decomposing minerals at high temperature, which are not readily attacked by acids ; under these conditions its hydrogen gives place to metals. OTHER COMPOUNDS OF POTASSIUM. Oxides of Potassium. There are several oxides of potassium, the best known of which is K 2 4 . This is the final product of the com- bustion of potassium in air or in oxygen. K 2 is thought to result when K 2 4 is heated to a high temperature or when the hydroxide and potassium are heated together. The evidence of the existence of this oxide is deemed by some good authorities as unsatisfactory. Potassium forms sulphides whose formulae are, K 2 S, K 2 S 2 , K 2 S 4 , K 2 S 5 , and K 2 S 7 . The compound KHS also exists. SODIUM; Na; 23. Sodium does not occur in a free state in nature. The most abundant natural compound of it is the chloride or common salt. Sodium, like potassium, in combination with silica and aluminutn, is a common constituent of certain feldspars which go to make up many igneous and metamor- 167 phic rocks — it is not however so abundantly present in the rocks as potassium. Sodium also occurs abundantly in the native sodium nitrate. The discovery of potassium naturally led Davy to the dis- covery of sodium which he also isolated in 1807 by a process entirely similar to that by which he obtained potassium. Sodium is now manufactured in a manner similar to that described for potassium, namely by reducing" the carbonate with charcoal, Na 2 C0 3 +2C— Na 2 +3CO. By distilling* a mix- ture of carbon and sodium hydroxide the reduction takes place at lower temperature; the sodium distils over and sodium carbonate remains in the retort, 3NaOH+C=Na 2 C0 3 +H 3 +Na. In Castner's method a mixture of iron and carbon is made by heating together tar and haematite iron ore, this mixture is sometimes called iron carbide, and is used in the process instead of charcoal alone as previously explained. The action of the iron is mechanical, serving to keep the carbon in contact with the fused hydroxide. Metallic sodium is now manufactured in this country by the Castner electrolytic process. In this process the sodium hydroxide is decomposed by electricity. At this writing the details of process cannot be obtained. Properties and Uses. Sodium is very similar in proper- ties to potassium. It is silver white in color and at ordinary temperature can be cut like wax but below 0° C. it is hard. It is slightly lighter than water its specific gravity being less than .97 and will float upon that liquid. It decomposes water with liberation of hydrogen, but inflammation does not gen- erally occur. If the water be warmed or the metal be placed on a slip of bibulous paper so that it will not move around, the temperature will rise sufficiently high to ignite the liber- ated hydrogen. The burning of the hydrogen volatilizes some of the sodium which gives a yellow color to the flame produced. Its action on water is not so energetic as that of potassium. 168 Freshly cut sodium is very lustrous but is immediately tarnished by exposure to the air. Sodium is a very important reducing agent, its principal application being in the prepa- ration of magnesium, aluminum, and silicon from their chlorides. It also finds valuable application when amalga- mated with mercury, such amalgam being more efficacious than mercury alone in extracting gold and silver from their ores. Sodium Chloride ; Common Salt ; NaCl. Next to air and water this substance is the most essential to the life and health of the animal world. In addition to this it is one of the most important raw materials in the industrial arts. It is used in enormous quantities in the alkali industries and is the source of all the chlorine. Occurrence. Sodium chloride occurs widely and is abund- antly distributed. Immense deposits of it occur in various parts of the world. The waters of the oceans contain about three per cent of it — the waters of many lakes and springs are impregnated with it. Preparation of Salt. In several countries salt is mined directly from the deposits. The most celebrated mine is that of Wielitzka, in Gralicia, near Cracow. This mine has been worked for several centuries. It is also mined in Germany, in England, and at several places in the United States. Rock salt is mined in Louisiana, Kansas, and in Grenesee, Wyoming, and Livingston counties, New York. Salt thus obtained is generally impure and is purified by solution and recrystallization . The principal portion of the world's supply of salt is obtained by the evaporation of natural or artificial *mmtt.l!uMjL4 Artificial nrises- are produced by admitting water to contact with the salt deposits and pumping it out after it has been heavily charged with salt. Both natural and artificial brines are often concentrated by exposing a large surface of the 169 liquid to the air, and this, in Europe, is accomplished by allowing the liquid to trickle over walls or towers of brush- wood. The concentration in suitable vessels is then con- tinued by artificial or sun heat. In some places in this country the evaporation is mainly by sun heat alone, being- carried on in shallow wooden vats. This is the process at Syracuse, N. Y., and in Bay and Saginaw counties, Michigan. At other places in these States the process is carried on entirely by artificial heat and known as the pan process. In warm climates, France especially, considerable salt is obtained by the evaporation of sea water. This is accom- plished in the marshes along the shore into which the water is admitted from the sea. As concentration is increased the liquid is let from one basin to another until it reaches the crystallizing area. In cold countries salt is sometimes obtained from sea water by exposing the water in shallow pits and allowing it to freeze. A large portion of the water may thus be sepa- rated and the solution left may be strong enough to pay for evaporation by artificial heat. In all these processes the purity of the salt depends upon the nature of the original brine and other salts are often obtained from the brines left (mother liquor), after as much common salt has been obtained as practicable. The size of the grain of the salt depends upon the temperature at which the crystallization takes place, the lowest temperature giving the largest grains. Properties of Sodium Chloride. The properties of com- mon salt are well known. Pure salt is very slightly deli- quescent, the presence of magnesium and calcium chlorides greatly increases the tendency and they are often present in table salt. It is soluble in a little less than three times its weight of water at 0° C, and its solubility is very slightly increased by raising the temperature. 170 Sodium Carbonate; Na 2 C0 3 . Preparation. Before the French Eevolution this salt was obtained from the ashes of sea weeds. The necessities of the French nation led Napoleon to offer a reward for the discovery of some other method for preparing" it. This appeal was answered by Leblanc in the discovery of a method of making it from common salt which not only cheapened the production of sodium carbonate but produced the most beneficial results upon many other manufacturing industries. It led to im- provements in the manufacture of sulphuric acid; it cheap- ened the production of hydrochloric acid and chlorine for bleaching, thus benefitting the manufacture of all textile fabrics; it gave a tremendous impulse to the industries of glass and soap making. Leblanc Process. A full description of a manufacturing plant can not here be attempted. Only the essential re- actions involved will be given. The Leblanc process consists of three steps. 1st, The conversion of common salt into sodium sulphate by heating it with sulphuric acid, 2NaCl+H 2 S0 4 =Na 2 S0 4 4-2HCl; the sodium sulphate is called the salt-cake and the process the salt-cake process. 2nd, The conversion of the sodium sulphate into the carbonate by heating it with powdered coal and limestone, the reactions may be indicated by the reactions — Na 2 S04+C 2 =Na 2 S+2C0 2 ; Na 2 S+CaC03 : =CaS+Na 2 C03 — the result of this process is called black-ash because of the dark color, from the carbon of the mixture of calcium sulphide and sodium carbonate. 3rd, The last step in the process is the extraction of the sodium carbonate from the black-ash by lixiviation with water, evaporation to the crystallizing point, and calcination. The salt thus obtained usually contains some common salt, some sodium sulphate, and some sodium hydroxide, the latter resulting from the action of the lime upon the sodium carbonate. To obtain pure carbonate the calcined soda is subjected to further treatment. 171 Solvay 's Process. This process which has now largely replaced the Leblanc, depends upon the fact that if a solu- tion of the acid carbonate of ammonium be brought into contact with a saturated brine solution double decomposition ensues, the less soluble acid carbonate of sodium being formed and crystallizing out, while ammonium chloride remains in solution. The result is accomplished by saturat- ing a strong brine solution first with ammonia and then carbon dioxide, when the acid sodium carbonate is pre- cipitated, NaCl+NH 3 +C0 2 +H 2 0=NaHC0 3 +NH 4 Cl. By heat the acid sodium carbonate is converted into the normal carbonate, 2NaHC0 3 (heated) =Na 2 C0 3 +C0 2 +H 2 0. The C0 2 liberated in this operation is again used in the first step of the process. The NH 4 C1 is decomposed by lime and the ammonia is used again, 2NH 4 Cl+CaO = CaCl 2 +2NH 3 + H 2 0. The manufacture of the carbonates by the Solvay process at Syracuse, N. Y., and at Saltville, Va., is now conducted on a large scale. Other extensive works for this process are being erected at Detroit and Cleveland. From the reactions indicated in the above processes it will be observed that in the Leblanc method the sulphur is finally left combined with calcium forming calcium sulphide and in the Solvay process the chlorine is left combined with the same metal forming calcium chloride both of which pro- ducts are of themselves worthless. This waste of raw material is a loss in economy of manufacture, and methods have been devised by which the sulphur and chlorine are recovered for continual use. The carbonate is also prepared to a small extent from cryolite, which is a double fluoride of sodium and aluminum. Properties and Uses of Sodium Carbonate. The normal carbonate crystallizes in oblique rhombic prisms containing ten molecules of water of crystallization (Na a COs,10 Aq.). In dry air the salt effloresces and crumbles to a powder losing the 172 greater part of the water of crystallization; when heated all the water of crystallization is driven off. The carbonate is very sohible in water. 100 parts of water at 14° C. dissolve more than half their weight of the. 10 Aq. salt. The solubility of this salt increases up to 36° C. but then decreases. At the boiling point water dissolves nearly four times its weight of the salt. The salt is less soluble than potassium carbonate and is often called washing soda. It is made in enormous quantities for use in the manufacture of giass and soap. The Acid Carbonate; Bicarbonate; NaHC0 3 . This salt is produced as described above in the Solvay process. It may also be produced by passing C0 2 into a solution or over crys- tals of the normal carbonate. It is used in medicine and quite extensively in the preparation of effervescing drinks. Both these carbonates are found impregnating the waters of certain lakes. Lake Mono is an example in our own country. , Sodium Hydroxide ; NaOH. This salt may be prepared by the action of lime upon a solution of sodium carbonate, the reaction being entirely similar to that for the preparation of potassium hydroxide, Na 2 C0 3 4-Ca(OH) 2 =2XaOH+CaC0 3 . Sodium hydroxide is very similar to that of potassium. It is the form to which the carbonate is generally converted preparatory to its use in the making of hard soap, it is then called soda-lye. Caustic soda is now produced from common salt by electrolysis. By the action of the electric current upon a solution of salt the chlorine is liberated and an amalgam of sodium and mercury formed. By mechanical means the amalgam is transferred to another compartment of the cell containing water, where the sodium is transformed into the hydroxide and the mercury returned to the first compartment for reamalgamation. In one compartment the mercury is the cathode and in the other the amalgam is the anode. 173 Sodium Nitrate; NaN0 3 . This salt occurs abundantly native associated with other salts, gypsum and common salt. It is found in enormous quantities in Chili and Peru and is known as cubic nitre or Chili saltpetre. It is purified by solution and crystallization. The pure salt is deliquescent and very soluble in water. The deliquescent property prevents its use in gun-powder but it is largely used in the manufacture of potassium nitrate and nitric acid. Borax, Sodium Biborate; Na 2 0,2B 2 3 . This substance occurs as a native mineral under the name of borax or tincal. It is also obtained from other native borates. Tincal and other native borates are obtained in large quantities from the salines or marshes of southern California and Nevada. These marshes are remnants of former fresh water lakes. It also occurs abundantly in the waters of Clear Lake, California. In California true veins of calcium borate have been found and worked for conversion into borax. Borax may be made by acting on sodium carbonate with boracic acid and most of the borax of com- merce is so made. Borax is an acid salt and when fused dissolves many oxides forming glassy beads which often have characteristic colors. This action makes it valuable in blow-pipe tests in mineralogy — upon the same property depends its use for soldering metals. It is now used in considerable quantities in glazing porcelain and earthen ware and in making enamels. Sodium Silicate. An artificial combination of sodium and silica has long been used under the name of soluble glass. It can be made by fusing sand and sodium carbonate together or boiling sand with a strong solution of caustic soda under pressure. This glass is used to coat wood and render it fire-proof, for wall- painting, and frescoing and to make artificial stone. Sand mois toned with it, pressed into moulds, dried, and highly heated gives an arti- ficial sandstone, the sodium silicate fusing and acting as a cement. Any required color may be imparted by mixing the necessary metallic oxide with the sand. Sodium Thiosulphite ; Na 2 S 2 3 . This salt is largely used in photo- graphy. It is commonly known as sodium hyposulphite e plates begin just in front of the screens. The pulp after passing through the screens is carried by the water over the outside copper plates, which catch more of the free gold. The amalgamated copper plates are cleared off at intervals and the amalgam "retorted" to separate the gold: sometimes the amalgam is washed by grinding in a pan before "retorting." The pulp after leaving the copper aprons is made to flow over blanket-sluices. These sluices are covered with specially prepared mill blankets. The nap of these blankets arrests still another portion of the gold, while most of the sand and lighter minerals are carried over them. These blankets are removed at intervals and washed and the washings are amal- gamated in a special apparatus. This amalgam is "retorted" to separate the gold. "When amalgamation begins in the "battery" the blanket sluices are less generally used. Whether the blanket sluices are used or not the sands or "tailings" carried away by the water are often subjected to further treatment. These "tailings" may be treated by amalgamation in grinding pans, but they are generally too 263 impure to be treated in this manner and are subjected to the next process to be described. Chlorine Leaching. Preliminaries. This process is seldom in this country applied directly to the ores from the mine but is used to obtain the gold which is not caught in the amal- gamation operations and which remains with the sands or "tailings." As these sands contain only a small per cent of gold, the first step usually taken is to separate mechanically as far as practicable the gold bearing material from that which carries no gold. This operation is termed "concentra- tion " and is accomplished by the mechanical action of water upon the gold bearing material. The object of "concentra- tion" may be stated to be, to get out of comparatively poor material a comparatively rich one. The process of "con- centration" is generally applied to the "tailings" though it is sometimes used to convert a poor ore into a richer one before it is subjected to other treatment. The gold to which the leaching process is applied is in the metallic state but so intimately associated with other min- erals that the mercury has failed to reach it in the amal- gamation. The minerals most commonly thus associated with gold in the " concentrated tailings " are sulphides of iron and other metals, the former usually constituting the larger portion. The next step is to roast the "tailings" to convert all the baser metals present into oxides. Chlorination. The roasted ore is next subjected to the action of chlorine by which gold chloride is formed. The chloride of gold is dissolved out of the chlorination vat by lixiviation with water and the solution received in a precipi- tating tank. The gold is precipitated from the solution in the metallic form by the addition of ferrous sulphate; the precipitated gold needs only to be fused. The above met hod of chlorination is known as Platner's process. Cyanide Leaching. The leaching of "concentrated" ores as well as "tailings" which are comparatively free from 264 sulphides, is now largely accomplished by treating- with a weak solution of potassium cyanide. This in the presence of oxygen forms a soluble compound with the gold from which the metal may be recovered by precipitation by metallic zinc or by electro-deposition. The principles employed and the general methods pursued in the amalgamation and leaching processes are outlined above, but the number of operations and the details of each vary with the kind and nature of ore. With some varieties of gold quartz so nearly all the gold is obtained by amalgamation that the "tailings" are not worth working. With some ores "concentration" may precede amalgama- tion instead of the reverse as described above. Sometimes the amalgamation process is preceded by the roasting of the ores and occasionally the ore is such that the leaching process is not preceded by amalgamation. When the ores to be leached by chlorine are rich in silver there is usually added a little salt to the roasting charge and the silver is converted into the chloride. The silver chloride can be dis- solved out before the ore is subjected to chlorination. Platner's chlorination process has been modified in this country by Mears so that the chlorine is delivered under pressure into revolving amalgamating barrels. The gas acting under pressure and the agitation and friction of the ore give some marked advantages to this modification but there were at the same time some disadvantages, one of the most marked beingthe escape of some of the compressed chlorine. Theiss improved on the Mears' method by generating the chlorine in the amalgamating barrel itself, though under less pressure the nascent chlorine was found to be very active and the Theiss barrel method has found extensive application in our western country. Gold from Sedimentary Deposits. A large proportion of the world's supply of gold has been obtained from sedi- mentary deposits. In this country the gold from this source is limited to alluvial deposits but in the rich mines of South Africa which have recently come into such prominence, the gold is found in the marginal sea deposits of previous ages which are now tilted and displaced and lie far inland. We shall first speak of the gold from the alluvial deposits of this country. Placer Mining. The gold from this source in this country is obtained by what is called placer mining. The placer deposits exist in the sands along the beds of the present 265 streams or in the sands and gravels which now occupy the beds of channels and banks of extinct streams. The gold is separated from the sands mainly by the action of water. When gold was first discovered in California in 1848 a large amount of it was obtained by simple pan- washing. This process was followed by cradle washing and then by sluice working. As the shallow placers were exhausted and the working was extended to the deep placers of former river channels, hydraulic mining was developed. By this means it became possible to economically wash very large masses of earth, in several places several million parts of earth were worked to obtain one of gold. The large amounts of water and earth thus handled required very extensive appliances. The sluices were made from a few hundred feet to several thousand feet long. The great difference between the specific gravity of the gold and the sands (19.3 and 2.6) rendered separation by washing possible, but amalgamated copper plates, riffles and mercury were used in the sluices to more perfectly catch the gold as the operations were extended. In these deep placers the richest sands were generally near the bed rock of the stream and sometimes were so consolidated that they had to be "weathered" or crushed before washing. In some places the deep placer deposits extended under rock formations that could not be removed. This led to drift mining. The auriferous sands from these mines were often found so consolidated that they had to be subjected to the milling and amalgamation process already described. ( Africa Gold Mines. The great mines of the Rand in South Africa deal with gold occurring; in a hard conglomerate which was originally a marginal sea-deposit. These deposits were tilted and displaced and now form part of the interior highlands of the country. The sheets in which the gold occurs are called "banket reef." These reefs are mined exactly as are quartz veins. The ore is crushed in stamps and treated by the amalgamation process above described. The amalgamation is begun in the mortars. The "tailings" are "concentrated" and sub- jected to the chlorination or cyanide process of leaching as already described, the cyanide process being the more common. 266 Properties of Gold. Gold is a metal of great antiquity and has from the earliest times been esteemed a precious metal. In a pure state it is only about as hard as lead. It is the most malleable and ductile of metals. Its specific gravity is 19.3. For commercial purposes gold is always alloyed with some other metal to increase its hardness and durability, silver and copper being the metals most generally employed for this purpose. The gold coin of the United States is nine-tenths gold, and one-tenth copper alone or an alloy of copper and silver. The purity of gold is generally indicated by carats; pure gold is 24 carats fine. Grold of 18 carats is only three-fourths fine. On account of its great malleability gold leaf can be made exceedingly thin. Gold is not affected by the atmosphere or moisture and does not tarnish. It is not acted upon by any of the ordinary acids but it is attacked by aqua regia or free chlorine. Com- mon gold alloyed with copper may be made to present a pure gold surface by heating and oxidizing the copper and dis- solving it out with sulphuric or nitric acid. The uses of gold are too well known to require mention. COMPOUNDS OF GOLD. Gold Chloride; AuCl 3 . The most important of the inorganic salts of gold is the gold chloride, AuCl 3 . It can be prepared by acting upon gold with aqua regia. The chloride is very easily reduced to the metal- lic state. Organic matter generally, and nearly every substance capable of combining with oxygen will reduce it. The property of the salt together with the permanency of the deposited metal renders the chloride useful in photography. Oxides and Sulphides. Three oxides of gold have been obtained but they are of no practical importance. Several combinations of gold with sulphur have been obtained but their compositions are not well determined and they are not of practical importance. The Purple of Cassius produced when stannous and stannic chlorides are added to dilute solutions of gold is used in enamel painting and in coloring glass. It gets its name from the discoverer, Andreas Cassius of Leyden. The exact composition of this substance is not known but it contains gold, tin, and oxygen. ORGANIC CHEMISTRY OR CHEMISTRY OF THE CARBON COMPOUNDS. CHEMISTRY OF THE CARBON COMPOUNDS. The term " organic chemistry " was formerly used to denote the chemistry of compounds found in the bodies of plants and animals. It was originally thought that these compounds could only be produced in living organisms, animal or vegetable, and that their production was due to the vital forces which were different from the chemical forces artificially brought into play in the laboratory. This view led to the separation of chemistry into two branches of organic and inorganic — the latter including the chemistry of those compounds whose existence in no way depended upon the "vital forces." The assumption as to the action of the different forces in the organic and inorganic worlds was rendered untenable when it was shown that many organic compounds could be formed by the direct combination of elements or the trans- formation of inorganic compounds. The preparation of urea accomplished in 1828 by Wohler, was the first step in the artificial formation of organic compounds from their inorganic constituents. Many organic compounds of great complexity have since that date been built up from the elements themselves and it is now universally recognized that the chemistry of the organic compounds is but a part of the general science of chemistry. Organic compounds all contain carbon, and organic chem- istry is really the chemistry of the carbon compounds but on 268 account of the large number of such compounds it is con- venient to study them separately rather than in connection with the element carbon. For the sake of convenience the division of chemistry into two branches is still generally retained, though the original reasons for the separation have been shown to be erroneous. There is however a distinction between organic compounds and organized bodies. The former have a definite chemical composition, many of them can be produced artificially and possess definite chemical and physical properties ; organized bodies consist of mixtures of definite compounds and have only been produced under the influence of vitality. The chemical relations of the organized bodies and the life pro- cesses which go on in them, are treated under physiological chemistry. CLASSIFICATION OF CARBON COMPOUNDS. The compounds of carbon outnumber the compounds of all the other elements taken together. The elements most usually combined with the carbon in these compounds are hydrogen, oxygen, and nitrogen. A large number contain only carbon and hydrogen; a still larger number consist of carbon, hydrogen, and oxygen; many consist of carbon, hydrogen, and nitrogen ; and still others of carbon, hydrogen, oxygen, and nitrogen. In addition to the four elements named, sulphur and phosphorus frequently occur. In the carbon compounds from organic sources the above named are the elements generally found, but almost all the elements, metals and metalloids have been artificially introduced as constituents of these compounds and some of the metals are found in the natural compounds. The classification of carbon compounds like all other classifications, is based upon simi- larity of properties and characteristics of the bodies grouped together. The nature of the carbon compounds permits a much 269 more perfect classification than is possible in the inorganic chemistry. The members of the same class and the different classes are derivable from each other by comparatively simple reactions. The system of classification includes nearly all artificially prepared carbon compounds and the greater proportion of those produced in living bodies, but there are many com- pounds formed in the vital processes of plants and animals whose chemical relations are not sufficiently known to permit their classification, such are the alkaloids and the albumi- noids yet to be mentioned. The compounds of carbon are usually grouped into thirteen classes based upon their rational or constitutional formulae, that is the formulae which indicate the radicals that compose the compound. There are other classes whose rational formulae are not made out, based upon certain similar characteristics. There are a great many carbon compounds which contain only carbon and hydrogen and most of the other well defined carbon compounds can with reason be considered as de- rived from these, so that the compounds of carbon in- cluded under the term "organic" are generally derivatives of those containing only carbon and hydrogen known as hydrocarbons. It is not the purpose of this text to consider the varied relations between the different classes nor between the members of the same class of the carbon compounds, and the classification of the compounds described will only be referred to when such reference helps to define and elucidate the characters which it is sought to set forth. The most general divisions of the carbon compounds which include all those just referred to, are the fatty and aromatic groups. The bodies which make up the first group are derivatives of the hydrocarbons whose general formula is C n H 2 n+2 (paraffin series) ; the second group is derived from the benzene series whose general formula is r„H,>n-«. These two groups, fatty and aromatic, are very convenient for general reference. 