■ ■ ■ WNm i ii 1 ■ WW Hffl IH IH mm m ■ B H IBS HI si ■ ■ 1 In' 1 * H ii B M^l«iiilglOillinniilnn»IIHttyirliif altli pi ^%. • *" •%_ ^^ ^ *\ o> : * S I " ^ << / ^ v I B ^ r. . . * $ >^ U ' * * s a\ .ill. Vi ^ SPECTRUM ANALYSIS. ELEMENTS OF MODERN CHEMISTRY. By ADOLPHE WURTZ, (SENATOR,) MEMBER OF THE INSTITUTE, HONORARY DEAN AND PROFESSOR OF CHEMISTRY OF THE FACULTY OF MEDICINE OF PARIS, MEMBER OF THE ACADEMY OF MEDICINE, ETC. SECOND AMERICAN EDITION. TRANSLATED AND EDITED, WITH THE APPROBATION OF THE AUTHOR, FROM THE FIFTH FRENCH EDITION, By WM. H. GREENE, M. D., PROFESSOR OF CHEMISTRY IN THE CENTRAL HIGH SCHOOL, PHILA- DELPHIA. MEMBER OF THE AMERICAN PHILOSOPHICAL SOCIETY, OF THE CHEMICAL SOCIETIES OF PARIS AND BERLIN, ETC. WITH ONE HUNDRED AND THIRTY-TWO ILLUSTRATION! s - ( APR 14 1884,'] LONDON AND PHILADELPHIA.: ~7 J. B. LIPPINCOTT & 18 84. (ALL NIGHTS RESERVED.) W»SH V -b\ ky -2 ..561 Glycols and their Derivatives . . . . • . . .562 Glycerin and Ethers 572 Polyatomic and Polybasic Acids 580 Uric Acid and its Derivatives ........ 608 Alcohols of high Atomicity 617 Sugars and Starches 619 Fermentation 630 Glycerides 641 Aromatic Compounds 646 Turpentine and its Derivatives 656 Benzol and its Derivatives ' 663 Aniline and its Derivatives ........ 674 Toluol and its Derivatives . . . 687 Xylols and their Derivatives 703 Trimethylbenzols 705 Unsaturated aromatic Compounds 707 Indigo and its Derivatives 709 Naphthalene 714 Anthracene and Phenanthene 716 Natural Alkaloids and Pyridic Bases 720 Albuminoid Matters 738 Products of Animal Disassimilation ....... 749 ELEMENTS OF MODERN CHEMISTRY. INTRODUCTION. The material objects surrounding us present striking and infinite differences. Sulphur is readily distinguished from charcoal, rock-crystal from flint, iron from copper, water from spirit of wine, and wood from ivory. It is known to all that these bodies differ not only in form, density, and structure, but also in their proper substance. They differ, too, in the changes through which they pass under the same conditions. When subjected to the action of heat they receive very differently the impression of that force. They become heated more or less quickly, and transmit the heat with greater or less rapidity throughout their own substance. A short bar of iron cannot be grasped in the hand by one extremity if the other be heated to redness ; under the same conditions a cylinder of charcoal may be handled with impunity. Communicate sufficient heat to water and it is converted into steam ; remove heat from it, and if the cooling be sufficient, it is frozen into ice. Spirit of wine cannot be congealed by the most intense cold known. If a magnet be placed among iron filings they attach themselves in tufts around the two poles ; on the contrary, copper filings are indifferent to the magnetic attraction. Rock-crystal is transparent to light ; flint is opaque. These two bodies are unalterable by fire. They may be heated to red- ness in a furnace, but after the temperature has abated, they will be found with their original characters unchanged. It is very different with the coal which we burn in our grates. This body disappears during the combustion, and leaves only a quan- tity of ashes. But it has not been destroyed, and its substance is found in entirety in a certain gas produced by the combus- tion. Like charcoal, sulphur is combustible, and is converted by burning into a gas, the suffocating odor of which is well known. Neither sulphur nor charcoal undergo any alteration when 7 8 ELEMENTS OF MODERN CHEMISTRY. exposed to damp air ; it is not the same with iron. In a moist atmosphere this metal experiences a striking and lasting change. Its surface becomes covered with rust and is no longer iron. In the forests, the leaves which fall and remain upon the moist soil are slowly consumed and disappear in the course of seasons. All of these changes, these phenomena, take place daily be- fore our eyes, and are familiar to all of us. On comparison, striking differences are discovered between them : some are but passing, and do not affect the proper nature of the body. They are the results of forces which act at sensible distances, and which leave the body in its primitive state as soon as their action has ceased. A piece of soft iron is attracted by the magnet before contact is established, and when under the mag- netic influence, is capable of attracting other soft iron in its turn : the action of the magnet has made the iron itself mag- netic, but it immediately loses this property when the magnet is withdrawn ; and further, this momentary change in property has brought about no alteration in the intimate nature of the iron. It is found after the experiment in precisely the same condition as before. In the same manner, rock-crystal undergoes no change in its specific identity by the passage of a ray of light. Withdraw from the vapor of water the heat which has been communi- cated to it, and the liquid water is recovered with all its prop- erties. Restore to the ice the heat which was abstracted in its formation, and water is regenerated as before. This is charac- teristic of the changes produced by physical forces. Under the influence of such forces, bodies experience modifications more or less profound, more or less lasting, but which never affect their specific nature. But the iron which rusts undergoes a complete and lasting change in its properties and in its substance. The rust is no longer iron, and vainly would it be sought to isolate the metal by mechanical means, or to discover its presence by the aid of the most powerful microscopes. The metal has disappeared as such ; it has undergone a complete transformation ; it has be- come another body. It has attracted one of the elements of the air, oxygen, and has, moreover, fixed to itself the moisture of the atmosphere. These latter bodies, which differ from iron in substance, have intimately united with the metal itself, and the result of this union, of this combination as it is called, is INTRODUCTION. V a new body, rust or hydrated oxide of iron. In this case the alteration is profound, the change is lasting ; the specific nature of the body is affected. This is characteristic of chemical action. In the same manner, when the charcoal and the sulphur are burned in the air, they attract oxygen and combine with it, forming two new bodies that are, called carbonic and sul- phurous acids. - These phenomena may be rendered more clear by simple and well-known experiments. Experiment 1. — A globe (Fig. 1) is filled with oxygen, a gas which constitutes one of the elements of the atmosphere, and which is eminently fitted to support combustion ; into it is plunged a morsel of charcoal lighted at one end ; immediately the coal glows with a brilliant light, the combination takes place actively, and the charcoal is rapidly consumed. But presently the light becomes paler, the combustion ceases, and the char- coal is extinguished. The oxygen is now nearly or quite con- Fig. 1. Fig. 2. sumed, and "the globe is filled with another gas which is' no longer oxygen, although it contains that oxygen. It contains also the matter of the charcoal which has disappeared, and these two bodies have combined to form a new body, which is carbonic acid. This latter will not support combustion, and further, it extinguishes burning bodies. It is then a body having entirely new properties, and is formed by a chemical action. Experiment 2.— Into another jar filled with oxygen (Fig. 2) is plunged a spoon containing ignited sulphur. The combus- 10 ELEMENTS OF MODERN CHEMISTRY. tion takes place with a beautiful blue flame, and in burning in the oxygen with so much energy, the sulphur unites with the gas and forms with it a new body, which is called anhydrous sulphurous acid. It is a suffocating gas, which extinguishes flame. It reddens, and afterwards bleaches, a solution of blue litmus poured into the jar. These are special properties which do not belong to the oxygen at first contained in the jar. They characterize a new body, the result of the combination of the sulphur with the oxygen, and formed by chemical action. Carbon, sulphur, and oxygen are simple bodies or elements. They are so called because from neither of them can more than one kind of matter be obtained. But when the charcoal in burning unites with the oxygen, the carbonic acid which re- sults from the union contains two kinds of matter. — carbon and oxygen ; and these two elements are united in such an intimate manner that the body which contains both does not resemble either carbon or oxygen : it is endowed with new properties which do not in any manner recall those of the elements which constitute it. In fact, it is a new substance, a compound body formed by the combination of the matter of the charcoal with the matter of the oxygen. Considering the preceding facts, we may give to chemistry the following definition : chemistry studies those intimate ac- tions of bodies upon each other which modify their natures and cause a complete and lasting change in their properties. Iron may be reduced to a fine powder. This may be mixed with sulphur itself reduced to powder, and if the mixture be sufficiently intimate, it will present neither the lemon-yellow color of sulphur nor the gray -black of finely-divided iron. Nevertheless, a homogeneous substance cannot be formed in this manner. If the powder be examined under the micro- scope, the particles of iron may be recognized disseminated among those of the sulphur, but not confounded with them. By the aid of a magnet the iron may be separated. On the other hand, if the mass be thrown into water, the particles of iron will sink first to the bottom, while the lighter particles of sulphur remain in suspension. Thus, after having triturated the sulphur and iron together, not only can each substance be recognized in the mass, but they can be again separated by mechanical means. Here there has been no chemical action, but simply a mixture. If, however, this mixture be heated, the sulphur will first be seen to melt, and afterwards the INTRODUCTION. 11 whole mass will blacken and enter into fusion if the tempera- ture be sufficiently elevated. After cooling, it is perfectly ho- mogeneous, and neither iron nor sulphur can be recognized. Both have disappeared as such, and in their place is found a substance having new properties ; it is the sulphide of iron. They have disappeared, but their substance is not lost ; and it may be proved by experiment that the weight of the sul- phide of iron produced is exactly equal to the sum of the weights of the iron and the sulphur. The ponderable matter of the iron is then added to the ponderable matter of the sul- phur, and has formed with it a union so intimate that there results a new body, the smallest particles of which are per- fectly similar to each other and to the entire mass. This ex- ample and a thousand others that might be given prove that when bodies combine there is neither loss nor creation of mat- ter. The result of the combination, that is, the compound body, contains the whole of the substance and nothing more than the substance of the combining bodies. This is an essen- tial characteristic of chemical combination. The force which presides over chemical combination is called affinity. It is important that this force be distinguished from another which is often opposed to it, and which is cohesion. In order to reduce to powder a solid substance, such as pyrites or sulphide of iron, it is necessary to overcome the resistance opposed by the particles of the mass to their separa- tion. This resistance is due to a special force, which brings and maintains in relation to each other the homogeneous par- ticles of the sulphide of iron, as indeed of all solid bodies. This is cohesion. The particles which are bound together by this force are not only those minute particles which are visible to the naked eye or under the microscope, and of which the most impalpable powder of a solid body is composed. - Such particles still present a magnitude that can be measured ; they must be considered as little masses, so to speak, indivisible by the mechanical means at our command, but formed in reality of particles still smaller. These smallest particles of a solid body which are bound by cohesion are called molecules. They are not in immediate contact with each other. In a perfectly compact and homogeneous mass, such as sulphide of iron, the molecules do not touch each other. Between them exist spaces of considerable magnitude, compared to the real volume of the molecule. This idea must not be confounded with po- 12 ELEMENTS OF MODERN CHEMISTRY. rosity, which is caused by those accidental spaces which form visible pores in solid bodies. These intermolecular spaces are those which separate the molecules of a homogeneous and com- pact solid body, and physicists have further been led to believe that even in solid bodies the molecules are not perfectly immo- bile, but that they execute vibratory movements in the spaces which separate them, at the same time maintaining their own relative positions. If a solid body be heated, a part of the heat is employed in raising the temperature, another part serves to increase the distances which separate the molecules : the body expands in becoming heated. But, as the distances between the molecules increase by the action of the heat and the effect of the expan- sion, the molecular attraction necessarily becomes more feeble. Cohesion is thus somewhat diminished, and if the heat be further increased, it may be so much diminished that the mole- cules, which have thus far been maintained in definite rela- tions, can move and glide freely over each other ; the solid body then enters into fusion : it becomes a liquid. The liquid state is produced by a diminution of cohesion, and is charac- terized by a greater mobility of the molecules. But if the liquid body be still further heated, at a certain point the additional heat may produce such a separation of the molecules that, already freed from all mutual attraction, they become completely independent of each other. This is char- acteristic of the gaseous state. It may be stated, then, that cohesion is considerable in solid bodies, but slightly energetic in liquids, and null in gases, and we have just seen that heat, by causing the changes of state of a body, can overcome and even practically abolish this physical force. Chemical force or affinity is at the same time more intimate and more powerful. It modifies the molecules themselves. It brings heterogeneous substances into intimate relations, and thus produces new molecules. A consideration of the examples already cited may indicate more clearly the meaning of this important proposition. We have brought together sulphur and iron, and by their reciprocal action and the aid of heat there has been formed a new body, — sulphide of iron. We know that the smallest mass of sulphur we can obtain is composed of a collection of per- fectly homogeneous molecules, aggregated by cohesion. In each INTRODUCTION. 13 of them but one kind of matter can be found. It is the same with iron : the particles of this metal are perfectly homoge- neous. Sulphur and iron are simple bodies or elements. Let us now consider the sulphide of iron which results from their combination. This body also is formed of a collection of molecules, bound together by cohesion and perfectly similar to each other, but not homogeneous, for in each molecule we dis- tinguish two kinds of matter. — sulphur and iron. It cannot be admitted that these two substances are con- founded in the molecule, or that the effect of the combination of sulphur with iron is an interpenetration of the two bodies so intimate that they both disappear in what might be called a homogeneous mixture. On the contrary, it is supposed that the combination results from the juxtaposition of two infinitely small masses, each of which possesses a real magnitude and a constant weight. These little masses that no force, chemical or physical, can divide further, constitute the atoms. In each molecule of sul- phide of iron there exist two of these masses. — one of sulphur and one of iron ; and the atom of sulphur and the atom of iron are bound together, but not confounded, by chemical force. And when sulphur combines with iron it is because the atoms of the sulphur arrange themselves in juxtaposition with those of the iron, and it is affinity which brings about the action. When these atoms again separate, the sulphide of iron is said to decompose. AVhen it attracts the atoms of another body, it is said to combine with that body. If sulphide of iron remain for some time exposed to moist air. its surface becomes covered with an efflorescence formed of a saline matter. In this case it has attracted one of the ele- ments of the air. oxygen, with which it has combined to form green vitriol or sulphate of iron. The molecules of oxygen, upon which cohesion has no hold, the body being gaseous, are each formed of two atoms, but these atoms are of the same kind ; the molecules of sulphide of iron, on the contrary, are each formed of two unlike atoms. — one of sulphur and one of iron. These latter attract four atoms of oxygen, which constitute two molecules of that gas, and these group themselves around the atom of sulphur and the atom of iron, forming with them one single molecule, more complex than the primitive molecule of sulphide of iron, for it contains in addition four atoms of oxygen. 2 14 ELEMENTS OF MODERN CHEMISTRY. 1 molecule sulphide of iron. 1 molecule 1 molecule oxygen. oxygen. © -I- • fixes and there results 1 molecule # sulphate of iron. 0-H-0 It is seen from what precedes that the words molecule and atom are far from being synonyms. The chemical molecule constitutes a whole of which the atoms form the parts, and these atoms are held together by affinity. In the preceding figure, this exchange of affinities between the atoms is indi- cated by lines of union. Chemical molecules have been well compared to edifices: the atoms constitute the materials, and it is readily conceived that such molecular edifices differ from each other according to the nature, number, and arrangement of the atoms, that is, the materials composing them. An edifice may be enlarged by the addition of new parts : it may be reduced in size or it may be entirely demolished. In the same manner a chemical molecule may be increased by the annexation of new atoms, or diminished by the separation of some of those which it already contains. In the first case there is combination, in the second, decomposition. We may still further consider these phenomena of combina- tion and decomposition. Since the combination of two bodies results from the recip- rocal action of their atoms, and has for effect a change in the nature of the molecules, it is evident that it can only take place when these atoms, and consequently the molecules, are brought into intimate relations ; or more precisely, when the molecules of one of the bodies enter within the sphere of action of the molecules of the other body. And this sphere of action is very limited, for the affinity or elective attraction of the atoms is only exercised at infinitely small distances. INTRODUCTION. 15 It results that affinity is often retarded by cohesion, which maintains the relations between the molecules of a solid body. These two forces are frequently in opposition, and that the first may attain the supremacy it is necessary that the other shall yield. To make manifest or to increase the affinity be- tween two bodies, it is then necessary to diminish their cohe- sion. On this condition the molecules can enter within the spheres of their reciprocal attraction, and the atoms of one body can attract those of the other. It has been seen from one of the experiments already cited that in order to combine iron with sulphur it is necessary to elevate the temperature. Now, the heat, by fusing the sul- phur, diminishes its cohesion, and, giving its molecules freedom of motion; puts them into more intimate contact with those of the iron. Chemical action then commences. Instead of heating the sulphur and iron to bring about chemical action, it would be sufficient to moisten the mixture with water. By the intervention of this liquid the particles of sulphur and of iron are, as it were, cemented together and thus brought into more intimate relations. For a stronger reason can chemical action between two solids be facilitated by dissolving them both in water and mixing the solutions. Dis- solved, they themselves assume the liquid state and lose, in great part, their cohesion. The ancients understood the in- fluence of the liquid state upon reactions, and stated it with exaggeration : Corpora rum agunt nisi soluta. Although the liquid state facilitates chemical reactions, it does not follow that it always determines them. Frequently liquids and even gases, after being mixed, must be heated before they will react upon each other. Experiment. — In a glass tube (Fig. 3) two gases, oxygen and hydrogen, are mixed in the proportion of one volume of the first to two of the second. Although the mixture is per- fectly homogeneous and very intimate, and although the cohe- sion of the gaseous molecules is null, no action takes place. But as soon as the mixture is heated by approaching a lighted taper to the mouth of the tube, combination takes place ener- getically. An explosion occurs and the two gases unite, form- ing water. In this case the heat has determined combination by increasing the intensity of the movements which animate the molecules of each gas. and so bringing the molecules of the one within the sphere of attraction of those of the other. 16 ELEMENTS OF MODERN CHEMISTRY. The electric spark produces the same effect, and it probably acts by the heat which it communicates to the mixture. Fig. 3. More rarely combination is brought about by the influence of light. If a small bottle be filled with a mixture of equal volumes of hydrogen and chlorine gases, and then thrown into the air so that it may be struck by the direct rays of the sun, the combination of the two gases takes place instantly and with explosion. Such are some of the conditions which favor or determine chemical combination. Let us now study the circumstances which accompany these phenomena. Experiment. — If sulphur be strongly heated in a small glass flask until it begins to boil, and some copper turnings be then thrown into the flask, a brilliant incandescence takes place im- mediately. It is produced by the combination of the two bodies. Charcoal, sulphur, and phosphorus produce a brilliant light when they are burned in oxygen. Their combination with the gas takes place with evolution of luminous heat. Whenever a combustible body of whatever nature burns in the air, the heat and light are developed by the combination of the body with oxygen, one of the elements of the air. In general, all chemical combinations give rise to the production of heat, more or less intense ; in certain cases it is luminous, but more often it is obscure ; sometimes it is scarcely perceptible. While heat acts as the determining cause of a great number INTRODUCTION. 17 of combinations, and while it is the result of such combination, it may play still another role in chemical reactions. In place of favoring combination, it may act in the opposite manner, separating atoms which are united by chemical attraction. Mercury retains indefinitely its brilliant surface when ex- posed to the air at ordinary temperatures, but at a temperature near its boiling-point it slowly attracts the oxygen of the air. and becomes covered with an orange-red powder, which is oxide of mercury. In this case heat has assisted the formation of a compound. If, however, this red powder be heated in a small retort to a temperature near redness, it is again resolved into mercury, which appears in drops in the neck of the retort, and into oxygen which may be collected. In this case an intense heat breaks up the compound which is formed at a temperature less elevated ; it occasions a decom- position. Heat acts thus in a great number of cases. A body is said to decompose when the elements composing it are separated from each other. The electric spark may occasion such separation when it is passed through compound gases. If a series of electric dis- charges be passed through ammonia gas, the latter is decom- posed, that is, resolved into its two elements, — nitrogen and hydrogen. In like manner, the current of the voltaic pile decomposes a great number of chemical compounds, the elements of which separate and appear, each at its appropriate pole of the bat- tery. The decomposing action exerted by the galvanic current upon chemical compounds was discovered about the commence- ment of the present century by Nicholson and Carlisle. These physicists were the first to decompose water by the voltaic current. Lastly, light may decompose certain bodies, among which are a great number of the compounds of silver. The art of photography is founded upon the decomposing action of light upon certain of these combinations. There is a certain class of decompositions which it is impor- tant to consider with attention. They are occasioned by the intervention of more powerful affinities than those which main- tain united the elements of a compound body. If copper be heated in the air, it attracts oxygen and is con- 2* 18 ELEMENTS OF MODERN CHEMISTRY. verted into a black powder, a compound of oxygen and copper, which is called oxide of copper. The affinity which unites the two bodies is considerable ; it cannot be overcome by the ac- tion of heat alone ; at any ordinary temperature to which the oxide so formed may be exposed, the atoms of copper still re- main intimately associated with those of the oxygen. But if this oxide be mixed with powdered charcoal and then heated, a moment arrives when the affinity of the charcoal for the oxy- gen is superior to that of the copper. The atoms of oxygen then abandon the copper and combine with the charcoal, thus forming a new compound, carbonic acid, which is disengaged in the form of gas. Here there is at the same time decompo- sition and combination. The molecules of oxide of copper are decomposed ; those of carbonic acid are formed. Nothing is created in combinations ; nothing is lost in de- compositions. In the preceding experiment only copper re- mains ; the charcoal and oxygen have disappeared, but their substance is not lost. All of the matter of the charcoal is Fig. 4. found combined with all of the matter of the oxygen in the product of their combination, the carbonic acid, in such a manner that the weight of the latter added to the weight of the copper remaining, exactly represents the weight of the oxide of copper and charcoal. INTRODUCTION. 19 Experiment. — Some oxide of mercury, of which we have seen the decomposition by heat, may be placed in a tube through which is passed a current of hydrochloric acid gas, a gas composed of chlorine and hydrogen (Fig. 4). An ener- getic reaction takes place. The orange-red powder is converted into a white crystalline substance, and much heat is produced. At the same time a small quantity of liquid condenses in the bulb. This is water, and the white powder formed is mercuric chloride, or corrosive sublimate, a compound of mercury and chlorine. The hydrochloric acid has converted the mercuric oxide into mercuric chloride. The mercury, at first combined with oxygen, is now combined with chlorine. But what has become of the oxygen ? It has combined with the hydrogen of the hydrochloric acid, forming water. We have brought into presence of each other two compound bodies : Mercuric oxide, Hydrochloric acid, and from their reciprocal action two new compounds result : Mercuric chloride, Water or oxide of hydrogen. This reaction has then occasioned an interchange of elements. The mercury of the mercuric oxide has combined with the chlorine of the hydrochloric acid, and the oxygen has left the mercury and combined with the hydrogen, which was aban- doned by the chlorine. The reaction has been as easy as energetic, thanks to the intervention of two affinities, for the affinity of chlorine for mercury has been aided by that of hy- drogen for oxygen. Two molecules are decomposed, and two new molecules are formed by an exchange which may be rep- resented in the following manner : BEFORE THE REACTION. Mercury -f Oxygen = Mercuric oxide. Hydrogen + Chlorine = Hydrochloric acid. DURING THE REACTION. AFTER THE REACTION. Mercury + Chlorine = Mercuric chloride. Hydrogen + Oxygen = Water. 20 ELEMENTS OF MODERN CHEMISTRY. Such reactions, characterized by an interchange of elements, are called double decompositions. They are the more usual reactions in chemistry. The examples cited have been demonstrated by experiments easy to comprehend and to repeat, and are sufficient to give an idea of chemical phenomena. We have seen how, on the con- tact of two heterogeneous bodies, this elective attraction, which is called affinity and which sets in motion the smallest particles of bodies, comes into play to produce either combination or decomposition ; we have seen how this force modifies the chemical molecules either by interposing other molecules, or under the influence of physical forces, such as heat and elec- tricity. The study of all these phenomena constitutes chem- istry, the science of molecular changes ; a science grand in purpose and in magnitude, since it penetrates to the very nature of the bodies surrounding us ; a science unlimited in its applications, since through it we learn to know and control the powerful forces which are at work in the most intimate structure of matter. If we trace the acquired facts to the most obvious and most certain conclusion, we must admit the diversity of matter. There exists, indeed, a certain number of bodies, each of which, when submitted to the various tests resulting from the applica- tion of physical and chemical forces, furnishes but one and the same substance, and it is impossible to obtain anything else than this substance from the body. We maintain, then, until proved to the contrary, that each of these bodies contains but a single kind of matter, and they are called simple bodies or elements. The chemical forces reside, as has been seen, in the most remote particles, in the atoms of these bodies. In uniting together, the elements form compound bodies, and it has al- ready been stated that such combinations result from the juxta- position of the atoms which attract each other. The idea of atoms is an hypothesis, but the hypothesis is based upon nu- merous and important facts, which it weaves together in the most natural manner. It is more than an hypothesis : it is a theory. Chemists have universally adopted it, for it has ren- dered immense service to the science. Let us proceed, then, to a consideration of the facts upon which it is based. LAW OP DEFINITE PROPORTIONS- 21 Fig. LAW OF DEFINITE PROPORTIONS. The proportions by weight according to which bodies combine are invari- able for each combination — These proportions are equivalent among themselves — Experiments demonstrating this fact. Experiment. — A test-glass (Fig. 5) contains a liquid which is universally known as sulphuric acid. Although largely di- luted with water, that is, mixed with a large quan- tity of that liquid, it still manifests its presence by energetic properties. It has a very sour and cor- rosive taste, — a quality of an acid. If a few drops of blue litmus solution be added to it the blue color instantly changes to bright red. Another glass contains a solution of caustic potash or potassium hydrate. This substance possesses a strong, lye-like, alkaline taste, very easy to. distinguish from that of the acid. The color of the blue litmus is not affected by this liquid, but if a few drops of the litmus solution, previously reddened by an acid, be added, the blue color is immediately restored. This caustic substance has properties which are different from those of acids, and which are called basic or alkaline properties. Potassium hydrate is an alkali or powerful base. If now the alkaline liquid, which has a blue color, be poured drop by drop into the acid, which is red. and the mixture be stirred with a glass rod, a moment arrives when the red color of the acid liquid changes to blue. Exactly at this moment we have a solution which has no action upon litmus ; it will not redden the blue solution, neither will it restore the blue color to the red. This may be demonstrated by dipping into it first a red and then a blue litmus-paper. Furthermore, this liquid possesses neither the acid taste of the oil of vitriol nor the alkaline taste of the caustic potash, but its taste is salty. By their mixture and reciprocal action the sulphuric acid and the potash have lost the energetic properties which they 22 ELEMENTS OF MODERN CHEMISTRY. manifested in the free state. They are exactly saturated ; they are 7ieutralized. That is, the liquid which now contains both, or more properly the product of their reaction, is neither acid nor alkaline ; it is neutral, and its neutrality is manifested both by its indifference to vegetable colors and by its effects on our organs of sense. There is no excess, neither of sulphuric acid nor of potash, but the two bodies have reacted exactly upon each other and have both disappeared, and from their recipro- cal action two new bodies result, — a salt called potassium sul- phate, and water. Whenever sulphuric acid is thus saturated by potash, there arrives a moment when the whole of the acid is precisely neu- tralized by the alkali, and when the two bodies are converted, without residue of either one or the other, into potassium sul- phate and water ; and it is always easy to recognize the instant at which this effect is produced by the action of the liquid upon vegetable colors, such as solution of litmus, or syrup of violets. The latter is reddened by an acid, changed to green by an alkali, and assumes its natural violet tint when the neutral point is reached. Now, it has been found that this last effect is only produced when the acid and the alkali are mixed in certain proportions, which remain invariable, whatever may be the quantities which are mixed. In other words, it has been found that the quantities of sulphuric acid and potash which reciprocally neutralize each other and form potassium sulphate, maintain a constant ratio to each other. It may be easily proved that when the state of neutrality has been once attained, it is immediately passed and disturbed by the least excess of either acid or base that may be added to the liquid. This is made evident by the immediate change in the color of the liquid to either red or green. Thus, in order to form sulphate of potassium with a given quantity of sulphuric acid, it is necessary to add an invariable quantity of potash ; and if the quantity of sulphuric acid be increased by a third, or in any proportion whatever, it is neces- sary to increase by a third, or in the same proportion, the quan- tity of potash. Experiments of this kind have been made with other acids and other bases, and have introduced into th^ science the fun- damental notion that these bodies react upon each other in definite proportions to form salts, and that consequently the composition of the latter bodies is perfectly fixed. A given DEFINITE PROPORTIONS. 23 quantity of the same base. This, then, is the first point. It may be added that similar researches made towards the close of the last century have led to a not less important result, namely, the respective quantities of several acids which satu- rate a given weight of one base are exactly proportional to the quantities of the same acids which saturate a given weight of another base. The law which governs the composition of salts was discovered towards the close of the last century by a Ger- man chemist, Richter. We cannot now expose it in detail ; such development will be better placed and better understood in that part of this work which treats of the formation of salts. For the present it is sufficient to state that the law mentioned is a consequence of the law of definite proportions, and that the latter law is universal. It applies not only to the reaction of acids upon bases, but is true for all chemical combinations. It is generally known as Dalton's first law, and may be thus expressed : the relative iceights according to which bodies com- bine are invariable for each combination. There is one feature of the laws which control the composi- tion by weight of bodies that it is important to comprehend well. It may be best illustrated by experiment : 100 gr. of mercury are put into the presence of chlorine gas, a body possessing very powerful affinities. In this man- ner mercuric chloride or corrosive sublimate is formed, and it is found that 35.5 gr. of chlorine are necessary to convert 100 gr. of mercury into this compound. These figures — 100 and 35.5 — express the invariable ratio in which these elements are combined in corrosive sublimate. Here we have the definite proportions. Now let the 135.5 gr. of corrosive sublimate be dissolved in water, and a plate of copper be placed in the solution ; this metal will displace the mercury, and combining with the' 35.5 gr. of chlorine will form with it cupric chloride, which will remain in solution, coloring the liquid green. The 100 gr. of mercury are then precipitated, and it will be found that 31.75 . gr. of copper have entered the solution and actually combined with 35.5 gr. of chlorine. Into this solution of cupric chloride a plate of zinc is now plunged ; all of the copper is precipitated in its turn, and 33 gr. of zinc enter into combination with the 35.5 gr. of chlorine, forming zinc chloride. 24 ELEMENTS OF MODERN CHEMISTRY. The 35.5 gr. of chlorine have now been combined success- ively with 100 gr. of mercury, 31.75 gr. of copper, 33" gr. of zinc. These numbers, which express the respective quantities of mercury, copper, and zinc which combine with the same quan- tity of chlorine, may be called the equivalents of these metals. In fact, these quantities are equivalent to each other in relation to the same quantity of chlorine, the experiment having shown us that in order to displace 100 gr. of mercury combined with 35.5 gr. of chlorine it is necessary to employ 31.75 gr. of copper or 33 gr. of zinc. To continue, 100 gr. of mercury are combined with oxygen, and it is found that this quantity of the metal requires 8 gr. of oxygen to form the red powder called mercuric oxide. But how much oxygen is necessary to form cupric oxide with 31.75 gr. of copper? Remarkable as it seems, exactly 8 gr. are required, and 8 gr. are also requisite to form oxide of zinc with 33 gr. of zinc. 100 gr. of mercury, 31.75 gr. of copper, 33 gr. of zinc, which are equivalent compared to 35.5 gr. of chlorine, are then also equivalent in relation to 8 gr. of oxygen. Chlorine itself may be oxidized, and there exists a gaseous compound of chlorine and oxygen which contains precisely 8 gr. of oxygen for 35.5 gr. of chlorine. Thus, there are required 35.5 gr. of chlorine to form chlorides with . . I 3] 3 r * ° ^coDDer' 8 gr. of oxygen to oxidize ( 33*gr. of zinc, ' and also 8 gr. of oxygen to oxidize 35.5 gr. of chlorine. In general, if A, B, C, combine with D, A, B, C, combine also with E, and further, D combines with E, the letters A, B, C, D, E, representing the weights of the dif- ferent elements which enter into combination, or the propor- tions according to which the bodies combine among themselves. MULTIPLE PROPORTIONS. 25 They are expressed by numbers that have been called combin- ing weights or equivalents ; these represent the ratio of weights or the relative weights. They are indeed relative to a unit which has served as a term of comparison, and which is the equivalent of hydrogen. That is, the quantity of hydrogen which combines with 35.5 of chlorine being 1, the equivalent quantities of oxygen, zinc, copper, and mercury will be repre- sented by the numbers 8 — 33 — 31.75 — 100. These are the facts of experiment. Let 33 gr. of zinc be treated with hydrochloric acid, the latter is immediately de- composed ; its chlorine combines with the zinc, forming chlo- ride of zinc, and its hydrogen is disengaged. In this experi- ment the hydrogen of the hydrochloric acid is simply displaced by the zinc. Now, 33 gr. of this metal will displace exactly 1 gr. of hydrogen. It is seen that the numbers which have been given do not express absolute quantities, but merely the relative weights ac- cording to which the bodies combine or replace each other in compounds, these relative weights being compared to that of hydrogen, which is taken as unity. Such is the signification of the numbers. f which represent 100 31.75 33 35.5 8 1 j equivalent quan- n r * £> c r tities of these of of of of of of I elements# mercury, copper, zinc, chlorine, oxygen, hydrogen. u This being admitted, in order to determine the equivalent of an element it is sufficient to find the quantity of that ele- ment which combines either with 1 of hydrogen or with a quantity of another element which is equivalent to 1 of hydro- gen, for instance, 8 of oxygen. The notion of equivalent proportions can be understood from the preceding considerations ; it appears as a consequence of the law of definite proportions ; it comprehends certain facts relative to the laws of the composition of bodies, but it by no means represents the full scope of these laws. The following developments add important features. MULTIPLE PROPORTIONS. Two bodies may combine in several proportions. Thus, with oxygen, carbon forms two compounds, both of which are gaseous. The less rich in oxygen is carbon monoxide ; the richer is carbon dioxide, or carbonic acid gas. Dalton was the b 3 . 26 ELEMENTS OF MODERN CHEMISTRY. first to perceive that for the same quantity of carbon, carbonic acid contains exactly twice as much oxygen as carbon monoxide. He made analogous observations concerning the composition of two compounds of carbon and hydrogen, the monocarbide of hydrogen or marsh gas, and the dicarbide of hydrogen or olefiant gas. From these observations he deduced the law of multiple proportions, which may be thus stated : when two bodies , simple or compound, unite in several proportions to form several compounds, the weight of one of these bodies being considered as constant, the weights of the other vary according to a simple ratio. Thus, taking up one of the examples given above, carbon unites with oxygen in two proportions : Carbon monoxide contains 16 parts of oxygen to 12 parts of carbon. Carbon dioxide contains 32 parts of oxygen to 12 parts of carbon. The numbers 16 and 32 are in the ratio of 1 : 2. Nitrogen forms five compounds with oxygen ; if such quan- tities of these compounds be taken as contain the same weight of nitrogen, the weights of the oxygen will be proportional to the numbers 1, 2, 3, 4, 5. Nitrogen monoxide contains for 28 parts of nitrogen 16 parts of oxygen. Nitrogen dioxide " 28 " " 32 " " Nitrogen trioxide " 28 " " 48 " " Nitrogen tetroxide " 28 " " 64 « " Nitrogen pentoxide " 28 " " 80 " " These numbers, 16, 32, 48, 64, 80, are multiples of the first by the numbers 1, 2, 3, 4, 5. Five compounds of manganese and oxygen are known, and similar relations exist between the quantities of oxygen con- tained in these compounds. The first contains 55 parts of manganese to 16 of oxygen. The second " 55 " " 24 " The third " 55 " " 32 " The fourth " 55 " " 48 " The fifth " 55 « " 56 " The numbers 16, 24, 32, 48, 56 are in the simple propor- tion 1 : 1.5 : 2 : 3 : 3.5. Such is the law of multiple proportions discovered by Dalton. HYPOTHESIS OF ATOMS. The brilliant researches of Dalton did not terminate with the acquisition of facts, but sought to account for them by a GAY-LUSSAC'S LAWS. — ATOMIC THEORY. 27 theoretical conception. Taking up the old idea of Lysippus and the word of Epicurus, he supposed all ponderable matter to be composed of indivisible particles which he called atoms. He gave a precise meaning to the vague and ancient notion by considering on one hand that the atoms of each kind of matter, of each element, possess an invariable weight, and on the other that combination between different kinds of matter results from the juxtaposition of their atoms. Such is the atomic hypothe- sis, the substance of which we have already indicated in treat- ing of chemical phenomena in a general manner. It permits a simple and rational interpretation of the laws of the compo- sition of bodies, and establishes between these laws a firm bond of theory. Indeed, if the combination of bodies results from the juxta- position of their atoms, the latter being considered as indivisi- ble and possessing a constant weight for each element, it is evident that combination can only take place in definite pro- portions, for these proportions represent the invariable relations between the weights of the atoms which are in juxtaposition. If, on the other hand, one body may combine with another in several proportions, such combination can only take place by the juxtaposition of 1, 2, 3, 4, etc., atoms of one body with one or more atoms of the other. It evidently results that the weight of the latter body being constant, the weights of the other in these various combinations must be multiples of each other. An hypothesis which gives such a simple and precise ex- planation of the facts relative to definite and multiple propor- tions is surely worthy of attention. It acquires still further import and becomes elevated to the rank of a theory when to these facts are added others entirely different from the first, but not less important. GAY-LUSSAC'S LAWS.— ATOMIC THEORY. Gases combine in simple volumetric proportions — Relations which exist between the volumes of gases and their atomic and molecular weights — Equal volumes of gases or vapors contain the same number of molecules — The molecular weights are equal to double the densities compared to hydrogen. ■ Among these new facts it is convenient to first notice those which were discovered by G-ay-Lussac, from 1805 to 1808. They relate to the volumes of gases which combine together. 28 ELEMENTS OF MODERN CHEMISTRY. Experiment. — 10 cubic centimetres of hydrogen and 5 cubic centimetres of oxygen are introduced into a tube (Fig. 6), which is inverted over the mer- cury-trough. The gaseous mixture occupies the up- per portion of the tube, which is an eudiometer. Into the upper extremity of this tube is hermeti- cally cemented a small iron wire with a little ball at each extremity. Another iron wire passes through the wall of the tube at a short distance from the upper extremity, in such a manner that the interior extremity of this second wire is opposite, and at a short distance from the lower ball of the superior and vertical wire. A little iron chain is at- tached to the exterior end of the horizontal wire, and dips into the mercury of the trough. Things being thus arranged, the inferior extremity of the eudiometer is closed by an iron cap, and the charged plate of an electrophorus is approached to the upper button. A spark instantly passes be- tween the two buttons in the eudiometer, and a bright flash is seen to fill the whole space occupied by the gaseous mixture. The combination of the two gases has taken place with the development of luminous heat. Water has been formed, and is condensed in drops too small to be perceptible. If now the eudiometer be opened, by removing the cap which closes it under the mercury, the latter at once rises to the top of the tube, and fills the whole of the space at first occupied by the hydrogen and oxygen. These gases have then combined exactly in the proportion of 10 volumes of the first to 5 of the second, or more simply, in the proportion of 2 volumes to 1 volume. If the eudiometer-tube be now surrounded by a wider glass tube, and the latter be filled with oil heated to 120°, the heat Fig. G. GAY-LUSSAC'S LAWS. — ATOMIC THEORY. 29 communicated to the eudiometer will be sufficient to convert into steam the water which was condensed, and it may be proved, all corrections being made, that the vapor occupies a volume equal to exactly 10 cubic centimetres ; that is. a volume equal to that of the hydrogen employed. From the facts thus established we draw the conclusion that 2 volumes of hydrogen exactly combine with 1 volume of oxygen to form 2 volumes of vapor of water. There is thus determined a simple ratio not only between the volumes of hydrogen' and oxygen which combine, but further, between the volume of vapor of water formed and the sum of the volumes of the composing gases. 3 volumes of the latter are reduced to exactly 2 by the combination. Analogous facts have been discovered for other gases, as shown by the following examples : 2 volumes of nitrogen -f 1 volume of oxygen = 2 volumes of nitrogen monoxide. 2 volumes of chlorine + 1 volume of oxygen == 2 volumes of chlorine monoxide. In other cases the combination of two gases determines a still greater contraction, and the initial volume is reduced one- half. Thus 1 volume of nitrogen + 3 volumes of hydrogen = 2 volumes of ammonia gas. Finally, when two gases combine in equal volumes, their combination usually takes place without contraction ; in other words, the volume of the gas produced is equal to the sum of the volumes of the component gases. From these collected facts we may draw the following general conclusions : 1. There is a simple relation between the volumes of gases which combine. 2. There is a simple relation between the sum of the volumes of the combining gases and the volume of the gas resulting from the combination. These laws were first signalized by Gay-Lussac, whose name is attached to them. Their importance is immense ; they have added a notable development to the atomic theory. If the definite proportions by weight in which bodies com- bine represent, according to Dalton, the relative weights of their atoms, it is natural to conclude that the definite and simple proportions by volume in which gases combine, accord- 3* 30 ELEMENTS OF MODERN CHEMISTRY. ing to Gay-Lussac, represent the volumes occupied by the atoms. Under the same volume gases would then contain the same number of atoms. This was first proposed by Am- pere, who based his conclusion on the important consideration that gases dilate and contract nearly equally when submitted to the same variations of temperature and pressure. Within certain limits the proposition is true ; it applies to a large num- ber of simple gases. But if equal volumes of these gases, measured, let it be well understood, under the same conditions of temperature and pressure, contain the same number of atoms, it is evident that the weights of these equal volumes should represent the weights of the atoms. In other words, the atomic weights of the simple' gases should be proportional to their densities. The densities of gases and vapors represent the weights of these gases or vapors compared to the weight of an equal volume of air. To determine the density, a certain volume of the given gas is weighed, and this weight is divided by that of an equal volume of air, under the same conditions of tempera- ture and pressure. The air is then the unit to which are com- pared the densities of gaseous bodies. On comparing these densities to that of hydrogen, 1 which we take as unity, we find that the same numbers express almost exactly the densities and the atomic weights, the unit to which the densities are com- pared, that is, hydrogen, being the same as that to which are compared the atomic weights. The figures in the following table demonstrate this to be the case : Elements. Densities of Gases or Vapors, Air being Unity. Densities, Hydrogen being Unity. Atomic Weights. Hydrogen Oxygen Nitrogen Sulphur (density at 1000°) Chlorine Bromine Iodine 0.0693 1.1056 0.9714 2.22 2.44 5.393 8.716 1 15.9 14 32 35.2 77.8 125.8 1 16 14 32 35.5 80 127 1 To do this it is sufficient to multi-ply the densities of the gases compared to air by = 14.44, which is the density of the air compared to hy- drogen as unity. GAY-LUSSAC's LAWS. — ATOMIC THEORY. 31 It is seen from this table that if the densities of gases be compared to hydrogen as unity, just as the weights of their atoms are compared to hydrogen as unity, the same figures, or very nearly the same figures, express both the densities and the atomic weights. We may add that, for all the elements taken in the gaseous state, there has been determined between the densities referred to hydrogen and the atomic weights, if not equality, at least a simple ratio. These remarkable rela- tions were pointed out by G-ay-Lussac. Equal volumes of the simple gases above enumerated con- tain the same number of atoms. Two volumes of hydrogen, then, contain twice as many atoms as one volume of oxygen ; and when these gases combine in the ratio of 2 volumes of the first to 1 of the second, we must admit that each atom of oxy- gen combines with 2 atoms of hydrogen. We say, then, that water is composed of 2 atoms of hydrogen and 1 atom of oxy- gen. These three atoms so united constitute the smallest quantity of water that can exist in the free state. This is called a molecule of water. But what volume does this molecule occupy ? The experi- ment has shown us. We have seen that 2 volumes of hydro- gen, in combining with 1 volume of oxygen, yield 2 volumes of vapor of water. One molecule of water in the gaseous state. then, occupies 2 volumes, if 1 atom of hydrogen occupy 1 volume, and if 1 atom of oxygen occupy 1 volume. It is seen that the volumes represent the atoms, and the relative weights of equal volumes, that is, the densities, represent the weights of the atoms. Let us now consider another compound gas, — ammonia, — composed of hydrogen and nitrogen. A very simple experi- ment will show in what proportion the atoms of these elements are combined in this gas, and the volume occupied by the compound compared with the volumes of its component gases. Experiment. — 100 volumes of ammonia gas are introduced into a tube inverted upon the mercury-trough (Fig. 7). and the walls of which are pierced at the upper end by two plati- num wires, between the ends of which a small space is left. To these wires are attached the extremities of the two con- ducting wires of a Ruhmkorff coil, and the current is passed so that a series of electric sparks traverses the ammonia between the extremities of the wires in the tube. The gas is imme- diately decomposed, and the level of the mercury in the tube 32 ELEMENTS OF MODERN CHEMISTRY. is depressed. When the experiment has terminated it is found that the volume of the gas has been doubled. Instead of 100 volumes, there are now 200, the gas being measured under the same conditions of temperature and pressure as before. It is found, by an analytical process that will be indicated further on, that these 200 volumes of gas resulting from the decompo- Fig. 7. sition of 100 volumes of ammonia are composed of 150 vol- umes of hydrogen and 50 volumes of nitrogen. These 150 volumes of hydrogen and 50 volumes of nitrogen are condensed by their union into 100 volumes of ammonia. In other words, 3 volumes of hydrogen and 1 volume of nitrogen are combined together in 2 volumes of ammonia. And as the volumes rep- resent atoms, it follows that in ammonia gas 3 atoms of hydro- gen are combined with 1 atom of nitrogen. But the quantity of ammonia containing 1 atom of nitrogen and 3 atoms of hydro- gen is the smallest quantity of ammonia that can exist. It is a molecule of ammonia, and this molecule occupies 2 volumes, if 1 atom of nitrogen or 1 atom of hydrogen occupy 1 volume. Here, then, is another compound gas, — ammonia, — of which the molecule occupies 2 volumes, like that of water. It is the same with all the gases. All of the atoms which are combined to constitute the molecule of a gas or vapor are so condensed that the molecule occupies the same volume as the molecule of vapor of water, or the molecule of ammonia. We may state, then, with the Italian chemist, Avogadro, that equal volumes of gases contain the same number of mole- cules, and that each of these molecules occupies 2 volumes, if 1 atom of hydrogen occupy 1 volume. It follows that the weight of 2 volumes of a compound gas represents the weight of its molecule, the weight of one volume of hydrogen GAY-LUSSAC'S LAWS. — ATOMIC THEORY. 33 being 1. But the weight of 2 volumes of a gas or vapor is nothing more than the double of its density compared to hy- drogen ; for the density is the weight of 1 volume compared with the weight of 1 volume of hydrogen. To find the weight of the molecule (the weight of 2 volumes) of a gas or vapor, it is then only necessary to multiply its density compared to hydrogen (the weight of 1 volume) by 2. The densities of gases and vapors are generally referred to air as unity. To bring them to the hydrogen standard, they are multiplied by the number expressing the relation of the density of hydrogen to that of air, which is -q * 93 = 14.44. The product thus obtained expresses the density compared to hydrogen, that is, the weight of 1 volume. To find the weight of 2 volumes, or the molecular weight, it is then only necessary to multiply the densities compared to air by twice the ratio of the density of the air compared to hydrogen, that is, by the constant factor, — 1 2 2 X 0^693 = (L0693 = 28 * 88 * It is seen that if the atomic weights of certain gases can be deduced from a comparison of their densities, this same physi- cal notion may also serve for the determination of the molecu- lar weights of compound gases. The numbers which represent double the densities of gases or vapors compared to hydrogen, express also the molecular weights of these gases or vapors, that is, the weight of all the atoms in the molecule, the weight of one atom of hydrogen being 1. Considering the examples already given, we may deduce the molecular weights of water and of ammonia from the densities of steam and ammonia gas. The density of vapor of water, determined by Gay -Lussac is 0.6235. To find the molecular weight of water, it is suffi- cient -to multiply this figure by 28.88. The product, 18, ex- presses the weight of a molecule of water, which is indeed composed of 2 atoms of hydrogen =2 1 atom of oxygen =16 1 molecule of water =18 Sir Humphry Davy found for the density of. ammonia the 34 ELEMENTS OF MODERN CHEMISTRY. number 0.5901. This being multiplied by 28.88, the product, 17.04, should represent the weight of one molecule of am- monia. Ammonia contains 3 atoms of hydrogen 3 1 atom of nitrogen 14 1 molecule of ammonia 17 The discovery of the laws which govern the combination of gases by volume has seconded in the most efficacious manner the progress of the atomic theory. In the first place, it has established a marked distinction be- tween the old idea of equivalents and the modern one of atoms. The equivalents represented merely the ponderable proportions according to which bodies combine ; the atomic weights repre- sent the relative weights of the volumes of gases which com- bine. The equivalent of hydrogen — unity — expressed merely that hydrogen was the unit to which were referred the weights of other bodies with which it entered into combination. The atomic weight of hydrogen is the weight of one volume of hydrogen, taken as unity, and to this unit are referred the atomic weights of other bodies. In the second place, the discovery of Gay-Lussac has shown how the atomic weights of simple bodies and the molecular weights of compound bodies can be determined from the den- sities of gases and vapors. However, this resource would be insufficient in very many cases. It only applies to gaseous bodies, or such as can be conveniently converted into vapor. Now, there are many sub- stances with which this is impossible, and serious difficulties would be encountered in the determination of the atomic weights of certain elements were it not for another physical law, discovered by two French physicists, Dulong and Petit. It denotes the relations which exist between the specific heats and the atomic weights. LAW OF SPECIFIC HEATS. It is known that in order to raise the temperatures of differ- ent bodies through the same number of thermometric degrees very different amounts of heat are required. Thus, one kilo- gramme of water requires 30 times more heat than one kilo- gramme of mercury to raise its temperature one degree, and if the quantity of heat required to raise the temperature of LAW OF SPECIFIC HEATS. 35 one kilogramme of water one degree be represented by 1, the quantity required to raise the same weight of mercury one degree will be represented by 0.0333 = -^. This fraction ex- presses the specific heat of mercury between and 100°. The specific heat of a solid or liquid body is then the amount of heat required to raise the temperature of a certain weight of the body one degree, the amount required to raise the tempera- ture of an equal weight of water one degree being taken as unity. In 1820, Dulong and Petit discovered the remarkable fact that if the figures which express the atomic weights of the elements, liquid or solid, be multiplied by those which express their specific heats, the product obtained is sensibly constant ; in other words, the specific heats of the elements are inversely as their atomic weights. It results that if such quantities of the elements be taken as represent their atomic weights, the amount of heat required to raise the temperature of each one degree will be sensibly the same. The law discovered by Du- long and Petit may then be expressed, — the atoms of the solid elements possess sensibly the same specific heats. This law permits the deduction of the atomic weights from the specific heats. Indeed, it is evident that if the product of the specific heats by the atomic weights be a constant, that may be called the atomic heat, dividing this product by the specific heat should give the atomic weight. The product which represents the atomic heat is 6.4, very nearly, as may be seen from the following table : Names of the Solid Elements. Specific Heats. Atomic Weights. Products of the Specific Heats by the Atomic Weights. Atomic Heats. Sulphur, between and 100° . . Selenium 0.2026 0.0762 32 79.5 129 80 127 31 75 12 11 28 39.1 6.483 6.058 6.115 6.744 6.873 5.850 6.105 5.52 5.5 5.66 6.500 Tellurium 0.0474 Bromine, between — 78 and — 20° Iodine, between and 100° . . Phosphorus, between -f 1 and 30° Arsenic 0.0843 0.0541 0.1887 0.0814 Carbon, diamond, at 600° . . . Boron, crystallized, at 600° . . Silicon, at 1000° Potassium 0.46 0.5 0.202 0.1695 36 ELEMENTS OF MODERN CHEMISTRY. TABLE.— Continued. Names of the Solid Elements. Sodium, between — 34 and + 7° . Lithium Thallium Magnesium Aluminium Manganese Iron Zinc Cadmium Cobalt Nickel Tungsten Molybdenum Lead Bismuth Copper Antimony Tin Mercury, between — 77.5 and — 44° Silver Gold Platinum Palladium Osmium Rhodium Iridium Specific Heats. 0.2934 0.9408 0.03355 0.2499 0.2143 0.1217 0.0110 0.09555 0.05669 0.1068 0.1089 0.0334 0.0722 0.0314 0.0308 0.09515 0.05077 0.05623 0.03247 0.05701 0.0324 0.03293 0.0593 0.03063 0.05803 0.03259 Atomic Weights. 23 7 204 24 27 55 56 65.2 112 59 59 184 96 207 210 63.5 120 118 200 108 197 197.5 106.5 199.2 104.4 198 Products of the Specific Heats by the Atomic Weights. Atomic Heats. 6.748 6.586 6.844 5.998 5.786 6.693 6.116 6.230 6.349 6.301 6.424 6.146 6.931 6.499 6.468 6.042 6.092 6.635 6.494 6.157 6.383 6.503 6.315 6.101 6.058 6.452 Carbon, silicon, and boron have long been regarded as ex- ceptions to Dulong and Petit's law. Their specific heats had been determined at comparatively low temperatures, and the products of the numbers obtained by the atomic weights fell much below 6.4. These exceptions have disappeared ; the ex- periments of M. Weber have shown that the specific heat of carbon, silicon, and boron increases with the temperature, and that for the first two elements it attains a limit, where it re- mains sensibly constant. The figures given in the preceding table for these three elements are those of M. Weber, and it is seen that on multiplying them by the respective atomic weights of carbon, silicon, and boron, values are obtained which are sensibly near 6.4. It will otherwise be remarked that there are sensible differ- ISOMORPHISM. — CHEMICAL NOMENCLATURE, ETC. 37 ences between the numbers expressing the atomic heats of the various solid elements, showing that Dulong and Petit's law. although true in its generality and striking in its enunciation, is not'free from certain perturbations which give to it the character of an approximate law. It is the same with other physical laws, Mariotte's law, for example. ISOMORPHISM. While considering the atomic theory and the determination of the relative weights of the ultimate particles of bodies, we cannot pass in silence a discovery which has had a great influ- ence upon the development of that theory. It is due to E. Mitscherlich, who, in 1819, made known the law of isomor- phism. This law may be thus stated : there is such a relation between the atomic constitutions of compound bodies belonging to the same group and their crystalline form, that " the same number of atoms combined in the same manner produce the same crystalline form, the latter being independent of the chemical nature of the atoms, and determined solely by their number and arrangement." The importance of the proposition as regards the atomic structure of bodies is self- evident. We will reconsider it when treating of the sreneral characteristics of salts, but we may remark here that it has been of great value in the determination of certain atomic weights. Indeed, in some cases considerations of a chemical nature cannot decide between two numbers for the atomic weight of a given element. The choice is then determined by the following considerations : such a value must be attributed to the atomic weight that the isomorphous compounds formed by the element and by another to which it is analogous,, may be represented by similar atomic formula. CHEMICAL NOMENCLATURE AND NOTATION. General Considerations. — Sixty-eight substances are now known which can be resolved into no simpler forms of matter, and which are consequently considered as simple bodies or ele- ments. By combining together, they form an innumerable mul- titude of compound bodies containing two or more elements. 4 38 ELEMENTS OP MODERN CHEMISTRY. In order to distinguish these bodies from each other it is neces- sary to give a name to each, for each constitutes a distinct sub- stance. The names of the simple bodies have been chosen at will, and in some cases recall some peculiar property of the sub- stances designated. It was formerly the same with compound bodies ; there was no definite rule for their nomenclature. From this there resulted a great complication of words which embarrassed the exposition of ideas, and often for the same sub- stance there were a number of synonyms, of which the least inconvenience was to uselessly fatigue the memory. Hence chemists have felt the necessity of a regular nomenclature, applicable to compound bodies, and capable of indicating their composition. Such is the principle of the chemical nomen- clature suggested by G-uyton de Morveau, and developed by Lavoisier, Berthollet, and Fourcroy. This nomenclature, with some modifications, introduced by the progress of the science, is still adopted. Independently of this language, the rules of which will presently be detailed, chemists have adopted a written nota- tion which expresses in concise form the atomic constitution of compounds. The name of each element is represented by a symbol, which also expresses one atom of the substance. This symbol is the initial letter of the name of the element, or the initial letter with another when the names of two ele- ments begin with the same letter. Thus, H represents one atom of hydrogen weighing 1 ; represents one atom of oxygen weighing 16. By combining these symbols together, it is easy to represent in a precise manner the atomic compo- sition of compound bodies. From such combinations result chemical formulas, the use of which was introduced into the science by Berzelius. In the following table will be seen the names of the ele- ments now known, together with their atomic weights, and the symbols by which the atoms of the elements are represented in the notation. The greater number of the elements possess certain physi- cal properties which characterize them as metals. They are opaque, and possess a peculiar lustre, which does not disappear under the burnisher. They are good conductors of heat and electricity. CHEMICAL NOMENCLATURE AND NOTATION. 39 Names op the Ele- QD a ,0 .J2 5 w> 1 Names of the Ele- = 1i) ments. s .- ments. 