270 STRUCTURAL OR CONSTITUTIONAL, AND RATIONAL FORMULAE. The basis for the classification of organic compounds is usually partially represented in their chemical formulae. Such formulas have already been referred to as structural formulae but it will be of convenience hereafter to state some- what more fully the significance of these formulae. By the careful consideration of the changes and the behavior of any chemical compound under a large variety of dissimilar cir- cumstances it is believed that the order of combination of the atoms in the molecule in many such compounds has been determined. A formula which gives the fullest knowledge as to the constitution of a compound is called its structural or constitutional formula. By such formula it is intended to indicate the connection between the atoms in a molecule. It should be kept in mind that the representation of the formula on paper is of no importance as the formulae are intended to express the manner of combination and not the actual positions of the atoms themselves. Thus the con- stitutional formula of methyl-alcohol is determined to be H H— C— H H O and of acetic acid is h— c— c— o— H. 1 I H— C— H. H I H A rational formula is one that from the way in which it is written, indicates the manner in which a compound breaks up or is formed under certain conditions, or shows the rela- tions of allied compounds to each other. It is an abridged constitutional formula which indicates certain relations not shown in an empirical or molecular formula; or it is a mole- cular formula so written as to indicate certain chemical relations of the compound. Thus the formula for acetic acid may be written C 2 H 3 2 H to show that the acid is monobasic 271 or it may be written C 2 H 3 0,HO which indicates the origin of the acid from certain salts. Since a compound may split up into different groups or radicals or may be formed in differ- ent ways the same body may often have a number of rational formulae each of which indicates certain characters under certain conditions. This fact has already been illustrated in the supposed constitution of certain inorganic salts, but owing to the larger number of atoms in many organic com- pounds the principle of resolution into rational formulae is much more frequently possible. Isomerism and Polymerism. Isomerides or isomeric bodies are those bodies which have the same percentage com- position and molecular weight but show different properties. Those isomerides which differ in physical properties but whose transformation under the action of the same agents closely resemble each other are called "isomers." Those isomerides which exhibit dissimilar transformation under similar circumstances are called "metamers." The phenome- non of isomerism is only explicable upon the supposition that the arrangements of the atoms in the molecules are different. Polymeric bodies or "polymers" are those which have the same percentage composition but different molecular weights and consequently different molecular formulae. The carbon compounds furnish many examples of isomers, metamers, and polymers. HYDROCARBONS. Of the carbon compounds the simplest are those contain- ing only hydrogen and carbon and from these, as already stated, most of the others can be derived. The hydrocarbons furnish several series of compounds and each series under the action of reagents yields derivatives so that the possible number of carbon compounds is very great. These com- pounds frequently exhibit a characteristic not common among inorganic bodies— their molecules contain a large number of 272 the atoms of the elements which enter them, thus rendering possible a great number of isomers. SATUEATED HYDEOCAEBONS. Paraffin Series; Formula C n H2n+2. The only hydrocarbon containing but a single atom of carbon is methane or marsh gas. Carbon being a tetrad and hydrogen a monad it is evident that on the theory of valency the constitutional formula of marsh gas must be represented thus H I H-C— H. I H indicating a saturated compound or one in which there are no free units of valency. A consideration of the formula above given will show that the relation between the number of atoms of the two elements is such that there are no free affinities. The hydrocarbons of this series can not form compounds with other bodies except by substitution, one or more of the atoms of the molecule must be removed to effect the introduction of others. Since hydrogen is a monad and can not act as a connecting atom, it is evident that on the theory of valency the carbon atoms in hydrocarbons must be connected directly to each other. The different ways in which the connection may be made and yet satisfy all the affinities of each element is thought to explain the frequent occurrence of "isomers." In the saturated hydrocarbons it is thought that no two carbon atoms are held together by more than one combining unit of each atom. Methane or marsh gas is the lowest member of this series, the others containing more than one atom of carbon. The formulse of the consecutive members of the paraffin series differ from each other by CH 2 , the first four are, methane CH 4 , ethane C 2 H 6 , propane C 3 H 8 , and butane CJLo. Such a series is termed an homologous series. The highest known member of this series contains 35 atoms of carbon. The 273 members of the series up to those containing four atoms of carbon are gases ; from four to sixteen they are liquid at ordinary temperatures; those containing a greater number than sixteen atoms of carbon are solid. Many of the hydrocarbons of the paraffin series occur abundantly in nature. The occurrence of methane as marsh gas and fire-damp has already been referred to. Petroleum. The great natural source of this group is the petroleum oil which is found most abundantly in this country and in Russia — it is also found in several other countries. American petroleum consists almost entirely of the paraf- fin hydrocarbons, some of the benzene group are present in small quantities. The Russian petroleum contains a consid- erable per cent of the benzene hydrocarbons and their deriv- atives. The petroleums are mixtures of the various members of these hydrocarbon series which are separated from each other by fractional distillation — a large number of valuable products is derived from them. In this country the oil wells are connected by pipe lines with the refineries at New York, Baltimore, Pittsburgh, Cleve- land, and Buffalo. The lines in some cases are over three hundred miles long and the oil is forced by pumps through the pipes from the wells to the refineries. At the refineries the oil is subjected to fractional distilla- tion. The products which first come off as the temperature rises, are of course the gaseous products. The more easily condensible of these are collected, liquefied by pressure, and used to produce cold by evaporation — in the manufacture of ice, etc. This product is mainly , composed of CJLo butane and is called cymogene. The names of the commercial prod- ucts vary at different places — some of the more important in the order of the boiling points are Rhigolene used as an an- aesthetic, Petroleum ether used as a solvent for rubber, Gaso- lene used for enriching coal gas, Naphtha used as the working substance in naphtha engines. Benzine used as a solvent is 18 274 largely substituted for turpentine and comes off between 120° and 150° F. ; it is entirely different from benzene, the latter not belonging to the paraffin series. Kerosene is the product which distills over between 150° and 300° F. and is the liquid so largely used as a burning oil. It is purified by agitating with acid and in alkaline solution before it is put upon the mar- ket. There are many grades of this oil depending upon the color and fire test to which the oil is subjected. The fire tests are in some cases fixed by law and differ in different places. An oil which when heated in an open vessel to 100° F. does not give off vapor enough to ignite when a flanie is brought near its surface, is safe under ordinary conditions of use. The residue of the crude oils after distilling off the kero- sene, is subjected to still higher temperature and from it are obtained the lubricating oils and the solid paraffins. The lubricating oils are daily increasing in importance and are now used in immense quantities. The softer of the solid paraffins are called vaselines, of which there is a number of varieties. The more solid wax-like paraffins are present only in small quantities in the American petroleum, less than three per cent ; they reach ten per cent in the Burmah petro- leums and are very much more in the petroleum from the shores of the Caspian. The greater proportion of the solid paraffin is prepared from the products obtained from the distillation of carbon- aceous shales. Scotland is the centre of the industry. In G-ermany and Austria large quantities of paraffin are ob- tained by the distillation of brown coal or lignite. These coals and shales yield also burning and lubricating oils simi- lar to those from petroleum. Paraffin is tasteless and without odor, insoluble in water but freely soluble in ether. It is largely used as a substitute for sulphur in dipping matches; it is used in the manufac- ture of candles, in water-proofing and finishing cloths, and 275 as an insulator in electrical apparatus. It has also been applied to preserve food from deterioration. Native solid hydrocarbons are found and known under the name of ozokerite. It is used in Europe in the manu- facture of candles. It closely resembles paraffin but is thought to contain a smaller per cent of hydrogen. The petroleum industries of the United States are of immense extent and of vast importance. The burning 1 and lubricating oils furnish one of the largest items of export. The refined oils are exported in tank steamers and a number of these steamers is engaged in such service running between American and European ports. UNSATUKATED HYDROCARBONS. All hydrocarbons which do not have the formula CnHsn+2 are found to be capable of uniting directly with certain other bodies without the removal of any of the constituent ele- ments, it is therefore assumed that in these hydrocarbons some of the carbon atoms are linked together by more than one unit of valency of each, hence ethene may be indicated thus H— C-C— H I I H H and acetylene thus H — C = C — H. In the saturated com- pounds no atom is connected to any other by more than one unit of valency of each ; in the unsaturated two atoms may be connected by more than one unit of each. It is readily conceivable that in these compounds the atoms which arc connected by more than one combining unit of each nun- extend this excess of affinity to other bodies, thus forming new compounds without any change of elements. define Series. These are unsaturated hydrocarbons whose general formula is CnIT>„. The lowest member of the series is olefiant gas, ethene, or ethylene C2H4. The series 276 « is an homologous one and results by the successive addition of CH 2 . The first three members of the series are gaseous — most of the remainder are liquid, but the four highest members are solid. The members of this series resemble in properties the corresponding members of the paraffin series — the boiling- points of the liquid members which have the same number of carbon atoms lie very close together. This series is obtained from petroleum oil and by the destructive distillation of car- bonaceous matter. Ethylene the lowest term of the series, has already been mentioned m connection with carbon — the highest member contains thirty atoms of carbon. Acetylene Series. The general formula for the series is CnILn-2. Acetylene is the lowest member of the series and the homologues differ consecutively by CH 2 . This series, as the two preceding, consists of gases, liquids, and solids. Acetylene is the only hydrocarbon that can be produced artificially — its production and uses were described under the element carbon. The terms of the olefine series differ from the corresponding: terms of the paraffin series by two hydrogen atoms and the acetylene series from the olefine series in the same manner; the hydrogen in proportion to the carbon growing less in the series in the order named. The latter two series may therefore be considered as derivatives of the paraffin or methane series. 4 Benzene Series; Aromatic Hydrocarbons. The general formula for the series is CnH 2n -6 where "n" is a whole number not less than six. The homologues differ successively by OIL. On account of the fragrant odor of some of the benzene derivatives they were formerly termed aromatic hydrocarbons, but equally fragrant odors are found among the methane derivatives, hence the term is no longer strictly applicable. Benzene. The lowest member of the series is benzene C 6 H 6 . This body is the basis from which a large number of organic compounds may be derived. Benzene is produced 277 in the destructive distillation of many organic substances, it is also found in petroleum. It is present in considerable quantity in the more volatile portion of coal-tar oil and this is the source from which it is principally obtained. The light oil from coal tar is subjected to fractional distillation by which the benzene is separated and purified. It is when pure a thin limpid liquid with an odor sug- gestive of coal gas. It solidifies at 0° C. It is insoluble in water but mixes with alcohol and ether. It dissolves sul- phur, phosphorus, iodine, and many fats and resins which are insoluble in water. It is manufactured in large quantity for conversion into aniline from which are obtained many beautiful and useful dyes. Its vapor constitutes one of the illuminating constituents of coal gas. Terpene Hydrocarbons. The empirical formula of this group is C 5 H 8 . They are volatile oils existing in certain plants; they have not been formed by artificial processes. Turpentine oil is the most important member of the ter- penes, its formula is GoH 16 . It exists in the wood, bark, and leaves of many coniferous trees and is generally prepared by distilling the thick juice which is obtained by tapping (making incisions into the bark) the trees. This juice is a mixture of turpentine oil and resin. In this country turpen- tine is principally obtained from two varieties of the pine the industry being most largely developed in North Carolina. Turpentine oil when pure is colorless and mobile — it has a penetrating and disagreeable odor. Its boiling point is 158- 160° C. Its specific gravity is .86. It is but slightly soluble in water but dissolves in strong alcohol, ether, and carbon disulphide. It burns with a smoky flame. It dissolves idione, sulphur, phosphorus, caoutchouc, resins, and many fixed oils. The consumption of turpentine oil or spirits in the preparation of paints and varnishes is very extensive. There is a large number of other essential oils belonging to this group which have the same empirical formula and 278 many of them the same molecular formula as turpentine oil. Such bodies are the oils of lemon, juniper, orange, birch, etc. These oils are generally obtained by distilling the leaves, flowers, seeds, or other vegetable products with water, or by passing a current of steam through these products. The boiling points of the oils are much higher than that of water but they readily distil with aqueous vapor. When the vapors condense the greater portion of the oil forms a layer on the surface of the water and may be entirely separated by shaking the water with ether or saturating it with salt. The ether dissolves the oil and can be separated by distilla- tion. The salt causes the oil to separate. In some of the more delicate perfumes the distillation is accomplished in a vacuum or the oil extracted by pressure or dissolved out by carbon disulphide. These oils when not isomeric with tur- pentine oil are mixtures of hydrocarbons, having the slame percentage composition, with compounds of carbon, hydro- gen, and oxygen. By exposure to the air they slowly absorb oxygen and lose their liquid state. They mix in all propor- tions with linseed, whale, and other fixed oils. The greasy stain communicated to paper by a volatile oil can be entirely removed by heating, which is not the case if it contains a fixed oil. Camphors. The camphors are crystalline bodies closely related to the t\rpenes, from which they appear to be formed by oxidation. Common camphor is obtained by distilling' the chopped wood of the camphor laurel of China and Japan. It has been produced by the artificial oxidation of several terpenes. Camphor is very slightly solu- ble in water but readily so in alcohol and ether. It burns with a smoky flame. Its formula is C 10 H 16 O. Resins and Balsams. The resins are closely related to the terpenes and appear to result from their oxidation. They are not definite com- pounds but mixtures, the essential ingredients being certain resin acids, which are rich in carbon and hydrogen and contain some oxygen. The resins are all, with unimportant exceptions, of vegetable origin. Common resin or colophony is the best example of the class. It is the substance remaining when crude turpentine is distilled and the oil of turpentine expelled. The resins are very widely distributed in the 279 vegetable kingdom. They are insoluble in water but dissolve in alcohol. There is a large number of resins used for industrial purposes. Shellac is employed in the manufacture of hats and is the chief constitu- ent of sealing-wax. The many varieties of varnish are prepared by dissolving resins in alcohol. Mastic, dammar-resin and sandarac are some of the common varnish resins. Amber and copal are fossil resins, though the latter is also obtained direct from the trees. Balsams. These are natural mixtures of resins and essential oils and sometimes acids. They are of different degrees of consistency and by keeping the softer kinds become harder. Caoutchouc — India Rubber. Caoutchouc is closely allied to the terpenes. The substance of which it is mainly com- posed has a formula which is some multiple of C 5 H 8 . The caoutchouc of commerce is obtained from some half dozen different genera of tropical plants including 1 certain climbing plants as well as trees. If the source is a tree an incision is made in the bark and the exudation collected in earthen or tin cups. As these receptacles are filled they are emptied into larger vessels all of which are brought together at some favorable location. The rubber juice is now brought to a solid form by evaporating it from a sort of bat or shovel which is dipped into the liquid juice and held over a fire until the moisture is driven off and a layer of caoutchouc left on the bat. The thickness of the layer is repeatedly in- creased by alternately dipping the bat into the juice and then drying it. When the layer has reached the desirable thickness it is split up one side and removed from the form and hung up to be further dried. There are several other methods of preparing the caoutchouc from the milky juice, the object in each case being to get rid of the liquid in which the caoutchouc is suspended. The manner in which the caoutchouc is dried and the source from which it is obtained account for the different forms that come into market. All raw caoutchouc contains albuminoid and resinous bodies and often mechanical impurities, as woody fibre, earthy matter, etc., from which it must be freed before it can 280 be used for manufacturing purposes. The mechanical treat- ment of the caoutchouc is interesting and varies with the object to "which it is to be put but it cannot be described here. The best caoutchouc comes from the province of Para in Brazil and other provinces of that country. It also comes from Central America. Africa, Madagascar. Asia and some of the East India Islands. Caoutchouc is almost equally valuable for its physical and chemical properties. Its lightness, elasticity, and imper- meability to water are among its most valuable properties. Caoutchouc is insoluble in alcohol but slowly dissolves in carbon disulphide, naphtha, petroleum spirit, turpentine, and benzene — the last two being the best solvents, but the petroleum solvents are generally equally used because of cheapness. Caoutchouc is not acted upon by the alkalies or the dilute acids. It is slowly oxidized in moist ah"-. It hardens and loses its elasticity by cold and softens and becomes sticky by heat. At about 12u : C. it melts and decomposes into a black viscous mass which does not harden and is a valuable lubricant for air-tight stoppers. Vulcanized Rubber. When caoutchouc is mixed with a small per cent of sulphur and the mixture heated to about 150 c C. it undergoes a most beneficial change and is said to be vulcanized. It is thought that some of the hydrogen of the caoutchouc is replaced by the sulphur and a sulpho- compound produced. The vulcanization of the rubber is accomplished after the rubber is mechanically purified. For this purpose about ten per cent by weight of sulphur is thoroughly incorporated with the rubber and the mixture subjected to the necessary temperature. Only a fraction of the entire sulphur seems to combine with the rubber but the presence of the remainder is necessary to secure the effect. The vulcanization by heat is always accomplished after the rubber articles are made into required form. Such articles are molded into shape or the different parts cut out and 281 joined together by rubber cement after the sulphur has been- incorporated with the rubber. Certain other bodies besides sulphur are often added to the rubber. These are not known to act otherwise than mechanically but seem to be beneficial; they are such as zinc, lead, and iron oxides, steatite, calcium and lead car- bonates. Water-proof cloths are made by spreading* the sulphurred rubber in a plastic state by machinery upon the surface of the fabric. Two pieces of cloth may be made to pass through rollers with their "spread-sides" toward each other which produces water proofing of double texture. The film of rubber spread upon the cloth may be made of any desired thickness. Water-proof cloths may be vulcanized by sub- jecting them to the required temperature or by what is known as the cold process. In this process the spread cloth is drawn slowly through a solution of sulphur chloride in carbon disulphide during which the thin rubber sheet takes up the required sulphur and need not be subsequently heated. The cold process is not as efficient as that first described. The effects of vulcanization are to greatly increase the elasticity of the rubber and to prevent its cohering under pressure and adhering to other bodies when warm. It is no longer affected by cold, its porosity is diminished, and it is no longer soluble in the solvents of common rubber. The water-proofing of fabrics by solution of rubber was patented by Mackintosh in 1824. Certain garments are still named from the inventor. The vulcanization of rubber was discovered by Goodyear in 1843. Vulcanite. With a greater proportion of sulphur (twenty to thirty-five per cent) and a still higher temperature the rubber is converted into vulcanite or ebonite. It is much harder and more rigid than rubber and is used in the manu- facture of combs, rulers, discs, etc. 282 Rubber Tubing and Threads. Knbber tubes are made in two ways — 1st, the rubber is brought to a semi-plastic condi- tion and forced through an annular mould or die, consisting of two concentric cylinders with the necessary space between them. 2nd, By cutting rubber bands of the proper width and joining their freshly cut edges by pressure, the bands being wrapped around a mandrel of the proper size. Rubber threads are either cut from the sheets or the semi- liquid rubber is pressed through sieve-like moulds. The first method gives the rectangular threads, the latter the round. Gutta-percha. This substance has the same empirical formula as caoutchouc. It is like that substance obtained from exudation of certain trees. It comes mainly from the Islands of the Indian Archipelago — its name signifies the gum of the percha tree. The crude gum is procured in the same way as caoutchouc and it is subjected to about the same mechanical process to free it from impurities. It is harder and less elastic than caoutchouc. It is not attacked by alkalies or dilute acids but is acted upon by strong nitric or sulphuric acid. It is an excellent electric insulator and is extensively used as a casing in submarine telegraphy, and for the covering of electric wires. It is largely used in the manufacture of medical instruments and for many cheap ornaments. Gutta-percha was for a long time obtained by felling the trees, the juice then exuding from incisions made at many places along the body and branches. This injudicious method was beginning to imperil the supply and has now been stopped. Because of the great demand for gutta- percha and caoutchouc, the English Government has at- tempted to cause the artificial production and spread of the parent trees. ALCOHOLS. This term is applied to a large number of bodies which in many respects differ widely from each other, but may all be considered as oxy- gen derivatives from the hydrocarbons. The relations of the alcohols 283 indicate that they may be considered as derived from the correspond- ing- hydrocarbons by the substitution of hydroxyl (OH) for an atom of hydrogen. Thus methyl-alcohol has the composition CH 3 ,OH which may be supposed to result by substituting (OH) for H in CH 4 ; propyl- alcohol has the composition C 3 H 5 (OH) 3 which results by substituting (0H) 3 for H 3 in propane, C 3 H 8 . It is evident therefore that they may be considered as compounds of hydroxyl and hydrocarbon radicals of different degrees of valency. Alcohols are said to be monatomic, diatomic, triatomic, etc., or monohydric, dihydric, trihydric, etc., according to the number of hydroxyl groups they contain. Each series of hydrocarbons has its derived alcohols. It will be necessary to refer to only a few of this large class of bodies. Alcohols of the Paraffin Series. The alcohols of this series are the most important of these bodies and embrace all of those that need to be referred to here. They may be considered as derived from the paraf- fin hydrocarbons by the substitution of (OH) for H. Monohydric Alcohols. The lowest members of the series of alcohols are mobile liquids, the middle members are oily liquids, and those con- taining twelve or more carbon atoms are solids. There are two very important monohydric alcohols, the methyl- alcohol and the ethyl-alcohol, their formula? beingCH 3 OHandC 2 H 5 OH, the corresponding paraffins are methane (CH 4 ) and ethane (C 2 H 6 ). Methyl-Alcohol; CH 3 (GH). This body is popularly known as wood-spirit and is found among' the products which result from the destructive distillation of wood. The condensed products from distilled wood separate into lighter and heavier parts. The lighter part is the crude wood- vinegar and con- sists mainly of an aqueous solution of acetic or pyroligneous acid with a small proportion of methyl-alcohol. By fractional distillation the alcohol can be separated and purified. In the impure state after one distillation it is sold as wood-naphtha. Large quantities of methyl-alcohol are now made by distil- ling certain residues which result in the beet-root sugar fac- tories after the fermentation of the molasses for the produc- tion of common alcohol. Pure methyl-alcohol is very similar in smell, taste, and appearance to common alcohol. It dissolves resins and volatile oils, can be burned in lamps, and for all these pur- 284 poses can be used as a substitute for common alcohol. When crude it has an offensive odor and a very disagreeable taste. Ethyl- Alcohol, Common Alcohol. This is the longest and best known of the alcohols and is generally designated sim- ply by the term alcohol. It is a monohydric alcohol derived from the second member of the paraffin series, ethane (C 2 H 6 ), by the hydroxyl substitution C 2 H 5 ,OH. Alcohol can be made artificially by the synthesis of its elements, C 2 H 2 being first produced, this converted into C 2 H 4 , and then converted into alcohol. Alcohol for commercial purposes is always obtained from the fermented products of certain kinds of sugar. Fermenta- tion is a slow process of transformation which is brought about in certain organic bodies by means of substances called "ferments." All ferments are unstable nitrogenous bodies and may be divided into two classes. 1st, Those having an organized structure and capable of growth and multiplica- tion; 2d, Those without structure and incapable of repro- duction. The alcoholic or vinous fermentation, by which alcohol is produced from sugar, is brought about by a ferment of the first class called yeast, which is a vegetable micro-organism. If to a solution of grape or cane sugar (which contains in addition the necessary elements for the growth of the yeast) a little yeast be added the process of fermentation will be set up, during which the sugar will be converted into carbon dioxide and alcohol. The precise action of the yeast is not known but it is during the growth of the yeast that the change is brought about. In the case of grape sugar or glucose (CeH^Oe) the molecule seems to split into carbon dioxide and alcohol, C 6 Hi 2 6 =2C 2 II 6 0+2C0 2 . Cane sugar (Ci 2 H 22 0n) is first converted by the yeast into glucose by the assumption of a molecule of water, Ci 2 H 22 Oii+H 2 0=2C 6 Hi 2 6 ; the glucose is then resolved as before. 285 Note. — During- the fermentation other substances are produced the most important of which are glycerine, succinic acid, and fusel oil, but about 95 per cent of the sugar may be converted into alcohol and carbon dioxide. Fermentation does not take place at a temperature below 32° F. nor above 95° F. Many chemicals arrest and prevent fermentation, such as the strong acids and antiseptics. Pure yeast spores will not ferment a pure solution of sugar because the constituents for the growth of the yeast are absent. Water containing more than one-half its weight of sugar in solution can not be fermented by yeast and the fermentation ceases when the alcohol produced constitutes one-sixth the weight of the solution. The yeast increases greatly in weight when the necessary food constituents are present. The sugars most generally fermented for the production of alcohol are not those from the cane and grape but those from the starch of grain and potatoes. The starch (C 6 Hio0 5 ) is first converted into glucose (C 6 Hi 2 6 ) by the action of dilute acid or into maltose (C12H22O11+OH2) by the process of malt- ing yet to be described. The maltose undergoes the vinous fermentation under the action of yeast just as do the other sugars mentioned. By successive fractional distillations of the fermented solutions pure alcohol is obtained. Pure alcohol is a colorless mobile liquid, has a pungent odor and a piercing, burning taste. Its boiling point is below that of water (78° C.) and it freezes at— 130° C. It burns with a pale blue flame free from smoke. It mixes with water in all proportions and has considerable affinity for it, absorbing its vapor from the air and abstracting it from animal and vegetable substances immersed in it. This fact partly ex- plains its action in preserving bodies. Its dilution with water results in contraction of volume and a considerable rise of temperature. Alcohol is very valuable in the laboratory as a solvent 286 standing next to water in this respect. It dissolves a large number of both organic and inorganic compounds and is especially useful in dissolving the resins, essential oils, etc. The strength of alcohol can be determined from its specific gravity and tables are prepared for this purpose. Absolute alcohol has a specific gravity of .79 at 15° C. Its strength decreases as its specific gravity increases. So-called proof-spirit has a specific gravity of .92 and contains 49 parts by weight of alcohol. If the alcoholic solution contains other bodies than water the specific gravity, of course, does not indicate the strength. It may be observed that ethyl-alcohol is a homologue of methyl-alcohol as appears from their formulas, CH 3 ,OH and C 2 H 5 ,OH, the two differing by CH 2 . The acetylene, olefine, and benzene series of hydro-carbons have their mono-hydric alcohols which may be regarded as formed from these hydrocarbons in the same manner as the ordinary alcohols are formed from the paraffin series. GLYCEKOLS; TEIHYDEIC ALCOHOLS. These alcohols may be considered as derived from the paraffin hydrocarbons by the replacement of three hydrogen atoms by three molecules of (OH). Only a few such are known. The most important of these only will be referred to. Glycerine; Propenyl or Propyl Alcohol. The basic mem- ber of the paraffin series for this alcohol is propane (C 3 H 8 ) in which three atoms of hydrogen have been replaced by three molecules of (OH). Preparation of Glycerine. It has already been stated that glycerine is produced during vinous fermentation, but it is always prepared by saponifying the natural fats. The natural fats are ethereal salts of the fatty, organic acids, that is, salts of the organic acids in which the typical hydrogen of the acid is replaced by the alcohol radical. The more important of the animal and vegetable fats and oils are 287 mainly composed of a fatty acid in which the hydrogen is replaced by the radical of propenyl-alcohol or glycerine (C3H5). Such fats are therefore termed glycerides and rep- resenting the fatty acid by HFt the formula for the fat or ethereal salt will be C 3 H 5 Ft 3 . When these fats are boiled with a caustic alkali there is produced a soap and an alcohol and the process is termed saponification. The reaction may be indicated thus, C 2 H 5 Ft 3 + 3KOH=C 3 H 5 (OH) 3 +3KFt, The potassium salt of the organic acid is a common soap. The term saponification is not now limited to the actual pro- duction of a soap but includes as well the processes by which ethereal compounds are resolved into an alcohol and a fatty acid. Pr^apa4io»-©i^€J'lyeeFitte». Glycerine is now produced by the action of super-heated steam upon fats, saponification by super-heated steam. The action of the steam is similar to that of the alkali and may be represented by the reaction C 3 H 5 Ft 3 (fat) +3H 2 = C 3 H 5 (OH) 3 +3HFt. The chemical re- sults of saponification are expressed in the above reactions and the subsequent preparation of glycerine is a question of purification. When pure fats or oils are saponified by steam the glycerine and the fatty acid are both obtained pure. Crude glycerine is obtained in large quantities in the prepa- ration of soap and of the fatty acids. Glycerine has been prepared artificially. Properties of Glycerine. Pure glycerine is a colorless viscid liquid without odor and it has a very sweet taste. It readily absorbs moisture and mixes with water in all propor- tions. Its boiling point is about 290° C. and it solidities a1 about 40° C. It burns with a bluish flame when heated to 150° C. At high temperature it volatilizes and partially decomposes yielding acrolein (C 3 H 4 0), which gives the dis- 288 agreeable odor often observed from a partially extinguished candle. Grlycerine is a very powerful solvent, dissolving many substances more freely and some that water will not dissolve. It ranks next to water as a solvent. Grlycerine is sometimes used in confectionery to sweeten and by brewers to increase frothing in beer. Because of its attraction for water it is used to prevent certain bodies from becoming dry and hard, such bodies being moist with it, as sponges when used for cushions or mattresses. Its most important use is in the manufacture of nitro-glycerine and other high explosives yet to be described. By a comparison of the formulae of the three alcohols described, it will be seen that they constitute an homologous series of which methyl- alcohol is the first term. These formula? will also show that ethyl- and propyl-alcohol may be considered as derived from the methyl-alco- atom of etc. The series might be continued to include other members of the mono- hydric alcohols. It will be seen by considering the formula? that the different alcohols appear to be derived from methyl-alcohol by the sub- stitution of hydrocarbon groups for an atom of hydrogen. An alcohol from methyl by the replacement of only one atom of hydrogen by a hydrocarbon group is a primary alcohol ; all of the above are primary alcohols. If two atoms of hydrogen in methyl alcohol are replaced by hydrogen radicals the result is a secondary alcohol and if three be thus replaced it is a tertiary alcohol. The general formula? for primary, secondary and tertiary alcohols would be represented as below in which R stands for a hydrocarbon radical. f R ( R f R ( 1 H C ] H ° 1 R [OH [OH [OH Primary alcohol, Secondary alcohol, Tertiary alcohol. The formula? representing the constitution of the alcohols are the results of generalizing from many experimental facts and they serve admirably to explain the facts. d1 by the substituti on of a hydrocarbon radical for an °] H [OH ( CH 3 ( CH 5 [OH I OH Methyl alcohol, Ethyl alcohol, Propyl alcohol 289 The oxidation of primary alcohols by which hydrogen is removed and no other (mange in the atomic constitution produced yields an aldehyde. The aldehydes from primary alcohols differ in constitution from the parent alcohol by two atoms of hydrogen — thus ethyl alcohol by losing two atoms of hydrogen yields acetic aldehyde (C 2 H 4 G). The other primary alcohols yield corresponding aldehydes. The similar oxidation of the secondary alcohols with the elimination of hydrogen yields the ketones or acetones, which are the aldehydes of the secondary alcohols. ACETIC ACID. This acid is a member of a group of organic acids which may be considered derivatives by oxidation of the primary alcohols or from the aldehydes of these alcohols. They are generally called fatty acids because many of them are contained in fats or derived from them. Preparation of Acetic Acid. Acetic acid occurs among the products of the destructive distillation of wood and much acid is obtained from this source. The crude acid from wood is called pyroligneous acid and is found in the aqueous or lighter of the two layers into which the condensable products of the wood separate. The acetic acid is generally obtained from the solution by first producing an acetate by the addition of a suitable base and then decomposing the acetate by a less volatile acid. The acid liquor is generally neutralized by sodium carbonate and concentrated to crystal- lization by evaporation. The sodium acetate is carefully heated to expel tarry matter and distilled with sulphuric or hydrochloric acid, NaC 2 H 3 2 +H 2 S0 4 =C 2 H i 2 +NaHSO,. Dur- ing this operation the acetic acid passes over and is collected. An impure acetic acid may be prepared by carefully dis- tilling the crude liquid without previous neutralization. Alcohol may be oxidized to acetic acid by means of platinum black in a very short time. Some chemical works especially on the continent of Europe have employed this method. The power of the platinum to accomplish this oxidation is undoubtedly due to its power of condensing gases already referred to. The alcohol is placed in evaporat- ing dishes in each of which stands a small tripod a couple of 19 290 inches high. The tripod supports a smaller dish or watch- glass in which the platinum black is contained. By a suitable temperature the alcohol is volatilized and the vapor oxidized by the oxygen condensed on the platinum. The operation is accomplished in a suitable case or chamber to which the air has to be admitted at proper intervals. The pure acid is prepared by distilling the pure sodium acetate with pure sulphuric acid. The pure acid is a clear colorless liquid and has a pleasant but penetrating odor. It has a very sharp acid taste and when pure blisters the skin. The boiling point is 118° C. and below 170 : C. it is generally solid giving glacial acetic acid. Its vapor burns with a pale blue name. Most of its salts are soluble, hence it can not be readily precipitated. Acetic acid is largely used in the dilute form as vinegar and in the preparation of various acetates many of which are used in the arts. The acid is an important solvent for many organic bodies and is accordingly valuable in the laboratory. Preparation of Vinegar. Acetic acid is the acidifying principle of common vinegar. Vinegar is always made by the oxidation of alcohol and the best vinegar is made by the spontaneous acidification of wine or cider. It is only necessary to expose the wine or cider to the action of the air at a suit- able temperature. The alcohol present in the liquor is gradually converted into acetic acid by oxidation, C 2 H 6 0+ O^CoILO-^HoO. The oxidation in this case is known to be brought about by a microscopic vegetable organism, mij co- derma aceti, in the fermented liquor. The wine or cider contains the necessary ingredients' for the growth of the organism and the oxidation of the alcohol is in some way brought about by the plant. Fermented liquors are very liable to become sour owing to this action but distilled liquors are not subject to the change since the food constituents for the organism do not exist in them. Vinegar is also made by mixing dilute alcohol or other 291 distilled spirits with yeast or other nitrogenous organic mat- ter and exposing it to the air. The added matter contains the constituents of growth necessary for the ferment and the action is the same as for fermented liquors. The conversion of the alcohol into the acetic acid may be hastened by per- fecting the exposure of the spirituous liquors to the air. The quick vinegar process consists in causing the wine or other prepared alcoholic liquor to trickle through casks containing shavings so as to expose a large surface to the air, the shav- ings having been steeped in vinegar to assure the presence of the ferment. Vinegar contains usually not over 5 per cent of acetic acid. In some countries it is permitted to add one-tenth of one per cent of sulphuric acid to the vinegar to prevent further mothering. In this country a large quantity of excellent vinegar is made by the farmers from cider. ACETATES. Acetic acid is a monobasic acid and forms a large number of salts. Many of these acetates are employed in the arts and some of the more important will be mentioned ; all of the normal acetates are soluble. Aluminum Acetate. This salt is prepared by bringing together in solution common alum (double sulphate of aluminum and potassium) and lead acetate. Lead sulphate is precipitated and separated by filtration. The solution of aluminum acetate is largely used in dyeing and calico print- ing. The cloth is impregnated with a solution of the salt and subjected to a moderate heat or other process of "fixing" by which it is converted into an insoluble basic acetate in the fibre of the cloth. The fibre is then capable of taking up and setting permanently the coloring matter. Such bodies are called mordants and the acetates of the sesquioxides or weaker bases are the most useful, for they are most easily 292 converted into insoluble basic salts. The sesquioxides of aluminum and chromium form very important acetates. The solution of aluminum acetate is generally termed red liquor in the factories owing to the fact that it is so generally employed in fixing red colors. The red liquor may be prepared from aluminum sulphate instead of alum. Lead Acetate. This compound is prepared by dissolving litharge in acetic acid or by acting upon sheet lead with the vapor of acetic acid. It can be obtained in distinct crystals but is usually indistinctly crystalline. It has a sweet taste and is frequently called "sugar of lead." It is very exten- sively used in the preparation of alum mordants and in the manufacture of certain pigments. It is a valuable article in the laboratory. Copper Acetates. Verdigris is a mixture of several basic copper acetates and results when copper is simultaneously exposed to the action of the air and the vapor of acetic acid. It finds some use in oil and water colors, in calico printing and in the preparation of certain paints. Sodium Acetate. Is prepared by the action of acetic acid upon sodium carbonate. The solubility of the acetate in water increases very rapidly with the increase of tempera- ture and the supersaturated solutions have been used in foot- warmers in certain European railways. The cooling of the heated solution is greatly retarded by the heat given out by the crystallization of the salt. SOME IMPORTANT VEGETABLE ACIDS. Four of the more common vegetable acids are oxalic, tartaric, malic, and citric — they are all paraffin derivatives. Oxalic Acid. This acid occurs free in certain varieties of boletus (pink or touchwood mushroom), combined with potassium in sorrel and certain plants of the rumex (dock) species and in garden rhubarb and as calcium salts in many plants. Oxalic acid is produced on the manufacturing scale by the oxida- tion of highly carbonized organic bodies such as starch, sugar, and 2m cellulose. The principal commercial process now is by the oxidation of sawdust. The acid can be obtained in colorless transparent crystals which are soluble in less than their own weight of hot water and in about eight parts of water at 15.5° C. The solution has a very sour taste and is very poisonous. Chalk or magnesia furnishes the best antidote. The acid is largely used as a discharge in calico printing and dyeing, for bleaching flax and straw, for removing ink and iron stains from linen, and for cleaning metals, marble, and wood. Oxalic acid is bibasic (CaH^O^) and its metallic salts are in general soluble, that of calcium being least so. Calcium chloride maybe used as test for a soluble oxalate. Tartaric Acid; C 4 H 6 O e . This term and formula include four isomeric bodies but they differ in physical properties. The ordinary tartaric acid is the acid of tamarinds, mulberries, pine-apples, grapes, and several other fruits. It occurs in the pure state in small quantity but is usually present in combination with potassium as an acid salt. The commercial supply of the acid is obtained from grape juice. During the fermentation of grape juice in the manufacture of wine an impure acid potassium tartrate is deposited, which is known as argol or cream of tartar. This tartrate is dissolved and neutralized by the addition of powdered chalk or lime by which calcium tartrate is precipitated. The calcium tartrate is heated with sulphuric acid when calcium sulphate is formed and the tartaric acid left in solution, which can then be crystallized by evaporation. Tartaric is one of the most important vegetable acids. It is largely used in the printing industries both as a "resist" and as a "discharge" and also as a mordant in dyeing wool. It is remarkable as forming a very slightly soluble acid potassium tartrate when a potassium salt in solution is added to a solution of the acid, thus serving as a prelimi- nary test for a potassium salt in solution. Tartaric acid forms a large number of single and double salts. Rochelle salt is a double tartrate of potassium and sodium. Tartar emetic is a double tartrate of potassium and antimony. Tartaric acid is bibasic. Malic Acid. This acid or its salts are widely distributed in the vege- table kingdom. The acid occurs in grapes, unripe apples, blackberries. and in considerable quantity in the garden rhubarb. It is generally prepared from the unripe berries of the mountain ash. Malic acid is bibasic and its formula is C 4 H e 5 . Citric Acid. Citric acid occurs in large quantity in the juice of lemons, limes, bergamots, and is present in many other fruits and in the sap of many plants. It is prepared in the largest quantity from Lemon juice. This juice is neutralized by chalk and the calcium citrate pro- 294 duced is decomposed by sulphuric acid. The uses of the acid are well known. Some of the citrates as those of iron and magnesium are used in medicine. The acid is tribasic, its formula being C e H 8 7 . Tannic Acid, Tannin. This name has been given to a group of plant constituents which are capable of precipitating a solution of gelatine and of uniting with animal membrane giving a more or less perfect leather. Gallotcumic Acid. This is the best known and most important of this group and is generally called tannic acid. It is present in large quantity in gall-nuts from which it may be obtained by digesting the powdered gall-nuts in an aqueous solution of ether. Upon filtering the solution and allowing it to stand, the ether separates from the water carrying with it the coloring matter, the water containing the acid. By evaporation the gallotannic acid is left as a yellowish, friable, amor- phous mass showing no tendency to crystallize. A strong solution of gallotannic acid gives a precipitate when mixed with sulphuric or hydrochloric acid. The acid precipitates albumin and gelatine. With ferric salts the acid gives a blue-black precipitate which is the basis of certain writing inks. A tincture of nut-galls is accordingly a delicate test for the presence of ferric salts. The tannins, extracted from the oak. hemlock and similar species and which are used for tanning leather are closely related to the gallo- tannic acid and are employed in tanning because of their similar action on gelatine. ALCOHOL ETHERS. This class of ethers may be considered as derived from the alcohols by replacing" the hydrogen in the hydroxyl of the alcohol by an alcoholic radical. Thns in ethyl alcohol C 2 H 5 ,OH, if the hydrogen of the hydroxyl be replaced by the ethyl alcohol radical (C 2 H 5 ), we shall have C 2 H 5 OC 2 H 5 . We may also consider them as oxides of the alcohol TT- radicals p 2 TT 5 0, or as anhydrides of the alcohols formed by the elimination of the water from two molecnles of alcohol, 2C 2 H 6 0— H 2 O = GH 10 O. Ethyl-ether, Common Ether. This compound can be pro- duced by the action of several dehydrating- agents upon alco- hol but the process is not one of simple dehydration. Ether is made on a large scale by distilling a mixture of alcohol 295 and sulphuric acid. The first action when the alcohol and acid are heated together results in the formation of ethyl- sulphuric acid, H 2 S0 4 +C 2 H 5 OH=C 2 H 5 H80 4 +H 2 0. When the ethyl-sulphuric acid is heated with more alcohol, ether results and the sulphuric acid is reproduced, C 2 H 5 HS0 4 + C 2 H 5 OH=C 4 H 10 O-fH 2 SO 4 . This acid will act upon fresh alcohol and if the supply of alcohol be properly regulated and the temperature kept within proper limits the etherification process can be made continuous. The continuous operation is effected by distilling the mix- ture of acid and alcohol in a retort so arranged as to admit fresh alcohol in regulated quantity so that the temperature of the mixture is kept within the required limits, about 140° C. The ether and water distil over and are condensed in a receiver together with some alcohol and a little sulphurous acid. The sulphuric acid is gradually used up so that the process can not be continued indefinitely with the same supply of acid. To avoid the danger of contact of the alcohol vapor with flame, coils of tubing conveying superheated steam or the vapor of some liquid of high boiling point are used as the source of heat. The distillate is shaken with water which removes most of the alcohol, a base (lime, potash or soda) is added to fix the sulphurous acid. The remaining water is removed by distilling over lime or calcium chloride. These operations may be partially repeated for greater purity. Properties of Ether. Ether when pure is a thin, mobile, transparent and colorless liquid with fragrant odor and peculiar taste. Its specific gravity at 15° C. is .70. Its boil- ing point in the air is 34.9° C. Under atmospheric pressure it evaporates rapidly producing great cold. It is very com- bustible and its vapor very dense, which properties make careful handling necessary for safety. It mixes with alcohol in all proportions but is slightly soluble in water (one part 296 in ten). This fact gives a means of separating- it from alcohol when the latter is not present in too large a qnantity. Ether is a solvent for resins, fats, alkaloids, and many other organic substances. It also dissolves phosphorus, iodine, and bromine. It is used to dissolve collodion cotton in photography and as an anaesthetic. CYANOGEN AND ITS COMPOUNDS. Cyanogen (C 2 N 2 ),is a colorless gas with the odor of bitter almonds. It is very poisonous. Cyanogen occurs in the gases of blast furnaces and can be prepared by heating silver cyanide strongly (AgCN). Silver cyanide is produced when potassium cyanide and silver nitrate are brought together in solution, KCN+AgN0 3 =KN0 3 +AgCN. Potassium cyanide is always produced when nitrogen, charcoal, and potassium carbonate are highly heated together. Cyanogen is generally obtained by heating mercuric cyanide. In many compounds, cyanogen acts like an element. It may be regarded as a monovalent group and is gener- ally represented by Cy. Hydrocyanic Acid; HCN. This acid commonly known as prussic acid is found in the kernel of the peach and plum stones and in the leaves of the cherry and the laurel. It can be prepared by acting upon metallic cyanides with hydrochloric acid, KCN+HC1=KC1+HCN. It is a colorless liquid and very volatile. The inhalation of the vapor is very dangerous and the acid taken internally is one of the most fearful poisons known. Potassium Ferrocyanide. Yellow prussiate of potash, (KCN) 4 , Fe(CN) 2 ,Aq., double cyanide of potassium and iron. This salt is the source of most of the cyanogen compound's and is made on the large scale by melting together potassium carbonate and iron filings or scraps, mixed with organic matter containing carbon and nitrogen. It crystallizes in large, lemon-colored crystals, readily soluble in water. This ferrocyanide is a chemical reagent of great importance and value, with a large number of metallic salts it gives precipitates which are frequently very characteristic. It is largely employed in the manufac- ture of colors, in dyeing and calico printing, and as stated, is the source of many of the compounds of cyanogen. Potassium Cyanide ; KCN, KCy. This substance as already stated, is produced when nitrogen is heated to a high temperature in contact with potassium carbonate and charcoal. It is also produced when potassium is heated in cyanogen gas or the vapor of hydrocyanic acid but it is generally prepared by fusing the ferrocyanide of potassium with potassium carbonate. The cyanide then generally contains some cyanate and carbonate of potassium, but for most applications this impurity is not important. 