5 ss >> <* 3£ Aluminium . . . Al 27.5 Molybdenum . . Mo 96 Antimony (stibium) Sb 120 Nickel .... Ni 59 Arsenic .... As 75 Niobium . . . Nb 94 Barium .... Ba 137 Nitrogen . . . N 14 Bismuth . . . . Bi 210 Osmium . Os 199.2 Boron Bo 11 Oxygen .... O 16 Bromine .... Br 80 Palladium . . . Pd 106.6 Cadmium .... Cd 112 Phosphorus . • P 31 Caesium .... Cs 133 Platinum . . . Pt 197.5 Calcium .... Ca 40 Potassium (kalium ) K 39.1 Carbon .... C 12 Rhodium . . . Rh 104.4 Cerium .... Ce 141.2 Rubidium . . . Rb 85.2 Chlorine .... CI 35.5 Ruthenium . . Ru 104.4 Chromium . . . Cr 52.5 Samarium . . . Sa 150 Cobalt Co 59 Scandium . . . Sc 44 Copper .... Cu 63.5 Selenium . . . Se 79.5 Didymium . . . Di 145.4 Silicon .... Si 28 Erbium .... Er 166 Silver (argentum) Ag 108 Fluorine .... Fl 19 Sodium (natrium) Na 23 Gallium .... Ga 69.9 Strontium . . . Sr 87.5 Glucinum .... Gl 9.5 Sulphur . . . S 32 Gold (aurum) . . Au 197 Tantalum . . . Ta 182 Holmium .... Ho 162 (?) Tellurium . . . Te 128 Hydrogen . . . H 1 Thallium . . . Tl 204 Indium .... In 113.4 Thorium . . . Th 234 Iodine I 127 Tin (stannum) . Sn 118 Iridium .... Ir 198 Titanium . . . Ti 50 Iron (ferrura) . . Fe 56 Thulium . . . Tu 170.4(?) Lanthanum . . . La 139 Tungsten (wolfra- Lead (plumbum) . Pb 207 mium) . . . W 184 Lithium .... Li 7 Uranium . . . Ur 120 Magnesium . . . Mg 24 Vanadium . . . V 51.37 Manganese . . . Mn 55 Yttrium . . . Y 172.5 Mercury (hydrar- Zinc Zn 65.2 gyrum) . . . Hg 200 Zirconium . . . Zr 90 Other elements, fewer in number, do not possess these prop- erties. They have been called the non-metallic bodies, some- times the metalloids. They include the following : HYDROGEN. CHLORINE. BROMINE. IODINE. OXYGEN. SULPHUR. SELENIUM. TELLURIUM. NITROGEN. PHOSPHORUS ARSENIC. antimony, (bismuth ?) SILICON. CARBON. FLUORINE. From a theoretic stand-point this distinction presents but 40 ELEMENTS OF MODERN CHEMISTRY. little value, for it is impossible to draw an exact line sepa- rating the metals from the non-metallic bodies. Nomenclature of Compound Bodies. — The principle of chemical nomenclature is to indicate the composition of com- pound bodies by their names. Among such compounds the most numerous and the most important are those containing oxygen. They are binary or ternary ; that is, the oxygen in them is combined with one or two other elements. Binary Oxygen Compounds. — We will first consider the more simple oxidized bodies, those which result from the com- bination of oxygen with but one other element, metallic or non-metallic. These compounds are called oxides, and differ as the element associated with the oxygen is metallic or non- metallic. In combining with non-metallic elements, oxygen generally forms compounds which are the anhydrides of acids, that is, compounds capable of uniting with water to form acids ; with the metals it forms metallic oxides. Experiments. — 1. A small piece of phosphorus is placed in a capsule floating on the surface of mercury. It is ignited and the capsule covered with a bell-jar (Fig. 8). The phos- phorus burns, giving off a thick smoke, which condenses in white flakes on the sides of the bell-jar. This substance re- sults from the combination of the phosphorus with the oxygen of the air : it is phosphorus pentoxide, or phosphoric anhydride. CHEMICAL NOMENCLATURE AND NOTATION. 41 2. If lead be heated in the air and maintained for some time in a state of fusion, its brilliant surface becomes tarnished and covered with grayish particles, which are finally converted into a yellow powder. This body is formed by the combina- tion of the lead with oxygen: it is plumbic oxidt. or oxide of had. But, as we have seen, such combination can take place in different proportions. An atom of a body may unite with 1. 2. 3. or more atoms of oxygen, and the names of the com- pounds so formed should indicate the degree of oxidation. Sulphur forms two compounds with oxygen : one contains 2 atoms of oxygen to 1 atom of sulphur ; the other. 3 atoms of oxygen to 1 of sulphur. They are designated* by the names sulphurous oxide, or anhydride, and sulphuric oxide, or anhy- dride. The written notation represents them by the symbols SO 2 , so 3 ; which express their atomic compositions. The number of atoms of any element is indicated by a small figure placed after and a little above or below the symbol of that element. The degree of oxidation is then expressed by the termina- tion in ous or ic of the name of the other element, which indicates the kind of oxide, ic denoting the superior oxide. Mercury forms two compounds with oxygen. The first contains 2 atoms of mercury for 1 of oxygen : the second. 1 atom of mercury to 1 of oxygen. They are designated by the names and symbols as follows : Mercurous oxide Hg 2 0. Mercuric oxide HgO. The names monoxide, sesquioxide. dioxide, etc.. as will be seen further on. are also employed. 1 A monoxide is a combination of 1 atom of metal with 1 atom of oxygen. A sesquioxide " " 2 atoms " u 3 atoms " A dioxide " " 1 atom ' " "2 " " It is easy then to understand the signification of the follow- ing names and symbols : 1 The prefixes proto. bi or dent, and ter have been, and are yet, frequently employed instead of mono, di, and tri. 4* 42 ELEMENTS OF MODERN CHEMISTRY. Manganese monoxide MnO. Manganese sesquioxide Mn 2 3 . Manganese dioxide MnO 2 . The oxide most rich in oxygen is sometimes called the per- oxide. Oxygen Acids and Metallic Hydrates. — The oxygen com- pounds that we have just considered may unite with the ele- ments of water to form more complex compounds, which are ternary, that is, they contain three elements. To the two ele- ments of the oxide is then added a third, independently of the oxygen of the water, that is, its hydrogen. The oxygen acids usually result from the union of water with the non-metallic oxides. Experiment. — Sulphur trioxide or sulphuric anhydride occurs in white silky tufts. It is very volatile, and if a bottle containing it be opened, its vapor comes in contact with the moist air and forms thick white fumes. If a small quantity of this substance be thrown into water, it immediately disappears and combines with that liquid. So great is the energy of the reaction that the heat disengaged gives rise to the production of steam, which, being suddenly formed and condensed in the midst of the cooler liquid mass, causes a peculiar noise, a sort of hissing. When the sulphuric oxide is dissolved in the water, the solution presents a very acid reaction. It contains sulphuric acid, the compound long known under the name of oil of vitriol. This reaction may be represented in the abbreviated lan- guage of the notation, which expresses the atomic composition of bodies with so much precision. The formula of sulphuric anhydride or sulphur trioxide is SO 3 ; that of water is H 2 0. Then if sulphuric acid result from the addition of all of the elements of water to those of sulphuric trioxide, it should contain SO 3 + H 2 = H 2 S0 4 . This is a chemical equation, and it is seen that the two terms of the first member express the atomic composition of the reacting bodies, while the single term of the second mem- ber gives the atomic composition of the product of the reac- tion. Such an equation accounts for all of the atoms, and CHEMICAL NOMENCLATURE AND NOTATION. 43 the sum of. all of the atoms written in the first member must exactly balance the sum of all those written in the second. There is a compound known as nitric anhydride, or nitrogen pentoxide. It results from the combination of nitrogen with oxygen, and its atomic composition is represented by the formula N 2 5 . In combining with water it forms nitric acid. N 2 5 + H 2 = 2(HN0 3 ). Nitric anhydride. Water. Nitric acid. (1 molecule.) (2 molecules.) These examples, which could be indefinitely multiplied, give an idea of the constitution of the ternary oxygen acids. The rules which have been already given for the nomenclature of the oxides apply also to the nomenclature of the acids. We have phosphorous acid and phosphoric acid. iZ^po-phosphor- ous acid is an acid of phosphorus containing still less oxygen than phosphorous acid. (Hypo, literally, under.) The metallic hydrates result from the combination of water with the metallic oxides. It is well known that when quick- lime is sprinkled with water it becomes heated, increases in volume, cracks into pieces, and is finally converted into a white, impalpable powder, which constitutes slaked lime, — a com- pound of the lime with water. Lime is the oxide of a metal called calcium. In combining with water it forms a ternary compound of calcium, hydrogen, and oxygen ; this is hydrate of calcium, or, as it is commonly called, hydrate of lime. CaO + H 2 =± CaH 2 2 . Calcium oxide. Water. Calcium hydrate. (Lime.) The metal potassium, the radical of potash, forms with oxy- gen a compound which contains two atoms of potassium com- bined with one atom of oxygen. The composition of this body is then represented by the formula K 2 0. It combines with water with great energy, and forms with it potassium hydrate or caustic potassa. K 2 + H 2 = 2KOH. Potassium oxide. Water. Potassium hydrate. (2 molecules.) Oxygen Salts. — The oxygen salts result from the action of the oxygen acids upon the oxides or upon the metallic hydrates. Experiment. — The formation of a salt may be illustrated by a modification of one of the experiments already described. A quantity of dilute nitric acid is slightly reddened by a so- 44 ELEMENTS OF MODERN CHEMISTRY. lution of blue litmus or syrup of violets. 1 Some dilute solution of caustic potassa is also treated with the same coloring matter ; the syrup of violets will assume a green color, or blue litmus will remain unchanged. The latter liquid, which is alkaline, is now added drop by drop to the acid, until the red color disappears, giving place to the violet color of the syrup of violets or the blue of the litmus. The liquid is now neutral. It contains neither free nitric acid nor free potassa. Both have disappeared as such ; they are reciprocally neutralized, the first having lost its acid taste, the second its extreme caustic properties. They have produced a body having a saline, cooling taste, and exerting no action upon vegetable colors. It is a neutral salt which has been formed. It is called potassium nitrate. It is the nitre or saltpetre of the ancient chemists. It is not, however, the sole product of the reaction. Water is formed at the same time, and if we would comprehend the entire phenomenon, the reaction will be expressed by the following equation : HNO 3 + KOH = KNO 3 + H 2 0. Nitric acid. Potassium hydrate. Potassium nitrate. Water. It is seen that the salt, potassium nitrate, is a ternary com- pound, similar in constitution to nitric acid itself. On com- paring the two formulae, HNO 3 nitric acid, KNO 3 potassium nitrate, it is seen that they only differ by the K in the second occupy- ing the place held by the H in the first. It may then be said that potassium nitrate represents in a manner nitric acid in which the hydrogen has been replaced by an equivalent quan- tity of potassium. This definition applies to the entire class of compounds under consideration. A salt represents an acid of which the hydrogen has been wholly or partially replaced by an equivalent quantity of metal. The acids constitute the salts of hydrogen : they are neu- tralized when this hydrogen is replaced by a metal. The acid or hydrogen salt differs from the metallic salt. From a theoretic point of view, an acid is a compound of the same order as a salt, and if these bodies are separated by such great differences 1 An infusion of common purple cabbage may be substituted for syrup of violets. CHEMICAL NOMENCLATURE AND NOTATION. 45 of properties, this is due to the nature of the base. What a difference, indeed, between hydrogen gas and the metals ! We have studied the formation of a salt by the action of an acid, nitric acid, upon a metallic hydrate, potassium hydrate. The anhydrous oxides may also form salts by reacting with the acids. Experiment. — Yellow oxide of lead, when digested with dilute sulphuric acid, is converted into a white, insoluble pow- der, which is lead sulphate. This is a salt, but it is not the only product of the reaction, for water is formed at the same time. H 2 SO + PbO = PbSO + H 2 0. Sulphuric acid. Lead oxide. Lead sulphate. Water. Lastly, among other modes of formation of salts, there is one which is worthy of interest, and of which an idea may be ob- tained from the following example. Sulphur trioxide, or sulphuric anhydride, combines energetic- ally with barium oxide or baryta, and from the union of all of the elements of both compounds there results a salt, — barium sulphate. SO 3 + BaO = BaO,S0 3 or BaSO. Sulphur trioxide. Barium oxide. Barium sulphate. But, whether this salt be formed under these conditions, or by the action of sulphuric acid, its composition only differs from that of the latter acid by the substitution of Ba for H 2 . H 2 SO sulphuric acid, hydrogen sulphate, BaSO 4 barium sulphate. The reactions which we have just studied, and which indicate the principal methods of the formation of salts, are sufficient to make clear the definition before given, that salts are derived from acids by the substitution of a metal for hydrogen. The nomen- clature defines and preserves these relations. To distinguish the different salts of the same acid, the name of the metal is placed first, and this is follow#d by the name of the acid, which is but slightly changed, — ic is changed to ate, and oils to tie. Thus Sulphuric acid gives sulphates. Nitric acid " nitrates. Perchloric acid " perchlorates. Sulphurous acid " sulphites. Hyposulphurous acid " hyposulphites. These generic names follow the names of the metals which enter into the composition of the salts, and which specify them, as it were. Thus, we have : 46 ELEMENTS OF MODERN CHEMISTRY. Potassium sulphate, copper sulphate, lead sulphate, etc. ; Sodium sulphite ; Potassium nitrate, barium nitrate, silver nitrate, etc. But we know that a single metal may form several com- pounds with oxygen. In reacting upon the same acid these different oxides give rise to the formation of different salts. Thus, two different sulphates of copper are obtained, as sul- phuric acid is caused to react with cuprous oxide, or with cupric oxide. H 2 SO + Cu 2 = Cu 2 S0 4 + H 2 0. Sulphuric acid. Cuprous oxide. Cuprous sulphate. Water. IPSO + CuO = CuSO + H 2 0. Cupric oxide. Cupric sulphate. It is easy to distinguish these two salts from each other by using the adjectives cuprous and cupric before the substantive sulphate. Thus, we have mercuroits and mercuric sulphates ; ferrous and ferric sulphates. The preceding considerations will give an idea, sufficient for the time being, of the constitution and the nomenclature of salts. Their further exposition will be completed farther on. Nomenclature of Non-Oxygenized Compounds. — The non metallic elements other than oxygen can combine among them- selves or with the metals. Such compounds are designated by the name of one of the elements followed by the abbreviated name of the other terminating in ide. Thus, the compounds of the metals with chlorine, bromine, iodine, sulphur, arsenic, and carbon are called chlorides, bromides, iodides, sulphides, arsenides, carbides. We thus have sodium chloride, potassium bromide, lead iodide, zinc arsenide, iron carbide. The termi- nation uret was formerly used in place of ide. But a non-metallic body, such as chlorine or sulphur, can, like oxygen, form several compounds with the same metal. In these compounds 1 atom of metal ma^be united with 1 or 2 atoms of sulphur, or with 1, 3, or 5 atoms of chlorine, or again with 2 or 4 atoms of chlorine. Such atomic composition is expressed by the following names and symbols : Iron monosulphide FeS. Iron bisulphide FeS 2 . Phosphorus bichloride ......... PCI 3 . Phosphorus ^eHtachloride PCI 5 . Tin bichloride SnCl 2 . Tin tetrachloride SnCl 4 . Antimony trichloride SbCl 3 . Antimony pentachlovide SbCl 5 . CHEMICAL NOMENCLATURE AND NOTATION. 47 The names thus express precisely the number of atoms of the second element in combination with 1 atom of the first. The compounds of chlorine, bromine, iodine, and several other elements with hydrogen are acids ; they readily exchange their hydrogen for a metal, so forming compounds that are analogous to the oxygen salts, and which constitute the haloid salts of Berzelius. Experiment: — The compound of chlorine with hydrogen is hydrochloric acid ; it is a gas, and dissolves in water, forming a fuming, strongly-acid liquid. When it is carefully poured into a concentrated solution of caustic potassa there appears a white precipitate, formed of little crystals and presenting the appearance of a salt. This is potassium chloride. It is formed according to the following reaction, and its formation is at- tended by the production of heat : HC1 + KOH = KC1 + H 2 0. Hydrochloric Potassium Potassium Water, acid. hydrate. chloride. The hydrogen compounds of bromine, iodine, fluorine, sul- phur, etc., possess analogous properties. They are called Hydrobromic acid HBr. Hydriodic acid HI. Hydrofluoric acid HF1. Sulphydric acid or sulphuretted hydrogen . . . H 2 S. The chlorides may combine among themselves. It is the same with the bromides, iodides, sulphides, etc. If a solution of potassium chloride be poured into a concentrated solution of platinic chloride, a yellow precipitate, constituting a com- pound of the two chlorides, is formed. It is the double chlo- ride of platinum and potassium, or potassium platino-chloride. There exist, likewise, double sulphides formed by the union of two simple sulphides. Such compounds constitute what are called sulphur salts. Alloys and Amalgams. — The compounds of the metals with each other are called alloys. Amalgams are the alloys of mercury, that is, the compounds of this liquid metal with another metal. 48 ELEMENTS OF MODERN CHEMISTRY. HYDROGEN. Density compared to air 0.0693. Atomic weight (1 volume taken as unity) H = 1. This body was discovered in 1766 by Cavendish. It is ono of the elements of water, hence its name, which was given by Lavoisier. Experiments. — 1 . A small piece of sodium is passed under a tube filled with mercury and inverted on the mercury-trough ; it rises to the top of the jar, and some water is then introduced (Fig. 9). As soon as the water touches the sodium a brisk disengagement of gas is ob- served ; this is hydrogen, produced by the decomposition of the water, and the reaction by which it is set at liberty is expressed in the following §§ equation : 2H 2 + Na 2 = 2NaOH + H 2 . FlG. 9. Water. Sodium, Sodium Hydrogen. hydrate. If the tube be now inverted and a lighted taper be rapidly brought to the orifice, the gas will burn with a pale flame. A piece of reddened litmus-paper plunged into the water con- tained in the tube has its blue color at once restored, and this change is produced by the sodium hydrate or caustic soda dissolved in the water. 2. Some thin sheet-zinc cut into small pieces is introduced into a rather large test-jar (Fig. 10), and some hydrochloric acid is then poured upon it. A rapid effervescence imme- diately takes place, and if a lighted taper be brought to the mouth of the jar, the stream of hydrogen evolved takes fire. This hydrogen is produced by the decomposition of the hydro- chloric acid by the zinc, which is converted into chloride. 2HC1 + Zn Hydrochloric Zinc. acid. (2 molecules.) = ZnCP + H 2 . Zinc Hydrogen, chloride. HYDROGEN. 49 Preparation. — A reaction analogous to the preceding is turned to advantage for the preparation of large quantities of hydrogen. Dilute sulphuric acid is de- composed by zinc. A two-necked bot- tle is about half filled with water, and gran- ulated zinc, or sheet- zinc cut into small pieces, is introduced; sulphuric acid is then added in small quan- tities by the aid of a funnel-tube which dips under the surface of the water (Fig. 11). The reaction at once commences, and hydrogen is disen- gaged. When the air at first contained in the bottle has been entirely expelled, the gas may be collected in jars or bottles filled with water and in- verted on the pneu- matic trough. In this reaction the zinc disappears and dissolves in the liquid with evolution of heat, and it often happens, if the liquid be sufficiently concentrated, that colorless crystals of zinc sulphate are formed on cooling. This salt and hydrogen are the sole products of the reaction of pure zinc upon sulphuric acid largely diluted with water. IPSO + Zn = ZnSO -f H 2 . Sulphuric acid. Zinc. Zinc sulphate. Hydrogen. Physical Properties. — Hydrogen is a colorless gas, and when pure has neither taste nor odor. It is the lightest of all known bodies, its density compared to air being 0.0693 ; that is, if one volume of air weigh 1, one volume of hydrogen, measured under the same conditions of temperature and pres- Fig. 10. 50 ELEMENTS OF MODERN CHEMISTRY. sure, weighs only 0.0693. Hydrogen is then 14.44 time lighter than air. The weight of one litre of hydrogen at 0° Fia.-ll. and under the normal pressure is 0.0895 gramme. Instead of comparing the densities of gases and vapors to that of air, it is preferable to compare them to that of hydrogen taken as unity (page 30). Hydrogen passes with great facility through vegetable and animal membranes, and through porous substances that are im- pervious to water. It cannot be kept in a glass vessel that presents the least crack, for it would pass through much more readily than air. This property is expressed by saying that hy- drogen is very diffusible. According to Magnus, it is the only gas gifted with an appreciable conductibility for heat ; in this respect it is related to the metals. From a consideration of its physical properties and its combined chemical properties, Fara- day long ago announced the metallic character of hydrogen. This theoretic prediction has recently received a remarkable confirmation. Hydrogen, which was long regarded as incoerci- ble, has been liquefied and even solidified. Cailletet, of Paris, obtained it in the form of a cloud by exposing it to a pressure of 300 atmospheres at a temperature of — 29° and then sud- denly relieving the pressure. Raoul Pictet, of Geneva, has advanced still further. By an apparatus of incomparable power, he subjected it to a temperature of — 140° under a pressure of 650 atmospheres. Under these circumstances, hy- drogen was liquefied, and was visible as a steel-blue, liquid jet HYDROGEN. 51 at the moment of its projection from the tube in which it was condensed. The cold produced by its passage from the liquid to the gaseous state was so great that a portion of the liquid was solidified, and fell to the ground in metallic grains, producing a shrill sound as it struck the floor. Another portion of the solidified hydrogen remained in the tube during several minutes. Among the physical properties of hydrogen may be men- tioned the remarkable faculty it possesses of passing through plates of iron or platinum at high temperatures (H. Sainte- Claire Deville and Troost). It is well known that it rapidly passes through thin sheets of caoutchouc, According to Graham, this property is related to that possessed by certain solid bodies, and particularly metals, such as iron, platinum, and palladium, of absorbing hydrogen gas. This chemist designated the phenomenon by the name, occlusion of hydro- gen by the metals. Palladium especially is distinguished by the energy with which it absorbs hydrogen. It can condense in its pores nine hundred times its own volume of the gas. A palladium wire may be charged with hydrogen by arranging it in a voltameter so that it constitutes the negative pole of a small battery, the positive pole being a stout platinum wire. When the current passes, the hydrogen set at liberty at the negative pole (see page 71) is condensed in the palladium. This metal undergoes at the same time a remarkable change. Its volume augments and its density diminishes, but its metallic lustre remains, as do also, to a certain degree, its tenacity and con- ductibility for electricity ; besides this it becomes magnetic. There is thus formed a sort of alloy of palladium and hydro- gen, containing about 20 volumes of palladium to 1 volume of hydrogen reduced to the solid state. The density of this solid hydrogen compared to that of water, according to the determi- nations of Troost and Hautefeuille, is 0.62 : it is a little greater than that of lithium. Graham insisted upon the metallic char- acter of hydrogen thus alloyed with palladium, and proposed for it the name hydrogenium. Chemical Properties. — Hydrogen is a combustible gas, and the product of its combustion is water. Experiments. — 1. A lighted taper may be thrust into a rather wide tube filled with hydrogen (Fig. 14). The gas takes fire on contact with the flame, but the taper is extinguished in the atmosphere of hydrogen. It may be relighted by withdrawing it through the burning gas. The experiment shows at the 52 ELEMENTS OF MODERN CHEMISTRY. same time that hydrogen is inflammable and that it is incapa- ble of supporting combustion itself. 2. A gas-bottle, A (Fig. 12), is arranged for the preparation of hydrogen, and water, zinc, and sulphuric acid are intro- Fig. 12. duced. The hydrogen evolved is made to traverse the tube CB, which is filled with fragments of chloride of calcium ; after having been dried by this substance, which is very avid of water, the gas escapes by the tube a, the end of which is drawn out to a point. The jet of gas is lighted, and burns with a pale flame. A bell-jar, D, is now held over the burning jet, and the sides of the glass soon be- come covered with dew, the drops of which unite and run down to the edge of the jar. This is water, and it is formed by the combustion of the hydrogen ; that is, by its combination with the oxygen of the air. 3. A jet of hydrogen may be lighted by holding in it a tuft of asbestos which has been dipped in platinum black, that is, finely-divided platinum. The con- densation of the hydrogen in the pores of the finely-divided metal is so rapid that the platinum becomes heated to redness, and then ignites the gas. HYDROGEN. 53 4. A tube filled with hydrogen may be held in the vertical position, bottom upwards, without the gas escaping rapidly by the inferior opening. If the tube be inclined, the hydrogen overflows and escapes upwards through the air. It may then be received in a second tube held vertically above the first, which is inclined more and more (Fig. 13). The passage of the gas into the upper tube can be demonstrated by approach- ing to the latter a lighted taper, when the hydrogen will burn with a faint explosion. Before igniting or collecting hydrogen escaping from a gen- erator, it should always be ascertained that the whole of the air has been expelled, otherwise dangerous explosions may result. 5. The explosions may take place with the production of a harmonious sound, if they are made to succeed each other Fig. 14. Fig. 15. rapidly and at regular intervals. These conditions are realized by burning a small jet of hydrogen in a somewhat large tube (Fig. 15). The flame is drawn away from the jet by the draft in the tube, but immediately recedes as the ascending hydro- 5* 54 ELEMENTS OF MODERN CHEMISTRY. gen gas mixes with the air, at the same time producing a faint explosion, and the rapid succession of these explosions produces a musical tone. The hydrogen condensed in palladium appears to have chem- ical properties more active than those of gaseous hydrogen (Graham). It combines in the dark and at ordinary tempera- tures with iodine and chlorine ; the direct union of ordinary hydrogen with iodine is impossible, and with chlorine it takes place at the common temperature only under the influence of light. Hydrogen will not support respiration, but it is not poisonous. OXYGEN. Density compared to air . . . . Density compared to hydrogen Atomic weight . 1.1056. . 16. = 16. Oxygen was discovered, in 1774, by Priestley, who obtained it by heating red precipitate or mercuric oxide. Experiment. — A tube, a (Fig. 16), contains a concentrated so- lution of the dis- infecting powder known as chlo- ride of lime ; a small quantity of the peroxide of cobalt, a com- pound of oxygen with the metal cobalt, is then introduced, and the whole is gen- tly heated. A brisk efferves- cence takes place, and if a match which has been just blown out and still presents a spark of fire OXYGEN. 55 be thrust into the mouth of the tube, it is instantly relighted, and burns with great brilliancy. This effect is due to a gas which is being disengaged, and which, to use the expression of Lavoisier, is eminently fitted to support combustion. It is the gas to which that great chemist gave the name oxygen. It is produced by a very simple reaction. Under the influence of the peroxide of cobalt, the calcium hypochlorite which we may consider is contained in the chloride of lime is converted into calcium chloride and oxygen. CaCPO 2 = CaCl 2 + O 2 . Calcium hypochlorite. Calcium chloride. Oxygen. Preparation. — Large quantities of oxygen may be prepared by a process analogous to the preceding. When potassium chlorate is heated, it is converted into potassium chloride, and gives up all of its oxygen. To facilitate this decomposition, a small quantity of manganese dioxide is mixed with the chlo- rate. The part taken by the manganese dioxide is analogous to that of the cobalt peroxide in the preceding reaction, and is not thoroughly understood ; it is probable that it is converted into an unstable higher oxide, continually formed and decom- posed during the reaction. If the temperature be sufficiently elevated, the decomposition of the chlorate is complete, and takes place according to the following equation : 2KC10 3 = 2KC1 + 20 2 Potassium chlorate. Potassium chloride. Oxygen. The operation may be conducted in a glass retort, which should be about one-third filled with the mixture of chlorate and dioxide ; to the beak of the retort is adapted a delivery- tube, which dips under the surface of the water or mercury in the trough (Fig. 17). The retort is then heated by an alco- hol or gas lamp, and the chlorate melts and disengages its, oxy- gen with effervescence. Towards the close of the operation, the heat is increased in order to decompose into potassium chloride and oxygen any potassium perchlorate that may have been formed by the union of a portion of the evolved oxygen with some of the chlorate. To make larger quantities of oxygen for filling the gas- holders of laboratories, etc., a mixture of potassium chlorate and manganese dioxide is heated in a sheet-iron or copper retort. At a bright red heat manganese dioxide gives up a third 56 ELEMENTS OF MODERN CHEMISTRY. of its oxygen, and is converted into the red oxide of manga- nese. 3Mn0 2 = Mn 3 4 + O 2 . Manganese dioxide. Red oxide of manganese. Oxygen. Oxygen can be cheaply manufactured on the large scale by the process of Tessie du Mottay. This depends upon the for- mation of sodium manganate by the action of air upon a heated Fig. 17. mixture of manganese dioxide and caustic soda, and the subse- quent decomposition of this manganate at about 450° by a current of steam, a decomposition which again sets at liberty the oxygen absorbed by the manganese dioxide to form sodium manganate. The operation is continuous. Physical Properties. — Oxygen is a colorless, odorless, taste- less gas ; it is a little heavier than the air. If one volume of hydrogen weighs 1, the same volume of oxygen, measured under the same conditions of temperature and pressure, weighs 16. This is expressed by saying that the density of oxygen compared to that of hydrogen is 16. A litre of oxygen weighs 1.437 gr. at 0° and under the normal pressure. Until lately oxygen had been considered as a permanent gas. By subjecting it to a pressure of 300 atmospheres and a tem- perature of — 29°, and then suddenly relieving the pressure, Cailletet obtained it in the form of a cloud. Raoul Pictet liquefied it by a pressure of 300 atmospheres and a temperature OXYGEN. 57 of — 140°. He attributes to liquid oxygen a density near that of water, — about 0.9787. Oxygen is but slightly soluble in water. A litre of water dissolves 0.041 litre, or 41 cubic centimetres, at 0° ; 0.032 litre at 10° ; 0.028 litre at 20°. The fractions 0.041, 0.032, 0.028, represent the coefficients of solubility of oxygen in water at the temperatures of 0°, 10°, and 20°. Chemical Properties. — Oxygen combines directly with most of the other elements, and the union often takes place with such energy that there results a great evolution of luminous heat : it gives rise to the phenomenon of combustion. Experiments. — A cone of charcoal of which the point is red- hot is plunged 'into a globe filled with oxygen (Fig. 18), and immediately combustion takes place with great brilliancy. The oxygen combines with the carbon, forming a colorless gas. which is carbonic acid gas. In like manner, sulphur and phosphorus burn in oxygen, the first producing a colorless, irritating gas known as sulphurous Fig. 18. Fig. 19. acid gas, the second emitting thick fumes, which condense in white flakes of phosphoric oxide. A watch-spring may be drawn out into a spiral, and a small piece of tinder attached to one end ; after igniting the tinder, the spiral is rapidly plunged into a bell-jar filled with oxygen, and resting upon a plate containing a layer of water (Fig. 19). The tinder burns energetically, and heats the end of the spiral to redness ; then the combustion of the iron itself commences, and goes on with unparalleled brilliancy, and a production of c* 58 ELEMENTS OF MODERN CHEMISTRY. heat so intense that the oxide of iron formed melts and falls in incandescent drops, which fuse themselves into the sur- face of the plate, even after having traversed the layer of water. In the same manner, the combustion of the metal magnesium may be effected in oxygen ; it takes place with dazzling splen- dor, and gives rise to the production of a white powder, which is magnesia, or magnesium oxide. The preceding experiments are examples of rapid combus- tion. We have seen that solid substances, such as charcoal, iron, and magnesium, beconfe incandescent in combining with oxygen : it is the phenomenon of fire. We have also seen that vapors, like those of sulphur and phosphorus, become lumi- nous in their combination with oxygen : this is the phenome- non of flame. But fire and flame are not necessary concomitants of the union of bodies with oxygen. It is true that such union is always accompanied by the production of heat ; but often this heat is not luminous ; sometimes it is imperceptible to our senses. Thus iron, the combination of which with oxygen at a red heat gives rise to such a brilliant combustion, may unite with this gas at ordinary temperatures under the influence of moisture. There is thus formed ferric hydrate, which consti- tutes rust. This oxidation of the iron, which takes place slowly, pro- duces a feeble disengagement of heat, which is, however, imme- diately dissipated. Such phenomena of oxidation are designated by the name slow combustion. The term combustion would then be synonymous with oxi- dation did we not know, on the other hand, that all chemical combination gives rise to the production of heat. If copper be thrown into boiling sulphur, a vivid incandescence is pro- duced, due to the union of the two bodies. Likewise antimony and arsenic, when projected in fine powder into an atmosphere of chlorine, unite with the latter body, producing a brilliant combustion. It is seen that in these cases the production of luminous heat indicates an energetic combination, but not an oxidation. Oxygen is one of the elements of the air ; it is the cause and the agent of all combustion, of all oxidation which takes place in our atmosphere ; and the oxygen fixes itself upon OXYGEN. 