297 A solution of KCy dissolves the chloride and iodide of silver, in con- sequence of which it finds use in photography. It is used in the extrac- tion of gold from its ores and its double cyanide with gold and silver are used in electroplating and gilding. Its great solvent powers make it useful in cleaning gold and silver. Potassium Ferricyanide ; (KCN) 3 , Fe(CN) 3 . This salt is often termed the red prussiate of potash. It is prepared by the oxidation of the yel- low T prussiate of potash. It is a powerful oxidizing agent when used with alkali; such a preparation bleaches indigo. It is used in calico printing. Mercuric Cyanide; Hg(Cy) 2 . This cyanide is prepared by dissolving mercuric oxide in hydrocyanic acid. It is used to obtain cyanogen. There is a large number of other cyanides, the most important of which are certain complex cyanides used as colors. Such are Prussian Blue, a complex cyanide of iron ; Hatchets Brown, a cyanide of iron and copper. PHENOLS. The phenols are benzene derivatives in which hydrogen of the benzene group is replaced by hydroxyl. They are derived from the benzene hydrocarbons in the same way that the alcohols of the fatty series are derived from the paraffins. Phenol, Hydrobenzene, Carbolic acid, Phenic acid, C 6 H 5 OH. Phenol is found among* the products resulting from the de- structive distillation of wood and coal. It is usually pre- pared from coal tar, being the chief constituent of the acid portion of this tar. It is concentrated by collecting apart that portion of the heavy oil from coal tar which distils over between 150° and 200° C. It is extracted from the distillate. •Phenol crystallizes in colorless needles which have the odor of coal tar. It liquefies at 42° C. and is then slightly heavier than water. It is soluble in 15 parts of water at common temperature. It is poisonous, blisters the skin and exerts an antiseptic action, arresting fermentation and putre- faction. There are several disinfecting powders which con- sist of carbolic acid mixed with mineral matter. 298 CARBOHYDRATES. This term includes three groups of bodies each of which contains six atoms of carbon or some multiple of six and oxygen and hydrogen in the proportion to form water. These groups are nearly allied to each other and widely distributed in nature. The three groups are the glucoses, the sucroses or saclia- rides, and the amy loses. The first two groups constitute the sugars, the last includes the starches and the celluloses. The formula of the glucoses is CeH^Oe; of the sucroses G2H22O11 and of the amyloses (C 6 Hi O 5 )n. The first two groups are among the most important foods of the civilized nations and the last supplies man with a large portion of both food and clothing. Some bodies are now classed as among the carbohydrates which do not contain six atoms of carbon. The general formula of the glucoses is C n (H 2 0)n but n is not always six; of the sucroses C n (H 2 0) n -i; of the amyloses (C 6 H 10 5 ) n . Several of the sugars have been shown to be aldehyde or key tone alcohols. Glucoses. Ordinary glucose; Dextrose C 6 Hi 2 6 . Ordinary glucose is the most important member of the glucoses. It exists in the juice of sweet grapes, in raisins, and in honey of which it forms the crystalline portion. Its presence in urine is characteristic of the disease called diabetes. Dextrose is made on a commercial scale from starch by heating it with dilute sulphuric acid. In this country it is made in enormous quantities from corn-starch, hence, is some- times called corn-sugar. The starch is obtained from maize or Indian corn and will be referred to under the subject of starch. In other countries starch from other sources is used. In this country the term glucose among the manufacturers is limited to the liquid products and such use of the term has become very general. The solid product is termed sugar. The manufacture of glucose in the United States is an immense industry and the products in both the solid and 299 liquid forms are very extensively used ; many kinds of syrup are composed of the liquid glucose and the solid is largely used in confectionery and as sugar. The conversion of the starch is accomplished by boiling it with water in large converters with from one to one and one-half per cent of sulphuric acid. The heating is often done in closed converters and under considerable pressure, steam being admitted for the purpose. The higher the pres- sure the shorter the time required for the conversion. For the liquid glucose less acid and less heating are required than for the sugars. During the heating the starch first passes into the isomeric dextrin and this takes up the elements of water to form dextrose, (CeHioO.^n+f^O^^CeH^OeK. The acid is removed by the addition of powdered chalk and the liquid filtered through animal charcoal and evapo- rated to the desired consistency. The evaporation is fre- quently done in vacuum pans. The glucose can be made perfectly colorless. A little cane syrup is often added to the glucose to give the desired color. Some glucose is employed in the preparation of artificial honey, the comb being made of paraffin. Liquid glucose obtained as above described contains con- siderable dextrin and maltose with some organic salts of calcium. The first two substances are less abundant in the solid glucose. Chemically pure glucose has to be obtained through further treatment. Dextrose is less sweet and the solid forms less soluble than cane sugar. The cellulose of wood fibre can be converted into glucose and some of the wood-paper manufacturers have attempted the commercial manufacture of glucose from this source. Fruit Sugar; Laevulose; C e H 12 6 . Fruit sugar nearly always ac- companies dextrose in the juice of sweet fruits. Is is more difficult to crystallize than dextrose. It is sweeter than dextrose and Less easy to ferment. A mixture of dextrose and lsevulose in equal proportions constitutes "invert" sugar. 300 SUCBOSES. Common Sucrose; Cane Sugar; Ci 2 H L >di. Cane sugar is the most important member of this group. It is very widely distributed in the vegetable kingdom but is obtained on a commercial scale from only a few plants. The principal of these are the beet-root, sugar cane, sorghum, sugar maple, and a species of palm. A small amount is made in this country from the ash-leaved maple or box-elder and from melons. More sugar is now derived from beets than from any other single source. The manufacture of cane sugar is an important industry of many countries and only the general principles involved in the operations can here be referred to. From the cane the juice is extracted by crushing between rollers. Lime is added to the juice to prevent the inversion of the sugar. It is also generally subjected to the action of sulphurous acid to prevent fermentation. The juice is then heated to coagulate albuminous matter, which rises to the surface as a scum. The liquid is then separated from the scum and sediment, and evaporated to the crystallizing point. It is then allowed to cool and crystallize and the molasses drained off. This product is the raw sugar and has to be still further treated to obtain refined sugar. The refining is accomplished by re-solution in hot water, filtra- tion, and decolorization by passage through animal charcoal and evaporation in vacuum pans. The steps in the prepara- tion of beet sugar are essentially the same as in cane sugar but the juice of the beet is generally extracted by the "diffusion" process and not by mascerating the beets and pressing the pulp. For diffusion the beets are cut into thin slices and subjected to the action of warm water by which the juice is effectually extracted. The diffusion process has also been applied to the cane. Nearly all the beet sugar is made in Continental Europe. 301 The cane sugar is derived from many localities, but mainly from Cuba, Java, Manila, Brazil, Mauritius, and Louisiana. Properties of Sugar. Many of the properties of sugar are too well known to mention. It melts at 160° C. and forms an amorphous mass upon cooling. If kept at that temperature for some time it is converted without loss of weight into dextrose and an uncrystallizable syrup, leevulosan (C 6 Hio0 5 ). At a higher temperature it loses water and becomes brown, yielding according to Bloxam, "caramelan" (Ci 2 Hi 8 0g). Cara- mel is composed of this body mixed with other substances and is the result of the action of heat upon sugar. Caramel is largely used to color alcoholic liquors. Maltose; C l . i W 22 O xt . This body results from the action of malt upon starch. The germinating grain (malt) contains a peculiar sub- stance "diastase" which causes the starch to undergo hydrolysis, forming maltose and dextrose. Crystallized out of alcoholic solution maltose has the same composition as cane sugar, but from aqueous solution its formula is C 12 H 2 . i 11 ,H 2 0. It becomes anhydrous at the boiling point of water. Amyloses, Starch and Cellulose (C 6 Hio0 5 )n. The best known and the most important members of the amylose group are starch and cellulose. Starch (C 6 Hi O 5 )n. This is one of the most widely diffused bodies of the organic kingdom. It occurs in all plants that have been examined except certain fungi and abundantly in the seeds of plants, especially of those cereals used for food. Rice, wheat, and Indian corn contain it in largest proportions. Fully two-thirds or more of the food of mankind is de- rived from the carbohydrate group and starch furnishes much the largest proportion. Starch is necessary to the growth of plants and its presence in the seeds affords nourishment to the young sprouts. Preparation of Starch. In the United States starch is generally prepared from maize (Indian corn); in England from rice and potatoes; on the continent of Europe from ■- potatoes and wheat. The obje : in ea }h ease is of eours^ to se] . ate the starch from the other constituents. The outline of the method adopted in this country will give an ide the principles involved in all eases. The cleaned grain (maize) is steeped in water for about 30 hours until soft enough to grind. It is then crushed by rollers or ground between mill-: nes and washed upon sieves. The pulpy mass left upon sieves may be reground and sub- jected to a second washing. The milky liquid carrying the starch flows int : inclined boxes known as starch- tables during which time the starch granules are dei - The liquid passing on from the starch-tables flows into tanks in which are leposited certain nitrogenous matter. This lat- ter is mixed with the husk- from the sieves and worked up for cow and pig-ieed. For further increasing the purity of the starch by the removal of the nitrogenous matter it is washed in a dilute solution of alkali (caustic soda) and again allowed to settle, the escaping liquid carrying off the nitrogenous matter, oils, etc. The starch is again thoroughly washed to remove alkali. The several subsequent operation are mechanical. The reports fi m -onie of the larg^- American factories show a yield of starch equal to one-half the weight of the maize employed. This indicates a heavy loss of the total starch contained. Single factories eonvert from five to twenty thousand bushels of eorn daily. The starch from the potato may be tained by seep- ing, crushing, and washing without the use of alkali. Rice contains the greatest percentage of starch but the use of alkali is necessary to separate it from the other constituents of the grain. In the manufacture of starch-sugar or dex- trc se already referred to. the first step in the prej aration of stai sh is that above describe .. The finest qualities of starch are use 1 for food, for mak- ing sugars and syrups, for sizing the finest papers, and for 303 laundrying. The other varieties are largely used in the in- dustrial arts, for weavers' dressing, for thickening mordants, etc. Besides the edible starches obtained from rice, pota- toes, maize, and wheat, there are several other forms. Arrow-root. The starch known under this name is ob- tained from the root of several kinds of plants widely dis- seminated in the tropics. The most important of these flourish in tropical America from Mexico to Brazil and in the West Indies. They belong to the genus Maranta. The Brazilian arrow-root is frequently called cassava-starch. Tapioca. This is a specially prepared form of the Cassava starch, other starches are obtained from the roots of various plants in widely separated places, Africa, Australia, East Indies, and China. Sago. This is starch obtained from the pith of certain varieties of the palm, indigenous to the East Indian archi- pelago and the adjacent regions. These last named starches differ materially from the grain starches in that they are more nearly pure starch, more readily gelatinize, and are thought to be more easily assimilated by the human system. Characteristics of Starch. To the naked eye starch appears as a white glistening powder but under the micro- scope it is seen to have an organized structure, to consist of granules generally ovoid, which are composed of concentric layers. The starch granules from different sources differ in appearance. The granules vary very much in size, those from the potato being 1-300 of an inch in the longest diameter while those from certain plants, as cactus, are not over 1-10000 of an inch. Starch is without odor, is insoluble in cold water and consequently without taste. The granules consist of starch-cellulose or farinose in the outer layers, the exterior layer being probably wholly composed of it. This cellulose is insoluble in cold water. The interior of the granules is partially soluble in cold water and is called granulose. The 304 insolubility of the outer layer prevents the action of cold water upon starch. When a mixture of starch and water is heated to about 70° C. the granules burst, the -granulose is dissolved to a viscous liquid slightly opalescent, due to the undissolved cellulose. The solution becomes gelatinous on cooling and gum like when dried. Iodine colors starch intensely blue and the action takes place upon the granules intact as well as upon the paste. Starch heated for some time up to about 200° C. is partially converted into dextrin. The conversion into the soluble form is important in the preparation of foods. Dextrin; (C 6 H 10 O 5 j n . This body has the same formula as starch.. It may be prepared by heating starch with dilute acids or by heating- dried starch to a high temperature. Dextrin is soluble in water. There are several modifications of dextrin which are used as substi- tutes for gum . Gums. These are amorphous bodies occurring in many plants. They are insoluble in alcohol but are soluble in water and form a vis- cous mass with it. Those which form a clear solution with water are real gums; the others vegetable mucilages. Cellulose (C 6 Hio0 5 )n. This substance is the principal ingredient in the framework of plants. It constitutes the walls of plant-cells and forms a large proportion of the solid parts of all vegetables. Woody- tissue consists of the membranous cells together with encrusting material. When all encrusting material has been removed by solvents the cellulose is left. Fine linen and cotton are composed of nearly pure cellu- lose, the treatment to which the fibre is subjected having removed nearly all the other material. Pure cellulose is insoluble in nearly all ordinary solvents, is tasteless, and for a long time was thought to be absolutely innutritious, but this point is now thought to be doubtful. It is known to constitute a large part of the food of beavers. Cellulose is soluble in an ammoniacal solution of cupric 305 hydroxide (Schweitzer's reagent.) Cellulose is not colored by iodine. If unsized paper be steeped for a few seconds in a mixture of strong sulphuric acid and half its volume of water, and then washed with water and dilute ammonia it is converted into a sort of parchment. It has the same composition as cellulose and is called vegetable parchment. It is trans- lucent, much stronger than paper, is very useful in diffusion, and is largely used for baggage labels. It is not easily torn and withstands rain. Strong sulphuric acid converts dry cellulose into a gummy mass, which by the proper manipulation may be converted into dextrose and then into alcohol ; linen rags may thus be converted into alcohol. VEGETABLE COLORS. The vegetable kingdom exhibits great beauty and variety of color but the compositions of the coloring principles have been determined in only a few cases and only a few of the colors obtained directly from plants find application in the arts. The most universally distributed color in nature is that of green and is due to the presence of chlorophyl which occurs in all the green parts of plants. Its composition is not known though iron is supposed to be a constituent of it. Wax and other substances are associated with it forming chlorophyl grannies. The blue coloring matter present in certain flowers has been called cyanin. It is made red by acids, consequently blue flowers can not contain acid juices, while red flowers do. Bloxam attributes the color of certain grapes and red wine to cyanin. Saffron, Turmeric, Madder, and Litmus are all vegetable colors. The litmus is obtained from certain varieties of lichens. It is made blue by alkalies and red by acids the original color being a purplish rod. Lac .is a red coloring matter extracted from a resin of the same name obtained from a tropical plant. Carmine is a red dye obtained from the cochineal, the dried body of a species of insect which feeds upon a certain variety of cactus. Indigo. This is obtained from the indigo plant growing chiefly in India, but also in China. Egypt, and South America. It has been known as -,\ dye for many hundreds of years. It does Dot exist ready formed in the plant but is the product of the alteration of the substance 20 306 known as indican which is nearly colorless. The indigo is obtained by ma§cerating the plants in water and allowing them to ferment. The indican is converted first into white indigo and then by oxidation into the common or blue indigo. The above named dyes are all composed of carbon, hydrogen, and oxygen except indigo which in addition contains nitrogen. Indigo is extensively employed for dyeing woolen fabrics. ALBUMINOUS SUBSTANCES. This term includes a number of complex bodies found in vegetable and animal organisms all of which in addition to carbon, hydrogen, and oxygen contain nitrogen and most of them sulphur. Not much is known in regard to the constitution of these bodies, their molecular formula? not having been determined. The percentage numbers indi- cate great conformity in chemical composition and the same conform- ity is shown in their general properties. The proportion of the nitro- gen to the carbon, hydrogen, and oxygen is much higher than is usual in organic bodies. The albuminous substances are sometimes divided into two classes — albuminoids and proteids. The second more closely resemble com- mon egg-albumin and are generally coagulated by heat, the first like bone-cartilage, yield gelatine with boiling water and are sometimes termed simply gelatinous bodies. Again both classes are sometimes included under the term proteids. Only a few of the most typical and common of the albuminous sub- stances will be mentioned here. Gelatine, Glutin. When the skin, tendons, and organic matter of the bones of the animal body are subjected to the long continued action of boiling water a solution is obtained which on cooling solidifies to a tremulous transparent mass which becomes hard and brittle on drying. Cold water softens but does not dissolve gelatine. It is dissolved in hot water and the solution gelatinizes on cooling. Tannin precipitates gelatine from its solution. The tissues which yield gelatine unite with tannic acid forming an insoluble non-putresci- ble compound, or leather. Isinglass is a pure form of gelatine obtained from the bladder of the sturgeon and other fish. Glue and size are impure gelatines made usually from th#parings of hides. Gelatine is largely used in food preparations, for clarifying wines, and in photography. Gelatine is sometimes called glutin. A gelatinous body closely resembling the animal gelatine is also obtained from silk. Albumins. There are several varieties of albumin differing but slightly from each other. These bodies are found in the blood, muscles, 307 nerves, and other organs of animals and also in nearly all parts of plants, especially the seed. It is thought that probably these bodies are synthesized by the plant and that they are taken up and appro- priated by the animal with but slight change. Egg-albumin. This exists in aqueous solution in the egg and is one of the most common varieties of albumin. It is coagulated and rendered insoluble in water by heat. Alcohol and ether also precipi- tate it from solution. The raw albumin of the egg does not affect silver but this metal is tarnished by cooked eggs, which also give a faint odor of sulphuretted hydrogen, indicating some decomposition in the cooking by which H 2 S is liberated. Serum T albumin. This is abundantly present in the blood and other animal secretions. It closely resembles egg-albumin but is not precipi- tated by ether. Plant-albumin. This occurs in nearly all vegetable juices, it is coagulated by heat and closely resembles the egg and serum albumins. Myosin. This is the albuminous substance present in solution in the sheaths of muscular fibres. Its spontaneous separation from the plasma after death produces the rigor mortis. Fibrin. Blood fibrin is the albuminous substance which separates from the blood during coagulation or clotting. It appears to be formed from soluble albumin in the blood, by a change which is set up when the blood is removed from the vital influences. The clot is red, due to the entanglement of the red corpuscles in the fibrin. By washing, the fibrin may be separated into elastic filaments which become hard and brittle upon drying. Vegetable Fibrin. This occurs in the undissolved state in plants and especially in the cereal grains. When wheaten flour is kneaded upon a cloth with water the soluble albumin and starch are separated and a tenaceous mass remains which is called gluten. When this gluten is boiled with dilute alcohol a portion is left undissolved and is called vegetable or plant fibrin. Milk Casein. Casein occurs in the milk of all mammalia, most plentifully in that of the caraivora. It is the chief constituent of the curd of milk. It exists in solution in the milk due to the presence of a little alkali. If the alkali be neutralized by the souring of the milk or the addition of a little acid the casein is separated. The most striking property of the casein is its coagulability by rennet, the mucous mem- brane of the calf's stomach. Casein does not coagulate spontaneously by heat. Vegetable Casein; Legumin. This substance is found most abund- antly in 1 he seeds of leguminous plants as beans and peas. It closely resembles animal casein and its solution is coagulated by rennet. 308 Gluten. It is stated above that gluten is the name given to the tenacious mass left when wheaten flour is kneaded upon a cloth with water. When treated with boiling dilute alcohol a portion of the gluten is left undissolved and is called vegetable fibrin. As the alco- holic solution cools, a white flocculent precipitate is deposited which closely resembles the casein of milk, it is called mucedin. On adding water to the cooled solution a third substance is precipitated, which closely resembles serum albumin and is called glutin or gliadin. It is pertinent to recall here the fact that the albuminous sub- stances of the animal organisms have their counterparts in the vegetable kingdom. ALKALOIDS. This name is given to a large class of nitrogenous vegetable com- pounds of a basic character. Many of them are of great medicinal importance because of the powerful action they exert on the animal system. They all contain carbon, hydrogen, and nitrogen, and nearly all contain oxygen in addition. They are soluble in alcohol and gener- ally have a bitter taste. Caffeine ; Theine. This is the principal alkaloid of tea and coffee in which it is thought to be present as a salt of some variety of tannic acid. Tea also contains a small quantity of some other alkaloids. Caffeine is composed of carbon, hydrogen, oxygen, and nitrogen. The fragrance which distinguishes prepared coffee does not belong to the raw berry but is developed by the roasting. In the same way the aroma of the tea is developed by heat during the drying of the leaves. Each is due to a volatile aromatic oil produced by the heat. Nicotine. This is one of the alkaloids that does not contain oxygen. It exists as a salt of malic acid in the leaves and seed of tobacco. It is a volatile oily liquid. Nicotine and its salts are power- ful poisons. Tobacco may contain from one to eight per cent of nicotine but seldom over four. Tobacco contains an unusual percent- age of mineral salts. This explains the large amount of ash it leaves upon burning. This ash may amount to one-fifth the weight of the dried leaf. The salts are mainly the malate, citrate, and nitrate of potassium. The presence of these salts, especially the last, explains the smouldering combustion which these leaves undergo. Opium. This is the thick juice which is obtained from the capsules of the opium-poppy (popaver somniferum). It is a complex substance containing a large number of bases, one of the most abundant and best known of these is morphine. Morphine. This is obtained from opium in which it is present often to the extent of ten per cent. It is a white powder, soluble in 500 parts of water and has a bitter taste. Its formula (C 17 H 19 N0 3 ) shows it to 309 contain carbon, hydrogen, oxygen, and nitrogen and representing it by "M," the common medicinal form of morphine is MHO, the hydrochlo- ride of morphine or the muriate of morphia. The alkaloid present in opium in most abundance next to morphine is narcotine. Quinine. The bark of several species of the cinchona order contain a number of alkaloids usually associated with some vegetable acids. The best known of these is quinine and this is the most important of the alkaloids. It is immensely used as a febrifuge. It is found most abundantly in the yellow cinchona or Peruvian bark. Quinine crystallizes in small crystals and to the naked eye appears as a white powder. It requires about 2000 parts of water to dissolve it and its solution is alkaline and bitter. Its composition is indicated by the formula C 20 H 24 N 2 2 . The form of quinine generally used in medicine is the basic sulphate, which may be represented by Q 2 H 2 S0 4 , Aq. in which Q stands for the formula above given. The cinchona barks were introducd into Europe from Peru in the first half of the seventeenth century by the wife of the viceroy of Peru, the countess of Chincon from whom they received their name. The cin- chonas are indigenous to the slopes of the Andes between 7° N. and 20° S. The barks richest in alkaloids grow at an altitude between 6000 and 12000 feet above the sea. The most highly prized cinchonas have been successfully cultivated in Java for nearly fifty years. Strychnine. This is obtained from the seeds and bark of the mix vomica, from St. Ignatius' bean, and from other tropical plants. It is slightly soluble in water, is bitter, and fearfully poisonous. It is said that it can be detected by its taste when it is dissolved in a million parts of water. Cocaine. This is obtained from the leaves of certain varieties of coca. Cocaine, in aqueous solution, is employed as a local anaesthetic and finds extended use in minor surgical applications. In small doses it acts as a stimulant and is one of the most insinuating of the poison- ous drugs. The medicinal form most generally employed is the hydro- chloride, BHC1. IMPORTANT INDUSTRIAL APPLICATIONS OF CHEMISTRY. CALORIFIC VALUE OR POWER. The calorific power of a substance is the amount of heat evolved due to its combustion. The calorific value of the ordinary hydrocarbon fuels may be approximately calculated from their compositions. Many of these fuels contain oxy- gen and it is assumed that the heat developed by the perfect combustion of the fuel is equal to that due to the perfect combustion of the carbon and so much of the hydrogen as is in excess of that necessary to form water with the oxygen present. In other words it is assumed that the oxygen pres- ent is combined with hydrogen in the form of water and that the oxidized hydrogen adds nothing to the heating power. This form of computation is illustrated below. Example. — Required the calorific value of 75 pounds of wood. Molecular formula of wood is taken as C 6 H 9 4 =C 6 H(H 2 0) 4 , molecular weigh t=145. {72 pounds of C ; 1 pound of C produces 8080 units of heat. 1 pound of H ; 1 pound of H produces 34462 units of heat. 72 pounds of H,0. Units of heat produced by the carbon in burning=72X8080=581760. Units of heat produced by the hydrogen in burning= 1X34462=34462. Total heat produced by the 145 pounds of wood=616222. 616222 Hence the calorific value of 75 pounds of \vood= " X75— 318735, 1 ■+•> 312 CALORIFIC INTENSITY. Calorific intensity may be defined as the temperature to which the heat generated by the burning fuel could raise the products of its own combustion. In the case of pure carbon, burning to carbon dioxide, the calorific intensity may be ob- C tained from the following formula: T=^q, in which T is the calorific intensity, C the calorific value, W the weight of the carbon dioxide produced, and S the specific heat of the carbon dioxide. In the above formula it is assumed that the specific heat of carbon dioxide is constant at all tempera- tures. In such computations it should be remembered that the specific heat of gases is less at constant volume than at constant pressure so that calorific intensities would be greater at constant volume. In the case of fuels containing hydrogen or hydrogen and oxygen in addition to carbon, there are certain considerations that do not enter the problem just given. In determining the calorific power of hydrogen the vapor of water resulting from its combustion was condensed in the calorimeter and the heat which was latent in the vapor became sensible and was properly included in the calorific value, but when the vapor is no longer condensed this heat can not be considered in the production of temperature and must be deducted from the calorific value in the formula for calorific intensity. In fuels containing oxygen the oxidized hydrogen exist- ing or supposed to exist as water is vaporized by part of the heat of combustion. This number of heat units must also be deducted from the calorific value of the fuel in the formula for intensity. Note. In addition to these deductions there is another slight deduc- tion which should be made from the calorific value. In the computation of the temperature produced, the initial temperature is 0°C. ; between this point and the boiling point the specific heat of water is greater than that of steam in the proportion (approximately) of one to five-tenths, so that for each pound of steam produced there should be further deducted 100X.5=50 units of heat. 313 The formula for the calorific intensity of fuel, like wood, containing hydrogen, carbon, and oxygen, is T _ C-(B) 1 ~ WS+W,S,+etc. in which T is the calorific intensity, C the calorific value, B the latent heat of steam produced, which comes partly from the combustion of the free hydrogen in the fuel, partly from the combined oxygen present as water and in part composing the fuel; W and W,, are the weights respectively of the car- bon dioxide and the water vapor produced; S and S,, are the specific heats respectively of the carbon dioxide and the water vapor. Example. — Required the calorific intensity of wood burned in a full supply of oxygen. When burning in full supply of oxygen, C+0 2 = C0 2 and H 2 -fO=H 2 0; atomic weights of carbon, hydrogen, and oxy- gen are 12, 1, and 16, hence 12 parts by weight of carbon require 32 parts by weight of oxygen and produce 44 parts by weight of carbon dioxide; 2 parts of hydrogen require 16 parts by weight of oxygen and produce 18 parts by weight of water, hence 1 part of carbon produces 3% parts of carbon dioxide and one part of hydrogen produces 9 parts of water. It has been seen by the formula, that in 145 parts of wood, by weight there are 72 parts of carbon, 1 part of hydrogen, and 72 parts of water. By combustion the one part of hydrogen produces nine parts of water, this with the seventy -two parts of water in the wood gives eighty-one parts of water to be evaporated, the latent heat of which is 81X537=43497. The 72 parts of C in the wood produce 264 parts of carbon dioxide. ( C0 2 r=.22 The specific heats are approximately \ { H.,0 (vapor) =.5. The calorific value of 145 pounds of wood as determined above is 616222. The heat rendered latent by the evaporation of 81 parts of water = 43497 Heat units availablefor heating products of combustion... = 572725 Number of heat units to raise the products of combustion from 145 pounds of wood 1° C.-=264X.22+81X.5, hence the calorific intensity of 572725 W00<3 iS 2«rX^2+SlXT5«) = 5S0!,O+ - The calorific intensity is independent of the weight of the body burned but is dependent upon the time and the atmosphere in which 314 the combustion takes place, being greatest in oxygen. If the combus- tion takes place in the air which is usually the case, the calorific intensity is lowered because of the large amount of nitrogen which has to be heated. The complete combustion of carbon requires 2% times its weight of oxygen and hydrogen requires 8 times its weight of oxygen. In the above example of wood the 72 parts of carbon will require 192 parts of oxygen and the 1 part of hydrogen would require 8 parts of oxygen, making necessary 200 parts of oxygen. Taking the formula of the atmosphere as 4N+0, we see that for 10 parts by weight of oxygen there are present 50 parts of nitrogen or 3% parts of nitrogen for one of oxygen. We have seen that 145 parts of wood would require 200 parts of oxygen for combustion; in supplying this oxygen by means of the atmosphere there would be introduced 3% times as much nitrogen or TOO parts of nitrogen. The specific heat of nitrogen is about .25. The formula for the calorific intensity in the air would be T— 572725 — 2oqq° C 204X. 22+81 X. 5+700 X. 25 In all ordinary furnaces in order to maintain the draught, much more air has to be introduced than would be required to supply the necessary oxygen. This extra amount of air still further reduces the intensity. In addition to this extra amount of air, all the heat can not be applied to heating the products of combustion as assumed in the discussion. Part of the heat is lost by radiation and some is lost in heating the grate and other parts of the furnace and in heating the unburned fuel. Again complete combustion does not always take place. From these considerations it is evident that the computed calorific intensity is only approximate. GLASS MAKING. The manufacture of glass is a very ancient industry, the earliest examples being 1 of Egyptian origin. A lion's head of glass found at Thebes and now in the British Museum bears an inscription which places its date at 2400 B.C. In the tombs of Beni Hassan dating at least 2000 B.C. the process of glass blowing is represented. These two facts prove that glass was made more than four thousand years ago. Glass is a mixture of several insoluble silicates and is des- titute of crystalline structure when not too slowly cooled. One of the silicates present is always that of an alkali metal, potassium or sodium, and with these are associated one or more of the silicates of calcium, barium, lead, iron or zinc. 315 The mixtures of these silicates display properties that are not possessed by the single silicates. The presence of alka- line silicates is necessary in the glass, for these silicates when fused dissolve silica readily, fuse more easily than any other class, and exhibit less tendency to crystallize on cooling. The silicates of the other metals named are more infusible and less readily acted upon. By mixing the silicates in the proper proportions the requisite properties are obtained in the glass. The most valuable and important properties of glass are its transparency, its plasticity before complete fusion, and its permanency. There are a great many kinds of glass dif- fering more or less distinctly from each other depending upon the proportions of the constituents. The two most im- portant divisions may be based upon the silicates present. First, The glass which contains alkaline and calcium silicates, and second, that which contains alkaline and lead silicates. To the first class belong the common window glass, plate glass, and crown glass; to the second belong the flint or crystal glass and the material of artificial gems. Common window glass is composed essentially of sodium and calcium silicates and is made by fusing together the proper proportions of sand, calcium carbonate, and sodium carbonate. It usually contains a little aluminum silicate owing to lack of purity in the materials employed. Plate glass has essentially the same composition as win- dow glass but is made from purer materials. Usually some potassium carbonate replaces some of the sodium as an ingredient. Croivn glass is composed of the silicates of potassium and calcium and is made by fusing together the proper propor- tions of sand, potassium carbonate, and calcium carbonate. Potassium is less likely to impart color to the glass than sodium. This glass is generally employed for optical pur- poses. 316 Bohemian glass contains the same constituents as crown glass but has a larger proportion of silica to which is due its greater permanency and infusibility. Lead or Flint Glass. This glass is made by fusing to- gether in proper proportions silica, lead oxide, and potas- sium carbonate. The oxide of lead generally used is the Pb 3 4 . The higher oxide is preferred because the excess of oxygen serves to oxidize any organic impurities that might accidentally be present. Colored glass is made by fusing certain metallic oxides with the ingredients of any of the above-named glasses. The glass from which bottles are generally made has essentially the same composition as common window glass though containing less sodium and in addition some iron silicate to which its color is due. The red oxide of copper gives a red color to glass ; cobalt oxide a blue color; oxide of manganese an amethyst color. Production of Glass. The principle of glass manufacture is simple. The materials of the glass are fused together and the silica combines with the metallic oxides forming silicates. The fusing was formerly accomplished in large pots or crucibles of refractory fire-clay. The pots varied in size from three to five feet high and two to four feet in diameter. A number of these pots were accommodated in a single furnace and heated by gaseous fuel which played around the pots. With lead-glass covered pots were required to prevent the reduction of the lead to the metallic state by the gases of the fuel, in other cases the pots were open. In the past dozen years the pot furnaces have been largely replaced by the open-hearth or tank furnaces, this is especially so in the manufacture of bottles and of window glass. Some of these modern furnace's are of astounding dimensions being from sixty to seventy-five feet long, from four to six feet deep and from ten to twelve feet wide, and 317 capable of containing over four hundred tons of melted glass. The fused constituents of the glass are converted into a great variety of finished products by processes which differ depending upon the kinds of products desired. In general after the constituents are fused together the manufacturing operations may be grouped into four. 1st, Croivn and Sheet Glass. A hollow glass sphere is obtained by blowing and this for crown glass is converted into a flat disc by rapid rotation. For sheet glass the globe is opened and extended into a cylinder, then split longitudi- nally, spread into a sheet, and flattened by suitable tools. Window glass is generally made in this way. 2nd. Plate glass by pouring the fused glass upon a flat table and subsequently grinding and polishing it. 3rd. Hollow Ware. Under this are classed all kinds of bottles as well as the more delicate glasses, vases, etc. Bot- tles are always made by blowing the glass into moulds, both the external and internal portions of the bottle assuming the shape of the mould. The process is a very rapid one; a " set " of five men generally work together in moulding bot- tles and they usually average two or three finished bottles per minute. Wine-glasses, vases, pitchers, etc., are made by blowing and hand manipulation but little use being made of patterns or moulds. Such ware requires the greatest manual skill and can only be fashioned by the most expert workmen. 4th. Pressed Glass. Many kinds of glass-ware for domes- tic purposes are now made by moulding into shape by press- ure. The external form is given by the mould and the internal by the shape of the plunger. This process has brought into use a very cheap ware suitable for nearly all domestic purposes. The lead glass was found most suitable for pressed ware but to diminish cost the lead oxide has been 318 replaced by barium carbonate which gives a clear glass suit- able for this manufacture. All finished glass products require to be annealed to avoid spontaneous fracture. By using a certain kind of glass called strass as a base all the precious stones can be imitated except opal. The pro- duction of artificial gems is an important feature of glass manufacture. De vitrified Glass. Certain kinds of glass containing but little alka- line silicate may be made to partially crystallize by heating nearly to the fusing point and then cooling slowly. It thus becomes opaque and is sometimes called Reamur's porcelain. It may be made transparent by refusion. Soluble Glass. If silica be fused with an excess of sodium or potas- sium carbonate it forms a glass which is soluble in water — a solution of which is sometimes used in making artificial stone. If sand be moistened with it and pressed into shape and heated highly, the glass fuses and binds the whole together. It is also used to preserve nat- ural stone from decaj^, in mural painting, and in rendering wood non- inflammable. The glass industries of the United States are mainly cen- tered in New York, New Jersey, and Pennsylvania. The abundance of suitable sand in this country affords marked advantages for this industry. Nearly all the sand employed in glass making is mined as sand-stone and this is crushed preparatory to use. The sands of the United States suit- able for making the finest grades of glass are abundant and found in many of the states. Among the beds most exten- sively worked are those of Berkshire County, Mass., Juniata County, Penn., Morgan County, W. Va., and some in Illi- nois and Missouri. MANUFACTURE OF POTTERY. Pottery in its widest sense includes all articles in which clay is the main ingredient and which have been hardened by the application of heat, natural or artificial. The chemi- cal principles involved in the manufacture of a few import- ant kinds will be given. 319 The properties of clay which make it the basis of all forms of pottery are its plasticity when moist which enables it to be kneaded, and its subsequent hardness when heated. The two most general divisions of pottery are the glazed and the unglazed forms, of the first, porcelain may be taken as the most characteristic variety and highest type. Porce- lain is made from the purest clay or kaolin, but a vessel made from clay alone would shrink and lose its shape in drying and be liable to crack in the kiln. To prevent this, other sub- stances are mixed with the clay of the ware which cause it to retain its form and which fuse at the temperature of the furnace and bind the whole into a homogeneous compact mass. These fluxing ingredients differ at different manu- factories and to these differences are due the various kinds of porcelain. In the celebrated Sevres porcelain there is added to the kaolin, feldspar and a little chalk. In the Meissen porcelain there is added feldspar and ground waste, porcelain. The other fluxes most commonly used in porcelain are sand, bone- ash, and gypsum. In each case the clay and other materials are brought to the finest state of subdivision and usually held suspended in water. The creamy liquids are then mixed in the proper proportions, allowed to settle, separated from the water, and the paste thoroughly kneaded. The proper pro- portions of the ingredients may be brought together in the dry state and the whole agitated together in water. In any case after the mixed ingredients are separated from the water the mass is usually left to stand for considerable time which improves the quality of the clay. This result is believed to be brought about by the oxidation of any organic matter present and to physical change brought about by drying and shrinkage which affect the plasticity of the clay. When ready for the workman the clay is moulded into the required shape by various forms of potters' wheels, jiggers and lathes, but principally by moulds. The most perfect specimens are always finished by hand. 320 The moulded articles are dried by exposure to the air, then packed in cases or saggers and subjected to a comparatively low heat of the kiln. The articles are thus sufficiently heated, dried, and hardened to receive the glaze without danger of breaking. The glaze for the porcelain must be similar to the material added for fluxing the clay. The glaze for the Sevres porcelain is ground feldspar and quartz, for the Meissen ware it is clay, silica, and ground ware. The glaze material is very finely ground and evenly applied to the surface of the ware by dusting, fe«t more generally the glaze is suspended in water and the article is deftly dipped in the water and removed. Enough of the material of the glaze adheres to the surface of the ware. The ware is now completely hardened and the glaze fixed by exposure for many hours to a high temperature ; the ware for this purpose is packed in saggers as during the preliminary heating. The Sevres and Meissen ware come under the head of hard porcelain. Hard porcelain has several characteristics which distinguish it from other forms of glazed ware. The glaze is thin and graduates imperceptibly into the body of the ware ; the ware is translucent and breaks with a chonchoidal fracture. Hard porcelain is unique in that the ware is sub- jected to but one burning, the ware being hardened and the glaze fixed at the same time. With all other forms of glazed ware there are two "firings," one known as the biscuit firing which hardens the ware and the other fixes the glaze upon it. Statue porcelain is a true hard porcelain but is not glazed. English soft porcelain is more fusible than the hard porce- lain and the glazing requires a separate "firing." STONEWAEE. This is a coarse kind of porcelain made from impure material. For glazing, the ware is coated with fine sand by dipping it in water holding the impalpable sand in suspen- sion. During the firing of the ware damp salt is thrown 321 into the kiln. Decomposition ensues by which hydrochloric acid and sodium oxide are formed, the latter combines with the silica and forms sodium silicate which fuses and consti- tutes the glaze. Decorating Porcelain. A uniform color can be given to the ware by mixing the proper mineral pigment with the glaze. Colors in pattern and design are put upon the ware after glazing and fixed by another firing by which the pig- ment is fused and firmly fixed upon the ware. The most expensive and finest decorating is done by hand, but the design is usually engraved on a copper plate and a print taken from it in mineral colors on a sheet of tissue paper. By gentle pressure the print adheres to the ware and after a short time the paper can be removed, the firing then fixes the design. The above general description of glazed ware applies usu- ally to that of all countries, but only on the continent of Europe is made the hard porcelain by a single firing. In this country the white wares suitable for household purposes may be fitly placed in four grades. The finest is a true por- celain having a vitreous translucent body and a perfect ac- cordance between glaze and ware. Pottery kilns are solidly built circular structures of ma- sonry rising to a crown inside and surmounted by a shaft or dome to secure draught. Around the base are the fire-places which open into the kiln. Except for hard porcelain the ware is fired twice, the first is called biscuit firing and re- quires the highest temperature and longest time. During this the body of the ware is solidified into a homogeneous mass and when withdrawn from the kiln it rings when struck almost like metal. The object of the second firing is to fuse and fix the glaze and is known as the "glost " tiring. This requires less time and the temperature is not so high as in the first firing. 21 322 The decorations in design are fixed by a third firing' which requires less time than either of the other two. The porcelain industries in this country are centered at East Liverpool, Ohio, and at Trenton, New Jersey. The Rockwood potteries at Cincinnati are celebrated for their special ware, but it is a Fayence or porous ware. The Balti- more potteries also produce a porous ware, parian and ma- jolica, the latter being quite celebrated. The common forms of pottery are produced at many other places in the United States. Fire-ware. For the manufacture of fire-bricks and such articles of pottery as have to withstand a very high tempera- ture it is of course necessary to employ infusible material. Nearly pure clay is used for these purposes to which is added a little sand or ground ware of the same description to" prevent shrinkage. Crucibles are also made from clay mixed with an equal weight of graphite, such crucibles will withstand rapid changes of temperature with impunity. Common bricks are made from less pure varieties of clay which contain sufficient fusible material to "clinker" the bricks during the burning. EXPLOSIVES. An explosion may in the most general sense be defined as a sudden and violent increase in the volume of a substance. In this general sense the increase may or may not be due to chemical transformations. This definition includes all action by which there may be violent increase of volume ; thus a compressed gas or vapor is said to explode the action being mechanical and the result of the energy originally expended in bringing the gas to the compressed condition. In a more purely chemical sense an explosion may be defined as violent increase in the volume of a substance brought about by chemical transforma- tion set up in it, resulting in large volumes of heated gases. A body capable of undergoing this sudden change by chemical transformation upon the application of the proper disturbing cause is an explosive. For our purposes it will only be necessary to describe a few of the more important solid and liquid explosives. In these explosives the energetic action is due to the rapid conver- sion of a solid or liquid into gases occupying many times the volume 323 of the original substance, the increased volume being due to the change of state and the expansion by heat, resulting from the chemical trans- formation of the explosive. It is evident therefore that the energy of the action of an explosive will depend largely upon the rapidity of the chemical transformation by which it is converted into gas and vapor. The heat of the transformation when the products are the same is independent of the time but the temperature is greater the shorter the time. In the useful explosives the heat liberated and the gases pro- duced in the chemical transformation are mainly the result of oxida- tion processes, the bodies oxidized and the oxygen for the purpose all being present in the explosives themselves and the oxidation is inde- pendent of the oxygen of the air. The more important explosives all con- tain carbon as an essential element to be oxidized, other elements are also generally present. We may thus conceive explosions to be cases of a special kind of combustion. From a purely chemical view explo- sives can not be classified in a definite manner, but they may with some convenience and often are grouped into explosive mixtures and explo- sive compounds ; these divisions are not entirely distinct nor accurate. PREPARATION OF EXPLOSIVES. EXPLOSIVE MIXTUKES. These consist of a mechanical mixture of two or more ingredients which upon the application of the proper dis- turbing" cause undergo the transformation defined as an explosion. Simple Explosive Compounds. These are definite chem- ical compounds which from the proper disturbing cause undergo explosion. In such a compound the elements which enter the trans- formed products are all constituents of the single original body. In mixtures the elements so entering are con- stituents of the different composing ingredients. These simple explosive compounds may be associated with other bodies simple or compound in such manner as to produce modified results in the explosion. The substances resulting from such association supply instances of ex- plosives which might with equal propriety be put in either of the above classes. The great majority of the explosives however can be placed in one or the other group bearing in 324 mind the distinction that in explosive mixtures the in- gredients are capable of mechanical separation and in snch explosive compounds as contain more than one substance, they are not capable of separation by mechanical means. Explosives are also sometimes classed as high and low explosives. The former term being* applied to those ex- plosives in which the transformation is so rapid as to pro- duce a rupturing effect, the latter to those in which the transformation is less rapid and the effect, in general, one of propulsion. Explosives are again sometimes classed as explosives of the first and second order depending upon the time involved in the transformation. In explosions of the first order the time is very short the action being practically instantaneous ; in the second order the action is much slower the time being appreciable. Explosions of the first order are also termed detonations. Every explosive may be detonated and the order of the explosions graduate into each other. It is there- fore evident that the classification just given (into high and low explosives and explosions of the first and second order) are without scientific basis and are not more distinctive than the divisions into explosive mixtures and explosive com- pounds. The terms, however, have a general significance and are convenient. Explosive Mixtures. We have stated that an explosion may be considered as a combustion which is accomplished independently of the air and by the oxygen present in the explosive. In explosive mixtures one of the ingredients sup- plies the oxygen and the others the combustibles for oxida- tion. The most common oxidizing agents in explosive mixtures are the nitrates and chlorates. These salts form the basis for dividing the mixtures into the nitrate and chlorate mixtures. The former are the more important, the latter are however employed to a considerable extent in pyrotechny and in igniting other explosives. 