59 burning bodies in such a manner that the product of the com- bustion contains all of the matter of the combustible body and all of the matter of the oxygen. This is one of the fundamental truths of chemistry, and for its discovery not less than a cen- tury and a half of work was required. The glory of the dis- covery belongs to Lavoisier. His researches on combustion revealed to him the true nature of the. phenomena of respiration. The respiration of animals is a slow combustion ; it is the source of animal heat. It gives rise to the formation of carbonic acid gas and water, products of the complete oxidation through which must pass those organic matters in the economy which no longer serve the purposes of life, and all of which contain carbon and hydrogen. The production of carbonic acid gas by the act of respira- tion is easy to prove. It is only necessary to blow, by the aid of a tube, the air contained in the lungs through clear lime- water, which soon becomes milky from the formation of insolu- ble carbonate of lime. An annular jet of hydrogen through which a jet of oxygen is forced constitutes what is known as the oxyhydrogen blow- pipe, and is one of the most intense sources of heat known. Platinum melts before it like wax. and iron and other combus- tible metals burn brilliantly when introduced into its flame. The flame of the oxyhydrogen blowpipe gives but little light. but when it is projected upon a piece of lime, the latter becomes heated to dazzling incandescence, constituting the Drummond or calcium light. OZONE, OR OXYGEN PEROXIDE. The repeated discharges of a good electric machine develop a peculiar odor. This is due to the production of a body which was discovered by Schonbein in 1840, and which he named ozone (from o^io, I smell). Experiment. — Some potassium permanganate is mixed with barium dioxide in a mortar, the mixture transferred to a flask, and moistened with sulphuric acid. The characteristic odor of ozone immediately becomes perceptible, and a moistened paper, impregnated with potassium iodide and starch and held in the neck of the flask, immediately assumes a blue color. 1 This effect is caused by the ozone evolved. 1 Such a paper is called ozonoscopic. It is colored blue by the combina- 60 ELEMENTS OF MODERN CHEMISTRY. This remarkable body is also formed under the following circumstances. 1 . By the passage of electric sparks through oxygen. — It is sufficient to pass a series of electric sparks through oxygen contained in a tube above a solu- tion of iodide of potassium and starch, in order to produce the blue color caused by the ozone (Fig. 20). It has been noticed that the largest quantity of ozone is pro- duced when the passage of the electricity through oxygen is ef- fected, not by sparks, but by non- luminous or obscure discharges (Andrews and Tait, de Babo). Dry and pure oxygen can be con- verted into ozone in this manner. But this conversion only takes place partially, the ozone formed remaining mixed with a large excess of oxygen. A contraction takes place at the moment the oxygen is transformed into ozone. These experiments prove that ozone is condensed oxygen (Andrews and Tait, de Babo, Soret). The proportion of ozone formed is increased when the oxygen is cooled. At — 23°, a mixture of oxygen and ozone, contain- ing 17.6 per cent, of the latter, may be obtained, under normal atmospheric pressures. (Hautefeuille and Chappuis.) 2. By the electrolysis of water, — When acidulated water is decomposed by the battery current, the oxygen which is disen- gaged at the positive pole contains small quantities of ozone, and the proportion of the latter may be increased by adding a quantity of sulphuric or chromic acid to the water. 3. During slow oxidation. — Some sticks of cleanly-scraped tion of the starch with the iodine set at liberty by the ozone. According to Houzeau, it is preferable to use a delicate, wine-colored litmus-paper, one-half of which is impregnated with potassium iodide. Ozone will change the color of this half to blue, for, in decomposing the potassium iodide, it forms potassium hydrate, and this restores the blue color to the litmus. Under these conditions, the other half of the paper undergoes no change in color, while it would be colored red by acid vapors, or blue by ammonia. Fm. 20. OZONE. 61 phosphorus are introduced into a bottle containing enough water to just about half immerse them, and the whole is agi- tated from time to time. In a short time the air in the bottle will be charged with a small quantity of ozone. According to Schbnbein. who observed these facts, ozone is produced during all slow combustions. Thus, when oil of tur- pentine is exposed to the air under the influence of sunlight, it is slowly oxidized, and in becoming resinified, it becomes at the same time charged with a small quantity of ozone, which dissolves in it. 4. By the decomposition of barium dioxide by sulphuric acid. — This decomposition gives rise to barium sulphate and oxygen charged with a small quantity of ozone (Houzeau). H 2 SO + BaO 2 = BaSO* + H'0 + The barium dioxide is introduced in small portions into sul- phuric acid contained in a flask, to the neck of which is fitted a glass stopper pierced for the passage of the delivery-tube, which is ground in (Fig. 21). Fig. 21. Properties of Ozone. — Ozone possesses an intense and pecu- liar odor. Hautefeuille and Chappuis have liquefied it by al- lowing the strongly compressed gas to expand suddenly : the liquid is sky-blue, and the compressed gas has the same color, the tint being deeper as the temperature is lowered or the press- ure increased. At a temperature of 290° it is reconverted into ordinary oxygen, the volume of which is greater than that occupied by the ozone. It is then certainly condensed oxygen. It has energetic oxidizing properties ; it even oxidizes bodies 6 62 ELEMENTS OF MODERN CHEMISTRY. which possess only feeble affinities for oxygen. In the presence of alkalies it combines with nitrogen, converting it into nitric acid, which combines with the alkali. It oxidizes silver at ordinary temperatures, converting it iuto the dioxide Ag 2 2 . It instantly decomposes potassium iodide, setting free the iodine. It is insoluble in water, but is entirely soluble in oil of turpentine and oil of cinnamon, both of which it slowly oxidizes. It oxidizes and destroys the greater number of organic substances. In most of these oxidations only a third part of the oxygen contained in ozone is active ; the other two- thirds become free as ordinary oxygen, the volume of which is exactly equal to that primitively occupied by the ozone. Hence it is concluded that 3 volumes of oxygen are con- densed into 2 volumes by their conversion into ozone, and if ordinary oxygen be the oxide of oxygen 00, ozone will be oxy- gen peroxide OO 2 (Odling). 0=0 = 2 vol. oxygen. / \ = 2 vol. ozone. 0—0 This conclusion of Odling's concerning the nature of ozone, has been verified by the determination of the density of this body. Soret has established that when ozone diluted with oxy- gen is absorbed by oil of turpentine or oil of cinnamon, there is a diminution of volume sensibly double the increase of volume noticed on subjecting the same gas to the action of heat. He naturally concludes that the density of ozone is one and a half times that of oxygen, or 1.658. These figures have been confirmed by direct experiments upon the rapidity of diffusion of ozone. It has been shown by the researches of Graham that when diffusion between two gases takes place through an opening, without the interposition of a diaphragm, the rapidity of diffusion is inversely as the square roots of the densities of the gases. Soret has demonstrated that the rapidity of diffusion of ozone is notably greater than that of chlorine, and very near but somewhat less than that of car- bonic acid. It results that its density is less than that of chlorine, and a little greater than that of carbonic acid, which is 1.525 ; this confirms the density 1.658. An important property of ozone is its reaction with hydrogen dioxide, yielding ordinary oxygen and water. OO 2 + H 2 2 = 2(00) + H 2 Ozone. Hydrogen dioxide. Ordinary oxygen. Water. THE ATMOSPHERE. 63 ATMOSPHERIC AIR. The air is a mixture of oxygen and nitrogen. It also con- tains traces of carbonic acid gas and a variable proportion of vapor of water. Its composition was established by Lavoisier by an experi- ment that has become celebrated. Having heated mercury in a limited quantity of air to a temperature near its boiling-point for several days, he observed the formation of a red powder, a combination of the mercury with oxygen. On the termination of the experiment, he found that the volume of the air had diminished about one-sixth. He carefully collected the oxide formed, introduced it into a small retort, and heated it to red- ness. He thus obtained a gas " eminently qualified to support combustion and respiration," and the volume of which was sensibly equal to that of the gas that had disappeared. This gas he named oxygen. He mixed it with the irrespirable resi- due from the first experiment, which would not support com- bustion, and so reconstituted atmospheric air. The composition of the latter was thus established by analysis and synthesis. This experiment was infinitely more instructive than that undertaken by Scheele at about the same time. The great Swedish chemist only absorbed the oxygen of the air by the alkaline sulphides. The nitro- gen remained as residue, but the oxygen combined with the sulphide could not be again separated. However, neither one nor the other of these methods could give the exact propor- tion according to which the oxygen and nitrogen are mixed in the atmosphere. This has been deduced from the follow- ing experiments. Experiments. — 1. Into a small bent tube closed at the upper end, filled with mercury and inverted in a vessel of the same metal, are passed 100 volumes of air (Fig. 22). A small piece of phosphorus is then introduced and brought into the upper limb, where it is heated by the aid of a spirit- lamp. It takes fire, and in burning consumes all of the Fig. 22. 64 ELEMENTS OF MODERN CHEMISTRY. oxygen of the 100 volumes of air. The operation has termi- nated when the flame of the phosphorus vapor has extended down to the column of mercury. The residual gas is then allowed to cool, and on being measured is found to be reduced to 79 volumes. It is nitrogen. 2. The absorption of oxygen by phosphorus will take place in the cold, if a long stick of this substance be in- troduced into a determined volume of air contained in a graduated tube. The experiment requires several hours, and gives the same result as the preceding. 3. 100 volumes of air are measured into a graduated tube on the mercury-trough. A concentrated solution of potassium hydrate is introduced, and then some pyro- gallic acid, a white, crystalline substance employed in photography; the whole is then rapidly agitated, the extremity of the tube being closed by the thumb. The alkaline solution is immediately blackened by the destruction of the pyrogallic acid. All of the oxygen is rapidly absorbed, and when the tube is opened, under the surface of the mercury, the 100 volumes of air are found reduced to about 79 volumes. Fig. 23. Fig. 24. 4. There is another method capable of still greater precision : Fig. 23 represents a Bunsen's eudiometer ; it is a stout glass tube about 60 centimetres long and 2 centimetres in diameter. Two platinum wires are hermetically sealed into the upper ex- tremity through the whole thickness of the glass. Each ter- THE ATMOSPHERE. 65 urinates exteriorly in a small loop, and on the interior follows the curve of the end nearly to the centre, so as to leave an interval of about 1 centimetre between the extremities of the two wires. The tube is graduated in millimetres, and the ca- pacity of each division is known. It is filled with mercury and inverted upon a small trough. 100 volumes of air and 100 volumes of hydrogen are then introduced. One of the plati- num loops is then put into communication with an electrical conductor, and the other with the earth, and a spark is passed through the mixture (Fig. 24). A flash appears in the tube, and all of the oxygen of the 100 volumes of air has combined with hydrogen to form water. There thus results a vacuum, which is filled by the mercury, and in place of 200 volumes of gas introduced into the eudiometer, we find, all corrections being made, only 137.21 volumes of a mixture of hydrogen and nitrogen. 62.79 volumes have then disappeared to form water, and this water contains all of the oxygen contained in 100 volumes of air ; as each volume of this oxygen must consume 2 vol- umes of hydrogen, it follows that the 62.79 volumes which have disappeared must have contained 20.93 volumes of oxygen and 41.86 volumes of hydrogen. Hence the 100 volumes of air introduced into the eudiom- eter contained 20.93 volumes of oxygen and 79.07 volumes of nitrogen. Such is the composition of the air by volume. As nitrogen is lighter than oxygen, these volumetric relations do not express the composition of the air by weight. This was determined very exactly by Dumas and Boussingault in the following manner. A globe, A (Fig. 25), having a capacity of 15 or 20 litres, and fitted with a brass cap and stop-cock, R", by which it may be connected with an air-pump, is joined to a hard glass tube, BB', having a stop-cock at each end, R and R/, and filled with metallic copper. The air is exhausted from the globe and tube, and the weight of each is then accurately determined. The tube BB' is placed in a combustion-furnace, and by its extremity B' is connected with the tubes K, I, H, Gr, F, E. D, C. The tube with bulbs C contains a solution of caustic po- tassa ; the tubes D and E are filled with pumice-stone impreg- nated with caustic potassa, and the tubes F and G with frag- ments of solid caustic potassa ; the bulbs H contain sulphuric 6* 66 ELEMENTS OF MODERN CHEMISTRY. acid, and the last tubes, I and K, are filled with fragments of pumice-stone saturated with sulphuric acid. The potassa serves to remove from the air the small quantity of carbonic acid gas which it contains, and the sul- phuric acid absorbs the moisture. The tube filled with copper is now heated to redness, its stop-cocks being open, and the stop-cock of the globe is gradually opened. Air immediately enters, but it is first obliged to tra- verse the series of tubes, where it is deprived of its carbonic acid gas and vapor of water, and also the tube filled with incandescent cop- per, which absorbs the oxygen. It is then pure nitrogen which, enters the globe. The experi- ment has terminated when the tension of the gas in the globe is equal to the exterior pressure, that is, when no more air enters. The stop- cock R" is now closed. The tube and globe are allowed to cool, and are weighed separately. The increase in weight of the globe gives the weight of the nitrogen which has entered. The increase in weight of the tube, which was first weighed exhausted of air, gives the weight of the oxygen which has THE ATMOSPHERE. 67 combined with the copper, plus the weight of the nitrogen remaining in the tube at the close of the experiment. The weight of this nitrogen is determined by exhausting the tube and weighing a third time. The difference between the second and third weighings indicates the weight of the nitrogen re- maining in the tube at the end of the experiment, and this weight added to that of the nitrogen contained in the globe constitutes the total weight of nitrogen in the air analyzed. The weight of the oxygen is given by the difference between the third and first weighings of the tube. By this method Dumas and Boussingault found that 100 parts of air contain by weight Oxygen 23.13 Nitrogen 76.87 These two gases are simply mixed in the air ; they do not exist there in a state of combination ; and the proportions of the mixture are universally the same with very slight varia- tions. At the summits of the highest mountains, at the centres of the continents, and over the vast expanse of the seas, the air has been shown to be nearly equally rich in oxygen. From a comparison of a great number of analyses, Regnault has es- tablished that as a rule the percentage of oxygen only varies from 20.9 to 21.0 ; air which has been collected on the open sea and close to the surface of the water, has been found to contain a somewhat smaller amount (20.6), a circumstance which may be attributed to the dissolving action of the water. Nitrogen and oxygen are by far the most abundant con- stituents of the atmosphere ; among the substances which are contained in small proportion must be mentioned particularly carbonic acid gas and vapor of water. Carbonic Acid Gas and Vapor of Water. — If lime-water be poured into a flat dish and exposed to the air, in a few hours its surface will be found covered with a white pellicle formed of little crystals of calcium carbonate. This experiment demonstrates the presence of carbonic acid gas in the atmosphere. The watery vapor may be condensed by exposing to the air a glass vessel containing a mixture of ice and salt. The sides of the vessel soon become covered with a layer of frost, resulting from the solidification of the water which has been condensed from the air by the cool surface of the glass. The exact quantities of carbonic acid gas and vapor of water 68 ELEMENTS OF MODERN CHEMISTRY. contained in the air may be determined by drawing the latter through tubes containing sulphuric acid and caustic potassa. The aspiration is obtained by means of a bottle or a tin vessel, V (Fig. 26), filled with water. On opening the stop-cock r ? Fig. 26. the water runs out, and air is drawn in through the tubes F and E, filled with fragments of pumice-stone wetted with sul- phuric acid, then through D and C, containing pumice-stone impregnated with caustic potassa, and finally B, which is like the first two. These tubes increase in weight from the absorp- tion of vapor of water in the first two, and carbonic acid in the others. The difference in weight of the tubes F and E before and after the experiment gives the proportion of con- densed water ; the difference of D, C, and B gives the propor- tion of carbonic acid gas. The volume of air is equal to that of the water which has run out of the aspirator. According to the experiments of Theodore de Saussure, the quantity of carbonic acid gas contained in the air varies from 4 to 6 ten-thousandths. It is increased in inhabited places. It is greater at night than during the day, a circumstance that must be attributed to the influence of vegetation. It is dimin- THE ATMOSPHERE. 69 ished after a rain, and is found in its minimum proportion above the surface of large lakes. The sources of this carbonic acid gas are various. In cer- tain regions fissures in the earth disengage large volumes ; vol- canoes emit immense quantities ; certain spring waters are supersaturated, and disengage it in abundance when they reach the surface of the earth. But the greater portion is produced by the phenomena of combustion which take place on the earth's surface ; and among these phenomena must be included respiration, which is a slow- combustion. Experiment. — If by the aid of a glass tube, a (Fig. 27), air from the lungs be blown through lime-water, the latter becomes clouded, by the formation of calcium carbonate. The carbonic acid gas thus fixed by the lime comes from the respiration, which is an abundant source of that gas. Does carbonic acid gas accumulate indefinitely in the atmosphere ? No. Re- jected and excreted by ani- mals, it serves for the res- piration of plants. The green parts of vegetables possess the power of de- composing this gas under the influence of the sun's light. The carbon is fixed, and serves for the nu- trition of the plant; the oxygen is rejected, if not wholly, at least in great part. This truth is one of the most important achievements of the science of the last century. It is due to the successive labors of Priestley, Bonnet, Ingenhouz, Senne- bier, and Theodore de Saussure. Independently of carbonic acid gas and vapor of water, air contains other matters mixed with or suspended in it in very small quantities. Among these must be mentioned : 1. Traces of ammonia, or rather of ammonium carbonate. These substances are dissolved by rain-water, and play an important part in vegetation. 70 ELEMENTS OF MODERN CHEMISTRY. 2. A trace of hydrogen carbide (Boussingault). 3. A small quantity of nitric acid in the form of ammonium nitrate. It is supposed that nitric acid is formed in the air by the direct union of the nitrogen and oxygen under the influ- ence of atmospheric electricity. Schonbein asserts that the air contains traces of ammonium nitrite : (NH 4 )N0 2 4. A body which possesses the property of imparting a blue color to papers saturated with starch and potassium iodide. It is held, and not without reason, that this substance is ozone. The phenomenon would also be caused by the presence of traces of nitrous vapors or chlorine in the air ; but Andrews has shown that air contains a principle which decomposes po- tassium iodide, and loses this property when it is brought to a high temperature. This fact can be explained if the air con- tain ozone, which is destroyed by heat ; it cannot be explained if it contain chlorine or nitrous vapors. Besides, the air con- tains only very slight traces of ozone, which vary greatly; often none is present. The relative proportion of ozone pres- ent is approximately estimated by the greater or less intensity of the blue color produced upon ozonoscopic paper. 5. Solid particles suspended in the air and carried to a dis- tance by the winds. In perfectly calm air these corpuscles are deposited, forming a dust of which the composition is very variable. It contains various microscopic vegetable and animal germs (Pasteur). WATER. Vapor density compared to air 0.623. Vapor density compared to hydrogen 1 ... 9. Molecular weight H 2 == 18. a Water is the product of the combination of hydrogen and oxygen ; its composition was established by Lavoisier in 1783. 1 The density of vapor of water compared to that of hydrogen is 9 j that is, if the weight of 1 volume of hydrogen be represented by 1, the weight of 1 volume of vapor of water will be 9 ; in other words, vapor of water is nine times more dense than hydrogen under the same conditions of tem- perature and pressure. 2 The weight of the molecule or the molecular weight expresses the weight of 2 volumes of vapor, if the weight of 1 volume of hydrogen be represented by 1. WATER. n The combination takes place exactly in the ratio of 2 volumes of hydrogen to 1 volume of oxygen, as demonstrated by the following experiments. 1. Analysis of Water by Electrolysis. — Water slightly acid- ulated with sulphuric acid is introduced into the vessel C (Fig. 28), through the bottom of which rise two platinum wires. These wires are hermetically sealed in the walls of the glass, and the free exterior ex- tremities are con- nected with the poles of a galvanic- battery. The cur- rent passing through the acidulated liquid decomposes the water, 1 and bubbles of gas are formed and rapidly rise from the two platinum wires which constitute the poles. If two small tubes filled with water be inverted over these wires, the gases may be collected, aud it will be found that the gas disengaged at the negative pole is sensibly double in volume that disengaged at the posi- tive. The first is hydrogen, and the second oxygen, and the proportion in which these gases are set free would be exactly that of 2 to 1, were it not that a small quantity of oxygen re- mains dissolved in the acid liquid, or, under certain condi- tions, combines with a portion of the water surrounding the negative pole to form a trace of hydrogen dioxide, as will be mentioned farther on. This experiment of the decomposition of water by the pile was made for the first time, in 1801, by two English physi- cists, Nicholson and Carlisle. 1 Under these conditions, it is really the sulphuric acid which is decom- posed : H 2 S0 4 breaks up into H 2 , which is liberated at the negative pole, and SO 4 , which separates at the positive pole, and is at once decomposed into SO 3 and 0. The is disengaged, and the SO 3 in the presence of the water becomes again hydrated, reforming sulphuric acid. SO 3 + H 2 = H 2 S0 4 . The electrolytic action is thus confined to the sulphuric acid, which alone is decomposed. *72 ELEMENTS OF MODERN CHEMISTRY. 2. Eudiometric Synthesis. — The composition of water can be established by synthesis, that is, by the combination of the two elements, hydrogen and oxygen. The experiment, which is made in an eudiometer, has already been described (page 28). It demonstrates that the two gases combine in the exact ratio of 2 volumes of the first to 1 of the second, and that these 3 volumes of gas are condensed into 2 volumes of vapor of water. These experiments establish the volumetric composition of water ; its composition by weight can be deduced from them, the densities of hydrogen and oxygen being known ; for the weighable matter of 2 volumes of hydrogen being added to the weighable matter of 1 volume of oxygen, it is only necessary to add twice the weight of 1 volume of hydrogen to the weight of 1 volume of oxygen in order to determine the weight of 2 volumes of vapor of water. That is to say, the ratio by weight in which hydrogen combines with oxygen to form water is that of double the density of hydrogen (the weight of 2 volumes of H) to the density of oxygen (the weight of 1 volume of 0). This ratio is 2 X 0.06 93 _ 0.1386 _ 1 1.L056" "~" 1.1056 ~8 It may be deduced in a more simple manner by a com- parison of the densities of hydrogen and oxygen. If 1 volume of hydrogen weighs 1, 1 volume of oxygen weighs 16 ; the weight of 2 volumes of hydrogen will then be 2, and it. will be seen that the two gases unite, by weight, in the ratio of 2 1 16 _ 8 18 grammes of water then contain 16 grammes of oxygen and 2 grammes of hydrogen. This composition, which can be determined only in an approximative manner by a compari- son of the densities, owing to the difficulties in the methods of weighing gases, has been established in the most rigorous manner by Dumas, in an experiment which has become classic, and will now be described. 3. Synthesis of Water by the Gravimetric Method. — In order to determine the composition of water by synthesis it is suffi- cient to combine an indeterminate quantity of hydrogen with a precisely determined weight of oxygen, and to weigh exactly the water formed. By subtracting from this latter weight that WATER. 73 of the oxygen contained in the water, the weight of the hydro- gen which has com- bined with that oxy- gen is obtained. In order to thus combine hydrogen with oxygen, it is convenient to make the former gas react upon an oxidized body which will read- ily yield its oxygen to the combustible gas. Cupric oxide, or black oxide of cop- per. CuO, first sug- gested by G-ay-Lus- sac, and employed for this purpose by Ber- zelius and Dulong, fulfils these condi- tions. Although un- decomposable by heat alone, it is readily re- duced by hydrogen when heated in an at- mosphere of that gas. Dumas employed the apparatus represent- ed in Fig. 29. Hydrogen is pre- pared by the action of dilute sulphuric acid upon zinc, and is purified by being conducted through a series of U tubes, the first containing frag- ments of glass wet with a solution of lead acetate, the second, fragments of glass wet with a solution of silver sulphate, and d 7 74 ELEMENTS OP MODERN CHEMISTRY. the third, pumice-stone, impregnated with caustic potassa, The lead acetate retains hydrogen sulphide ; the silver sulphate absorbs hydrogen arsenide, and the potassa absorbs any traces of carbides of hydrogen. The hydrogen thus purified is dried by passage through an- other series of U tubes, the first containing calcium chloride, and the others pumice-stone saturated with sulphuric acid. The latter tubes are cooled by being surrounded with ice. The gas is lastly passed through a smaller tube containing phosphoric oxide. The weight of this tube must remain constant during the whole of the experiment. It is called the control-tube. The pure and dry hydrogen now passes through a green glass bulb, which contains pure cupric oxide. The weight of this bulb, together with the oxide which it contains, is deter- mined with care. The receiver B', as well as the U tubes which terminate the apparatus, are also accurately weighed. When the whole of the air contained in the apparatus has been expelled by the hydrogen, the flask is heated and the cupric oxide is reduced. Water is formed and is in great part condensed in the liquid state in the receiver, but a portion of the vapor remains uncondensed and is carried off by the excess of hydrogen. This vapor is retained in the second series of U tubes, which contain calcium chloride and pumice-stone satu- rated with sulphuric acid. When the reduction has almost terminated, the bulb is allowed to cool, the current of hydro- gen being continued ; this gas is finally displaced by a current of air, and the weighings are then made. The weight of the bulb has decreased by that of all of the oxygen which has been taken from the oxide of copper by the hydrogen, and which now exists in the water formed. The weight of the receiver and the condensing apparatus con- nected with it is increased by the weight of all the water formed. By subtracting the weight of the oxygen from that of the water we find the weight of the hydrogen. By the aid of this rigorous method Dumas has found that 100 parts by weight of water contain Hydrogen 11.11 Oxygen 88.89 100.00 These numbers are in the exact ratio of Hydrogen 1 Oxygen 8 9 WATER. 75 Physical Properties. — Pure water has neither taste nor odor. It is limpid and colorless. It occurs in three states in nature ; during the colds of winter it is solid. Ice, snow, frost, sleet, and hail* are the different forms which it assumes in this state. The temperature at which ice melts is one of the stand- ard points in the thermometric scale. To this temperature corresponds the of the centigrade scale, which is adopted in this work. Snow is composed of an agglomeration of little crystals ; these are hexagonal prisms, which often present the forms rep- resented in Fig. 30. Fig. 30. At the moment of freezing, water expands, and its density is then less than that which it possesses in the liquid state. The density of ice is 0.93. Water contracts in volume from to -f 4°, and presents its maximum density at the latter tem- perature. Its density at this point is chosen as the unit of comparison for the densities of solid and liquid bodies. Water and even ice are continually emitting invisible vapors which mix with the air, and are, as it were, dissolved in it. This vaporization takes place more actively as the temperature is raised. The air is said to be saturated with vapor at any given tem- perature when it refuses to take up any more vapor at that temperature. Under these conditions, if the temperature be lowered, a portion of the vapor is condensed in fine drops. which remain suspended in the air in the form of mist or visi- ble vapor. The point at which the moisture of the air is con- densed is called the deic-point. Water begins to boil when its vapor acquires sufficient ten- sion to overcome the atmospheric pressure. This is the boil- ing-point, and under a pressure of 0.760 metre corresponds to 100° of the centigrade scale. 76 ELEMENTS OF MODERN CHEMISTRY. Chemical Properties. — Water is partially decomposed by the highest temperatures at our command. On pouring melted platinum into an iron mortar containing water. Grove observed a disengagement of bubbles composed of an explosive mixture of oxygen and hydrogen. According to H. Sainte-Claire De- ville, vapor of water undergoes a partial decomposition, which he calls dissociation, when exposed to a temperature between 1100 and 1200°. In order to collect the gases resulting from this decomposition it is necessary to separate them before they have reached a part of the apparatus where a less elevated temperature would permit their recombination. For this pur- pose Deville directed a current of steam through a porous clay tube, a (Fig. 31), surrounded by a tube of glazed porcelain, 6, Fig. 31. which was heated to whiteness in a powerful furnace. A cur- rent of carbonic acid gas was passed through the annular space between the two tubes, by means of the tube c. The vapor of water was decomposed by the heat into hydrogen and oxygen ; but these two gases separated from each other : the hydrogen, being the more diffusible, passed in great part through the porous tube, while the oxygen was delivered by the interior tube, together with a small quantity of carbonic acid gas, which entered by diffusion. The gases evolved by the two tubes were collected in a small jar filled with a solution of caustic potassa by which the carbonic acid gas was absorbed, and there re- mained an explosive mixture of hydrogen and oxygen. Water is decomposed by an electric current, as already seen. WATER. 77 It is likewise decomposed by many of the elements, metallic and non-metallic, which combine with one or the other of its component elements. Thus, chlorine decomposes it at a red heat, uniting with the hydrogen to form hydrochloric acid, and setting free the oxygen ; also under the influence of light at ordinary temperatures. A number of the metals decompose water, liberating the hydrogen. Iron decomposes it at a red heat, taking up the oxygen and setting free the hydrogen ; potassium and sodium, as we have seen in the case of the latter metal, produce the same effect at ordinary temperatures. Many compound bodies seize upon the elements of water, and are decomposed by it. Such are the chlorides of phos- phorus and antimony. In these reactions, which will be studied farther on, the hydrogen of the decomposed water unites with the chlorine, the oxygen with the other element. We have already noticed the action of water upon the non- metallic and metallic oxides. It combines with many of these compounds, forming either acids or metallic hydrates. Certain of these reactions are worthy of reconsideration. It is especially important to fully appreciate the part played by the water which enters into them. When potassium oxide becomes hydrated to form caustic potassa, the reaction takes place by a double decomposition, which may be expressed by the following equation : « k}° + i}° = i}° + g}° Potassium oxide. Water. Potassium hydrate. Potassium hydrate. It will be seen that both the potassium oxide and the water are converted into potassium hydrate by the exchange of an atom of potassium for an atom of hydrogen. Potassium hydrate is, as it were, derived from water by the substitution of an atom of potassium for an atom of hydrogen. This substitution takes place directly when water is decomposed by potassium. (2) 2H 2 H- K 2 = 2KOH + H 2 The potassium hydrate in its turn may lose the remaining atom of hydrogen ; if it be heated with potassium, this hydro gen is displaced, and potassium oxide is formed. (3) 2KOH + K 2 = 2K 2 + H 2 • Potassium hydrate. Potassium. Potassium oxide. Hydrogen. 78 ELEMENTS OF MODERN CHEMISTRY. It will be seen from what precedes that, starting with water, we may form potassium hydrate (2), potassium oxide (3), and this again may be converted into potassium hydrate (1). The three compounds are then closely related. Each contains 1 atom of oxygen combined with 2 atoms of another body, hy- drogen or potassium, and the relation is clearly expressed in the following formulae : ?}° h}° k}° Water. Potassium hydrate. Potassium oxide. If hypochlorous oxide, CPO, be poured into water, it is in- stantly dissolved and converted into hypochlorous acid. The reaction is expressed in the following equation : «}0 + =}0 = H}0 + £'}o Hypochlorous oxide. Water. Hypochlorous acid. Hypochlorous acid. Both the hypochlorous oxide and the water are converted into hypochlorous acid by the exchange of an atom of hydro- gen for an atom of chlorine, so that the hypochlorous acid may be said to represent water in which 1 atom of chlorine is substituted for an atom of hydrogen. Thus, by their atomic constitution both potassium hydrate and hypochlorous acid are closely related to water. But on comparing them together they are found to differ widely in their properties, both from each other and from water itself. How could it be otherwise with bodies containing elements as unlike as potassium and chlorine ? Indeed, the distance which separates potassium hydrate and hypochlorous acid is not greater than that which separates potassium and chlorine. Thus, a difference of elements may imply a marked difference of properties between bodies which otherwise present a similar con- stitution, and which may be said to belong to the same type. Water is one of these types. Its constitution serves as a sort of model for that of a multitude of compounds. It will be sufficient to reconsider the examples already cited, and we may say that water, potassium hydrate, potassium oxide, hypochlo- rous acid, and hypochlorous oxide belong to the water type. TYPE. «}0 «}0 g}0 K}0 l}0 Hypochlorous Hypochlorous Water. Potassium Potassium oxide. acid. hydrate. oxide. WATER. 79 The preceding considerations give but a limited idea, but one sufficient for the present, of the role played by water in chemical phenomena. This role is one of great importance, for water takes part in an immense number of reactions, either by its decomposition, its formation, or its combination. Water presents still another mode of action. It dissolves very many bodies, and this solvent action is exerted upon gases, liquids, ^nd solids. Solvent Properties of Water. — When a gas dissolves in water, it changes its state, it becomes itself liquid, and in lique- fying it evolves heat. In the same manner a solid body be- comes liquid by the act of solution, but in order to become liquid it must absorb heat. Consequently, the solution of a gas in water takes place with a production of heat ; that of a solid body takes place with a lowering of temperature, or, to use a common expression, a production of cold. But sometimes this physical phenomenon of the solution of a solid body in water, that is, its liquefaction and diffusion in the liquid, is complicated by a chemical action. Experiment. — If water be poured upon fused and powdered calcium chloride, the salt is instantly dissolved with a produc- tion of heat. This heat is the evidence of a chemical com- bination, and the water has indeed combined with the calcium chloride ; if now the solution be sufficiently evaporated, it will deposit fine transparent crystals of hydrated calcium chloride. The water contained in these crystals, and which is necessary for their formation, is what is called water of crystallization. It is contained in definite proportions, and is retained in the crystals by affinity. For this reason the combination of water with calcium chloride is accompanied by a production of heat. If these crystals of calcium chloride be dissolved in water, they disappear, and the temperature of the liquid is depressed. The physical phenomenon of the solution of a solid body in water can thus be separated from the chemical phenomenon of its combination with that liquid. Natural State of Water. — Water is not met with in a pure state in nature. Whether it has rested upon or has flowed over the surface of the soil, whether it has fallen in the form of rain, mist, or dew, or whether it has just issued from its subterranean passages, it always contains various matters in solution. It takes up the gases from the atmosphere, and also certain bodies which it there finds suspended or in vapor. On the 80 ELEMENTS OF MODERN CHEMISTRY. surface or in the bosom of the earth it dissolves the soluble substances which it encounters. Hence the composition of natural water presents great variations, according to the origin of the water and the localities where it has collected, or the soils through which it has travelled. In general, meteoric waters^ that is, those which result from the condensation of the aqueous vapor diffused through the atmosphere, are more pure than those which have collected upon the earth's surface. The latter present in their physical and chemical properties, in their composition, and in their action upon the animal econ- omy, such differences that they are classified in several groups. Soft or potable waters are distinguished from hard waters. The first are such as hold only small quantities of foreign mat- ters in solution, and are essentially fit for domestic use. The second are too highly charged with saline matters, and princi- pally the salts of calcium, to be fit for such purposes. Good potable water should be cool, limpid, without odor, should have a faint but agreeable taste, which should be neither insipid, saline, nor sweet, and should cook and soften vegetables and dissolve soap. The purest water is not necessarily the best. Thus distilled water, rain-water, and that coming from the melting of ice and snow, although more pure, are less salubrious than good spring or river water. Good potable water should be aerated, that is, it should hold in solution the gases contained in the atmosphere : oxygen, nitrogen, and carbonic acid. Rain-water takes from the atmos- phere a proportion of oxygen, and especially of carbonic acid gas, much greater than that in which these gases are contained in the air. This must be so, for Dalton has shown that the solvent action of water upon a gaseous mixture is measured for each gas by the product of its coefficient of solubility and the figure expressing the proportion of that gas in the mixture. These gases are driven out of water by boiling. The following figures give the proportions of the atmospheric gases expelled by boiling from a litre of water from the Seine, in the month of January, and also the proportions contained in a litre of rain-water (Peligot) : Water of the Seine. Rain-Water. Carbonic acid gas Nitrogen . . . Oxygen . . . 22.6 cubic centimetres. 0.5 c. 21.4 15.1 10.1 7.4 54.1 23.0 1.77 64.47 33.76 100.00 WATER. 81 It is seen that the running water contains a larger amount of all of the gases than rain-water, and a notably larger pro- portion of carbonic acid. Solid Matters dissolved in Water. — Soft waters generally contain a small proportion of fixed matters, among which are certain salts of calcium and magnesium, certain alkaline salts, silica, and organic matters. The calcium salts are the carbonate and sulphate, and some- times traces of the chloride, nitrate, and phosphate. Calcium carbonate, or carbonate of lime, is almost insoluble in pure water, but dissolves readily in water charged with carbonic acid gas; in such solutions it exists as dicarbonate. When water thus charged with calcium dicarbonate is boiled, that salt is decomposed, carbonic acid gas is disengaged, and neutral calcium carbonate is precipitated. When the propor- tion of calcium dicarbonate contained in spring-water is large, it may happen that as the water loses carbonic acid gas the calcium carbonate is deposited at ordinary temperatures. This effect is favored by the tumultuous movements to which spring- water is subjected either in flowing over an inclined bed or in conducting-pipes. The carbonate then forms a crystalline de- posit, which incrusts the interior walls of the pipes and, in general, whatever objects may be plunged into such waters, which for this reason are called incrusting ox petrifying waters. The presence of small quantities of calcium dicarbonate in drinking-water may be considered as a good condition, from a hygienic stand-point, for the system needs calcareous salts for the development and nutrition of the bony structures. Calcium sulphate, or sulphate of lime, exists in solution in many waters, especially in spring and well waters. When the proportion does not exceed fifteen or twenty centigrammes per litre, such water may be used without inconvenience for do- mestic purposes. Water largely charged with calcium sulphate is called selenitous water ; it does not become clouded on ebul- lition. Like all other strongty calcareous water, it does not dis- solve soap without first forming a flocculent precipitate. Salts of barium produce with such water an abundant white precipi- tate of barium sulphate, which is insoluble in nitric acid. Such water is unfit for economic purposes. In general, the propor- tion of calcareous salts in potable water should not exceed five or six decigrammes per litre ; water containing more than this is difficult to digest, and is called hard water. Potable water 82 ELEMENTS OF MODERN CHEMISTRY. should not contain more than mere traces of organic matter. If the organic matter be due to sewage, the water yields am- monia when boiled with an alkaline solution of potassium per- manganate : more than 0.10 per million of such ammonia indi- cates an unwholesome water. Mineral or Medicinal Waters. — These are waters that by virtue of their temperature or chemical constituents exercise a special action upon the animal economy, and consequently have a therapeutic value. They are cold or warm. They are called warm when their temperature at the moment of emergence is above 12 or 15°. Of course their temperatures vary greatly, covering the whole thermometric scale from 25 to 100°. There are numerous hot springs in California, Colorado, and Virginia. The tempera- ture of the Grand Geyser in Iceland is even above 100° in the depths of the tube from which it issues. According to their chemical constituents, mineral waters are classified in a number of characteristic groups, distinguished either by the predomi- nance of certain constituents, or by the presence of principles particularly active. These groups are as follows : Acidulous or gaseous waters, characterized by the presence of free carbonic acid. Alkaline waters, characterized by the presence of a greater or less proportion of sodium dicarbonate, or of an alkaline silicate. Chalybeate waters, holding a salt of iron in solution. Saline waters, or those containing certain neutral salts. Sulphur waters, characterized by the presence of hydrogen sulphide or other solu- ble sulphide. On arriving at the surface of the earth, certain of these mineral waters undergo a change in chemical constitution. Such are the sulphur waters which absorb oxygen, as will be noticed presently. Those containing free carbonic acid lose a part of the.ir gas, and it often happens that some of the car- bonates held in solution by an excess of carbonic acid become insoluble, and are deposited after the escape of that excess. This is the principal cause of the deposits which form in the basins and conducting-pipes of many mineral waters. These deposits vary greatly in composition ; sometimes they are floc- culent or pulverulent, and collect in the form of mud ; some- times they form hard concretions or scales. Calcium and magnesium carbonates, ferric hydrate, alumina, and silica are the most ordinary constituents of such deposits. Besides these, arsenic, various metallic oxides, and materials which it would be difficult to detect in the water itself, are sometimes concen- trated, as it were, in these deposits. Thus, arsenic is detected WATER. 83 much more readily in the ochrey deposits around a ferruginous spring than in the water of the spring itself. Acidulous or Gaseous Waters. — Free carbonic acid is the characteristic and predominant element of these waters ; it is dissolved in the depths of the earth under a pressure much greater than that of the atmosphere ; hence a certain portion of the gas is disengaged as soon as the water emerges from the soil, giving rise to a greater or less effervescence. Gaseous waters are cold ; their taste is piquant at the moment of emer- gence, but often becomes saline or even alkaline after the dis- engagement of the greater part of the carbonic acid gas. Nat- ural gaseous waters never consist of a solution of carbonic acid in pure water ; they always contain a small quantity of saline matters, principally traces of sodic, calcic, and magnesic carbonates, and even traces of chlorides and sulphates. Such is the composition of the celebrated Seltzer water and of Soultz- matt water. The water of certain of the Saratoga springs approximates in composition to Seltzer water. Alkaline Waters. — These waters possess an alkaline re- action, either immediately on their emergence or after the loss of their free carbonic acid. This reaction may be due to an alkaline silicate, but is generally referable to an alkaline car- bonate. Sodium acid carbonate, NaHCO 3 , commonly called bicarbonate of soda, exists in nearly all waters of this class, together with an excess of carbonic acid. Vichy water con- tains about 5 grammes of this salt per litre. Chalybeate Waters. — Nearly all waters contain traces of iron in solution ; chalybeate waters are such as contain sufficient of that metal to give them an astringent taste and special therapeutic properties. The iron may exist in three conditions : 1. As ferrous carbonate held in solution by carbonic acid. 2. As ferrous crenate. Berzelius gave the names crenic and apocrenic acids to two bodies which are related to peculiar acids existing in the soil or humus, and which are known as ulmic, humic, and geic acids. Ferrous crenate is soluble in water ; its constitution is not known. 3. As ferrous sulphate. Consequently, chalybeate waters may be carbonated, cre- nated, and sulphated. The ferrous salts are never contained in these waters in large proportions. Many ferruginous waters of undoubted efficacy 84 ELEMENTS OF MODERN CHEMISTRY. do not contain more than 4 or 5 centigrammes per litre. When exposed to the air they lose the greater part of their carbonic acid, and ferrous carbonate is deposited, but this loses its carbonic acid and is converted into brown ferric hydrate. Such is the manner of formation and the nature of the ochrey deposits always noticeable around ferruginous springs. Chalybeate waters are widely diffused. Those of Spa and Pyrmont, Belgium (carbonated), Bussang in the Vosges, and Forges (crenated), and Passy, at Paris, are well known. Cele- brated springs of this class exist at Bedford, Pennsylvania ; others are widely diffused throughout the United States. Saline Waters. — This class includes a great number of waters charged with various neutral salts, among which are the chlorides, bromides, and iodides. The salts of sodium, mag- nesium, and calcium are those more usually met with in these waters. According to the predominating or peculiarly active principle present, they are classified as chlorinated, sulphated, and bromo-iodated waters. The Saratoga springs yield an acidulo-saline water. Chlorinated Saline Waters. — The chlorides generally found in mineral waters are those of sodium, magnesium, and cal- cium ; the former is much the more abundant, and constitutes one of the most common constituents of mineral waters. It communicates to them a pure salty taste, free from bitterness. A great number of saline springs serve for the extraction of sodium chloride. After the evaporation of the water and the deposition of the salt, a mother-liquor remains in which various less abundant salts are concentrated, principally the alkaline bromides and iodides. Sea-water is a chlorinated water. It is well known that it contains a notable proportion of sodium chloride (2.5 to 2.7 per cent.). The common salt is accompanied by the chlorides of magnesium and potassium, and by a considerable quantity of magnesium sulphate (0.6 to 0.7 per cent.). The Dead Sea and the Great Salt Lake of Utah are the most concentrated saline sources known. The water of the latter contains 20 per cent, of sodium chloride. Sulphated Saline Waters. — These are characterized by so- dium, magnesium, or calcium sulphate. The springs of Carls- bad, in Bohemia, contain a large proportion of sodium sulphate, together with sodium bicarbonate and sodium chloride. The purgative waters of Epsom, England, contain magne- HYDROGEN DIOXIDE. 85 siuni sulphate. The waters of Sedlitz, Saidschtitz, and Pullna, in Bohemia, contain magnesium sulphate and sodium sulphate. Their taste is bitter. The Avon Spring, New York, is of this class. Bromo-iodated Waters. — Many mineral waters contain small quantities of bromides and iodides, independently of the chlo- rides which generally exist in much larger proportions. The water of the Dead Sea, so rich in magnesium and sodium chlorides, contain 0.43 per cent, of magnesium bromide. The Iodine Spring at Saratoga " contains a notable proportion of alkaline iodides. Sulphur Waters. — By this name are designated those waters containing a soluble sulphide or sulphuretted hydro- gen. They are either natural sulphur waters or accidental sulphur waters. The first contain sodium sulphide ; they are generally warm, and contain but little solid matter. They all disengage nitrogen on their emergence from the soil. They contain a nitrogenized organic matter (baregine), and some- times deposit a gelatinous precipitate (glairine). Celebrated springs exist in the Pyrenees and at Bagneres- de-Luchon. The sulphur springs of Sharon and Avon, in New York, and the Bed and White Sulphur Springs of Virginia are well known. Accidental sulphur waters are those which are formed upon the spot by the reduction of sulphates, and particularly calcium sulphate, contained in the waters. This reduction is accom- plished by the action of organic matters which impregnate the soil, and of which the combustible elements, carbon and hydro- gen, remove the oxygen of the sulphates. It is thus that the sulphur water of Enghien is formed at the gates of Paris. HYDBOGEN DIOXIDE. H 2 2 This remarkable compound was discovered by Thenard in 1818. It is formed by the action of barium dioxide upon di- lute hydrochloric acid. Barium dioxide, powdered and made into a fine paste with water, is introduced by small portions into cold and dilute hydrochloric acid. It dissolves without disengagement of gas, yielding barium chloride and hydrogen dioxide. BaO 2 + 2HC1 = BaCP + H 2 2 Barium dioxide. Hydrochloric acid. Barium chloride. Hydrogen dioxide. 86 ELEMENTS OF MODERN CHEMISTRY. The barium chloride is converted into sulphate, which is insoluble, by the cautious addition of dilute sulphuric acid, and at the same time hydrochloric acid is regenerated, so that an additional quantity of barium dioxide may be added, and the operation is several times repeated. BaCP + H 2 SO = BaSO 4 + 2HC1 Sulphuric acid. Barium sulphate. The barium chloride finally remaining in solution is exactly precipitated by a solution of silver sulphate, and the hydrogen dioxide poured off and evaporated in vacuo. Pure hydrogen dioxide is a syrupy, colorless, odorless liquid, having a density of 1.452. It is very unstable, and readily gives up half of its oxygen, being converted into water. This decomposition takes place with a brisk effervescence when the dioxide is heated towards 100° ; it is also produced by con- tact with a great number of bodies, some of w r hich are them- selves unaltered, some oxidized, and others even reduced. Hence hydrogen dioxide enters into three classes of reactions. 1. If hydrogen dioxide, or more simply, water charged with hydrogen dioxide, be poured into a test-tube containing man- ganese dioxide, the hydrogen dioxide is instantly reduced with effervescence into water and oxygen. The manganese dioxide remains unchanged. Finely divided platinum, gold, silver, and carbon act in the same manner. 2. Hydrogen dioxide energetically oxidizes arsenic and sele- nium into arsenic and selenic acids. It converts lead sulphide into sulphate. PbS + 4H 2 2 = PbSO + 4H 2 Lead sulphide. Lead sulphate. 3. Potassium permanganate, KMnO*, is a salt very rich in oxygen ; it dissolves in water, forming a solution having an intense purple color. If hydrogen dioxide be added to it, it is immediately reduced and decolorized. The oxygen from the decomposition of the hydrogen dioxide is in this case added to that from the reduction of the permanganate, and both are dis- engaged in the free state. If hydrogen dioxide be added to a solution of potassium di- chromate, the latter assumes a deep blue color, but this rapidly disappears, giving place to a green tint. At the same time an evolution of oxygen takes place. In this case the reaction is complex : a portion of the hydrogen dioxide oxidizes the HYDROGEN DIOXIDE. 87 chromic acid for an instant into blue percliromic acid, but the latter is instantly reduced, with disengagement of oxygen, by another portion of the hydrogen dioxide, which at the same time loses half of its oxygen. The oxygen gas liberated comes then at the same time from the perchromic acid and the hydrogen dioxide, both of which are supersaturated with oxygen, and which mutually reduce each other. The perchromic acid formed may be removed from the action of the excess of hydrogen dioxide by imme- diately agitating the liquid with ether : the latter dissolves the acid and assumes a dark-blue color. These experiments of reduction are of great interest, and permit of but one explanation. The fact of the reciprocal reduction of two bodies each supersaturated with oxygen can only be explained by admitting that the oxygen of one body possesses an affinity for that of the other, and that the oxygen which is set free is formed by the union of two atoms, one from the hydrogen dioxide, the other from the perchromic or per- manganic acid. These two atoms unite to form a molecule of oxygen 00. This would represent oxygen in the free state, and occupy two volumes. It would be a true combination, and we here encounter for the first time the important notion that the atoms of certain elements are not isolated when in the free state, but combined in pairs, each pair being held together by chemical force. Free oxygen would then be oxygen oxide, a combination of two atoms of oxygen, both together forming a molecule, and occupying two volumes like the molecule of water. 1 molecule of water .... H-O-H = 2 volumes. 1 molecule of oxygen . . . 0=0 = 2 volumes. While the molecular structure of free oxygen or oxygen oxide corresponds in a measure to that of hydrogen oxide or water, there exists a peroxide of oxygen which corresponds in a measure to hydrogen peroxide ; it is ozone. Hydrogen dioxide H-O-O-H Oxygen dioxide (ozone) q^ \ 88 ELEMENTS OF MODERN CHEMISTRY. SULPHUR. Vapor density compared to air 2.22 Vapor density compared to hydrogen . . , . 32. Atomic weight S =32. Sulphur has been known from the greatest antiquity. It exists in combination in a large number of sulphides, among which are those of iron and copper (pyrites), of lead (galena), zinc (blende), mercury, etc. In certain volcanic countries it is found on the surface of the earth in the native state. Sicily and Iceland contain large deposits in the neighborhood of extinct volcanoes (solfatares). In order to separate it from the earthy matters which accompany it, it is subjected in Sicily to distilla- tion in earthen pots (Fig. 32). Fig. 32. These are arranged in two rows in furnaces, and communicate by lateral tubulures with other pots which are placed outside of the furnace, and in which the sulphur vapor is condensed. Crude sulphur is thus obtained ; it is still mixed with foreign matters, from which it is separated by a new distillation. This operation, which is called refining, is conducted in an apparatus represented in Fig. 33. A horizontal cast-iron cylinder, A, receives the melted sul- phur from the vessel C, which is heated by the waste gases from the furnace, and which serves as a reservoir. The sulphur vapor enters a large masonry chamber, B, the floor of which is SULPHUR. 89 slightly inclined in order that the condensed liquid sulphur may flow towards a tap, H, which can be opened as is necessary. A damper, R, that can be regulated by an articulated wire, per- mits the closing and opening of the mouth of the cylinder. The vault of the chamber is provided with a safety-valve, K, which allows of the escape of the expanded air. At the commencement of the operation, when the walls of the chamber are cold, the sulphur condenses in the form of a fine powder, which is known as flowers of sulphur. But when the walls of the chamber become heated above the melting- point of sulphur, the vapor condenses into a liquid, and on opening the tap at H, it is drawn off into a vessel, E, from which it is distributed into slightly conical or cylindrical moulds, where it solidifies. Roll sulphur is thus obtained. Physical Properties. — Sulphur is a lemon-yellow solid. It is tasteless, odorless, and brittle ; it is a non-conductor of heat and electricity. A stick of sulphur pressed in the hand or plunged into warm water produces a crackling sound, and finally breaks into pieces ; this is due to the unequal expan- sion from the circumference to the centre of the non-conduct> 90 ELEMENTS OF MODERN CHEMISTRY. ing mass of sulphur, the crystalline particles of which are but slightly held together by cohesion. The density of sulphur is about 2.03. At 111.5° it melts into a brownish-yellow, transparent liquid. If this liquid be allowed to cool slowly until a crust forms upon the surface, and the crust be pierced and the part still' remaining liquid be decanted, after removing the crust the interior of the vessel is found covered with long, transparent, flexible needles of a brownish-yellow color. These crystals are oblique-rhombic prisms having a density of 1.98; This is not the only crystal- line form assumed by sulphur. If a solution of sulphur in carbon disulphide be allowed to evaporate spontaneously, right-rhombic octahedral crystals are deposited having a den- sity of 2.05. This form is also that of native crystallized sulphur. Sulphur crystallizes, then, in two distinct forms belonging to two distinct crystalline systems. It is dimorphous. It is a curious fact that the prisms formed by way of fusion do not long retain their transparence and their flexibility. When aban- doned for some time to ordinary temperatures, they become opaque and brittle. They are then found to be traversed by a multitude of planes of cleavage, which are the faces of microscopic octahedra similar to those obtained by way of solution. Reciprocally, the transparent octahedral crystals become opaque when maintained for some time at a temperature of 111° ; they are then transformed into a multitude of little crystals of prismatic sulphur. It is seen that the two crystal- line modifications of sulphur can be transformed into each other. It is a curious instance of dimorphism. Sulphur melted in a sealed tube will remain liquid for a long time at temperatures below its ordinary point of solidifi- cation ; it is then said to be in a state of superfusion. When it finally solidifies, it crystallizes in voluminous octahedra having the form of crystallized native sulphur. There are other and amorphous modifications of sulphur. Experiment. — If sulphur be melted in a flask, and the tem- perature be gradually raised above its point of fusion, it assumes a thick consistence and a dark color. At 220° it has a brown- red color and is very thick. Above 260° it again becomes fluid ; if while in this state it be poured into cold water, it is converted into a soft, transparent, brownish-yellow, and elastic SULPHUR. 91 mass. It has become amorphous, and is now soft sulphur. When abandoned to itself for several days, it hardens, becomes opaque, and reassumes the properties of ordinary sulphur. This change takes place immediately if the soft sulphur be heated to 90 or 95° ; is then accompanied by a sensible disen- gagement of heat (Regnault). There are two modifications of soft sulphur. If it be treated with carbon disulphide, a part of it is dissolved, and a residue remains. The soluble part constitutes soluble soft sulphur; the residue is insoluble soft sulphur (Ch. Sainte-Claire Deville). In recently-sublimed flowers of sulphur the sulphur exists in the amorphous condition. The octahedral, prismatic, and amorphous varieties are dis- tinguished as a, ft and y sulphur. Sulphur boils at 440° ; its vapor is red. At 500° it has a density of 6.654 (Dumas). Towards 1000° its density is only about one-third as great. According to H. Deville and Troost, the vapor density of sulphur, determined at 860° and reduced by calculation to 0°, is 2.22. Compared to hydrogen, this density is equal to 32, which is the normal density of sulphur vapor, and gives its atomic weight. If 1 volume of hydrogen weighs 1, 1 volume of sulphur vapor weighs 32 ; the latter figure is therefore the atomic weight of sulphur. But at a temperature a little above its point of ebullition the vapor density of sulphur is 6.6, or three times greater than at 860° ; this is accounted for by the fact that sulphur does not assume the true gaseous state below a temperature of 860°. Sulphur is insoluble in water, but very slightly soluble in alcohol, a little more soluble in ether % and benzine. Its best solvent is carbon disulphide. Chemical Properties. — Sulphur possesses energetic affini- ties. It combines directly with a great number of the other elements. It is well known that it is combustible, burning with a blue flame. Its combustion in air or oxygen produces sulphurous oxide. Sulphur combines directly with chlorine, bromine, iodine, phosphorus, arsenic, and carbon, and with very many of the metals. Iron and copper burn in the vapor of sulphur. The sulphides thus formed generally possess the atomic constitution of the corresponding oxides. Thus, the compound of sulphur and carbon, carbon disulphide, is analogous to carbonic acid gas. This analogy is maintained between a great number of 92 ELEMENTS OP MODERN CHEMISTRY. oxygen and sulphur compounds, as will be seen by the follow- ing examples : H 2 water. H 2 S hydrogen sulphide. KOH potassium hydrate. KSH potassium sulphydrate. CO 2 carbon dioxide. CS 2 carbon disulphide. K 2 potassium monoxide. K 2 S potassium monosulphide. BaO barium monoxide. BaS barium monosulphide. K 2 C0 3 potassium carbonate. K 2 CS 3 potassium sulphocarbonate. SULPHYDRIC ACID, OR HYDROGEN SULPHIDE. Density compared to air 1.192 Density compared to hydrogen 17. Molecular weight H 2 S =34. This gas, known also as sulphuretted hydrogen, was discov- ered by Meyer and Rouelle, and studied by Scheele, in 1777, and by Berthollet. Preparation. — Hydrogen sulphide may be prepared by Fig. 34. gently heating antimony trisulphide in a flask with hydrochlo- ric acid (Fig. 34). The gas is first passed through a wash- HYDROGEN SULPHIDE. 93 bottle, B, containing a little water, and may then be collected over the pneumatic trough. The reaction which takes place is expressed by the following equation : Sb 2 S 3 + 6HC1 = 2SbCP + 3H 2 S Antimony trisulphide. Hydrochloric acid. Antimony trichloride. The gas is generally prepared in the laboratory by the reaction of dilute sulphuric acid with ferrous sulphide. The operation requires no heat, and the reaction is as follows : FeS + IPSO 4 = FeSO + IPS Ferrous sulphide. Sulphuric acid. Ferrous sulphate. As hydrogen sulphide is largely used in the laboratory, the apparatus represented in Fig. 35 is convenient for its ready production. It is composed of two large bottles, of which the Fig. 3d. lower apertures are connected by a large caoutchouc tube. ' In one of these bottles is placed a layer of broken glass or coke, which is not attacked by sulphuric acid ; upon this is placed the ferrous sulphide in fragments. The neck of this bottle is closed by a cork, through which passes a glass tube bearing a stop-cock. The second bottle is nearly filled with dilute sul- phuric acid. The stop-cock of the first bottle being opened, the sulphuric acid enters until it attains the same level in both bottles, and as soon as it reaches the ferrous sulphide the reac- tion commences and hydrogen sulphide is disengaged. If the 94 ELEMENTS OF MODERN CHEMISTRY. stop-cock be closed, the continued evolution of gas drives the liquid back into the second bottle, until the disengagement of gas ceases, which takes place as soon as the sulphuric acid no longer touches the ferrous sulphide. The first bottle then serves as a reservoir of hydrogen sulphide, containing the gas under a pressure greater than that of the atmosphere, and which can be increased by elevating the second bottle. In order to obtain a current of the gas, it is sufficient to open the stop-cock, and the flow can be regulated at will. Physical Properties. — Hydrogen sulphide is a colorless gas. It has a penetrating odor of putrid eggs. Under a pressure of 17 atmospheres, it condenses to a transparent, strongly refract- ing liquid, having a density of about 0.91. At — 85.5° this liquid solidifies to a white crystalline mass (Faraday). Hydro- gen sulphide is soluble in water. At 0°, one volume of water dissolves 4.37 volumes; at 10°, 3.58 volumes; and at 20°, 2.90 volumes. Composition. — 2 volumes of hydrogen sulphide contain 2 volumes of hydrogen and 1 volume of sulphur vapor. If a given volume of this gas be introduced into a bent tube over mercury (Fig. 22), and a morsel of tin be then introduced and heated for about twenty minutes, the hydrogen sulphide is decomposed ; the sulphur combines with the tin, and the hy- drogen is set free. After cooling, the latter gas occupies a volume exactly equal to that of the hydrogen sulphide at first contained. If, then, from the vapor density of hydrogen sulphide = 17 we subtract the density of hydrogen = 1 we find the number 16 which represents half the density of sulphur vapor. It is hence concluded that one volume of hydrogen sulphide contains half a volume of sulphur vapor to one volume of hy- drogen. It is also seen that hydrogen sulphide has exactly the same chemical constitution as vapor of water. H 2 = 2 volumes or one molecule of vapor of water. H 2 S = 2 volumes or one molecule of hydrogen sulphide. The analogy between sulphur and oxygen is here manifested in a striking manner. One atom of each of these elements requires two atoms of hydrogen. This is expressed by saying that both oxygen and sulphur are diatomic elements. HYDROGEN SULPHIDE. 