325 Gunpowder. This substance is an intimate mixture of charcoal, sulphur, and nitre. For a satisfactory powder great attention must be paid to the purity of the ingredients. The source and general preparation of the ingredients have already been described. The proportions of the ingredients are usually taken as nitre 75 per cent, charcoal 15 per cent, and sulphur 10 per cent. Nitre, KNOz. This is the oxidizing agent in gunpowder. The commercial nitre is always carefully refined before incor- poration with the other ingredients. The great difference of solubility of nitre in hot and cold water is made use of in this refining. The impure salt is dissolved in hot water, the solution filtered to remove insoluble matter and allowed to cool under continual agitation. The nitre solidifies in minute crystals during the cooling and gives saltpeter flour. This flour is subjected to two or three washings in small quantities of water insufficient to dissolve it, to remove adhering liquid and then drained, when it is ready for incorporation. The nitre for gunpowder should give no cloudiness in solution with a soluble salt of silver or of barium. Sulphur. The crude sulphur of commerce is refined by distillation and the distilled sulphur is the variety used in the manufacture of gunpowder. It has been pointed out that the distilled sulphur belongs to the soluble or electro-negative variety while the sublimed sulphur belongs to the electro- positive variety. The first belongs to the same electro- chemical group as oxygen and it is conceivable that this fact may explain the difference in properties of the two varieties. It is generally thought that the sublimed sulphur from its mode of deposition may contain acid vapors in its interstices which would act detrimentally. The sulphur for powder should burn without residue and water in which it has been steeped or agitated should not show distinct acid properties. Sulphur lowers the igniting point of powder, accelerates 326 the combustion, increases the temperature of combustion, and the volume of gases evolved. It also gives permanent solidity to the grain and prevents crumbling to dust. Charcoal. This is the principle combustible of the pow- der. By its oxidation are produced the gases carbon mon- oxide and carbon dioxide, with great evolution of heat. The charcoals employed result from the destructive distillation of several kinds of wood, all of which belong to the light woods as alder, dogwood, and willow. The temperature at which the distillation is accomplished affects the quality of charcoal. The higher the temperature the more nearly pure the charcoal. In general it may be said that black charcoal results from temperatures above 340° C; red from temperatures between 300° and 340° C; and brown below 300° C. The higher the temperature at which the charcoal is pro- duced the less easily it ignites but the combustion is more rapid after ignition. In some powders the percentage of the constituents is different from that given above. The cocoa powder contains more nitre and less sulphur. The Duponts in this country have made a brown powder in which the sulphur is less, the nitre more than that given, and a carbohydrate is used to replace some of the charcoal. Many attempts have been made to replace potassium nitrate in black powder, but it has not been successfully accomplished. Sodium, ammonium, and barium nitrates have all been tried, but the first two are deliquescent and the last is too expensive. In the brown cocoa powder the carbon is obtained from rye straw. The effects of powder when fired in guns depend both upon the composition and the physical texture and structure of the powder. These are all varied to meet the demands of the military service, and the discussion of these subjects does not pertain especially to chemistry. 327 Products from the Explosion of Gunpowder. The pro- ducts from the explosion of powder vary with the conditions under which the explosion occurs. In general it may be said that the oxygen of the nitre combines with the carbon pro- ducing* carbon monoxide and carbon dioxide. A part of the carbon dioxide combines with the potassium forming potas- sium carbonate. The sulphur is mainly converted into potassium sulphate. The nitrogen present in the powder is liberated. The nitrogen, the carbon monoxide, and the carbon dioxide expanded by the heat of the oxidation ac- count for the explosive effect. The formula usually assumed to represent the general results of the explosion is 4KN0 3 + C 4 +S=K 2 C0 3 +K 2 S0 4 +N 4 +2C0 2 +CO. Besides the products indicated there are always others present in small quantity. From the above formula by the consideration of molecular weights, it is seen that solids constitute nearly two-thirds by weight of the products of explosion and the gases a little over one-third. With brown, slow-burning powders the proportion of solids is less and that of gases more. The smoke from gunpowder is due to the solid constituents. G-unpowder explodes at 316° C. It can be exploded by percussion. Chlorate Mixtures. A large number of chlorate mixtures has been invented but none of them has found general application as powder. They are mainly used in pyrotechny and as fuse mixtures. EXPLOSIVE COMPOUNDS. It has already been stated that a simple explosive com- pound is composed of a single substance. Other explosive compounds are composed of more than one substance ami while they are not definite chemical compounds their in- gredients can not be separated by purely mechanical means as in the case of explosive mixtures. 328 The most important bodies which are classed as explosive compounds are the nitro-explosives or those explosives as- sociated with other substances or with each other. In the nitro-explosives there is present as a constituent in the mole- cules an N0 2 group which supplies the oxygen involved in the chemical transformations of the explosive. This N0 2 group is introduced into the explosive by the action of nitric acid upon a hydrocarbon or a hydrocarbon derivative. The most important of the nitro-explosives are the nitro- compounds and the organic nitrates. The most important group of the nitro-compounds are those resulting from the action of nitric acid upon the benzene hydrocarbons. Nitro- glycerine and gun-cotton are the most important examples of organic nitrates. Gun-cotton was formerly thought to be a nitro-substitution compound but it is now classed among the organic nitrates. Nitro-glycerine is an ethereal salt of nitric acid. All these classes are produced by the action of nitric acid upon hydrocarbon derivatives and in each case the resulting molecular change consists in the substitution of one or more groups of XO2 for one or more atoms of hydrogen in the derivative. The precise distinction between substitution compounds and organic salts will be stated after we have described some of the bodies. We may without any incon- venience consider the classes named as derived by the re- placement of one or more hydrogen atoms by one or more groups of N0 2 . We shall first describe the two principal organic nitrates and some of their derivatives. XITEO-GLYCEEIXE OE XITEIC GLYCEEIDE. Nitro-glycerine is prepared by the action of a mixture of strong nitric and sulphuric acids upon glycerine. The func- tion of the sulphuric acid seems to be to preserve the strength of the nitric acid by combining with the water liberated during the transformation of the glycerine. The 329 reaction for the conversion is represented by C 3 H 5 (OH) 3 + 3HN0 3 =C 3 H 5 (N0 3 ) 3 +3I1 2 (). It is prepared by gradually adding* glycerine to a mixture of strong nitric and sulphuric acids, the best proportions being three of nitric to five of sulphuric by weight, both acids being of great strength. Properties of Nitro-glycerine. Nitro-glycerine is a heavy oily liquid of specific gravity 1.6 at 15° C. When pure it is white, without odor, but the commercial product is usually pale yellow. It is poisonous when taken internally. It is insoluble in water, soluble in ether, benzene and methyl- alcohol; it is less soluble in ethyl- than in methyl-alcohol. When pure it has been kept ten years without deterioration. It solidifies at about 8° C. though the freezing point varies with the quality of the nitro-glycerine. In the solid form it is much less sensitive than in the liquid state. It explodes by concussion. If a small quantity of it be ignited it will burn away without explosion. In a confined space it explodes when heated up to 180° C, though in small quantity it has been heated to a higher temperature without explosion. Nitro-glycerine which has not been thoroughly freed from acids or when subjected to too high a temperature is liable to become dangerous from spontaneous decomposi- tion. It is exploded by detonation through mercuric fulmin- ate. It will undergo the sympathetic detonation referred to by means of gun-cotton. The products of the explosion of nitro-glycerine are shown by the reaction, 2C 3 H 5 (N0 3 ) 3 (exploded) =5H 8 0+6C0 2 +0+ 6N. The temperature of combustion or calorific intensity of nitro-glycerine, that is the temperature to which its heat of combustion would raise the products, is 3005° 0. accord- ing to Vuick. The gaseous products from the explosion of nitro-glycerine are about 1500 times the volume of the ex- plosive taken at 15° C, the gases being measured at the tem- perature of 100° C. and under atmospheric pressure. Owing to the dangerous nature of liquid nitro-glycerine 330 its use in this form has long since been abandoned in Europe and it is now not generally used in this country. Nitro-glycerine Derivatives. To overcome the objections to the fluid form many explosives of which this is the basis have been tried. These derivatives of nitroglycerine may be grouped into two classes, 1st, When nitro-glycerine is associated with a chemically inert substance, and 2nd, When with a substance that takes chemical part in the explosion. The most important of the first group is common dyna- mite, usually termed dynamite No. 1. It consists of nitro- glycerine absorbed by a porous siliceous earth which is mainly composed of the shells of diatomacese. The better forms of this earth will absorb three times their weights of nitro-glycerine. The earth only serves to give solid form to the explosive. To the second class belongs a large number of explosives consisting of nitro-glycerine associated with chemically active substances. Charcoal and charred sawdust are used to absorb it and it is mixed with gunpowder and other nitrate and chlorate mixtures. Nitro-glycjine is also mixed with other nitro-explosives some of which will be mentioned later. The objects aimed at in associating other substances with nitro-glycerine are to get it in less dangerous form than the liquid and at the same time to increase its effect by using as auxiliary substances bodies capable of combining with free oxygen seen to be present in the gases from the explosion of nitro-glycerine alone. GUN-COTTON, PYEOXYLIN. This body is the nitrate of cellulose and results from the action of strong nitric acid upon cellulose. The N0 2 groups of the acid replace the corresponding number of hydrogen atoms in the cellulose. We have given the formula of cellu- lose as (C 6 Hio0 5 )n which may be written (C 6 Hio0 5 )2 or C12H20O10. Using this formula the reaction for the production 331 of gun-cotton is C 12 H 14 4 (OH) 6 +6(HO,N0 2 )=C 12 H 14 4 (0,N0 2 ), +6H 2 0. Gun-cotton is a hexanitrate, six atoms of hydrogen being replaced by six N0 2 . The formula Ci 2 Hi 4 4 (0,N0 2 ) 6 may be written 2C 6 H 7 05(N0 2 )3, not forgetting its actual for- mula is a hexanitrate ; its production for convenience may be represented thus C 6 H 10 O 5 +3(HO,NO 2 )=C 6 H 7 O5 (N0 2 ) 3 +3H 2 0, making it similar to that for the production of nitro-glycerine. Gun-cotton like nitro-glycerine is prepared by the action of a cold mixture of strong nitric acid and sulphuric acid upon cellulose. The sulphuric acid serves the same purpose as in the manufacture of nitro-glycerine. The cotton is perfectly freed from all grease and oil. It is next opened up by carding and cutting into short fibres. It is then ready for treatment with the acids, after which it has to be thor- oughly washed to remove the acid. After washing, the cotton is now generally converted into a pulp by a machine similar to a rag-engine in a paper mill. It is then subjected to a final washing to remove every trace of the acid, drained and moulded into blocks, discs, and other forms that may be required. The gun-cotton is now seldom employed in the form of cotton wool. From the chemical change indicated in the reaction it is seen that the cotton increases greatly in weight. In England from motives of economy, cotton waste is the material used for the conversion into gun-cotton. Properties of Gun-cotton. Gun-cotton wool can not be distinguished from the raw cotton by the eye. It is harsher to the touch. It dissolves in acetic ether and acetone. If ignited when loose in the air, it flashes with a yellow flame. It can be exploded by a blow but generally only the particles struck explode. Fully nitrated cotton has often been heated rapidly to 180° C. without explosion but it is very risky to heat it above 175° C. and it often explodes below this. Ignited in a confined space the burning of the first portion raises the remainder to the temperature of explosion. Either 332 the dry or wet cotton may be detonated by fulminate. Both nitro-glycerine and gun-cotton will undergo sympathetic detonation, that is, the detonation can be communicated along a row of cartridges of either of these explosives, though not in contact, when one of them is exploded. Gun- cotton like nitroglycerine may be detonated under water. The products of the explosion of gun-cotton vary some- what with the conditions of the explosion but when perfectly detonated they may be expressed by the reaction 2C 6 H 7 5 (N0 2 )3=7H 2 0+3C0 2 +9CO+6N, which shows that it does not contain sufficient oxygen for the complete combustion of the carbon. All the products being gaseous as in nitro-glycerine there is no smoke. In mining operations the absence of smoke is advantageous but the effects of the carbon mon- oxide produced are detrimental. By associating the gun- cotton with some oxidizing agent the effect of the explosion may be increased and the carbon monoxide converted into carbon dioxide, thus for many purposes some nitrate is often associated with the gun-cotton. Collodion Cotton; Soluble Pyroxylin. The common gun- cotton just described is a hexanitrate and is insoluble in a mixture of alcohol and ether.' The collodion cotton is a mixture of several lower nitrates and is soluble in the alcoho] and ether mixture. It is made by the action of weaker nitric and sulphuric acids upon the cotton. It is less explosive than gun-cotton but is largely manufactured for preparation of celluloid, smokeless powder, and gelatine explosives. Gelatine Explosives. It has been seen that gun-cotton contains too little oxygen for the complete combustion of its carbon. As collodion cotton is composed of lower nitrates it contains still less in proportion to the carbon. The de- ficiency of the oxygen in the gun-cotton can be supplied by associating it with other substances and this is done in the gelatine explosives. 333 The simplest and one of the most important of the gela- tine explosives is blasting gelatine. This consists of abont seven parts of collodion cotton dissolved in about ninety- three parts of nitro-glycerine. The excess of oxygen in the latter supplies the deficiency of that element in the former. This explosive is more powerful than either of its con- stituents. Its sensitiveness may be increased by the addition of a little gun-cotton and decreased by the addition of a little camphor. Blasting gelatine is an amber-colored soft elastic mass, which can be bent without permanently losing its shape. Gelatine Dynamite. To diminish the violence of blasting gelatine, it is sometimes thickened with other ingredients, the nitro-glycerine in the gelatine being diminished. G-ela- tine dynamite and gelignite consist of the same ingredients as blasting gelatine in different proportions, incorporated with potassium nitrate and wood-pulp. Celluloid. This substance is not classed as an explosive though masses of it have been known to explode. It is composed of collodion cotton and a large percentage of camphor. The proportions usually employed are two parts of collodion cotton and one part of camphor. Celluloid appears to be a mechanical mixture, the camphor being capable of extraction by proper solvents. Celluloid is generally made from tissue paper. Xylonite and artificial ivory are forms of celluloid. NITRO-EXPLOSIVES FEOM THE BENZENE GROUP. Nitro-compounds. As already stated the nitro-explosives from the benzene derivatives are nitro-substitution com- pounds as distinguished from organic nitrates. The distinc- tion between the two classes will be referred to later, but as stated, for our purposes both classes may be assumed to be formed the same way, that is by the replacement of one or 334 more atoms of hydrogen in the hydrocarbon by one or more groups of X0 2 . Nitrocompounds of Benzene. By the action of nitric acid upon benzene three nitro-benzenes may be produced, mono-, di-, and tri-nitro-benzenes, C 6 H 5 X0 2 , C 6 H 4 (NQ_) 2 , and C 6 H 3 (X0 2 ) 3 . The first two are not explosive in themselves but are associated with other substances in the preparation of certain explosives. Tri-nitro-benzene is said to be explo- sive though it has not yet been used as such. The nitro- benzenes need not therefore be here considered as explosives. Mono-nitro-benzene is largely used to prepare aniline, from which is obtained a host of beautiful dyes. Tri-nitro-pkenol; Picric Acid. This is an important nitro- compound from the benzene derivative phenol. It is ob- tained by the nitration of phenol, carbolic acid, C 6 H 5 OH. The action of nitric acid upon phenol may be represented by the equation, C 6 H 5 OH+3(HO,X0 2 ) =C 6 H 2 (X0 2 ) 3 OH+3H 2 0. Picric acid is explosive and is used to a limited extent as such, but the acid is far more important because of the salts it produces which are more stable than the acid and very explosive. It may be said that the nitro-compounds from the ben- zene group are not in general explosive and are not used alone but they are all used as auxiliaries in the preparation of explosives. It will only be possible to mention a few of the important examples. Rack-a-Rock the explosive used in the great explosion at Flood Eoek (Hell Gate), New York, consisted of mono-nitro-benzene absorbed by potassium chlorate. Bellite. This is a mixture of ammonium nitrate and di-nitro- benzene. Several military powders hare been made which consist of mix- tures of ammonium and potassium picrates with nitre or with nitre and charcoal. Xitro -co in pounds and Organic Nitrates. The distinction between anitro-compound or substitution product and a nitro-ether or ethereal 335 salt is based upon the transformations they undergo when subjected to the action of certain reagents. From this basis the N0 2 group which is present in both classes is believed to be differently attached in the molecule. Some of the nitro-compounds have the same molecular for- mulae as certain nitro-ethers but they are found to be metameric bodies and not isomeric; thus the ether salt, C 2 H 5 ONO, (ethyl nitrite) is metameric with the substitution compound nitro-ethane C 2 H 5 N0 2 . The reactions which the two classes undergo justify the belief that the hydrocarbon radical is connected to the nitroxyl group through the N atom in the substitution compound and through an O atom in the ethereal salt. There is also reason for thinking that the mode of for- mation of the two classes is different. This difference can be better understood by an illustration. The nitro-compound C e H 5 N0 2 (nitro- benzene) may be considered as produced by the action, C 6 H 5 ,H(ben- zene)+HO,N0 2 =C 6 H 5 N0 2 --|-H 2 0, in which either the N0 2 replaces the H of the benzene or the C 6 H 5 replaces the OH of the acid. Nitro- glycerine, the nitric ether of glycerine, is an ethereal salt of nitric acid resulting from the replacement of the hydrogen of the acid by the basic alcohol radical of glycerine, C 3 H 5 (OH)3+3(OH,N0 2 )=C 3 H 5 (0,N0 2 )3+ 3H 2 0. In this the trivalent radical C 3 H 5 replaces three atoms of hydrogen, or the acid radical N0 2 replaces the hydroxyl hydrogen of the alcohol. Considering the hydrocarbon radical in the two cases, it is seen that in nitro-benzene the radical has replaced OH, in the nitro-glycerine it has replaced H. All ethereal salts may be considered as formed in this way, by the replacement of the hydrogen in the acid by the alcohol radicals. These ethereal salts are also called esters and the distinction between the constitutional formulae of these and nitro-compounds may be generally represented by R-— NO, and R— O— N0 2 , in which R stands for a hydrocarbon radical, the N atoms being directly connected with the radical in the compounds and through O atoms in the ethers. Gun-cotton was formerly classed as a nitro-compound but it is now thought to be an organic nitrate, cellulose nitrate. This conclusion is reached from the fact that under the action of reagents its reduction products place it among the organic nitrates rather than among the nitro-substitution compounds. SMOKELESS POWDEKS. It was natural that in the first efforts to prepare a smoke- less powder as a propelling agent, it should have been attempted to use some of the known high explosives which left no solid residue in exploding. Many attempts were made to adapt gun-cotton to this purpose as it was thought to promise most favorable results. These early attempts were all mainly based on a physical manipulation of the cotton wool and resulted in failure. The smokeless powders of the present day may be grouped into three general classes. 1st. Those in which the only explosive used is some form of nitro-cotton: 2nd. Those in which nitro-glycerine and some form of nitro-cotton are used: 3rd. Those in which nitro-derivatives of benzene alone or with nitro-cellnlose are used. The more important and successful powders belong to the first class. The first class includes a number of powders made by kneading the nitro-cotton in a proper solvent and bringing it to such a consistency that it can be rolled into tenaceous sheets after which it is cut into flakes. These powders are known as flake powders and are largely made in several European countries. By a little different manipulation the kneaded mass is converted into grains and gives granulated powders. The solvents used are acetic ethers or acetones. These powders sometimes contain some additional substance to retard then action when ignited, but by careful manipula- tion they are now made without such addition. The effect of the solvent and the physical treatment produce the desired result. Some of the powders are glazed which has a retard- ing effect upon their explosion. The second class includes a number of noted powders made by dissolving collodion cotton in nitro-glycerine or gun-cotton in nitro-glycerine and acetone. In these powders the ingredients are kneaded or thoroughly mixed together and may be then rolled into sheets or cut into flakes or may be pressed through small cylindrical openings into cords or fibres. Ballistite, cordite, and the American Leonard and Peyton powders fall into this class. Each of these powders contains a small addition of certain other sub- stanses for decreasing rapidity of action. The third class includes a number of powders resulting from associating picric acid or the picrates with other 337 « substances, the picrates of potassium and ammonium are employed. In indurite invented by Professor Monroe formerly of the Naval Torpedo Station, gun-cotton is dissolved in nitro-benzene. One of the American smokeless powders by the Duponts is also made by dissolving nitro-cellulose in benzene. As already stated the last class is of little import- ance compared with the other two. The number of explosives and powders is entirely too great to be here described or even mentioned. The physical manipulation involved in their preparation does not properly belong here and only their general chemical relations have been referred to. FULMINATES. The fulminates are the salts of fulminic acid. The acid has not been isolated but its formula is assumed to be C 2 N 2 2 H 2 . The princi- pal salts of this acid are the fulminates of mercury and silver; the other metallic fulminates are obtained from these. The most important is that of mercury commonly known as ful- minating mercury. This fulminate is prepared by dissolving mercury in nitric acid and acting- upon it with alcohol, its formula is C 2 N,0 3 Hg. It is a, white solid when pure but is usually of a grey color. It is extremely sensitive to explosion and detonates by percussion, by heat (187° C), by the electric spark, or by contact with nitric or sulphuric- acid. Its explosion is represented by the reaction HgC 2 N 2 2 (ex- ploded)=Hg+2CO+N 2 . It is used mainly to detonate other explosives. For this purpose it is employed either singly or with other substances. Potassium chlor- ate, nitrate, meal powder, and antimony sulphide are some of the com- mon substances used with it. The fulminate or the fulminating mixture is enclosed in thin metal- lic cylinders for use as detonators. It will be observed that mercuric fulminate contains an N0 2 group and a hydrocarbon derivative (alcohol) is employed in its preparation though it does not contain hydrogen. The rational formula of the body has not yet been agreed upon. ILLUMINATING GAS. COAL GAS. The idea of preparing an illuminating gas from coal seems to have become first well denned in the mind of 22 338 William Murdoch, a Scotchman, in 1792. In this year he lighted his house with coal gas. By the year 1800 he had extended the use of the new illuminant to all the principal shops and foundries near Birmingham. Murdoch's inven- tion did not become known on the continent of Europe until the beginning of the nineteenth century. The French claim the invention for their countryman Lebon, who in 1801 illuminated his house with gas from wood. Gas lighting was first introduced into the streets of London in 1807 and had become general by 1814. Paris was lighted by gas in 1820 and after this date the use of gas rapidly spread over Europe. The manufacture of gas has ever since been an industry of great extent and magnitude. The gas generally designated as coal gas and used for illuminating purposes is a mechanical mixture of a number of permanent gases some of which are luminous while others produce little light when separately burned. There are also present the vapors of many substances which greatly add to the light-giving power of the gas. Coal gas is generally manufactured by the destructive distillation of bituminous coal. Bituminous coal is essentially composed of carbon, hydro- gen, oxygen, nitrogen, sulphur, and a little mineral matter. In general the carbon amounts to about seventy-five per cent of the coal. When bituminous coal is subjected to the action of heat out of contact with air, there results a large number of compounds composed of two or more elements of the coal. There have already been distinguished nearly a hundred bodies among the products of the distillation of coal. It is evident from this fact that coal is a complex body. The original arrangement of the elements in the coal has not been determined but it is certain that the numerous distilla- tion products are not primary constituents of the coal but result from the application of heat. They are products of the distillation and not mere educts from the coal. 339 COAL GAS MANUFACTUKE. Retorts. In the manufacture, bituminous coal is placed in fire-clay retorts capable of being hermetically sealed. The retorts are generally D shaped cylinders about ten feet long and from fourteen to twenty inches in diameter. The charge of coal is usually from two hundred to four hundred pounds and remains in the retort from four to six hours. The coal is always introduced into a heated retort. The retorts are arranged in benches so that a number can be heated by the same furnace and they are kept above a red heat. During the heating the volatile products of the distillation are driven off and coke is left in the retorts. The principal products of the distillation which pass from the retorts are vaporized liquid hydrocarbons, water vapor, hydrogen, marsh gas, acetylene, olefiant gas, ammonia, hydrogen sulphide, carbon dioxide, carbon monoxide, cyano- gen, nitrogen, and carbon disulphide. Ascension Pipe and Hydraulic Main. From the front upper surface of each retort rises an iron pipe. These pipes extend upward and then curve down and enter a large iron cylinder called the hydraulic main which runs perpendicular to and above the retorts and receives the pipes from all the retorts. The hydraulic main is kept partially full of water and other condensed liquid-products of distillation. The ends of the pipes from the retorts dip beneath the liquid in the main. A portion of the heavy hydrocarbon vapors are condensed in the hydraulic main and nearly all of the aqueous vapor. The former constitutes tar and the condensed aqueous vapor takes up ammonia, carbon dioxide, hydrogen sulphide, and cyanogen forming what is known as the ammoniacal liquor. The gases and more volatile products of the distillation bubble up through the liquid in the main. This liquid acts as a seal to prevent the gases from returning to the a spon- sion pipes when the retorts are open for recharging. 