95 Chemical Properties. — Hydrogen sulphide is combustible, burning with a bluish flame. The products of its complete combustion are water and sulphurous oxide. When mixed with one and a half times its volume of oxygen, it explodes on the application of a flame or the passage of an electric spark. H 2 S + O 3 = SO 2 + H 2 Two volumes. Three volumes. Two volumes. Two volumes. When the supply of oxygen is insufficient, the combustion is incomplete and sulphur is deposited. In the presence of water, this oxidation takes place at ordi- nary temperatures, occasioning a deposit of sulphur. In the presence of moisture and porous matters it goes further, sul- phuric acid being formed. Hydrogen sulphide has a feeble acid reaction ; it changes blue litmus to a wine-red color. When it reacts with potassium hydrate, water and potassium sulphydrate are formed. + l|° - 5}" + 1} Hydrogeu sulphide. Potassium hydrate. Potassium sulphydrate. Chlorine, bromine, and iodine decompose hydrogen sulphide, combining with its hydrogen. When these bodies are dry, the action is energetic, and the sulphur combines with the excess of the element employed. If water be present, the sulphur is set at liberty. Bodies rich in oxygen readily decompose hydrogen sulphide. Experiments. — 1. If a few drops of the strongest nitric acid be poured into a jar filled with hydrogen sulphide, the gas is instantly inflamed. The nitric acid gives up oxygen, water is formed, sulphur is set free, and abundant red fumes appear at the same time. 2. If four volumes of hydrogen sulphide be mixed with /two volumes of sulphurous oxide over the mercury-trough, a deposit of sulphur is at once formed. 2H 2 S + SO 2 = 2H 2 + 3S Hydrogen sulphide. Sulphurous oxide. Water. Sulphur. (4 volumes.) (2 volumes.) Hydrogen sulphide decomposes a great number of metallic solutions, forming insoluble sulphides, which are precipitated. Experiments. — 1. If a solution of hydrogen sulphide be added to a solution of blue vitriol or cupric sulphate, a brown 96 ELEMENTS OF MODERN CHEMISTRY. precipitate of cupric sulphide is formed. The reaction is expressed by the following equation : CuSO + H 2 S = CuS + H 2 SO Cupric sulphate. Cupric sulphide. Sulphuric acid. 2. By an analogous reaction, a solution of plumbic acetate, or a paper impregnated with that salt, is at once blackened by the presence of hydrogen sulphide. Hydrogen sulphide acts as a poison if inhaled in large quantities or for any length of time. HYDROGEN PERSULPHIDE. This compound, discovered by Thenard, is analogous to hy- drogen dioxide. It is prepared by pouring, drop by drop, a solution of calcium disulphide into dilute hydrochloric acid. CaS 2 -f 2HC1 = CaCl 2 + H 2 S 2 Calcium disulphide. Hydrochloric acid. Calcium chloride. Hydrogen disulphide. Hydrogen disulphide is formed and collects at the bottom of the vessel in the form of a yellowish oil, having a disa- greeable, irritating odor. Towards 60 or 70° it decomposes rapidly into hydrogen sulphide and sulphur. H 2 S 2 = H 2 S + S This decomposition takes place slowly at ordinary tempera- tures. Hofmann attributes to this body the formula H 2 S 3 . He has obtained a compound of this sulphide with an alkaloid, strych- nine, the analysis of which has led him to conclude that there are three atoms of sulphur in a molecule of the persulphide of hydrogen. OXYGEN ACIDS OF SULPHUR. 1 . Sulphur forms three compounds with oxygen : a ! i . -, aA2 ( sulphurous anhydride or sulphurous oxide bO < in v -j r ( sulphur dioxide. Sulphuric oxide SO' | ™ ] V h ™° f nh y d / ide OT r ( sulphur trioxide. Persulphuric oxide S'O' j ^b^^ 00 ™^ by SULPHUROUS OXIDE. 97 2. By combining with a molecule of water, these oxides are converted into the corresponding acids. 50 2 +.IPO = H 2 S0 3 sulphurous acid. 50 3 + H 2 = H 2 S0 4 sulphuric acid. 3. There are two other important acids of sulphur, hypo- sulphurous and hyposulphuric acids. The former may be con- sidered as sulpho-sulphuric acid, that is, sulphuric acid in which 1 atom of oxygen is replaced by an atom of sulphur. IPSO sulphuric acid. H 2 (S0 3 )S sulpho-sulphuric or hyposulphurous acid. Hyposulphuric acid may be considered as resulting from the addition of sulphurous oxide to sulphuric acid. SO 2 + H 2 SO = H 2 S 2 6 hyposulphuric acid. 4. These are not the only known sulphur acids. Hyposulphuric acid, which is called also dithionic acid, is the first of a series of acids, each of which contains 2 atoms of hydrogen and 6 atoms of oxygen, the number of sulphur atoms regularly increasing. This series is called the tliioiiic series. The following is the nomenclature and composition of the acids : H 2 S 2 6 dithionic, hyposulphuric acid. H 2 S 3 6 trithionic acid. H 2 S 4 6 tetrathionic acid. H 2 S 5 6 pentathionic acid. 5. Schutzenberger has recently made known a new sulphur acid, which he has named hydrosulphurous acid, and which is formed by the action of zinc upon sulphurous acid, as will be described farther on. The composition of this acid is repre- sented by the formula H 2 S0 2 . There is an interesting relation between this acid and' sul- phurous and sulphuric acids. H 2 S0 2 hydrosulphurous acid. H 2 S0 3 sulphurous acid (not yet isolated). H 2 SO* sulphuric acid. SULPHUROUS OXIDE. Density compared to air 2.234 Density compared to hydrogen 32. Molecular weight SO 2 =64, E 9 98 ELEMENTS OF MODERN CHEMISTRY. Sulphurous oxide or sulphurous acid gas may be prepared by decomposing sulphuric acid with copper. The metal in small clippings and the acid are introduced into a flask fitted ed Fig. 36. with a delivery-tube (Fig. 36) ; heat is applied and the gas collected over the mercury-trough. The reaction which takes place is expressed by the following equation : Cu + 2H 2 S0 4 : Copper. Sulphuric acid. = CuSO + Cupric sulphate. 2H 2 + SO 2 A solution of sulphurous acid in water is often needed in the laboratory. It may be conveniently prepared by reducing sulphuric acid by charcoal ; the products of the reaction are water, and sulphurous and carbonic acid gases. 2H 2 S0 4 + C Sulphuric acid. 2H 2 + 2S0 2 + CO 2 Carbon dioxide. The mixed gas is passed through a series of bottles contain- ing water, which dissolves the sulphurous oxide, but takes up only an insignificant quantity of the carbon dioxide. Physical Properties. — Sulphur dioxide is a colorless gas having a pungent, suffocating odor. It is readily liquefied by being led into a vessel surrounded by a mixture of ice and salt. It condenses at ordinary temperatures, under a pressure of about two atmospheres. The liquid has a density of 1.45 ; it boils at — 10°, and produces great cold by its evaporation ; on this account it is used for the manufacture of ice, and in other cases where intense cold is required. — 73° may be obtained SULPHUROUS OXIDE. 99 by the evaporation of liquid sulphurous acid aided by double- acting pumps (Kaoul Pictet). Water at 0° dissolves 79.9 times its volume of sulphurous oxide, and only 39.4 volumes at 20°. Experiments. — 1. If a small quantity of mercury contained in a porcelain capsule be covered with a deep layer of liquid sulphurous oxide, and the evaporation of the latter be favored by directing a rapid current of air over its surface, the mercury is frozen into a solid button. 2. When liquid sulphurous acid is poured into not too great a quantity of water, a part of it is dissolved, but the excess absorbs heat from the mass of liquid, volatilizes suddenly, and the water is frozen. Chemical Properties. — Sulphurous oxide is not decom- posed by heat. It is incombustible, and extinguishes burning bodies. Its most striking property is its affinity for oxygen. If a mixture of two volumes of sulphurous oxide and one volume of oxygen be passed through a tube containing slightly heated spongy platinum, the two gases combine, forming sulphuric oxide (Kuhlmann). A solution of sulphurous oxide in water slowly absorbs oxy- gen, and is converted into sulphuric acid. It may be admitted that the aqueous solution contains the veritable sulphurous acid. H 2 S0 3 + = H 2 S0 4 Sulphurous acid. Sulphuric acid. Sulphurous acid reduces a great number of oxidized bodies. At ordinary temperatures it takes the oxygen from iodic acid, setting free the iodine ; but the latter disappears on the addi- tion of an excess of sulphurous acid, sulphuric and hydriodic acids being formed. H 2 S0 3 + H 2 + I 2 = H 2 SO + 2HI It decolorizes the purple solution of potassium permanganate, forming manganese sulphate and potassium sulphate. It con- verts arsenic acid into arsenious acid. It combines directly with lead dioxide, forming lead sulphate. PbO 2 + SO 2 = PbSO 4 Lead dioxide. Lead sulphate. Chlorine will unite directly with sulphurous oxide. If a mixture of equal volumes of chlorine and sulphurous oxide be 100 ELEMENTS OF MODERN CHEMISTRY. exposed to sunlight, the two gases combine, forming a liquid having a suffocating odor. It is sulphuryl chloride. Its den- sity is 1.66, and its boiling-point is 77°. It may be regarded as sulphur trioxide in which one atom of oxygen is replaced by two atoms of chlorine. SO 3 = (S0 2 )"0 sulphuryl oxide or sulphuric oxide. S0 2 CP = (S0 2 )"CF sulphuryl chloride. In these reactions in which the sulphurous oxide combines directly with either one atom of oxygen or two atoms of chlorine, it plays the part of an element ; it is a compound radical, and this radical is diatomic, because it unites with two atoms of the monatomic element chlorine, or with one atom of the diatomic element oxygen, which is equivalent to two atoms of chlorine. In the formulae given, the diatomicity is expressed by the accents " . Sulphurous acid bleaches various vegetable and animal mat- ters. A bouquet of violets or a rose is bleached in a few minutes by a solution of sulphurous oxide. Sulphurous oxide is employed in the arts to bleach wool. HYDRO-SULPHUROUS ACID. H 2 S0 2 While sulphurous acid reduces a number of bodies, it is in its turn reduced by the action of zinc upon its aqueous solution. A yellow liquid is thus obtained which energetically bleaches indigo and litmus solutions (Schonbein). Schtitzenberger has shown that the liquid gifted with these properties contains the zinc salt of a new acid, which he has named hydrosulphurous. This acid is formed by the combination of hydrogen with sul- phurous oxide. The reaction is expressed by the following equations : H 2 S0 3 + Zn = ZnSO 3 + H 2 Sulphurous acid. Zinc. Zinc sulphite. SO 2 + H 2 = H 2 S0 2 Sulphurous oxide. Hydrosulphurous acid. When this liquid is treated with very dilute sulphuric acid, it gives a liquor of a dark orange-yellow color, having ener- getic bleaching powers. It then contains hydrosulphurous acid. It soon becomes clouded and deposits sulphur. This SULPHUR TRIOXIDE, OR SULPHURIC OXIDE. 101 acid is not stable, but its acid sodium salt is more so ; the latter has the composition NaHSO 2 . It readily absorbs oxygen from the air, being converted into sodium acid sulphite. NaHSO 2 + = NaHSO 3 This oxidation is also brought about by the presence of cer- tain metallic salts, such as those of copper, mercury, and lead, In this case the metal is reduced and precipitated, and the hydrosulphite is decomposed, yielding sulphurous oxide. NaHSO 2 + CuSO* = NaHSO 4 + SO 2 + Cu Sodium hydrosulphite. Cupric sulphate. Sodium acid sulphate. Sodium acid hydrosulphite may be obtained by the electro- lysis of a solution of sodium acid sulphite. In this case the hydrogen, which would otherwise be disengaged at the negative pole, accomplishes the reduction. NaHSO 8 + H 2 = NaHSO 2 + H 2 SULPHUR TRIOXIDE, OR SULPHURIC OXIDE. (sulphuric anhydride.) Vapor density compared to hydrogen 40. Molecular weight SO 3 ... = SO. Sulphur trioxide is formed by the union of oxygen with sul- phurous oxide in the presence of finely-divided platinum. It is prepared by gently heating fuming sulphuric acid in a retort ; vapors are given off which, when condensed in a re- ceiver surrounded by a freezing mixture, solidify into a white mass, having a fibrous appearance and a silky lustre. Sulphur trioxide boils at a temperature between 30 and '35°. At ordinary temperatures it produces white fumes in the air by condensing the atmospheric moisture. Its most striking property is its affinity for water ; when thrown into that liquid, it becomes hydrated with such energy that a portion of the water is suddenly vaporized, and a hissing noise is produced similar to that heard on plunging a red-hot iron into water. Sulphuric acid is formed by the reaction. SO 3 + H 2 = H 2 SO* 9* 102 ELEMENTS OF MODERN CHEMISTRY. SULPHURIC ACID. Molecular weight H 2 S0 4 =98. This acid, which has been known for centuries, was formerly obtained by the distillation of ferrous sulphate. Large quan- tities of it are now consumed in the arts, and it is manufac- tured in extensive apparatus known as leaden chambers. Sul- phurous oxide is conducted into these chambers, where it meets with nitric acid, by which it is oxidized. SO 2 + 2HN0 3 = H 2 S0 4 + 2N0 2 Nitric acid. Nitrogen peroxide. The products of the first reaction are sulphuric acid and nitrogen peroxide (red vapors) ; but the latter is decomposed by steam, which is injected into the chamber ; nitric acid is regenerated and nitrogen dioxide is formed. 3N0 2 + H 2 = 2HN0 3 + NO Nitrogen peroxide. Nitrogen dioxide. But the nitrogen dioxide is not lost ; it combines with the oxygen of the air contained in the chamber, and is reconverted into nitrogen peroxide. NO + = NO 2 The latter is again decomposed into nitric acid and nitrogen dioxide by the action of water, and the sulphurous oxide which continually arrives in the chamber always encounters nitric acid, by which it is converted into sulphuric acid. It is a continuous operation, which theoretically leaves no residue, and permits of the conversion of an indefinite amount of sul- phurous oxide into sulphuric acid. It is really the oxygen of the air, continually absorbed and given up by the nitrogen dioxide, which effects the oxidation of the sulphurous oxide ; the nitric acid is the direct agent, and the nitrogen dioxide is intermediate, for it is the vehicle for the transfer of the oxygen. Fig. 37 represents a section of a series of leaden chambers for the manufacture of sulphuric acid. Sulphur is burned in two furnaces, AA, and the heat gen- erated is employed to boil the water contained in the boilers SULPHURIC ACID. 103 104 ELEMENTS OF MODERN CHEMISTRY. above the flame, the steam being distributed to the chambers by the pipes c d. The sulphurous oxide, together with a great excess of air, passes through the pipes BB into a leaden drum, C. A thin layer of sulphuric acid charged with nitrous products trickles over the inclined shelves in the drum. The gases pass first into the chamber C, then into D, where they meet with nitric acid, which falls in thin layers over a double cascade, EE, in such a manner as to present a large surface for the action of the sulphurous oxide. The sulphuric acid which is formed in this chamber is charged with nitrous products ; it is therefore allowed to flow by the inclined tube F into the chamber C, where it encounters an excess of sulphurous oxide, and which is called the denitrifier. The sulphurous oxide, the excess of air, and the nitrogen peroxide pass from D into the large chamber HH, into which steam is projected by several jets. Here the larger portion of the sulphuric acid is pro- duced, and the reaction is completed in another chamber. In the engraving the last two chambers are not fully represented. The gases from the last chamber enter a refrigerator, in which the condensation takes place ; they are lastly conducted into a leaden column, R, filled with coke which is kept saturated with sulphuric acid by a thin stream from the reservoir 0. This acid completely absorbs the nitrogen dioxide, and descends by the tube ha into the reservoir t, situated near the furnace. As soon as this reservoir is full, the stop-cock r is closed, and r' is opened ; the pressure of the steam then forces the acid up into the reservoir g, which feeds the first drum. The gas which escapes from the last column, which is known as Gray- Lussac's column, consists of nitrogen charged with an insig- nificant quantity of nitrous products. The acid which is drawn from the chambers is not suffi- ciently concentrated, having a density of only about 1.5. It is first evaporated in leaden vessels until it becomes strong enough to act upon the lead, and the concentration is then fin- ished in large platinum retorts. The excess of water is thus driven out. The concentrated acid possesses a density of 1.842. In many manufactories pyrites is burned instead of sulphur. Sulphurous oxide is produced, and a residue of ferric oxide remains. Purification of Sulphuric Acid. — The sulphuric acid of commerce contains impurities. It holds in solution a small SULPHURIC ACID. 105 quantity of lead sulphate, formed in the evaporating basins ; it is often charged with nitrous products, and sometimes with ar- senic acid, when the sulphurous oxide employed in its prepa- ration has been obtained by the combustion of arsenical pyrites. It may be freed from these impurities by distillation. The nitrous products are first disengaged, and are found in the first portions of the distillate, which must be rejected. Pure sul- phuric acid then passes ; the lead sulphate and arsenic acid remain in the retort with the last portions of the acid, which must not be distilled. The operation may be conducted in a glass retort connected with a cooled receiver. The retort should be heated laterally by an annular flame so that explosive evolution of vapor may be avoided, and it is well to introduce some platinum wires with the acid, and to cover the retort with a sheet-iron hood. Constitution of Sulphuric Acid. — Since oxygen combines directly with sulphurous oxide to form sulphuric oxide, the latter may be regarded as sulphuryl oxide, S0 2 0. Sulphuric acid is the hydrate of this oxide. SO 3 + H 2 = H 2 S0 4 The following experiment indicates the relations which exist between the elements composing this hydrate. If sulphuryl chloride be poured into water, it disappears, sulphuric acid and hydrochloric acid being formed. 802 {c! + HOT = S ° 2 {0H + 2HC1 • Sulphuryl 2 molecules . Sulphuric 2 molecules chloride. of water. acid. hydrochloric acid. Sulphuric acid is thus formed by the decomposition of 2 molecules of water, of which 2 atoms of hydrogen have been removed by 2 atoms of chlorine, and replaced by the group SO 2 . It may then be truly said that sulphuric acid is derived from two molecules of water by the substitution of the diatomic radical (SO 2 )" for two monatomic atoms of hydrogen. H.OH ^an2v f OH H.OH (bU ) JOH 2 molecules of water. Sulphuric acid. If the composition of sulphuric acid be compared to that of sulphuryl chloride, from which it may be formed, it will be e* 106 ELEMENTS OF MODERN CHEMISTRY. seen that both compounds contain the same nucleus or radical SO 2 , and that instead of the two atoms of chlorine of the chloride, the acid contains two groups OH. The group OH is a residue, as it were, which represents a molecule of water minus one atom of hydrogen, and which is called hydroxyl. It is a monatomic group, and sulphuric acid is formed by the saturation of the affinity of the diatomic radical sulphuryl by two monatomic groups hydroxyl, which replace the two atoms of chlorine of sulphuryl chloride. Williamson has described an intermediate compound in which the radical sulphuryl is combined with one atom of chlorine and one OH group. SO* {g SO'j^ so'l^ Sulphuryl chloride. Sulphuryl chlorohydrate. Sulphuric acid. The sulphur in sulphuric acid is hexatomic. HO-S-OH ii O Physical Properties. — Sulphuric acid is a colorless oily liquid ; its density at 12° is 1.842 (Marignac). Its boiling-point is 325°, and it solidifies at — 34°. If it be crystallized several times at a low temperature, and the part remaining liquid be decanted off each time, the melting-point is gradually raised to + 10.5°, where it remains stationary. According to Marignac, the acid which solidifies and fuses at -(-10.5° constitutes the true monohydrated acid, H 2 SO*. At a temperature about 40° it emits some fumes, and between this point and 290° it disen- gages a small quantity of vapor of sulphuric oxide. At 290° it begins to boil, but its boiling-point soon rises to 338°, where it remains. Such are, according to Marignac, the properties of monohydrated sulphuric acid. According to this chemist, the acid purified by simple distillation, and boiling at 325°, still contains a small amount of water. Chemical Properties. — When exposed to a red heat, sul- phuric acid decomposes into sulphurous oxide, oxygen and watPT* H 2 S0 4 = SO 2 + O + H 2 Many bodies having an affinity for oxygen reduce sulphuric SULPHURIC ACID. 107 acid by the aid of heat. Thus sulphur effects the reduction, being at the same time oxidized to sulphurous oxide. 2H 2 SO + S = 3S0 2 + 2H 2 We have already studied the action of charcoal and copper upon sulphuric acid when boiled with that liquid, and we have seen that zinc and iron decompose the dilute acid with evolu- tion of hydrogen and formation of a sulphate. Sulphuric acid has a strong affinity for water. When four parts of sulphuric acid are quickly mixed with one part of water, the temperature rises to above 100°. If the experiment be made with large quantities, it is not without danger, and re- quires prudence lest part of the acid be projected from the vessel. Experiments. — If four parts of sulphuric acid be quickly added to one part of snow, the latter is immediately liquefied and a notable elevation of temperature takes place ; for the energy of the combination of the sulphuric acid with the water is so great that the heat produced by the union is greater than that consumed in the liquefaction of the ice. But if four parts of snow be mixed with one part of sul- phuric acid, the result is the reverse ; there is a lowering of temperature. The affinity of sulphuric acid for water is manifested in a number of reactions. In the following it is sufficiently power- ful to cause the formation of the water it requires : If a morsel of sugar be moistened with sulphuric acid, it becomes blackened and carbonized in a few minutes. The sugar contains no water already formed, but independently of carbon it contains hydrogen and oxygen in the proportions necessary to form water, so that the latter compound is produced by the influence of the sulphuric acid, and a carbonaceous matter remains. This water which is absorbed by sulphuric acid with so much energy, combines with the acid in a manner analogous to that in which water of crystallization combines with certain salts. Indeed, if sulphuric acid to which 18.3 per cent, of water has been added be exposed to a temperature of 0°, large prismatic crystals are formed, which remain solid even at a temperature of -j-7° or -{-8°. The composition of these crystals is ex- pressed by the formula H 2 SO,H 2 0. They constitute a dihy- drated acid, for they result from the union of two molecules of water with one molecule of sulphuric oxide. 108 ELEMENTS OF MODERN CHEMISTRY. Sulphuric acid is a dibasic acid ; that is, it contains two atoms of hydrogen that are replaceable by an equivalent quantity of metal. This substitution takes place when the acid is treated with a hydrate, such as potassium hydrate, or with an oxide, such as lead oxide. IPSO + 2KOH — K 2 SO + 2H 2 Potassium hydrate. Potassium sulphate. IPSO 4 + PbO = PbSO + H 2 Lead oxide. Lead sulphate. When saturated with potassium hydrate, the sulphuric acid is converted into potassium sulphate, and, in the salt, two atoms of potassium replace the two atoms of hydrogen of the acid. In the case of the lead oxide, on the contrary, the reaction, which is only a double decomposition, takes place so that a single atom of lead replaces the two atoms of hydrogen. The metal lead is then said to be diatomic ; that is, one atom of lead is capable of replacing two atoms of a monatomic element such as hydrogen, and one atom of lead is equivalent to two atoms of potassium. Sulphuric acid may be detected by the following reactions, which are also applicable to the soluble sulphates. In solutions containing sulphuric acid or a sulphate, barium baits produce a white pulverulent precipitate, which is insolu- ble in either cold or hot nitric acid ; this precipitate is barium sulphate. When mixed with an excess of charcoal and heated to whiteness, it is converted into barium sulphide. BaSO* + 40 = 4CO + BaS Barium sulphate. Carbon monoxide. Barium sulphide. The sulphide of barium disengages hydrogen sulphide when it is moistened with hydrochloric acid ; this gas may be recog- nized by its odor and by its blackening a paper impregnated with lead acetate. FUMING SULPHURIC ACID. Fuming sulphuric acid, or Nordhausen sulphuric acid, as it was formerly called, can be regarded as a combination of sul- phuric acid and sulphuric oxide. so.< OH HW -|- SO 3 = H 2 S 2 0' = S0 2 < OH HYPOSULPHUROITS ACID. 109 It is a light-brown, oily liquid. At 0° it solidifies into a leafy mass. It gives off white fumes in the air. When heated, it decomposes into sulphuric oxide and sulphuric acid. It is ob- tained in the arts by the distillation of ferrous sulphate that has been previously transformed into ferric subsulphate by roasting. This subsulphate is calcined in stoneware retorts ; it gives off sulphuric oxide when it is perfectly dry, but as it is difficult to entirely free it from water of crystallization, the vapor of sulphuric oxide is mixed with that of sulphuric acid, and the mixed vapors are condensed in cooled receivers. The residue of the distillation is ferric oxide, Fe 2 3 . Fuming sulphuric acid is used by dyers to dissolve indigo. THIOSULPHURIC ACID. H 2 S(S0 3 ) This acid, called also hyposulphurous and sulphosulphuric acid, is not known in the free state. When sodium thiosulphate is treated with dilute sulphuric acid, the thiosulphuric acid set free is at once decomposed into sulphurous acid and sulphur. Na 2 S 2 3 + IPSO 4 = Na 2 S0 4 + H 2 S0 3 + S Sodium thiosulphate. Sodium sulphate; Sodium thiosulphate is formed when sulphur is boiled with a solution of sodium sulphite. Na 2 S0 3 + S = Na 2 S(S0 3 ) Sodium sulphite. Sodium thiosulphate. It is a very soluble salt, forming voluminous crystals. It is used in photography and in the manufacture of paper. HYPOSULPHURIC ACID. H' 2 S 2 06 If fuming sulphuric acid represent a combination of sul- phuric acid and sulphuric oxide, hyposulphuric acid can be regarded as resulting from the union of sulphuric acid with sulphurous oxide. S0 3 .H 2 S0 4 fuming sulphuric acid. S0 2 .H 2 S0 4 hyposulphuric acid. Preparation. — Hyposulphuric acid is prepared by passing sulphurous oxide into water in which manganese dioxide is sus- pended. 2S0 2 + MnO 2 = MnS 2 6 Manganese dioxide. Manganese hyposulphate. 10 110 ELEMENTS OF MODERN CHEMISTRY. Manganese hyposulphate is thus formed, and this is con- verted into barium hyposulphate by a double decomposition with barium sulphide. The liquid is separated from the man- ganese sulphide by filtration, and exactly decomposed with dilute sulphuric acid. Barium sulphate is precipitated, and the hyposulphuric acid remains in solution. The liquid is then concentrated in vacuo. Properties. — Hyposulphuric acid is a very acid, syrupy liquid, having a density of 1.347. It is not stable ; when boiled it decomposes into sulphuric acid and sulphurous oxide. PERSULPHURIC OXIDE. S 2 0? This body has been very recently discovered by Berthelot, who obtained it in the pure state by the action of silent elec- tric discharges of high tension upon a mixture of equal vol- umes of sulphurous oxide and oxygen, both perfectly dry. Persulphuric oxide is formed, and there remains a residue of oxygen. S 2 0* + O = S 2 7 + 4 vol. sulphurous oxide. 4 vol. oxygen. Persulphuric oxide. Oxygen. When pure it is solid at ordinary temperatures, crystallizing sometimes in grains, sometimes in thin and flexible transparent needles. Sometimes it remains liquid. It is not stable, and decomposes spontaneously in about two weeks. When heated, it decomposes rapidly into sulphuric oxide and oxygen. S 2 7 = 2S0 3 + Persulphuric oxide. Sulphuric oxide. Water dissolves it with production of dense fumes and a brisk effervescence due to the disengagement of oxygen. The liquid then contains sulphuric acid. At the same time a small quantity of persulphuric acid, H 2 S 2 8 , or HSO, is formed, which soon decomposes into sulphuric acid and oxygen. This persulphuric acid, which is very unstable, would be analogous to permanganic acid ; its formation is expressed by the following equation : S 2 7 + H 2 = 2HSO SELENIUM AND TELLURIUM. Ill According to Berthelot, persulphuric acid is formed by the electrolysis of concentrated solutions of sulphuric acid. It would also be formed by the careful addition of a solution of hydrogen dioxide to sulphuric acid slightly diluted with water. 2H 2 SO + = H 2 + 2HS0 4 It is by no means certain that the formula HSO 4 represents the composition of a molecule of persulphuric acid. It is pos- sible that this formula must be doubled as indicated above. At present this point cannot be decided. SELENIUM AND TELLURIUM. These two rare elements present a great analogy to sulphur. Selenium was discovered by Berzelius in certain Swedish pyrites. Like sulphur, selenium has two allotropic forms, one crystalline, the other vitreous and amorphous. The crystalline variety begins to melt above 217°, but liquefies only at 250° (Regnault) ; after rapid cooling it solidifies into a dark-brown mass. Its density is 4.8 when crystallized, and 4.3 when vit- reous. When heated in the air to a temperature above its melting-point it takes fire and burns with a blue flame, being converted into selenious oxide, SeO 2 . When sulphurous acid is added to a solution of selenious oxide the latter is reduced,, sulphuric acid is formed, and the selenium is precipitated in the form of brown -red flakes. Its compound with hydrogen is a colorless gas having a fetid and irritating odor. Tellurium is still more rare than selenium ; it occurs com- bined with gold and other metals in certain minerals of Tran- sylvania and Hungary, and also in the Rocky Mountain gold region in the United States. It has the external appearance and the lustre of a metal. Its color is silvery-white ; its den- sity 6.25. It melts at about 500°, and can be volatilized at a white heat in a current of hydrogen. It has a great tendency to crystallize. When heated in the air it burns with a green- ish-blue flame, forming tellurious oxide, TeO 2 . Its compound with hydrogen is a gas having an odor analogous to that of hydrogen sulphide. The following table shows the analogy between the principal compounds of sulphur, selenium, and tellurium : 112 ELEMENTS OF MODERN CHEMISTRY. H 2 S Hydrogen sulphide. SO 2 Sulphurous oxide. so s Sulphuric oxide. [H 2 S0 3 ] Sulphurous acid. H 2 SO Sulphuric acid. H 2 Se Hydrogen selenide. SeO 2 Selenious oxide. [SeO 3 ] Selenic oxide. H 2 Se0 3 Selenious acid. H 2 SeO* Selenic acid. H 2 Te Hydrogen telluride. TeO 2 Tellurious oxide. TeO 3 Telluric oxide. H 2 Te0 3 Tellurious acid. H 2 Te0 4 Telluric acid. CHLORINE. Density compared to air 2.44 Density compared to hydrogen 35.5 Atomic weight CI = 35.5 Chlorine was discovered by Scheele in 1774, and was first recognized as an element by Gay-Lussac and Thenard in 1809, and by Sir Humphry Davy in 1810. It is one of the elements of common salt, or sodium chloride. Preparation. — One part of manganese dioxide in coarse powder and six parts of common hydrochloric acid are intro- o duced into a flask fitted with a safety-tube and delivery-tube (Fig. 38). The reaction begins in the cold; chlorine gas is CHLORINE. 113 disengaged, and may be collected over salt water. As soon as the disengagement of gas diminishes, it may be re-established by the application of a gentle heat. It is more convenient to collect the gas by dry displacement, and it may be obtained pure and dry by being conducted through a wash-bottle containing a small quantity of water, and a tube containing calcium chloride, as represented in the figure. It is then passed, by means of a tube bent at a right angle, into a dry jar. The chlorine being heavier than the air, col- lects at the bottom of the jar and gradually drives out the air, and the uniform greenish color of the whole of the gas in the jar indicates when the latter is completely filled. If it be desired to prepare a solution of chlorine in water, the gas may be passed through a series of Wolff's bottles con- Fig. 39. taining water, the contents of the first bottle being rejected, serving merely to wash the gas (Fig. 39). The reaction which takes place in the preparation of chlo- rine is a double decomposition between the manganese dioxide and the hydrochloric acid. Water and manganese chloride are formed, and chlorine is set free. MnO 2 + 4HC1 = 2H 2 + MnCP + CI 2 Manganese dioxide. Hydrochloric acid. g Manganese chloride. Physical Properties. — Chlorine is a greenish-yellow gas 10* 114 ELEMENTS OF MODERN CHEMISTRY. having a strong and suffocating odor. A litre of this gas weighs 3.16 gr. It may be liquefied at 15° by a pressure of four atmospheres. A small quantity of the liquid may easily be prepared in the following manner : Some crystals of chlorine hydrate are introduced into a tube of thick glass closed at one end and bent in the middle ; the other end is then hermetically sealed at the blast-lamp. The branch containing the crystals is then heated in a water-bath, while the other branch is cooled in a freezing mixture (Fig. 40). The hydrate of chlorine breaks up into water and chlorine, and the greater part of the latter is disen- gaged, and condenses by its own pressure into a deep-yellow liquid, "p7 G 40. which collects in the- cooler limb of the tube (Faraday). Chemical Properties. — One volume of water at 8° dissolves 3 volumes of chlorine ; at 17°, 2.42 volumes. The saturated solution has a yellow color. When it is exposed to a tempera- ture of 0°, it deposits crystals containing 27.7 per cent, of chlorine, and 72.3 per cent, of water, and constituting a hydrate of chlorine corresponding to the formula CI 2 -f- 10H 2 O (Fara- day). Chlorine possesses powerful affinities. It unites directly with the greater number of the other elements, and the com- bination frequently takes place with such energy that luminous heat is produced. Experiments. — If powdered antimony or arsenic be sprinkled into a jar containing dry chlorine, each particle of the black powder burns with a bright spark as soon as it enters the atmos- phere of chlorine, producing thick, white fumes of antimony or arsenic chloride as the case may be. If a morsel of phosphorus, contained in a deflagrating spoon, be plunged into a jar of chlorine, the phosphorus melts and inflames spontaneously, and the sides of the jar become covered with a yellow, crystalline deposit of phosphorus pentachloride, PCI 5 . But the affinity of chlorine is most strikingly manifested by its action on hydrogen and hydrogen compounds. CHLORINE. 115 When a lighted taper is applied to a mixture of equal vol- umes of chlorine and hydrogen, the two gases unite instantly and explosively. Such a mixture will also explode violently on being exposed to direct sunlight ; the rays of the sun may even be replaced by the flame of magnesium or that of carbon disulphide. So great is the affinity of chlorine for hydrogen that it de- composes all hydrogen compounds, except hydrochloric and hydrofluoric acids. When it is dissolved in water, it slowly decomposes that liquid under the influence of sunlight, com- bining «vith the hydrogen and setting the oxygen at liberty. If a tube filled with an aqueous solution of chlorine be inverted over the pneumatic trough and exposed to direct sun- light, small bubbles of gas will be seen to rise through the liquid and collect at the top of the tube. This is the oxygen result- ing from the decomposition of the water. At a red heat, the vapor of water is rapidly decomposed by chlorine ; hydrogen sulphide gives up its hydrogen to chlorine at ordinary temperatures. All organic substances contain hydrogen ; they are therefore generally modified, and often destroyed by the action of chlorine. Coloring matters of organic origin are bleached. Experiment. — If a solution of chlorine be added to a solu- tion of litmus, sulphate of indigo, or ink, the intense colors peculiar to these substances disappear, giving place to a pale yellow or brown tint. This effect is due to the more or less profound decomposition which these coloring matters undergo by reason of the removal of a certain portion of their hydro- gen in the form of hydrochloric acid. This bleaching property of chlorine is of great service in the arts. A wax taper will burn in chlorine gas with a red, smoky flame. The hydrogen of the wax combines with the chlorine, while the carbon is set free as smoke. A piece of paper satu- rated with oil of turpentine takes fire spontaneously when introduced into a jar of chlorine, producing a dense cloud of smoke ; the turpentine contains only carbon and hydrogen the latter is attacked by the chlorine, the former being set free. Chlorine is also an efficacious disinfectant. It decomposes hydrogen sulphide. It destroys odorous matters of organic origin, the effluvia resulting from putrid fermentation, and the miasms which are sometimes diffused in the air. It 116 ELEMENTS OF MODERN CHEMISTRY is employed to disinfect privys, etc., and to purify the air in certain epidemics. The bleaching properties and disinfecting properties of chlorine are due to the same cause, — its powerful affinity for hydrogen. HYDROCHLORIC ACID. Density compared to air 1.27 Density compared to hydrogen 18.33 Molecular weight HC1 = 36.5 Hydrochloric acid exists among the gaseous products* disen- gaged by volcanoes. r Fig. 41. Preparation. — Fragments of fused common salt are intro- duced into a flask fitted with a safety-tube and delivery-tube, like that for the preparation of chlorine, and concentrated sul- phuric acid is added. Hydrochloric acid gas is disengaged, and HYDROCHLORIC ACID. 117 may be collected over mercury. Sodium acid sulphate remains in the retort. H 2 SO + NaCl = NaHSO 4 + HC1 Sodium chloride. Sodium acid sulphate. In the arts, the operation is conducted in cast-iron cylinders or furnaces (Fig. 41), at a high temperature. Under these conditions, one molecule of sulphuric acid acts upon two mole- cules of sodium chloride, yielding sodium neutral sulphate. and two molecules of hydrochloric acid. H 2 SO + 2NaCl = Na 2 S0 4 + 2HC1 Sodium sulphate. The hydrochloric acid gas evolved is passed into stoneware bottles, C, C, C' r , containing water. It is thus dissolved, and the solution obtained constitutes the muriatic acid of com- merce. A solution of hydrochloric acid may be prepared in the laboratory by passing the gas through water contained in a series of Wolff bottles surrounded by cold water, the contents of the first bottle being rejected (Fig. 42). Fig. 42. Composition of Hydrochloric Acid. — The composition of this gas may be deduced from the following experiments : 118 ELEMENTS OF MODERN CHEMISTRY. 1. A bottle, B (Fig. 43), the neck of which is adapted by grinding with emery to the flask A, is filled with dry chlorine ; A, which has exactly the same capacity as the bottle, is filled with dry hydrogen ; the two vessels are then fitted together, and by means of the ground joint are hermetically sealed. The apparatus is now abandoned for a time to diffuse light, and as the two gases slowly mix they combine. The union is completed by exposing the apparatus to direct sunlight. When the tint of the chlorine has entirely disappeared, the two vessels are separated under the surface of mercury, and it is found that no change in volume has taken place. The chlorine and hydrogen have both disappeared to form hydrochloric acid, which occupies precisely the same volume as the two primitive gases. Consequently 2 volumes of hydrochloric gas contain 1 volume of chlorine and 1 volume of hydrogen ; and if the weight of one volume of hydrogen (unity) be added to that of one volume of chlorine (its density compared to hydrogen as unity), the sum will be the weight of two volumes of hydrochloric acid, and will also represent the weight of the molecule. Fig. 43. Densities com- pared to H. Weight of 1 volume of hydrogen .... 1 Weight of 1 volume of chlorine .... 35.5 Weight of 2 volumes of hydrochloric acid 36.5 Densities com- pared to Air. 0.0693 2.44 2.5093 2. Two volumes of hydrochloric acid gas are passed into a bent tube over mercury (Fig. 44), and a small piece of sodium is passed up into the bulb and heated by the flame of a spirit- lamp. The sodium combines with the chlorine setting the hydrogen at liberty, and after the experiment one volume of hydrogen remains in the tube. This second experiment con- firms the first, both proving that hydrogen and chlorine unite in equal volumes, and without condensation, to form Fig. 44. HYDROCHLORIC ACID. 119 hydrochloric acid. One volume of hydrochloric acid contains half a volume of hydrogen and half a volume of chlorine, but we cannot admit that the atoms of these elements are divided into two in the formation of hydrochloric acid ; such a sup- position would be contrary to all ideas of atoms, which repre- sent the smallest particles of an element that can exist in a compound. It is more natural to conclude that two vol- umes of chlorine and two volumes of hydrogen react together in the formation of hydrochloric acid. Two volumes of chlorine contain two atoms, constituting one molecule of chlo- rine. In the same manner two volumes of hydrogen contain two atoms, constituting one molecule of hydrogen. CI CI H H 2 volumes or 1 molecule of chlorine = C1C1. 2 volumes or 1 molecule of hydrogen = HH. It is these molecules which are separated into two when chlorine combines with hydrogen : they exchange their atoms, and from the exchange, which is a double decomposition, there result two molecules of hydrochloric acid, which occupy pre- cisely the same volume as the two molecules of the simple gases. CI CI + H ! H = = H CI + |H CI 2 vols, of chlorine + 2 vols, of hydrogen = = 2 vols, of hydro- + 2 vols, of hydro- chloric acid chloric acid. We encounter here again the notion that certain elements in the free state are composed of molecules, each of which con- tains two atoms of the same kind. The force which unites them is not different from affinity. It is affinity which unites chlorine to chlorine in the molecule of that element ; hydrogen to hydrogen in the molecule of free hydrogen (Gernardt). When, however, these two molecules are brought together, the affinity of chlorine for hydrogen preponderates, and brings about an exchange, a double decomposition. Physical Properties. — Hydrochloric acid is a colorless gas having a pungent odor. It forms thick white fumes in the air by condensing the atmospheric moisture. It may be liquefied by a pressure of 40 atmospheres. It is one of the most soluble of gases in water. If a jar filled with this gas and inverted on a plate containing mercury 120 ELEMENTS OF MODERN CHEMISTRY. so that the mouth is sealed, be depressed in the pneumatic trough, and the plate be then quickly removed, the water im- mediately rushes into the jar as it would into a vacuum. The shock of the column of water is sometimes sufficient to break the jar. One volume of water at 0° dissolves 500 volumes of hydro- chloric acid; at ordinary temperatures, about 480 volumes. The water becomes heated and increases in volume. The cold saturated solution has a density of 1.21 and contains 42.4 per cent, by weight of the dry gas. It is a colorless liquid, giving off white fumes. When it is heated, it loses a large quantity of the gas which it holds in solution, but the whole of the gas is not disengaged, and when the temperature reaches 110° the liquid distils without further loss of gas. A dilute hydrochloric acid is thus obtained, having a uniform density of 1.10 (Bineau). Chemical Properties. — Hydrochloric acid is an energetic acid ; it strongly reddens litmus-paper. It is not decomposable by heat, but is partly decomposed by a series of electric sparks. All of the metals which decompose water also decompose hy- drochloric acid with the liberation of hydrogen and the for- mation of a chloride. Such metals are sodium, zinc, iron, aluminium, tin, etc. Hydrochloric acid decomposes the metallic oxides and hy- drates with the formation of water and a chloride. If hydrochloric acid be added in small quantities to a con- centrated solution of potassium hydrate, the liquid becomes heated and deposits potassium chloride as a crystalline powder. HC1 + KOH = KC1 + H 2 Potassium hydrate. Potassium chloride. Hydrochloric acid is then a true acid although it contains no oxygen, for it contains an atom of hydrogen that is replaceable by an atom of metal. In its action upon potassium hydrate it resembles nitric acid, for this acid also contains one atom of hydrogen, which is replaceable by an atom of metal. HNO 3 + KOH = KNO 3 + H 2 Nitric acid. Potassium nitrate. It is seen that the acids are compounds containing a strongly electro-negative atom or group of atoms, united with hydrogen, which hydrogen can be replaced by a metal. In nitric acid, H(N0 3 ), the group NO 3 plays the part taken by chlorine in OXYGEN COMPOUNDS OF CHLORINE. 121 hydrochloric acid ; like the chlorine, it renders the hydrogen replaceable by a metal. The action of hydrochloric acid upon the metallic oxides is analogous to that which it exerts upon the hydrates. If a current of hydrochloric acid be passed over mercuric oxide contained in a tube (Fig. 45), the oxide becomes heated, Fig. 45. and is converted into a white powder which is mercuric chlo- ride ; at the same time water is formed and condenses in the bulb. HgO + 2HC1 = HgCP + H 2 Mercuric oxide. Mercuric chloride. OXYGEN COMPOUNDS OP CHLORINE. With oxygen, chlorine forms compounds which may be an^ hydrous or hydrated ; the latter are acids. The oxides are : Hypochlorous oxide C1 2 Chlorous oxide C1 2 3 Chlorine peroxide C1 2 4 The acids are : Hypochlorous acid HCIO Chlorous acid HCIO 2 Chloric acid HCIO 3 Perchloric acid HCIO 4 F 11 122 ELEMENTS OF MODERN CHEMISTRY. HYPOCHLOROUS OXIDE AND ACID. Hypochlorous oxide is prepared by passing a current of dry chlorine over mercuric oxide contained in a tube surrounded by cold water, and may be condensed in a long-necked matrass placed in a freezing mixture (Fig. 46). H g O + 2CP = HgCl 2 + CPO Mercuric oxide. Mercuric chloride. Fig. 46. The oxide condenses as a brown-red liquid, boiling at 20°. Above that temperature it is a reddish-yellow vapor, having a density of 2.977, or, compared to hydrogen as unity, 43.5. Two volumes of this vapor contain two volumes of chlorine and one volume of oxygen, a composition represented by the formula CPO. Hypochlorous oxide is a dangerous body, and cannot be kept for more than a few hours without spontaneous decomposition ; its vapor frequently explodes. In combining with the elements of water, hypochlorous oxide forms hypochlorous acid, the solution of which is almost color- less. S}« + Z}° = ?,}<> + g}o Preparation of Hypochlorous Acid. — 1. A solution of hypochlorous acid may be prepared by agitating mercuric oxide CHLOROUS OXIDE. 123 with water in jars filled with chlorine gas. The water will then contain hypochlorous acid and mercuric chloride, and there re- mains a brown powder, which is mercury oxy chloride. (Balard.) 2. A current of chlorine is passed through water holding recently-precipitated calcium carbonate in suspension. The latter disappears, carbonic acid gas is disengaged, and the water becomes charged with calcium chloride and hypochlorous acid. The mixture is distilled, and the acid which passes with the water is condensed in a cooled receiver (Williamson). CaCO 3 + 2CP + H 2 = CO 2 + CaCl 2 + 2HC10 Calcium Carbon Calcium Hypochlorous carbonate. dioxide. chloride. acid. When chlorine is passed into a rather dilute solution of an alkaline hydrate, a chloride and a hypochlorite are formed : 2KOH + 2C1 = KC1 + KCIO + H 2 In this manner are prepared solutions containing potassium hypochlorite (Javelle's solution), and sodium hypochlorite (Labarraque's solution), extensively used for bleaching and disinfecting. Properties of Hypochlorous Acid. — Concentrated hypo- chlorous acid is a dark-yellow liquid, having the peculiar smell of chlorinated lime or bleaching-powder. It is very caustic, and rapidly destroys the skin ; its bleaching power is very en- ergetic, double that of the chlorine it contains. Hydrochloric acid decomposes it into chlorine and water. HCIO + HC1 = CI 2 + H 2 CHLOROUS OXIDE. C1 2 3 Chlorous oxide is formed when potassium chlorate is decom- posed by dilute nitric acid in the presence of a body capable of uniting with oxygen, such as.arsenious oxide. At a gentle heat a greenish gas is disengaged which does not liquefy at a temperature of — 20°. This gas is not stable; above 57° it decomposes with explosion into chlorine and oxygen. It dissolves in water, forming a dark golden-yellow solution containing chlorous acid, a body quite unstable itself. C1 2 3 + H 2 = 2HC10 2 Chlorous oxide. Chlorous acid. 124 ELEMENTS OF MODERN CHEMISTRY. CHLORINE PEROXIDE. C1 2 0± This compound, which was discovered by Sir Humphry Davy, is prepared by the ac- tion of concentrated sulphuric acid upon fused potassium chlorate. The salt is finely pulverized and added in small quantities to sulphuric acid cooled to —10°. The pasty mass is then introduced into a small test-tube fitted with a delivery-tube (Fig. 47), and is gently heated in a water- bath ; the gas disengaged is collected in dry jars by down- ward displacement. = KCIO 4 + 2KHS0 4 + H 2 + CPO 4 Potassium Potassium acid perchlorate. sulphate. Chlorine peroxide is a yellow gas having a sweetish aromatic odor. At — 20° it condenses to an orange-red liquid. Its den- sity in the gaseous state is 33.75 (hydrogen being unity). This density is anomalous, and indicates that at the instant the liquid CPO 4 assumes the gaseous state it is dissociated into two more simple molecules, CIO 2 + CIO 2 , which occupy four volumes. is resolved into 3KC10 3 Potassium chlorate. Fig. 47. 2H 2 S0 4 a O 2 The density of gaseous chlorine peroxide is then only half that required by the formula CPO 4 . If one volume of hydrogen weighs 1, one volume of C1 2 4 ought to weigh .... 67.5. But it weighs only 33.75, which proves that CPO 4 in the gaseous state occupies four volumes instead of two. These four volumes contain, 2 volumes of CI, weighing 2 X 35.5 = 71 4 volumes of 0, weighing 16 X 4 =64 135 135 "Weight of one volume, or density, compared to H = 33.75 CHLORIC ACID — PERCHLORIC ACID. 125 Chlorine peroxide is a dangerous body ; it sometimes de- composes spontaneously with violent explosions. It is soluble in water, and the solution may be prepared by heating on a water-bath a mixture of equal parts of oxalic acid and potassium chlorate. Carbonic acid and chlorine peroxide gases are disengaged, and may be passed into water. Chlorine peroxide is absorbed by alkaline solutions with the formation of a chlorate and a chlorite. 2KOH + CPO = KCIO 8 + KCIO 2 + H 2 Potassium hydrate. Potassium chlorate. Potassium chlorite. CHLORIC ACID. HCIO 3 This acid is formed by the spontaneous decomposition of solutions of hypochlorous and chlorous acids and chlorine per- oxide. It may be prepared by treating barium chlorate with dilute sulphuric acid. Barium sulphate precipitates, and is removed by nitration, and the solution of chloric acid is concentrated by evaporation in vacuo. If chlorine be passed into a concentrated solution of an alkaline hydrate, a chloride and a chlorate are formed. 6KOH + 6C1 = 5KC1 + KCIO 8 + 3H 2 Chloric acid is a syrupy liquid, ordinarily of a yellow color ; it is not very stable ; at a temperature of 40° it commences to decompose, and at a higher temperature it is resolved into per- chloric acid, chlorine, oxygen, and water. It has extremely energetic oxidizing properties ; when concentrated, it at once inflames sulphur, phosphorus, alcohol, and paper. It oxidizes sulphurous and phosphorous acids and hydrogen sulphide. With hydrochloric acid it forms water and chlorine. •HCIO 3 + 5HC1 = 3H 2 + 3C1 2 PERCHLORIC ACID. HCIO* This is the most rich in oxygen of all the chlorine acids, and it is a curious circumstance that it is also the most stable. It may be prepared by distilling potassium perchlorate with concentrated sulphuric acid. Roscoe obtains it by distilling chloric acid, which is prepared by decomposing a solution of potassium chlorate by hydrofluosilicic acid. The insoluble po- ll* 126 ELEMENTS OF MODERN CHEMISTRY. tassium fluosilicate is separated by filtration, the filtered liquid is concentrated until white fumes appear, and then the distil- lation is commenced. The product must be rectified after being freed from the chlorine which is formed at the same time. The perchloric acid thus obtained is a heavy, oily, colorless liquid, resembling concentrated sulphuric acid. It still con- tains water, which may be removed by distillation with four times its weight of concentrated sulphuric acid. At about 100° dense vapors pass and condense into a very mobile, yellow liquid ; this is the perchloric acid HCIO 4 ; the temperature then rises, and at 200° a liquid passes which solidifies to a crystalline mass on cooling. These crystals are a hydrate, HC10 4 + H 2 0. The pure or normal perchloric acid has a density of 1.782 at 15.5°. When brought into contact with water, it combines with that liquid, producing a hissing noise. Its oxidizing powers are so energetic that it explodes on contact with paper, wood, or charcoal. It may be mixed with alcohol, but with ether it explodes. It cannot be distilled. The hydrate HCIO 4 + H 2 melts between 50 and 51°. CHLORIDES OF SULPHUR. When a current of dry chlorine is passed over sulphur heated in a retort, a liquid condenses in the receiver which fumes in the air, has a yellow color, and an irritating, fetid odor. This is sulphurous chloride, S 2 CP. In order that this compound may be formed, the sulphur must be maintained in excess, and the operation must be stopped before it has all disappeared. The product is purified by rectification, that part being collected which passes at 139°. When chlorine is passed for several hours "through the chloride of sulphur just described, the yellow color of the latter changes to deep red. The liquid obtained is mobile, fumes in the air, and continually disengages chlorine. It can- not be distilled without decomposition. The product which passes is at first red, but afterwards assumes a lighter color, and when the temperature reaches 139° there remains in the retort only sulphurous chloride, S 2 C1 2 . The red liquid has a composition which corresponds to the formula S 2 C1 4 . It is called perchloride of sulphur. Carius BROMINE. 127 regards it as a mixture of the chloride S 2 C1 2 with a tetra- chloride SCI 4 , corresponding to sulphurous oxide. SO 2 sulphur dioxide. SCI 4 sulphur tetrachloride. This tetrachloride has been recently isolated by Miehaelis, but it can only exist at a low temperature ; it decomposes into chlorine and sulphurous chloride. S 2 CP 3 as soon as it is removed from the freezing mixture where it has been condensed. The chlorides of sulphur are employed in vulcanizing caoutchouc. BROMINE. Vapor density compared to air . . . 5.393 Vapor density compared to hydrogen . 77.9 (nearly 80) Atomic weight Br =80. Bromine was discovered by Balard in 1826. Preparation. — It is obtained by decomposing potassium bromide by manganese dioxide and sulphuric acid. Potassium sulphate and manganese sulphate are formed, and the bromine is liberated. 2KBr + MnO 2 + 2H 2 S0 4 = K 2 S0 4 + MnSO 4 + 2H 2 + Br 2 Potassium Manganese Potassium Manganese bromide. dioxide. sulphate. sulphate. The operation is conducted in a tubulated retort, heated on a sand-bath, and the bromine is condensed in a cooled receiver fitted to the retort by the aid of an adapter. The potassium bromide may be replaced by magnesium bromide, which exists in the mother-liquors of salt-springs. In this case magnesium sulphate is formed. The mother- liquors of the soda varech from which the iodine has been ex- tracted are also employed for the preparation of bromine. Properties. — Bromine is a dark-red liquid, which solidifies at — 24.5°. Its density at 15° is 2.99. It boils at 63°, and at ordinary temperatures gives off red, irritating vapors, for its vapor tension is considerable even in the cold. It stains the skin yellow, and immediately corrodes the tissues. It dissolves in about 33 times its weight of water at 15°, forming an orange- red solution. At a low temperature it combines with water, forming a crystalline hydrate, Br 2 -f- 10H 2 O, analogous to that formed by chlorine. Moist bromine will freeze at — 7°. 128 ELEMENTS OF MODERN CHEMISTRY. Bromine dissolves in carbon disulphide, in chloroform, and in ether. Experiment. — A small quantity of solution of potassium bromide is introduced into a long tube, closed at one end, and the tube is then nearly filled with chlorine- water ; when the two solutions are mixed, the liquor assumes an orange-red color from the liberation of the bromine. The tube is now filled up with ether and agitated briskly, the open end being closed with the finger. The ether passes through the aqueous solution and dissolves out all of the bromine, assuming at the same time a dark-red color. The affinity of bromine for hydrogen is powerful, but not as energetic as that of chlorine. Like chlorine, it has remarkable bleaching properties. HYDROBROMIC ACID. Density compared to air 2.73 Density compared to hydrogen 40.5 Molecular weight HBr =81. Preparation. — This gas is prepared by the action of water upon phosphorus tribromide. PBr 3 + g!Jo 3 = ]p} s + 3HBr Phosphorus tribromide. 3 molecules water. Phosphorous acid. The operation may be conveniently conducted in a doubly- curved tube (Fig. 48). Into the long branch CD fragments of phosphorus are introduced, carefully separated from each other by moistened broken glass. The bromine is introduced into the bend A. The shorter end is then corked, a delivery- tube adapted to the end D, and the bromine is gently heated until it boils. The vapor comes into contact with the phosphorus and forms phosphorus tribromide, but this is at once decomposed by the water into phosphorous acid and hydrobromic acid. The latter may be collected in jars over the mercury-trough. Amorphous phosphorus may be advantageously employed in this operation, and the process conducted as directed for hydri- odic acid (Personne). HBr may also be prepared by passing hydrogen charged with bromine vapor over heated platinum. Properties. — Hydrobromic acid is a colorless gas, producing dense white fumes in the air. A litre of this gas weighs 3.547 grammes. It liquefies at — 73°, and may be solidified at a lower temperature. It is formed by the union of equal volumes OXYGEN ACIDS OF BROMINE. 129 of bromine vapor and hydrogen without condensation, so that its composition corresponds to that of hydrochloric acid. It is very soluble in water ; its concentrated solution fumes in the air, and is very corrosive. ChloriDe decomposes hydrobromic acid, liberating chlorine. Fig. 48. OXYGEN ACIDS OF BROMINE. There are known three bromine oxygen acids : Hypobromous acid, HBrO. Bromic acid, HBrO 3 . Perbromic acid, HBrO 4 . % They correspond to hypochlorous, chloric, and perchloric acids. Hypobromous Acid, HBrO. — When mercuric oxide is agitated with an aqueous solution of bromine, a yellowish liquid is obtained which contains hypobromous acid, and can be distilled in vacuo. W. Dancer has obtained this acid by the action of bromine upon silver oxide suspended in water. 2Br 2 + Ag*0 + IPO = 2AgBr -f 2HBrO Silver oxide. Silver bromide. In this process it is necessary to operate rapidly and avoid 130 ELEMENTS OF MODERN CHEMISTRY. the contact of an excess of silver oxide with the hypobromous acid, as the latter would be destroyed by the oxide with evolu- tion of oxygen. 2HBrO + Ag 2 = 2AgBr + H 2 + O 2 The solution of hypobromous acid has a yellow color and bleaching properties analogous to those of hypochlorous acid. Bromie Acid, HBrO 3 . — Potassium bromide and potassium bromate are formed by the action of bromine upon a concen- trated solution of potassium hydrate. This reaction is similar to that of chlorine upon potassa. Kammerer recQmmends the preparation of bromie acid by the action of chlorine upon bromine in presence of water. 5C1 2 + Br 2 + 6H 2 = 10HC1 + 2HBr0 3 The hydrochloric acid is driven out by evaporation, and bromie acid remains in the form of a liquid that cannot be con- centrated to a syrupy consistence without partial decomposition. Perbromic Acid, HBrO 4 . — Kammerer has obtained this acid by decomposing perchloric acid with bromine : chlorine is disengaged. After concentration on a water-bath, the per- bromic acid remains as a colorless oily liquid.. It is relatively stable, as are the corresponding chlorine and iodine acids. Like them, it resists the reducing action of sulphurous acid and hydrogen sulphide. IODINE. Vapor density compared to air . . . 8.716 Vapor density compared to hydrogen . 125.1 (nearly 127) m Atomic weight I = 127. Iodine was discovered by Courtois in 1811, and was studied by G-ay-Lussac in 1813 and 1814. Natural State. — Iodine is widely disseminated in nature. It is found in the mineral kingdom combined -with various metals, such as potassium, sodium, calcium, magnesium, silver, mercury. The alkaline iodides exist in small quantity in sea- water, in a great number of salt-springs, and in certain rock- salts. The sodium nitrate found native in Chili contains traces of sodium iodate, and the mother-liquors from which the nitrate has been deposited contain enough iodate to be profitably employed for the preparation of iodine. The ashes of certain IODINE. 131 sea-plants, such as the algae and fuci, are the most abundant sources of iodine. Preparation. — The ashes of sea-weeds, called kelp, are ex- hausted with water and the solution concentrated. Various salts, such as sodium and potassium sulphates and chlorides and sodium carbonate, are deposited, and the potassium iodide, which is contained in smaller quantity than these salts, remains in the mother-liquor. A regulated current of chlorine is passed into this solution as long as it continues to set free iodine, which is deposited as a pulverulent, black precipitate. An excess of chlorine must be avoided, as this would redissolve a portion of the iodine, forming iodine chloride. Another process consists in mixing the mother-liquor with ordinary nitric acid and gently heating the mixture. The alka- line iodide is decomposed by the acid, a nitrate is formed, red vapors are disengaged, and iodine is set free. 4HX0 3 + 2KI = 2KX0 3 + *2N0 2 + 2H 2 + I 2 Nitric Potassium Potassium Nitrogen acid. iodide. nitrate. peroxide. The precipitated iodine is collected, drained, and after drying is sublimed in stoneware vessels. The same process that has been described for the manufacture of bromine froni potassium bromide may also be applied for the extraction of iodine. It consists in treating the iodide with manganese dioxide and sulphuric acid. Properties of Iodine. — The iodine obtained by sublimation occurs as scales or crystalline plates, having a brilliant, dark bluish-gray surface, and a density of 4.948 at 17°. It may be obtained crystallized in rhombic octahedra by exposing to the air a solution of hydriodic acid. Iodine melts at 107°. It boils at about 175°, but volatilizes sensibly at ordinary temperatures. Its vapor has an intense rich violet color. A litre of this vapor weighs 11.32 grammes. Iodine is but very slightly soluble in water ; one part of iodine requires 7000 parts of water for its solution, but com- municates a light-brown color to the whole of that liquid. Alcohol and ether dissolve iodine freely, forming dark-brown solutions. Carbon disulphide, benzine, and chloroform also dissolve it. assuming a beautiful violet color. Experiment. — If a few drops of chlorine-water be added to a very dilute solution of potassium iodide, the chlorine will ELEMENTS OF MODERN CHEMISTRY. combine with the potassium, displacing the iodine, which will color the liquid brown ; if now the solution be agitated with a small quantity of chloroform, the latter will take up all of the iodine, assuming a violet color. Iodine strikes an intense blue color with starch. The reac- tion is very delicate and permits the detection of the smallest trace of free iodine. Experiment. — If a few drops of a solution of potassium iodide be added to a solution of starch, no coloration takes place, because the iodine is in combination ; but if a drop or two of chlorine-water be added, the iodine will be set free, and combining with the starch will at once produce the character- istic blue color. An excess of chlorine will again destroy the color. HYDRIODIC ACID. Density compared to air 4.443 Density compared to liydrogen 64.1 Molecular weight HI =128. Preparation. — Hydriodic acid is prepared by the action of iodine upon phosphorus in presence of water ; phosphorus triiodide is first formed, and this is decomposed into phos- phorous acid and hydriodic acid. PP + g!!}0 3 = | 3 J0 S + 3HI Phosphorus 3 molecules Phosphorous triiodide. of water. acid. Amorphous phosphorus in powder is introduced into a glass- stoppered retort the neck of which is soldered to the delivery- tube (Fig. 49), and covered with a layer of water ; the iodine is then added, and on the application of a gentle heat a regular current of hydriodic acid is obtained. The gas may be col- lected, like chlorine, by downward displacement in dry jars. Properties. — Hydriodic acid is a colorless gas producing white fumes in the air. Ik may be condensed to a yellow liquid by strong pressure or intense cold, and can even be solid- ified. Dry oxygen decomposes it at a high temperature, water being formed and the iodine being set at liberty. If a lighted taper be applied to a mixture of hydriodic acid and oxygen, the violet vapor of the iodine set free is instantly apparent. This decomposition of hydriodic acid by oxygen takes place at ordinary temperatures in the presence of water. A solution HYDRIODIC ACID. 133 of hydriodic acid exposed to the air rapidly becomes brown, and after a time deposits crystals of iodine. Solution of hydriodic acid is prepared by passing the gas into water cooled to 0°. It may also be made by passing a current of hydrogen sulphide through water holding iodine in suspen- sion ; hydriodic acid is formed, and sulphur is precipitated. H 2 S + P = 2HI + S The saturated solution of hydriodic acid has a density of 1.7, and fumes in the air. When freshly prepared, it is color- Fig. 49. less ; when heated, it loses part of its gas, and finally distils unaltered at 126°. The saturated solution contains 57.7 per cent, of the dry acid. Chlorine and bromine at once decompose hydriodic acid, combining with the hydrogen and setting free the iodine. The experiment may be made by pouring a few drops of bromine into a jar filled with hydriodic acid gas, when the appearance of a violet vapor immediately indicates the liberation of iodine. Potassium, zinc, iron, mercury, and silver decompose hydri- odic acid, but with unequal energies, setting free the hydrogen. 