340 Condensers. From the hydraulic main the uncondensed products are carried by an iron pipe called the foal main to the condensers. The condensers are a series of pipes through which the gas passes and which furnish a large cool- ing surface ; the condensers may be cooled by running water or simply by exposure to the air. In the condensers are deposited the liquid hydrocarbons (tar), ammoniacal salts, and aqueous vapor which have passed through the hydraulic main. The condensed products are conducted by pipes to suitable receptacles for removal. Exhausters. Immediately after the condensers exhausters are usually placed. The exhauster is a form of pump for pulling the gas away from the retort and forcing it through the subsequent parts of the plant into the holder. If it were not for the exhauster the pressure of the gas in the retorts would have to be sufficient to overcome all the resistances in the different parts of the plant and thus cause loss of gas by leakage in the retorts. Washers and Scrubbers. From the exhausters the gas passes through the washers and scrubbers or through scrub- bers alone. The washers are arrangements in which the gas is made to traverse thin layers of liquid. In scrubbers the gas is not forced to pass through the water but is brought into inti- mate contact with wetted surfaces . A common form of scrubber is a cylinder filled with coke over which water continually trickles. In the passage through the washers and scrubbers the remaining ammonia and some of the hydrogen sulphide and carbon dioxide are removed. Purifiers. From the scrubbers the gas passes through the purifiers, the object of which is to remove the remaining hydrogen sulphide from the gas. The purifiers are generally square iron boxes, divided by a number of horizontal sieves. The purifying material is placed in layers upon these sieves i J I- 38 ! 341 and the gas is made to traverse the several layers before leaving the purifiers. The materials used in the purifiers are slaked lime or iron oxide either separately or in succession. The slaked lime takes out both hydrogen sulphide and carbon dioxide while the iron oxide removes only the hydrogen sulphide. The carbon dioxide diminishes the illuminating power of the gas and when not removed the illuminating power can only be kept up by enriching the gas in a manner yet to be explained. The great advantage of the iron oxide is that its purifying power can be restored a number of times by simply exposing it to the atmosphere. The lime can not be used again and can not be economically used except where it is very cheap and can be readily disposed of when spent. If the substances are used in succession it is better to pass the gas through the iron oxide first and then through the lime. When lime is employed as the purifying agent calcium sulphide and calcium carbonate are produced ; when iron oxide is employed the mono- and sesqui-sulphides of iron are produced. When these sulphides are exposed to the air the iron oxide is repro- duced and the sulphur deposited. The oxide may thus be repeatedly revivified until the separated sulphur amounts to 55 per cent. Purification by iron oxide is the method now generally employed. The reactions in the iron purifiers are Fe 2 3 -f 3H 2 S = Fe 2 S 3 +3H 2 0; ' Fe 2 3 +3H 2 S=2FeS+S+3H 2 0. The oxide is reproduced by exposure to the air and the reactions are 2FeS+0 3 =Fe a 3 +S 8 and Fe 2 S 3 +0 3 =Fe 2 3 +3S. The oxide of iron used may be a natural product, bog iron ore, or it may be artificially prepared by the oxidation of iron borings or filings. In this country the oxide is very generally pre- pared in the manner mentioned. The carbon disulphide is one of the most difficult im- purities to remove from the gas when it is there present, and 342 there is demanded for this result special provision not deemed necessary for description here. The Gasometers. From the purifiers the gas passes to the holders or gasometers and is stored for use, and dis- tributed as required to consumers. The composition of purified coal gas differs at different places, in general it may be stated that the composition is approximately H=50 per cent: saturated hydrocarbons of the paraffin series mainly marsh gas =30 to 40 per cent; un- saturated hydrocarbons, mainly benzene, acetylene, and ethene, 3 to 5 per cent; nitrogen, 3 to 5 per cent; carbon monoxide, 3 to 5 per cent, with small quantities of oxygen and carbon dioxide. The luminosity of the gas is believed to be due to the combined action of the hydrocarbons and can not in a great degree be attributed to any one of them alone. The quality of the gas is of course affected by the temperature of the distillation. At too low a temperature the solid and liquid hydrocarbons are too abundant, at too high a temperature the gaseous hydrocarbons are decomposed, carbon being deposited as gas carbon and hydrogen being liberated. The illuminating power of gas from common coal was formerly l^eq uefiUy ^ increased by adding to the charge of the retort a small quantity of cannel coal. This result is now frequently brought about by impregnating the gas with vapor of the volatile hydrocarbons. This is often done in this country by introducing into the retort a small iron cylinder (called cartridge) containing paraffin oil obtained from petroleum. Secondary Products from Coal Gas Manufacture. The secondary products from the gas manufacture are numerous and important. The hydraulic main, the condensers, and the scrubber constitute the source of nearly all the am- moniacal salts of commerce. The coal tar by distillation 343 readily yields two portions, the light and heavy oil. From the light oil naphtha, benzine, toluene, and other less im- portant bodies are obtained ; from the heavy oil naphthalene and carbolic acid are obtained. Besides the bodies named there are many others of great theoretical importance to organic chemistry. ALCOHOLIC BEVERAGES. The different alcoholic beverages of mankind may be grouped into two classes — 1st, fermented, 2nd, distilled. The fermented may be divided into the less general classes, leers and wines. These classes with the general principles of their production will be briefly described. Fermented Liquors; Beers and Wines. Beers are the products of fermentation of glucose which has been directly produced by the transformation of starchy substances. Wines are the products of the fermentation of glucose exist- ing as such in the fruits used. BEER-MAKING. Malting. Beer is generally produced from barley. In the operation of malting, the grain is first soaked in water until it has swollen and become soft. It is then spread in layers, under the proper condition for germination, in a dark place kept at a constant and moderate temperature. Under these conditions the grain sprouts and when the radicle or sprout has grown to about half an inch, the vitality of the grain is destroyed by kiln-drying and the radicle made brittle by the final temperature, to which it is subjected so that it is easily broken off and can be removed by sifting. The radicle is valuable as a manure as it contains about one-ninth the nitrogen of the grain. During the germination the seed absorbs oxygen and gives off carbon dioxide and there is produced a Substance known as diastase which converts some of the starch into 344 dextrin and glucose, which then serve as food for the de- veloping radicle. Diastase contains carbon, hydrogen, oxy- gen and nitrogen but its formula is not known. The malted grain contains about one-fifth per cent of its weight of diastase. Brewing. Preliminary to brewing the malted grain is ground to an even grist and infused in water at the tempera- ture of about 77 = C. when it is left for several hours, during which the diastase acts upon the unaltered starch and con- verts the greater portion of it into sugar and dextrin. The water with its dissolved constituents is called wort. It is drawn off from the exhausted malt and run into a wort- boiler. The exhausted malt contains some starch and nitro- genous matter and is used as food for animals. The wort is next boiled with the requisite quantity of hops. The flowers of hops contain a bitter principle called lupulin and an essential oil. They confer upon the beer its aromatic flavor and odor and tend to prevent the con- version of the alcohol into acetic acid. The boiling also effects the removal of a considerable quantity of nitro- genous matter resulting from the gluten of the grain, which matter would be deleterious upon the keeping properties. After boiling with the hops the wort is drawn off and cooled rapidly to about 15° C. to avoid the action of the air in producing acid fermentation, if cooled slowly. The wort is then transferred to the fermenting vessels or tuns and made to ferment by the addition of the proper quantity of yeast. Yeast is a vegetable micro-organism (already referred to) which possesses the power of converting sugar into alcohol and carbon dioxide. It is also capable of inducing the con- version of cane sugar into glucose. The fermentation is the most important part of the opera- tion of brewing. The process is controlled by attention to the temperature of the liquid and the general appearance of 345 the tuns. The extent to which the fermentation has pro- ceeded can be well determined by the density of the wort. The yeast is always removed before the fermentation is com- pleted and the beer drawn off into casks where it undergoes a slow fermentation and then becomes charged with carbon dioxide. The finished beer besides the water, alcohol and carbon dioxide, contains some unchanged glucose and dextrin, the extract from the hop, some nitrogenous matter from the grain, and the soluble mineral matter of the grain except the phosphates, which are consumed by the yeast. There are present in small quantity other secondary products of the fermentation as acetic acid, glycerin, etc. Porter, stout, and highly colored beer are made by having a small quantity of the malt strongly dried or charred so as to convert some of the sugar into caramel. The amount of alcohol in beers varies from two to nine per cent. The beer yeast if deprived of moisture by drying at a low temperature or by pressure can be kept for a long time with- out losing its powers but if heated to 100° C. it is killed and is no longer capable of producing fermentation. The yeast plant grows and increases at the expense of the phosphates and nitrogenous matter of the wort, these being necessary to its growth. As previously stated it is during the growth of the yeast that fermentation takes place. In a solution of pure sugar the yeast will transform only a limited quantity of the sugar and is destroyed by the action. WINE-MAKING. We have stated that the wines result from the fermenta- tion of the glucose existing in the fruits from which the wine is made. The term is generally applied only to those beverages made from grapes. Wine further differs from boor in that the maker adds no ferment. The expressed juice of the grape undergoes spontaneous fermentation. This fer- mentation is due to the fact that the yeast spores are! gen- 346 erally present on the skin and stalks of the grape and are carried about by the air. The grape juice contains the necessary constituents for the sustenance of the yeast, and when the yeast spores are deposited in it they readily grow, with the resulting vinous fermentation. If all the sugar be fermented the wines are said to be dry, otherwise the wine remains sweet. The skins, stalks, and seeds of the grape contain tannic acid with several coloring matters. The color and slightly astringent taste of the red wines are due to the fact that the skins are left for a certain time in the fermenting juice and the alcohol produced, dissolves out the tannic acid and the coloring matter. In white wine the fermentation does not take place in contact with the skins. Red wines are generally fermented in vats, white wines in casks. After fermentation the wines are decanted and very fre- quently clarified in addition. Eed wines are usually clarified by albumen, while the white are clarified by gelatin (isin- glass). The action of the albumen or gelatin is purely mechanical. The tannin in the wine acts upon these bodies forming a precipitate which carries with it any suspended impurities of the wine. The great amount of tannin in the red wines permits the use of albumen, while isinglass is used with white wines. Acid potassium tartrate is present in considerable quantity in the grape juice. The solubility of the salt decreases with the increase of alcohol so that the slight fermentation which goes on after the bottling or casking causes a deposition of the salt. With the removal of the tartrate the coloring mat- ter becomes less soluble and falls giving the wine a lighter color. In effervescent wines the fermentation is continued after bottling, and the carbon dioxide liberated under pressure, is retained in the liquid. Champagne is the most important effervescing wine. Its manufacture requires great care and 347 skill hence the wine is very expensive. For champagne the must or grape juice is very carefully clarified and the wine bottled before the fermentation has entirely ceased, sugar being added at the same time, as there is not enough left in the wine to continue the fermentation to the desired point. After fermenting for a time in the bottles the corks are removed and the compressed gas discharges the yeast and other impurities. The bottles are then refilled with a specially prepared white wine or liquej, recorked, and sealed for the market. The different processes require six or seven months and during the fermentation in the bottles there is much loss due to breakage. In the dry est champagnes the pressure of the gas often reaches five or six atmospheres. In the manufacture of red wines it was formerly the cus- tom in wine-making countries, and still is in some places, to crush the grapes by the bare feet of men treading upon them. This crushing is the preliminary to the pressing of the grapes. In the making of champagne the grapes are not crushed before being put into the presses, the only crushing- being by the press; this gives a, purer juice. The reason that the grape is superior to all other fruits for wine-making is that its vegetable salt is potassium tartrate which as above explained is deposited as the alcohol in- creases and the sugar disappears. Wine made from goose- berries, currants, apples, etc., contains malic and citric acids which can not be thus removed and consequently their acidity must be overcome by the addition of sugar. Cider is a wine which results from the fermentation of the fruit sugar of the apple. It may contain from seven to ten per cent of alcohol. A solution containing more than one-third its weight of sugar will not undergo vinous fermentation and when the alcohol produced amounts to about seventeen per cent of the solution the fermentation ceases. This limit fixes the max- imum strength of fern urn ted liquors. 348 DISTILLED LIQUORS. The stronger alcoholic beverages of mankind result from the distillation of fermented liquors. They may be brought into two general classes, whiskies and brandies. Brandies. These result from the distillation of wines. The brandy from^wmes is considered the best. In this country a brandy is made from apple cider and one from the juice of the peach. Whiskey. Whiskey is made by distilling the fermented products of various starchy substances. Those generally used are Indian corn (maize), rye, barley, rice, and oats. In this country whiskey is made in large quantity, corn and rye being the principal grains employed. That from corn is generally known as Bourbon whiskey. The grain is malted quite similarly as for beer, but as the diastase for the. malt is far greater than necessary to convert its sugar into al^nSt - distillers generally add a large portion of unmalted grain whose starch is also converted. The extract from the grain is fermented as in beer-making and as the distiller endeavors to produce as much alcohol as pos- sible the fermentation is urged to its utmost. This fermented liquor is then subjected to distillation, the portion passing over during the process constituting the whiskey, the re- siduary liquid being of little value. The alcoholic strengths of both fermented and distilled liquors vary between wide limits and there is such a large number of each kind that it is impracticable to give detailed descriptions. The genuine wines, whiskies, and brandies are to a considerable extent now imitated by mixing liquors of different strengths and adding certain flavoring and coloring materials. BREAD=MAKINQ. The essential constituents of bread-making grains are water, starch, nitrogenous matter, dextrin, cellulose, a little 349 sugar and some fat, and inorganic salts. The nitrogenous matter is mainly in the form of gluten and albumin. The gluten is composed of vegetable fibrin, of a substance resembling casein and of vegetable glutin. The gluten is the most important constituent for bread-making. It is because of the tenacity of the wheat gluten that it is supe- rior to all other grains for bread-making. This tenacity is due to the vegetable glutin or gliadin, it is this compo- nent of the gluten that gives adhesiveness to the dough. - When wheaten flour is kneaded upon cloth the gluten is left as an elastic, tenacious mass. The gluten is the main flesh-forming constituent of the flour, but in its natural state it is tough and difficult of digestion. In good bread the dough is so manipulated that the whole is rendered light and porous, thus becoming more palatable and more digesti- ble, exposing a large surface to the action of the digestive fluids. Eye stands next to wheat as a bread-making grain, and it is largely used for that purpose in northern Europe. Wheat is the chief bread-making grain. The essential and desired qualities of lightness and poros- ity are conferred upon bread by incorporating with the dough, carbon dioxide under pressure. The tenacity of the gluten prevents the ready escape of the gas and as it expands the required texture is produced in the dough. This vesiculated texture is made permanent in the bread by the solidification which results from baking. The carbon dioxide employed may be produced by fer- mentation within the dough or is otherwise introduced therein. In the former case fermented bread results, in the latter unfermented. Fermented Bread. In this kind of bread various kinds of yeast are employed, the result being a vinous fermentation by which the sugar of the dough is converted into carbon dioxide and alcohol. These escaping through the gluten cause the dough to rise. A little yeast incorporated with 350 some dough is placed in a suitable temperature. When this charge has worked a while it is kneaded with the remaining batch of dough. The fermentation then pervades the whole and after a short interval the loaves are formed and placed in the oven. Sometimes leaven is employed to bring about fermenta- tion. Leavening has been practiced from remote ages. It consists in placing a small quantity of dough under favor- able conditions to undergo natural fermentation, and when this has set in. the leaven is mixed with the dough and the whole undergoes fermentation. In this case the cause of the fermentation is minute organisms introduced into the dough from the air. In fermented bread the sugar which is fermented is that present in the grain and it is also partly derived from the con- version of starch into sugar. It is seen that vinous fermenta- tion plays an important part in bread-making. A considerable amount of alcohol is given off in the making of such bread, and it acts like the carbon dioxide to lighten the bread. Efforts have been made to collect and save the alcohol given off m the manufacture of fermented bread, but the necessary arrangements injured the quality of the bread and were abandoned. Unfermented Bread. The most direct method of pre- paring unfermented bread is illustrated in the making of aerated bread. In this process the flour is brought to the state of dough by kneading with water charged with carbon dioxide. The whole operation is mechanically performed in closed vessels. When the mixing is complete an opening is made at the lower part of the vessel and the dough is forced out by the pressure of the gas. The vesiculation is produced by the expansion of the gas, with which the dough is thoroughly impregnated. The expansion begins when the dough is removed from the vessel and is still further increased by the heat of the oven. In this process 351 the dough and bread are untouched by the hands of the baker until removed from the oven. Unfermented bread is also made by the use of certain powders, which react upon each other when moistened with water and liberate carbon dioxide. The most common of these is a mixture of tartaric acid and acid sodium car- bonate. If the powders be thoroughly incorporated with the flour the gas will be liberated during the kneading with water. Another method is to mix the sodium carbon- ate with the flour and then knead with slightly acidulated water; dilute hydrochloric acid is frequently employed. Ammonium carbonate is sometimes used, it being volatile at the temperature of baking. Flour is injured if it becomes damp or moist, its gluten becoming somewhat soluble and less tenaceous. Such flour is greatly improved by adding to the water used in making the dough, lime water in the proportion of twenty-seven pints to one hundred pounds of flour. Hard Bread. This kind of bread is made by baking the prepared dough without vesiculating material of any sort. All the moisture is expelled from such bread and it is much more dense than soft bread and keeps far better. It is accordingly better for military and naval stores. Other grains than wheat and rye can be used for making hard bread. One hundred pounds of flour will make considerably over one hundred pounds of soft bread, depending upon the proportion of the crust and this depends upon the size of the loaves. Ordinarily the weight of soft bread will exceed the weight of flour by about one-third. The weight of hard bread is less by about one-seventh. The staleness of bread is not due to its becoming dry, as is frequently supposed, but results from molecular change. Its freshness can be re- stored by rebaking in a closed oven. The cereal grains are richer in inorganic 1 salts and fatty 35* matter in and near the husk. As there is frequently some of the integument carried away with the husk, it is evident that- unbolted flour has some superiority over the bolted. If bread supplied the only article of food this difference be- tween the flours would be more important. Besides the physical condition of bread which makes it more palatable and more digestible than dough, other important changes are brought about by the baking. The state of nitrogenous constituents is altered and made more digestible. The starch granules are ruptured and some of it transformed into dextrin and sugar both of which are soluble : this latter effect is especially noticeable in the crust and in toast. THE PREPARATION OF SOAP. A fuller account of the fats and fixed oils, than has yet been given, will lead to a better understanding of the chemi- cal principles of soap-making. Fixed Oils; Fats; Glycerides. These are terms applied to a large number of analogous bodies found in both plants and animals. It is an interesting fact that there should be such a striking resemblance in composition and properties between bodies from such distinct sources. The term fixed oils is generally used for those members of the group which are liquid at ordinary temperature and the term fats for those that are solid. A fat is a solid fixed oil. These bodies are ethereal salts of the fatty acids. The basic part of the salt is the alcohol radical C 3 H 5 , They are all capable of saponification yielding glycerine and a fatty acid. Owing to the above facts the class is very properly termed glycerides. Some of the characteristics of the glycerides are as follows. Composition. They are all composed of carbon, hydrogen and oxygen, being very rich in hydrogen and carbon. They yield glycerine and a fatty acid by saponification. 353 Solubility. They are practically insoluble in water, but dissolve in ether, carbon disulphide and mix in all propor- tions with essential oils. Stability. If the air be excluded they can be preserved for a long time. In contact with air some of them absorb oxygen and in thin layers become solid. Such of the fixed oils are called drying oils. This oxidation may take place with considerable elevation of temperature. If the oil ex- pose a large surface, as when tow or cotton waste is moist- ened with it, spontaneous combustion may result. Other of the fixed oils when exposed to the air do not dry up but become rancid and ropy. This change is attributed to the presence of impurities. Such oils are called non-drying. The fixed oils cannot be distilled without decomposition. They are unctions to the touch and the more liquid leave a permanent stain on paper. Some of the more important of these oils and fats are the following: Palm, cocoa-nut, castor oil, cotton-seed and olive or sweet oil. Hemp, poppy oil and linseed oil are drying oils, the last named being much used by painters. Its drying powers are increased when it is boiled with certain metallic oxides. Such oxides are termed siccatives. The oils just named are of vegetable origin. Some of the others ordinarily obtained from animal sources are stearin, Palmitin, margarin and olein. Butter is mainly composed of Palmitin, stearin and olein. Bees-wax is a fat. It will be seen that the above characters establish a broad dis- tinction between the fixed oils and the essential or volatile oils. MANUFACTURE OF SOAP. Soap manufacture is an ancient and important industry. The remains of a complete soap-making establishment were found in the excavations of Pompeii, with soap still perfect though made over seventeen hundred years ago. It has just been stated that the more important vegetable and animal fats and oils are composed of a fatty acid in 23 354 which the hydrogen is replaced by C 3 H 5 , the radical of glycerine or propenyl alcohol, the oils and fats being glycer- ides. The general significance of the term saponification has been given. Soap is here nsed in the ordinary sense. The natural fats or glycerides may be represented by the formula C3H5FT3, in which (Ft) stands for a complex mole- cule of carbon, hydrogen and oxygen. The fatty acid from which the glyceride is derived would be represented by FtH. A soap may be defined as the salt of a fatty acid in which the hydrogen has been replaced by an alkali metal. Soaps are made by the action of an alkali upon the glycerides (fats) or sometimes upon fatty acids. The al- kalies employed are potassa and soda. The action is brought about by boiling the fat with the caustic solution and may be indicated by the reaction C3H 5 (Ft)3+3NaOH=3NaFt+C 3 H 8 03, Soda Soap Glycerine or potassium hydroxide may be used instead of sodium hydroxide with the resulting production of a potash soap. It will be observed that the alkali metal has replaced the basic radical C 3 H 5 . Soaps are generally stearates, oleates or palmitates of potassium and sodium. Soaps containing sodium are generally hard and those containing potassium are generally soft, though it is possible to produce a soft soda soap and a hard potassium soap. The soaps of the alkali metals are soluble, those of other metals generally insoluble. Soap can be produced from a large number of fats and oils, but only a comparatively small number is employed. The principal animal fats are tallow, suet, lard, whale, seal and fish oils; the vegetable oils commonly used are palm, olive, cocoa-nut and cotton seed. Fish oils contain a large proportion of olein, a liquid fat, and are generally used with potash to form soft soap, especially in Europe. In this country the farmers, in the south and south-west, frequently make soap for domestic use from kitchen fats and the alkali obtained from wood-ashes. 355 The alkali used is generally in the form of the hydroxide when soaps are made from fats. Certain soaps are made by boiling" the alkaline carbonates with free fatty acids obtained in other operations. The alkaline hydroxides are prepared in enormous quantity for use in soap-making. The glycerine formed during saponification may or may not be separated from the soap. Castile soap is made from olive oil and marine soap from palm oil. Soap may contain from 25 to 75 per cent of water. In the high dry regions of our western country soaps have been known to lose nearly one-half their weight by evaporation of water. The subsequent treatment of the soap after removal from the boiling vessels depends upon the object desired and is very varied. Many different kinds of ingredients are incor- porated for the purpose of affecting the color, odor and other properties of the soap. Cleansing Power of Soap. This property of soap is largely due to its alkalinity. Even a neutral soap gives an alkaline solution when treated with water, some of the alkali separating and leaving a soap with a greater amount of fatty acid than previously existed. The excess of alkali acts upon the grease or other insoluble matter and often ren- ders its removal possible. To increase the detergent power of soap substances are often added which act merely mechanically, such are sand and silicate of soda. MANUFACTURE OF LEATHER. The antiquity of this industry is unknown, but it is cer- tain that it was practiced by the ancient Egyptians, for pieces of leather taken from a mummy and now in the British Museum, bear marks showing that it must have been made 900 years B.C. It is well known that the Rom- ans attained much skill in the preparation and finishing y^\' leather and it is thought that the Chinese were acquainted with the art from remote ages. On the other hand it is 356 strange, when we recall how universally the skins of ani- mals are used by savages, that so many of them should have remained ignorant of the art of tanning almost up to the present time. Leather. If the fresh skin of an animal, cleaned and divested of hair, fat and other extraneous matter, be im- mersed in a dilute solution of tannic acid a chemical com- bination ensues and the gelatinous tissue of the skin is converted into a non-putrescible substance, impervious to and insoluble in water. This is leather. TANNING. Preparation of Hides; Cleansing. The first step in the preparation of leather is the softening and cleaning of the hides. This is done by soaking in water, with frequent changes, until the skins are pliable. They are then put through a kneading process. The length of time that the hides must be soaked depends upon the manner of their orig- inal curing. The hides from hot dry countries sometimes require two or three weeks 7 soaking. ©epilation. The hair is removed from the cleaned skins by soaking them in lime water; the lime saponifies the fat around the roots of the hair and loosens them; or the same result may be accomplished by what is termed siveating. In this process the hides are suspended in pits and kept at a uniform temperature (18° C.) and a moist atmosphere until they undergo partial decomposition. The ammonia pro- duced acts in the same way as the lime. The sweating process is almost exclusively followed in this country in the treatment of dried hides. The time necessary in this opera- tion varies with the character of the hides treated so that no particular statement applies. After the hair is scraped off the hides are treated for the removal of lime when this substance has been used as a 357 depilatory. This is generally done by steeping in a dilute solution of sulphuric acid. In this country hides for heavy leather are generally subjected to acid treatment though the sweating process has been employed. The acid, if properly used, exerts a beneficial action in preparing the skin for tanning. The acid is said to plump the fiber. The skins for sole leather are generally colored during the plumping. In leathers which are required to be soft it is found necessary to remove the lime by treating the hide with some putrefactive or fermenting bate. This softens the hide by its action on the fibrous tissue and abates plumpness. Such bates are sour bran, hen's or pigeon's dung. Conversion Into Leather. In this country the tanning materials used are almost exclusively oak and hemlock barks. The greater part is tanned by hemlock. The bark is first thoroughly ground and then leached to extract the tanning principle from it. The bark liquors are then run into the vats, where the hides are packed. The hides are successively transferred to vats in which the liquor is stronger. In many American tanneries the process is com- pleted in from sixty to seventy-five days from the time the hides are first subjected to the action of the liquors. In England and America the tanning materials are gen- erally leached or exhausted and the aqueous extract or decoc- tion used in the tanning vats. The operation of tanning is thus shortened. On the continent of Europe and at many places in this country after the hides are subjected to a weak infusion of the bark, they are packed in pits with alternate layers of bark; the pit is filled with water and the whole left for two or three months. The hides are then removed and treated in the same way in another pit with fresh bark, the order of the hides in the pit being reversed at each transfer. By this method the tanning often requires trom ten to fifteen months. During tanning the hide increases in weight from 30 to 40 per 358 cent. The above description applies to the common heavier leathers. Many different tanning materials are used in dif- ferent countries and a great variety of leathers produced, of these it is here practicable to refer to only a few of the more common forms. Morocco. The genuine original morocco was made from goat skins, but it is now said that an equally good article is made from the skin of the hairy seal. Imitation morocco is made from sheep-skins. For morocco the depilation is by lime and the lime is removed by bate (pigeon's dung). The skins are tanned by extract of sumach. They are sewed into bags, filled with the tanning liquid and floated in a tank of the same. The process is usually complete in twenty- four hours. Morocco is generally colored after the tanning and the aniline dyes are largely used for this purpose. Russian Leather. This form of leather is tanned with willow or larch bark. It owes its peculiar odor to the essential oil of birch-tar with which it is treated after tan- ning. Many imitations of this leather are now made. Tawing. Kid. The leather for kid gloves is made from the skin of goats and lambs. The skins are unhaired by lime and the hair^ removed by sour bran. The tanning is accomplished by agitating the skins in a drum containing a mixture of flour, alum, salt and yolk of eggs. The alumi- num chloride produced prevents putrefaction of the skin and the oil and albuminous matters increase softness and pliability. This process is called tawing. The kid is col- ored after tawing. Buckskin; Chamois Leather. These leathers are made from the skins of goats, sheep and deer. The skins are prepared, limed and bated in the same manner as for mo- rocco. They are then thoroughly impregnated with fish, whale or other oils by repeated steeping and drying. All 359 the water of the hides is thus removed and its place taken by oil. The skins are then exposed to a warm atmosphere during which some of the oil oxidizes and the skins take a yellow color. The excess of oil is then removed by an alkaline solution. It is not thought that any chemical change occurs in the skin itself, but the fibers are coated by the oily products and are very permanent and will not yield gelatine with boiling water. Kid does yield gelatine. Thicker hides than those above named may be used for this leather, but in that case they are made thin by splitting and rejecting the grain side. Animal Parchment. This parchment is made by the mechanical treatment of lamb and goat or other thin skins after the hair is removed in the usual way. The skins are stretched on frames and rubbed to the necessary thickness by sand or pumice stone. It is now possible to imitate very closely the natural grain of any leather. The thickness desired can also be secured, for the modern splitting machines have succeeded in splitting a common cow-hide into three and even four layers. By these means all the fancy kinds of leather can be imitated. Split leather is not so lasting as the natural skin of the same thickness, but it is cheaper. The splitting is best done before tanning. The skins from which leathers are made are those of the ox, horse, sheep, goat, pig, seal, deer and kangaroo. PREPARATION OF CHEESE. For the better understanding of the process of cheese-making it will be well to specify the composition of milk. The milk of all ani- mals, both carnivorous and herbivorous, contains about the same constituents, though the proportions of the constituents vary con- siderably. Milk consists essentially of water slightly alkaline, in which are dissolved casein, milk sugar and inorganic salts, and in which float numerous fatty globules. The fatty matter is the source of butter. Good fresh milk is alkaline, its alkalinity is due to soda, which holds the casein in solution. If left to itself it soon becomes acid, from 360 the formation of lactic acid through the fermentation of the milk sugar. Milk is admirably adapted to the nourishment of the animal frame. CHEESE. Cheese is made by coagulating* the milk by the addition of rennet, which is part of the stomach of the calf. A piece of rennet is added to a large quantity of milk, which is then slowly heated to about 50° C. In a short time after this temperature is reached the milk separates into a white coagulum or curd, and a slightly yellow translucent liquid called whey. The curd contains the casein of the milk, much of the fat and some of the inorganic salts. The whey contains the sugar, some of the fat and the remainder of the inorganic salts. The curd is separated from the whey, well kneaded with some common sail and often some coloring substance is added. It is then pressed in moulds and set away in an airy and cool place to ripen. During the ripening the cheese undergoes a peculiar putrefactive fer- mentation, not well understood, by which it acquires its character- istic taste and odor. The changes during ripening are brought about by the decomposition of the casein and probably of some of the fat. The quality of the cheese, of course, depends upon the kind of milk employed and the extent to which the ripening is carried. The amount of fat largely determines the quality of the cheese, the best qualities containing considerable fat. while the poorer are made from skimmed milk. The vesicular appearance of certain kinds of cheese is caused by the imperfect removal of the whey from the curd. The sugar of the whey ferments during the ripening, producing alcohol and carbon dioxide: these expanding produce the vesicles. Cheese with less fatty matter keeps better than richer cheese. From the constituents of cheese it is evident that it possesses con- siderable dietetic value. In many places it is an important article of daily diet. Cheese cau be made from the milk of any animal, but gen- erally comes from the milk of the cow : it is a product of many coun- tries. It is largely made in this country and of excellent quality. The curd can be separated by adding a little acid to the milk and heating, but this is seldom done in cheese-making. The successful preparation of artificial butter ( oleo-niargarine) has led. in some places, to the use of this substance for the fatty principle of cheese, thereby permitting the use of skimmed milk. It is reported that this is done to a considerable extent in this country and that cotton-seed oil is also here used for the same purpose. The red and blue moulds which groAv upon cheese are vegetable fungi. The cheese maggot and the cheese mite are animal organisms. Cheese like meat may and has been known to undergo decomposition with the development of poisonous properties. 361 DYEING. Dyeing is the art of imparting color to various substances, usually textile fabrics, in such manner that it is permanent under the conditions to which the fabric is subjected. In dyeing the color penetrates the material dyed, which is not the case in painting. In order that the dye may penetrate the fabric it is evident that the former must be in solution. It is often only necessary to steep the fabric in a solution of the coloring matter, the attraction between the two imparting a permanent color. In the absence of the necessary attraction between the fabric and the dye-stuff, a third substance is employed which has an attraction for both ; such substances are called mordants. When mordants are used there are usually two steps in the operation of dyeing — first, the application of the mordant; second, of the coloring matter. The nature of the action between the fabric and the mordant and between the fabric and the dye when mordants are not used, is not clearly understood. The facts and evidence at present seem to indicate that in some cases the action is physical and in others that it is chemical. In cotton, linen and vegetable substances generally, the action seems to be more of a physical one than in the case of silk, wool and other animal substances. As a general fact the coloring material permeates the latter class more fully than the former, and they may be dyed with greater facility and more permanently — the vegetable substances more frequently require mordants. The action between the mordant and the dye is in most cases a chemical one. Mordants. The mordants can generally be classed as acid or basic. The principal mordant of the first class is tannic acid. Other vegetable acid principles and fatty acids are used for the same purpose. The basic mordants comprise a number of metallic salts, the principal of which are salts of aluminum, iron, chromium and tin. The processes of mordanting cloth are too numerous even for present mention. The fibers of the cloth are impregnated with the mordanting substance in soluble form and by subsequent treatment it is rendered insoluble, if not naturally so after its union with the fiber. Usually mordanting precedes dyeing, but sometimes the operations are simultaneous and occasionally the dyeing precedes the mordanting. Dyestuffs. The chemical character of many of the numerous dye- stuffs classes them as either basic or acid. Each of them requires to be combined with a mordant of the opposite character to yield a dye. We may illustrate the mordanting action by a simple case. If cot- ton be steeped in a solution of tannic acid it will absorb it : if it is then dipped into a basic coloring matter the acid combines with it ami the fiber is dyed. Again, if cotton be steeped in a solution of aluminum acetate and then boiled, a basic acetate is deposited in the fiber. If the 362 cotton be now dipped into the solution of an acid coloring principle it will be permanently dyed. Printing. If the dye be applied to only parts of the cloth, so as to produce patterns it is called printing. In goods requiring mordants this is easily accomplished by mordanting only those parts to be printed. Sometimes the cloth is uniformly dyed and the pattern effect produced by removing the color from certain parts. This can be done by bleaching agents and is known as the discharge method. I N DEX NUMBERS REFER TO PAGES. Acetylene, 98 preparation, properties, 99 series, 276 Acids, basicity, 25 characteristic property, 25 how formed, 14 Affinity, conditions affecting, 19 defined, 18 Air, 68 composition, 69 Albumins, 306 egg, 307 plant, 307 serum, 307 Alcoholic beverages, 343 beer making, 343 distilled liquors, 348 wine making, 345 Alcohols, 282 classes, 288 common, 284 ethyl, 285 how derived, 283 methyl, 283 propyl, 286 Alkali metals, 159 Alkaloids, 308 Alum, common, 193 ammonia, 194 Aluminum, occurrence, 190 hydroxide, 194 oxide, 194 [191 preparation and properties, sulphate, 192 Ammonia, 113 chemical properties, 115 preparation, 116 physical properties, 116 Ammonium, 174 acid carbonate, 176 chloride, 175 nitrate, 176 sulphide, 176 sulphate, 175 Antimony, 224 Aqua Regia, 128 Argon, 158 Aromatic hydrocarbons, 276 Arsenic, 155 acid, 157 oxide, 155 sulphides, 157 Arsenious acid, 157 Atmosphere, 68 composition, 69 Atomic theory, Dalton's, 9 Atomic weights, 28 determination by an- alysis, 29 determination by Avo- gadro's law, 35 determination by de- composition, 31 determination by sub- stitution, 30 Atoms, number in molecule, 39 Balsams, 279 Barium, 177 carbonate, 177 chlorate, 178 chloride, 177 hydroxide, 178 nitrate, 178 properties of salts, 178 sulphide, 178 sulphate, 177 Bellite, 334 Bases, 23 Basic anhydrides, 24 Benzene, 273 series, 276 Binary compounds, 13 Bismuth, 223 Borates, 113 Boric acid, 112 Boron, 112 Bread making, 348 fermented, 349 unfermented, 350 Bromine, 108 preparation, properties. 129 Caffeine, 308 Calcium, 178 364 Calcium, carbonate, 179 chloride, 183 fluoride, 183 hydroxide, 180 salts, reactions of, 183 sulphide, 183 sulphate, 182 sulphate, hydrous, 182 Calorific intensity, 312 power or value, 311 Camphors, 278 Candle flame, 103 Carbon, 73 animal charcoal, 88 chemical properties, 89 coke, 88 common charcoal, 85 diamond, 83 , graphite, 84 lampblack, 84 Carbon compounds, 267 Carbon dioxide, 90 chemical properties, 92 physical properties, 91 preparation, 94 Carbonic acid and its salts, 94 Carbon monoxide, 95 Carborundum, 112 Casein, 307 Catalytic action, 20 Caoutchouc, 279 Celluloid, 333 Cerium, 227 Cheese, preparation, 359 Chemistry, definition, 6 Chlorine/ 122 oxygen compounds, 128 -preparation, properties, 123 uses, 124 Chromium, 222 Cobalt, 220 Cocaine, 309 Coke, 88 Collodion cotton, 332 Colors, vegetable, 305 Copper, 237 ' carbonate, 245 oxides, 244 properties, 243 sulphate, 244 uses, 244 Copper, dry reduction, 237 concentration of native, 238 oxides, 238 sulphides, 239 Copper, extract'n of precious metals, 242 electrolytic method, 242 liquation process, 243 Copper, Ziervogel's method, 243 Copper, smelting without fuel, 241 Copper, wet reduction, 241 Davy's lamp, 108 Diamond, 83 Disposing affinity, 21 Dissociation, 21 Di-sulphuric acid, 148 Dynamite, 330 Elements, definition, 5 table, 7 Equivalent weights, 27 Ethene, 98 Ethvl alcohol, 285 Ethylene, 99 Explosives, 332 compounds, 327 mixtures, 324 Fats, fixed oils, 352 Ferments, 284 Ferro-manganese, 222 Fibrin, 307 Fire wire, 322 Flame, 100 blowpipe, 106 candle, 103 hydrocarbon, 103 lighting, 104 luminosity, 101 oxy-hydrogen, 107 structure, 102 Fluorine, 131 preparation, properties, 132 Formulae, constitutional, 270 rational, 270, structural, 270 to determine, 53 Furnace, iron, 197 Gas, illuminating, 337 manufacture, 339 secondary products, 342 water, 96 Gelatine, 306 Gelatine dynamite, 333 Gelatine explosives, 332 Gelignite, 333 Germanium, 227 Glass, 314 Bohemian, 316 crown, 315 devitrified, 318 flint, lead, 316 plate, 315 pressed, 317 production, 316 window, 315 365 Glue, 307 Gluten, 307 Glycerides, fats, 352 Glycerine, 286 preparation, properties, 277 Gold, 260 chloride, oxide, sulphide, 266 properties, 266 metallurgy, 260 African extraction, 265 amalgamation, 262 chlorination, 263 chlorine leaching, 263 cyanide leaching, 263 extraction from vein quartz, 261 extraction from sedimentary de- posits, 264 extraction by smelting, 261 Graphite, 84 Gutta percha, 282 Gun cotton, 331 Gunpowder, 325 Helium, 158 Hydracids, 6 Hydrocarbons, 271 aromatic, 276 saturated, 272 unsaturated, 275 Hydrobromic acid, 129 Hydrochloric acid, 125 Hydrofluoric acid, 132 Hydrogen, 62 chemical properties, 64 heat of combustion, 65 peroxide, 82 preparation, 66 physical properties, 63 reducing power, 66 Hydrogen sulphide, 136 action with metals and oxides, 137 action with metal- lic salts, 138 preparation, 139 properties, 137 Hydrozine, 117 Hyposulphurous acid, 149 India rubber, 279 applications to fabrics, 281 vulcanized, 280 Indigo, 305 Iodine, 130 compounds, uses 131 Iron, 195 carbonate, 219 Iron, chemical properties, 217 oxides, 218 reaction of salts, 220 sulphate, 219 sulphides, 219 Iron, cast, 196 composition, 203 fuel for reduction, 198 furnace, 197 furnace gases, 202 [ores, 197 preliminary treatment of reduction from ores, 198 slag and fluxes, 201 uses of slag, 202 Iron, wrought, manufacture, 206 Eames process, 209 properties of bar iron, 210 puddling, mechanical, 208 puddling, manual, 206 Isinglass, 306 Isomerism, 271 Isomorphism, 41 Kerosene, 274 Lamps, safety, 107 Davy's, 108 Stephenson's, 109 Laughing gas, 121 Law, Avogadro's, 32 definite proportions, 8 even numbers, 48 insolubility, 19 multiples, 9 periodicity, 51 Pettit and Dul volatility, 19 volumes, 42 Lead, desilverizing, 230 cupellation, 232 Parke's process, 231 Pattinson's process, 232 occurrence, 227 carbonates, 235 oxides, 236 Lead, reduction, 227 [method, 229 American wester n other processes, 228 Leather manufacture, 355 buckskin, 358 kid, 358 morocco, 358 Russian. 358 Legumin, 307 Magnseium, 184 [ide. sulphate. 185 carbonate, chloride. ox- Manganese, 222 366 Marsh gas, methane, 97 properties, 98 Mercury, 252 chlorides, oxides, 256 metallurgy, 253 sulphides, 255 properties, uses, 256 Molecular weights, 32 [law, 32 from Avogadro's by other means, 34 Molecule, definition, 11 unsaturated, 49 Molybdenum, 223 Morphine, 308 Naphtha, 273, Nascent state, 20 Nickel, 221 Nicotine, 308 Niobium, 224 Nitrates, 121 Nitric acid, 118 properties, 119 oxide, 122 Nitro-compounds, 333 [334 Nitro-compounds and organic nitrates, Nitrogen, 67 oxides, 118 pentoxide, 122 preparation, 68 tetroxide, 122 Nitro-glycerine, 328 derivatives, 330 Nitro-muriatic acid, 128 Nitrous anhydride, 122 oxide laughing gas, 121 Nomenclature, 13 prefixes, 14 suffixes, 15 Notation, 11 Olefiant gas, 99 Olefine series, 275 Opium, 308 Organic chemistrv, 267 Oxides, 13 Oxygen, 57 action on metals, 59 non-metals, 58 preparation, 60 properties, 57 Ozone, 61 Paraffin series, 272 Petroleum, 273 Phosphorus, 150 amorphous, 153 common. 152 Phosphorus, compounds of, 155 oxy-acids of, 154 pentoxide, 154 preparation, 152 uses, 154 Picric acid, tri-nitro-phenol, 334 Platinum, 257 compounds, 259 related metals, 259 Potassium. 159 bicarbonate, 162 bromide, 163 chlorate, 165 chloride, 163 hydroxide, 162 nitrate, 163 oxides and sulphides, 166 sulphate, 166 Potassium carbonate, 161 from ashes, 161 from beet-root, 161 from chloride, 162 from sheep's wool, 162 properties, etc., Potterv, 318 [162 kilns, 321 Polvmerism, 271 Porcelain, 319 Pressure, influence on chemical action, Pyro-sulphuric acid, 148 [21 Quinine, 309 PiACK-A-ROCK, 234 Radicals, 22 Resins, 278 Selenium, 149 Silica, 110 Silicon, 111 Silver, 245 chloride, nitrate, 251 properties, uses, 249 reaction of salts, 252 Silver, reduction from ores, 245 amalgamation process, 246 leaching process, 248 smelting for, 245 Smokeless powders, 335 Soap making, 353 Soda, caustic, 172 Sodium, 166 bicarbonate, 170 chloride, 168 367 Sodium, borate, 173 hydroxide, 172 manufacture, 167 nitrate, 173 silicate, sulphate, 173 thiosulphite, 173 Sodium carbonate, manufacture, 170 Leblanc process, 170 Salvay process, 171 properties, 171 Spiegeleisen, 222 Steel, manufacture, 210 cementation process, 213 crucible steel, 215 Bessemer process, acid, 211 basic, 212 open hearth, 212 compared with iron, 216 Stochiometry, 52 Stoneware, 320 Sulphates, 147 Sulphur, 133 chemical properties, 135 dioxide, 140 extraction, native, 133 [135 extraction from sulphides, physical properties, 136 trioxide, 142 Sulphuric acid, 142 di-sulphuric, 148 manufacture, 143 properties, 146 Strychnine, 309 Tantalum, 224 Tellurium, 150 Terpenes, 277 Thallium, 195 Theine, 308 Thiosulphuric acid, 149 Thorium, titanium, 227 Tin, 224 alloys, 226 oxides, salts, 227 reduction, 225 Tungsten, 222 Turpentine, 277 Uranium, 223 Valency, 47 variable, 50 Vanadium, 224 Vegetable colors, 305 Vulcanite, 281 Water, 71 chemical properties, 75 physical properties, 71 solvent powers, 74 of crystallization, 73 Waters, natural, 76 action on soap, 80 deposits from, 79 hard and soft, 78 mineral, 81 purification of, 81 river and sea, 81 Xylonite, 333 *Zinc, 186 chloride, oxide, sulphate, 189 reactions of salts, 190 uses, 188 Zirconium, 227 fc ^F