12 ELEMENTS )ERN CHEMISTRY. Sulphuric acid also decomposes it, and is itself reduced to sul- phurous oxide. H 2 SO + 2HI = 2H 2 + SO 2 + I 2 Nitric acid is still more readily reduced by hydriodic acid. 2HN0 3 + 2HI = 2H 2 + 2N0 2 + I 2 Nitric acid. Nitrogen peroxide. IODINE OXIDES AND OXYGEN ACIDS. Among the compounds of iodine and oxygen, iodic and peri- odic oxides are the only ones known with certainty. The ex- istence of the other oxides, although possible and even probable, has not been fully demonstrated. These compounds would form the following series : Hypoiodous oxide I 2 Iodous oxide I 2 3 Iodine peroxide I 2 4 Iodic oxide FO 5 Periodic oxide . I 2 7 In combining with water, these oxides form acids ; it is only necessary to describe here iodic and periodic acids. r0 5 + H 2 _ 2HI0 3 ,2 molecules iodic acid. p 7 + H 2 = 2HI0 4 ,2 molecules periodic acid. IODIC ACID. HI03 = I0 2 (OH) Iodic acid is formed when iodine is submitted to the action of energetic oxidizing agents, such as concentrated nitric, acid or a mixture of nitric acid and potassium chlorate. It is also formed by the action of an excess of chlorine on iodine in presence of water. I 2 + 5C1 2 -f 6H 2 = 10HC1 + 2HI0 3 Preparation. — Iodic acid may be conveniently prepared by heating iodine and potassium chlorate with dilute nitric acid. The oxygen of the chlorate oxidizes the iodine to iodic acid, and on adding barium nitrate to the liquid, barium iodate is precipitated. The latter salt is decomposed by sulphuric acid ; iodic acid is set free in the solution, and barium sulphate is precipitated ; the filtered solution is concentrated by evapora- tion in vacuo. Properties. — Iodic acid is solid, and crystallizes in hex- agonal tables. When heated to 170° it loses water and is PERIODIC ACID. 135 converted into iodic oxide, and at a red heat the latter is decomposed into iodine and oxygen. It is seen that iodic acid is much more stable than its ana- logue, chloric acid ; nevertheless it is easily reduced by bodies avid of oxygen. If sulphurous acid be added to a solution of iodic acid, a precipitate of iodine is formed instantly, but an excess of sul- phurous acid redissolves the precipitate, part of the water being decomposed and hydriodic and sulphuric acids being formed. Iodic acid is also decomposed by hydriodic acid. If a solu- tion of iodic acid be poured into a solution of starch, no color- ation appears, but the characteristic blue color is at once developed on adding a drop of hydriodic acid. HIO 3 + 5HI = 3H 2 -f 3F PEEIODIC ACID. This acid has been obtained from disodic periodate, a salt which is precipitated when a current of chlorine is passed through a solution of sodium iodate mixed with sodium hydrate. XalO 3 + 3XaOH + CT = IO 5 j J^EPO -f- 2XaCl Sodium iodate. Sodium hydrate. Disodic periodate. Sodium chloride. The crystalline precipitate is dissolved in nitric acid, and lead nitrate is added to the solution ; lead periodate is precipi- tated, and this salt is exactly decomposed by sulphuric acid ; the liquid is filtered to separate the lead sulphate, and evapo- rated at a gentle heat. The periodic acid crystallizes out in colorless, deliquescent, rhombic prisms, fusible at 130°. These crystals contain H 3 I0 5 — H 2 0. At 160° they lose water and are converted into a white mass of periodic oxide. 2(H 3 I0 5 .H'0) = I 2 7 + 5H 2 Between 180 and 190° periodic oxide abandons oxygen, and is converted into iodic oxide. I 2 5 . Periodic acid forms several varieties of salts. There is a diargentic periodate, IO 5 < tt c ,H 2 = I0 2 <^tt + H 2 0, corresponding to the disodic salt before mentioned ; but there is also a silver periodate. AglO 4 , to which corresponds an acid, HIO 4 . having a composition analo- gous to that of perchloric acid, but which has not yet been obtained. 136 ELEMENTS OF MODERN CHEMISTRY. Analogy between Chlorine, Bromine, and Iodine. — Chlo- rine, bromine, and iodine present a striking analogy in their chemical properties, and this analogy is seen in all of their compounds. They combine with hydrogen, atom for atom, forming the acids HC1 HBr HI and it is seen that the atoms of chlorine, bromine, and iodine are equivalent to each other and to an atom of hydrogen ; each of these elements is monatomic. Their affinities for hydrogen are far from being equal ; in this respect chlorine is more powerful than bromine, and bromine than iodine. The contrary has been noticed regarding their affinities for oxygen, for the oxygen acids of iodine are more stable than those of chlorine. The analogy between these three elements is followed out in the constitution of their oxides and acids, and in their com- binations with the metals. The chlorides, iodides, and bro- mides possess in general the same constitution, and it is to be remarked that the greater part of these binary compounds are soluble in water and are crystallizable like salts, of which they otherwise present the characters. Hence the name halogen bodies, which was applied by Berzelius to this group of elements, to indicate that they form salts in combining with the metals. FLUORINE. PI = 19. This is a body belonging to the same group just considered, and having a chemical energy much superior to that of chlorine. It exists in the common mineral fluor spar, which is a combina- tion of fluorine and calcium. But fluorine has never been isolated ; it attacks all vessels, and it would be necessary to have apparatus and vessels cut from fluor spar in order to con- tain it. There is a compound of fluorine and hydrogen. HYDROFLUORIC ACID. Molecular weight HF1 =20 . This compound is prepared by decomposing powdered cal- cium fluoride with sulphuric acid. CaFP + H 2 S0 4 = CaSO 4 + 2HF1 Calcium fluoride. Calcium sulphate. HYDROFLUORIC ACID. 137 The operation is conducted in a leaden retort, to which is adapted a receiver of the same metal surrounded by a freezing mixture (Fig. 50). The hydrofluoric acid condenses as a very acid liquid, which fumes strong- ly in the air. Its density is 1.06. In this state it still re- tains water ; but Fremy obtained it anhydrous by de- composing dry hy- drofluoride of fluor- ide of potassium, KF1,HF1, by heat in a platinum retort. Fig. 50. This salt breaks up into potassium fluor- ide, which remains, and hydrofluoric acid, which is disengaged and must be condensed in a platinum receiver cooled to — 20°. Pure and anhydrous hydrofluoric acid is liquid at ordinary tem- peratures ; it is very mobile, and boils at 19.4° (Gore). It is extremely corrosive, and manipulations with it should be con- ducted with great care. Its affinity for water is so great that each drop of the acid let fall into that liquid produces a hissing- noise, as would a red-hot iron. The solution is employed for etching upon glass, for hydrofluoric acid attacks and corrodes that substance. This effect is due to the action of the acid upon the silica of the glass, which it converts into either sili- con fluoride or hydrofluosilicic acid, as will be seen farther on. Fig. 51. A design may readily be engraved on glass by covering the glass with a thin coating of wax, through which the design is 12* 138 ELEMENTS OF MODERN CHEMISTRY. traced with a sharp point ; the glass is then placed over a leaden capsule containing a mixture of powdered calcium fluoride, and sulphuric acid (Fig. 51), which is gently heated by a spirit-lamp. Hydrofluoric acid vapor is disengaged and attacks the glass wherever it is not protected by the wax. When the wax is re- moved, the design is found to be permanently etched on the glass. A dilute solution of hydrofluoric acid or a bath of hydro- fluoride of potassium fluoride may be employed instead of the vapor in the former experiment, but in this case the etched portions are transparent and not opaque as when produced by the vapor ; they may be rendered opaque by adding a salt, such as potassium or ammonium sulphate, to the bath. NITROGEN. Density compared to air ........ 0.9714 Density compared to hydrogen 14.1 Atomic weight N =14. Nitrogen is one of the elements of the air, and it was" from air that it was first obtained in a pure state by Lavoisier and Scheele, in 1777. To obtain nitrogen from the atmosphere it is only necessary to remove the other element, oxygen. Preparation. — A flat piece of cork, B (Fig. 52), floating in the pneumatic-trough, supports a small capsule containing a fragment of phos- phorus. The latter is inflamed, and the capsule immediately covered with a bell- jar. The heat pro- duced by the com- bustion at first ex- pands the air and drives out a portion, but in a few minutes the water rises in the jar, taking the place of the oxygen which has been con- sumed. When the phosphorus is extinguished, the experiment has terminated. The water gradually dissolves the white smoke of phosphoric oxide which fills the jar, and there remains a colorless, irre- Fig. 52. AMMONIA. ' 139 spirable gas that will not support combustion. This gas is nitrogen, still mixed with traces of oxygen and carbonic acid gas. Pure nitrogen may be obtained by passing a current of air, previously freed from moisture and carbon dioxide, through a porcelain tube containing incandescent copper. The copper absorbs the oxygen, and pure nitrogen passes oufc at the end of the tube and may be collected over the pneumatic trough. Pure nitrogen may also be obtained by heating ammonium nitrite in a glass retort ; heat decomposes this salt into nitrogen and water. (NH 4 )N0 2 = 2H 2 + N 2 Ammonium nitrite. Properties.— Nitrogen is a colorless gas, somewhat lighter than the air. A litre of this gas weighs 1.257 grammes. It extinguishes burning bodies, and is not combustible itself; it produces no precipitate in lime-water. Water dissolves only ^- of its volume of nitrogen at 0°. Animals are quickly suffo- cated in an atmosphere of pure nitrogen, but the gas does not exert a poisonous influence upon the economy. The affinities of nitrogen are not energetic. It combines directly with only a very small number of elements, among which may be mentioned carbon, silicon, boron, and titanium. Under the influence of a series of electric discharges it will unite with oxygen, forming nitrogen peroxide ; with hydrogen, forming ammonia. AMMONIA. Density compared to air 0.596 Density compared to hydrogen 8.60 Molecular weight NH 3 = 17. Ammonia was discovered by Priestley, studied by Scheele, and analyzed by Bertholet in 1785. Preparation.- — Equal weights of quick-lime and sal am- moniac, both in powder, are rapidly mixed in a mortar, and the mixture introduced into a glass flask, which is then filled up with fragments of quick-lime. A cork and delivery-tube are adapted to the flask, which is then gently heated and the gas disengaged collected over mercury. The calcium oxide or lime decomposes the ammonium chloride (sal ammoniac), with the formation of calcium chloride, ammonia gas, and water ; the latter is absorbed by the fragments of lime which fill up the flask. 2NH*C1 + CaO = 2NH 3 + CaCP + H 2 Ammonium chloride. Calcium oxide. Ammonia. Calcium chloride. 140 ELEMENTS OF MODERN CHEMISTRY. A solution of ammonia in water may be prepared by passing the gas through a series of Wolff's bottles, about half filled with water, excepting the first, which should only contain a small quantity destined to wash the gas. Physical Properties. — Ammonia is a colorless gas, having a powerful and pungent odor, which excites tears. Its taste is burning and caustic. It may be liquefied by a temperature of — 40°, or at 10° under a pressure of 6 J atmospheres. Fara- day's method of liquefying it is as follows : ammonia is passed over dry silver chloride, by which it is absorbed. The silver chloride, saturated with ammonia, is introduced into a bent tube (Fig. 53), the empty limb of which is then sealed at the Fig. 53. Fig. 54, blow-pipe. The end containing the chloride is now heated in a water-bath, while the empty end is cooled in a freezing mix- ture (Fig. 54). The ammonia is driven out from the silver chloride, and condenses into a transparent liquid in the cooler branch. Faraday succeeded in solidifying ammonia by subject- ing this liquid to rapid evaporation. In the solid state it is a white, crystalline, transparent substance, fusible at — 75°, and having only a feeble odor. According to Bunsen, liquid ammo- nia boils at — 35° under a pressure of 0.7493 metre ; its density is 0.76. Ammonia gas is very soluble in water, which dissolves 1000 times its volume at 0°, and about 740 times its volume at 15°. The rapid absorption of ammonia by water may be strik- ingly shown by the following experiment. A bottle, A (Fig. 55), is filled with ammonia gas, and fitted with a cork, through which passes a tube drawn out at both extremities, and the outer end of which is sealed. If this end be plunged under water and the point be broken off, the water at once rises into AMMONIA. 141 the bottle, forming a fountain, and the vessel becomes filled with water in a very short time. The aqueous solution of ammonia possesses the odor of the gas; it is caustic, and was formerly called vol- atile alkali and spirits of hartshorn. It is largely used in the arts and as a reagent. Its density is 0.855. When heated, it loses ammonia gas, the whole of which may be driven out by boiling. Composition of Am- monia. — 200 volumes of ammonia gas are in- troduced into an eudi- ometer, and electric sparks are passed through the gas for some time by means of a Ruhmkorff coil (Fig. 56). When the experiment has terminated, the volume of gas will be found to have doubled. 200 volumes of oxygen are added to the 400 volumes of gas thus obtained, and a spark is passed ; an explosion takes place, and after making the Fig. 55. necessary corrections for temperature and pressure, the 600 volumes of gas are found to be reduced to 150 volumes ; 450 volumes have thus disappeared to form water. 142 ELEMENTS OF MODERN CHEMISTRY. These 450 volumes must have contained 300 volumes of hydrogen, 150 volumes of oxygen. Consequently the 200 volumes of ammonia gas, which were decomposed by the spark into 400 volumes, must have been formed by the union of 300 volumes of hydrogen, 100 volumes of nitrogen. The latter gas remains in the eudiometer, together with the 50 volumes of oxygen that were employed in excess. From this analysis it is seen that two volumes of ammonia contain three volumes of hydrogen and one volume of nitrogen, a composition which is expressed by the formula NH 3 . Chemical Properties. — Ammonia gas is decomposed by a high temperature, as by a series of electric sparks. The experi- ment may be made by passing the gas through a porcelain tube Fig. 57. filled with fragments of broken porcelain and heated to white- ness, and collecting the gas resulting from the decomposition in vessels filled with water (Fig. 57). This gas is found to be a mixture of three volumes of hydrogen and one volume of nitrogen. The decomposition takes place more readily if iron, copper, or platinum wires be introduced into the porcelain tube. The A3IM0NIA. 143 latter metal is not altered, but the iron and copper become brittle and retain a few per cent, of nitrogen. The decompo- sition of the ammonia seems here to be favored by the forma- tion of metallic nitrides, unstable compounds which are almost entirely decomposed by the prolonged action of the heat. Ammonia gas will not burn in the air, but a mixture of four volumes of ammonia and three volumes of oxygen will explode on the application of a flame. 2NH 3 + O 3 = 3H 2 + N 2 Ammonia will burn in an atmosphere of oxygen. A jet of ammonia escaping through a tube drawn out to a point may be ignited on the instant that it is plunged into a jar of oxygen, and will continue to burn with a yellowish flame until the oxygen is consumed (Fig. 58). Independently of this rapid combus- tion, ammonia may undergo a slow com- bustion under the fol- lowing conditions : The vessel A (Fig. 59) contains a solution of ammonia, above which is suspended a spiral of platinum wire. The solu- tion is gently heated, and a rapid current of oxygen gas is forced through it. The mixed ammonia and oxygen gases come in contact with the platinum spiral and combine together, their union developing so much heat that the spiral is heated to redness. The vessel sometimes becomes filled with white fumes of ammonium nitrite. The nitrous acid is produced by the slow oxidation of the ammonia. If a mixture of oxygen and ammonia gases be passed through a heated tube contain- ing spongy platinum, nitric acid and water will be formed and disengaged in vapor. Action of Chlorine and Iodine upon Ammonia. — Chlorine instantly decomposes ammonia, combining with its hydrogen. If a drawn-out tube through which a jet of ammonia is escaping Fig. 58. 144 ELEMENTS OF MODERN CHEMISTRY. be plunged into a bottle filled with dry chlorine (Fig. 60), the ammonia takes fire immediately, and white vapors of ammo- nium chloride are formed. 4NH 3 + CI 3 = 3NH 4 C1 + N If a long tube closed at one end be almost entirely filled with saturated chlorine -water and then filled up with a solu- tion of ammonia, and quickly inverted on the pneumatic trough, the lighter solution of ammonia will rise through the chlorine-water and will be de- composed according to the pre- ceding equation. Ammonium chloride will remain in solution, while the nitrogen will collect at the top of the tube. Nitrogen Chloride. — Under other conditions the nitrogen may combine with the chlorine,, forming a very explosive and dangerous compound, nitrogen chloride. This experiment may be made as folio ws : A small jar of chlo- rine is inverted in a saucer con- taining a solution of ammonium chloride. The ammonia of this salt is slowly decomposed by the chlorine, with the for- mation of hydrochloric acid and nitrogen chloride. As the chlorine is absorbed, the level of the liquid in the jar rises and a drop of a yellow liquid soon collects on the surface. A light tup on the vessel causes it to sink through the solution into the saucer. This oily body is nitrogen chloride. The jar may now be removed and a small piece of phosphorus thrown into the saucer, and pushed from a distance towards the drop of nitrogen chloride by the aid of a long wooden rod. Fig. 59. Fig. 60. AM310NIA. 145 As soon as the two substances come into contact, the nitrogen chloride explodes and the saucer is broken into pieces. The formula NCI 3 has been attributed to this body. Nitrogen Iodide. — There is another explosive compound analogous to nitrogen chloride, but containing iodine. It is obtained as a black powder by treating powdered iodine with ammonia; when dry it explodes with great violence on the lightest touch, and sometimes spontaneously. Bunsen has attributed to it the formula N 2 H 3 I 3 . According to Stahlschmidt, the composition of nitrogen iodide corresponds to the formula NF, when this body is pre pared by the action of an alcoholic solution of iodine upon aqueous ammonia ; but if both bodies be in alcoholic solution, an iodide is obtained having the formula XHP. If this be correct, these bodies present very simple relations with ammonia. (H (CI fl (I X-s'H N^ CI X^I N-Jl (h (ci (i (h Ammonia. Nitrogen chloride. Triiodammonia. Diiodammonia. Trichlorammonia. Nitrogen iodides. The substitution of the chlorine or iodine for hydrogen takes place atom for atom. Action of Potassium upon Ammonia. — When potassium is heated in an atmosphere of ammonia, the brilliant surface of the metal becomes covered with a greenish-black liquid, and at the same time hydrogen is disengaged. The metal entirely disappears little by little, and. on cooling, the liquid solidifies to an olive-green mass. This substance represents ammonia in which one atom of hydrogen has been replaced by an atom of potassium. H > X = Ammonia. H > X = Potassium amide. H) HJ When it is treated with water, ammonia is regenerated and potassium hydrate is formed. KXH 2 + H 2 = KOH + XH 3 Potassium amide. Potassium hydrate. Ammonium Amalgam* — If liquid amalgam of potassium or sodium and mercury be treated with a saturated solution of ammonium chloride, the amalgam increases in volume, assumes a buttery consistence, and is converted into a soft, light mass a 13 146 ELEMENTS OF MODERN CHEMISTRY. having the metallic lustre of mercury. It will retain- the impression of the finger and will float upon water ; but it gradually decomposes, losing hydrogen and ammonia, and only mercury remains. This unstable body is called ammonium amalgam. In it the mercury is combined with a group, NH*, which contains all of the hydrogen of the ammonium chloride, the chlorine of which has combined with the potassium. NH 3 .HC1 — CI = NH* Ammonium chloride. Radical ammonium. It has recently been found that the ammonium amalgam is very compressible, and that its diminution in volume under pressure sensibly follows Mariotte's law. It has hence been concluded that the ammonium does not exist in combination with the mercury, and that the increased volume of the latter is due simply to an absorption of gas. It is difficult to admit this, for the compressibility of the ammonium amalgam proves only that the compound has no stability, and begins to decom- pose almost immediately on its formation. The disengaged gases, which are in the exact proportion NH 3 -f- H, may be retained by the pasty amalgam remaining : they could not be absorbed by the liquid mercury. Ammonium Theory. — The reaction which has just been described is of great importance, and directly supports the ammonium theory suggested by Ampere. According to this theory, the ammoniacal salts are analogous in constitution to ordinary salts, from which they differ only by the substitution of a compound radical, ammonium, for a simple radical. The following formulae explain this proposition : NH 3 .HC1 = (NH*)C1. analogous to KC1 Ammonium chloride. Potassium chloride. NH 3 .HN0 3 = (NH 4 )N0 3 analogous to KNO 3 Ammonium nitrate. Potassium nitrate. NH 3 .H 2 S = N h{s analogous to ||1 S Ammonium sulphydrate. Potassium sulphydrate. (NH 3 ) 2 .H 2 S = NH* } S anal °gousto |Js Ammonium sulphide. Potassium sulphide. AMMONIUM CHLORIDE. NH*C1 This salt was formerly obtained from Egypt, where it was made by subliming the soot produced by the combustion of AMMONIUM SULPHYDRATE AND AMMONIUM SULPHIDE. 147 camel's dung. It is now prepared in large quantities from gas- liquor, or the water condensed in the manufacture and purifi- cation of illuminating gas from coal. This liquor is heated with lime, ammonia is disengaged and is conducted into hydro- chloric acid. Ammonium chloride is obtained by simply evaporating the solution. It is purified by sublimation in stoneware pots which are heated in a furnace out of which the upper parts of the pots project. There the volatilized chloride condenses, and the sublimed product is known in commerce as sal ammoniac, or muriate of ammonia. It generally occurs as white or grayish, compact masses, having a crystalline fibrous structure. Its taste is sharp and salty. It dissolves in two and a half parts of cold, and in its own weight of boiling water. It is deposited from a satu- rated solution in small octahedra, grouped together in needles. and presenting a fern-leaf-like appearance. At a high tem- perature it volatilizes without melting; its vapor is dissociated. but the resulting XH 3 and HC1 at once recombine on cooling. Ammonium chloride is formed by the union of equal vol- umes of hydrochloric acid and ammonia gases. AMMONIUM SULPHYDRATE AND AMMOXIl 31 SULPHIDE. Hydrogen sulphide and ammonia gases unite in the cold in two different proportions, forming two compounds, ammo- nium sulphyclrate and ammonium sulphide. H 2 S + NH 3 = Jj S Hydrogen sulphide. Ammonia. Ammonium sulphvdrate. (2 vol.) (2 vol.) H 2 S + 2XH 3 = xhM S Hydrogen sulphide. Ammonia. Ammonium sulphide. (2 vol.) (4 vol.) These compounds are definite, but are decomposed into their elements by heat. Horstmann and Salet have shown that hy- drogen sulphide and ammonia gases may be mixed in all pro- portions without contraction in volume taking place, provided the temperature be maintained above 60°. Ammonium sulphvdrate is generally obtained in solution by saturating aqueous ammonia with hydrogen sulphide. This solution is colorless, but acquires a yellow color on exposure to 148 ELEMENTS OF MODERN CHEMISTRY. the air. When a quantity of ammonia is added to it equal to that which it already contains, ammonium sulphide, (NH 4 ) 2 S, is formed, which corresponds to potassium sulphide, K 2 S. Ammonium sulphide is largely employed in the laboratory as a reagent for the detection of certain metals. If ammonium sulphide be added to a solution of ferrous sulphate, a double decomposition takes place ; ammonium sul- phate is formed and remains in solution, while ferrous sulphide forms a black precipitate. FeSO 4 + (NH*) 2 S = FeS + (NH*) 2 SO Ferrous sulphate. Ferrous sulphide. Ammonium sulphate. The salts of zinc, manganese, cobalt, and nickel are likewise precipitated as sulphides by ammonium sulphide. The smalts of aluminium and chromium are precipitated as hydrates, hydrogen sulphide being disengaged. The preceding salts are not precipitated by hydrogen sul- phide (the zinc salts are not precipitated if they be acid), but the latter reagent precipitates in the form of sulphides the salts of lead, bismuth, copper, cadmium, mercury, silver, antimony, tin, gold, and platinum. The sulphides of the latter four metals dissolve in an excess of ammonium sulphide. The sulphides of arsenic, tin, antimony, gold, and platinum all form compounds with ammonium sulphide, in which the latter plays the part of a base. AMMONIUM NITRATE. . (NH4)N0 3 Ammonium nitrate is prepared by saturating nitric acid with ammonia. It crystallizes in large, transparent, fusible prisms, which are very soluble in water and produce a notable depression of temperature in the act of solution, extending even to — 15°. At 300° ammonium nitrate is decomposed into nitrogen monoxide and water. It is used for the prepa- ration of nitrogen monoxide, much used as an anaesthetic. AMMONIUM CARBONATE. When dry carbon dioxide and ammonia gases are mixed in the proportion of 2 volumes of the first to ^ volumes of the second, they condense, forming a white powder, which is am- AMMONIUM SULPHATE — HYDROXYLAMINE. 149 monium carbamate/ a compound which was formerly called anhydrous carbonate of ammonia. co 2 + 2NH* = co gg* Nitryl chloride. Nitric acid. Nitrogen pentoxide. PHOSPHORUS Vapor density compared to air 4.32 Vapor density compared to hydrogen .... 61.1 Atomic weight P =31. Brandt, an alchemist of Hamburg, while attempting to ex- tract the philosopher's stone from urine, discovered phosphorus in 1669. But urine contains only a small quantity of phos- phates and can yield but traces of phosphorus, so that this body only became generally known to chemists after Grahn demonstrated its existence in bones, and Scheele discovered the process for its extraction. The process of the latter chemist is still in use ; it consists in treating bone-ash with dilute sulphuric acid, by which means the tricalcium phosphate of the bones is converted into mono- calcium phosphate, ordinarily called acid phosphate of lime. Ca 3 (P0 4 ) 2 + 2H 2 SO* = CaIP(P0 4 ) 2 + 2CaS0 4 Tricalcium Calcium acid Calcium phosphate. phosphate. sulphate. The latter phosphate being soluble is separated from the calcium sulphate by nitration, and the solution is evaporated and mixed with powdered charcoal. The mixture is dried and gradually heated to redness in cast-iron vessels. By this means the calcium acid phosphate is converted into calcium nieta- phosphate by the expulsion of two molecules of water. CaH 4 (PO*) 2 = 2H 2 + Ca(P0 3 ) 2 Calcium acid phosphate. Calcium metaphosphate. 14* 162 ELEMENTS OF MODERN CHEMISTRY. The latter is strongly heated with charcoal in clay retorts (Fig. 66), and is decomposed, yielding carbon monoxide and phosphorus which distils over, and leaving a residue of calcium pyrophosphate. 2Ca(P0 3 ) 2 + 5C = Ca'FO* + 5CO + P Calcium Calcium Carbon metaphosphate. pyrophosphate. monoxide. The phosphorus condenses in the water in the receiver A, in which the neck of the retort C is engaged. Fig. 66. As it is impossible to expel all of the water from the calcium acid phosphate, this water is decomposed by the charcoal, hy- drogen and carbon monoxide being formed, together with a small quantity of phosphoretted hydrogen. 100 kilogrammes of bone yield between 8 and 9 kilo- grammes of phosphorus. The latter is purified by enclosing it in a chamois-skin sack, and strongly compressing it under water at 50° ; the phosphorus passes through the leather and collects* under the water. It is moulded into sticks by being drawn up into slightly conical glass tubes, which are then plunged into cold water. The phosphorus solidifies and is easily drawn from the tubes. Physical Properties. — Recently-fused phosphorus is trans- parent, colorless, or having a pale-yellow tint, flexible, and soft PHOSPHORUS. 163 enough to be easily scratched by the nail. One-tenth per cent, of sulphur renders it hard and brittle. It has a well-marked odor, slightly resembling that of garlic. Its density at 10° is 1.83. It melts at 44° and boils at 290° ; its vapor is colorless and has a density of 4.32 compared to air, or 61.1 compared to hydrogen. If one volume of hydrogen weighs 1, one volume of vapor of phosphorus weighs 61.1, and this number should represent the weight of one atom of phosphorus ; now it represents the weight of two atoms, and the vapor of phosphorus presents the singular anomaly that it contains in the same volume twice as many atoms as the simple gases, such as hydrogen or nitrogen. If one volume of hydrogen contain one atom, one volume of phosphorus vapor contains two, and heat cannot dissociate these two atoms in such a manner that they may occupy two volumes instead of one. The vapor of arsenic presents the same anomaly. H N 1 As 2 1 volume of 1 volume of 1 volume of 1 volume of hydrogen. nitrogen. phosphorus vapor. arsenic vapor. Phosphorus volatilizes below its boiling-point and even below its melting-point. At ordinary temperatures it emits vapors in a vacuum and even in the air. It is luminous in the dark, from which property it derives its name, which signifies light- bearer. The cause of this phenomenon is still obscure, but is generally attributed to the slow oxidation which phosphorus undergoes in the air. When a stick of transparent phosphorus is kept under water, it gradually becomes opaque and covered with a yellowish-white pulverulent powder, while the central parts retain their trans- parence. This white phosphorus is still pure, but the surface of the stick has divided into a multitude of little particles which present a crystalline appearance. Some of them become de- tached and remain suspended in the water, giving to the latter the property of being luminous in the dark. Phosphorus is rapidly dissolved by carbon disulphide and is deposited in rhombic dodecahedra on the slow evaporation of the solution. There is an amorphous variety of phosphorus which differs so much from ordinary phosphorus that it presents the prop- 164 ELEMENTS OF MODERN CHEMISTRY. erties of an entirely different substance. It has a dark brown- red color, and is not luminous in the dark. It is insoluble in carbon disulphide ; it does not melt and take fire like ordi- nary phosphorus when heated to 50°. It is amorphous, and presents a conchoidal fracture. Its density is 2.14. Ordinary phosphorus is one of the most dangerous poisons, but this red body exerts no action upon the economy. At 260° amor- phous phosphorus melts, is converted into ordinary phospho- rus, and presents the properties of the latter substance on cooling. Amorphous phosphorus results .from a physical change brought about by the action of light or heat on the ordinary variety. If a stick of phosphorus be exposed to direct sun- light, its surface assumes a red color ; or if it be maintained for a long time at a temperature of 240°, it is entirely con- verted into the amorphous variety. This transformation is also accomplished by the influence of certain chemical agents. If a small stick of ordinary phos- phorus be introduced into a test-tube and a very minute por- tion of iodine be allowed to fall upon it, the iodine unites with the phosphorus with the production of light and heat. A trace of phosphorus iodide is formed, and the remainder of the phos- phorus is converted into a hard, black mass, which yields a red powder ; this is amorphous phosphorus (E. Kopp, Brodie). Thus prepared, this body volatilizes like arsenic, without melting, and can be distilled without alteration, condensing in a black mass, which contains only traces of iodine. Chemical Properties. — Ordinary phosphorus possesses a strong affinity for oxygen. When exposed to the air it slowly oxidizes, and the slow combustion, aided by the moisture of the air, produces a mixture of phosphorous and phosphoric acids. Schonbein has shown that the slow oxidation of phosphorus is accompanied by the formation of small quantities of ozone and hydrogen dioxide, and he asserts that ammonium nitrite is formed at the same time. When heated in the air to a temperature of 60°, phosphorus takes fire and burns, producing a bright light and white vapors of phosphorus pentoxide. In pure oxygen the combustion is accomplished with great brilliancy. Phosphorus may be burned under warm water by passing a current of oxygen through the melted element by means of a tube drawn out to a point (Fig. 67) ; each bubble of oxygen HYDROGEN PHOSPHIDE. 165 which comes in contact with the phosphorus produces a bright flash. Phosphorus takes fire spontaneously in an atmosphere of dry chlorine, phosphorus pentachloride being produced. Uses of Phosphorus. — This body is principally employed in the manufacture of matches. The inflammable tips of friction- matches contain either ordinary or amorphous phosphorus. In the first case, the phosphorus is mixed with inert substances, such as sand or ochre, held together by strong glue ; in the Fig. 67. second case, the ignition of the amorphous phosphorus, which is but slightly combustible, is determined by potassium chlorate, to which is also added antimony sulphide. All of these sub- stances are made into a paste, into which the ends of the matches are dipped. Sometimes the match-sticks are tipped with a paste composed of potassium chlorate and antimony sulphide, a mixture which only takes fire by friction upon a prepared surface, composed generally of amorphous phosphorus and antimony sulphide. All of these mixtures are held to- gether by strong glue. HYDROGEN PHOSPHIDE (PHOSPHINE), Density compared to air 1.134 Density compared to hydrogen 17. Molecular weight Pfl 3 = 34. This gas was discovered by Gengembre in 1783. When phosphorus is heated with a solution of caustic potassa, there is a gas disengaged, which inflames spontaneously on con- tact with the air ; this is hydrogen phosphide. It is formed according to the following equation : 3KOH + 4P + 3H 2 = 3KH 2 P0 2 + PH 3 Potassium hydrate. Potassium hypophosphite. 166 ELEMENTS OF MODERN CHEMISTRY. Preparation. — 1. Hydrogen phosphide may be prepared by heating phosphorus with a strong solution of potassium hydrate, or with thick milk of lime, with which the flask (Fig. 68) should be almost entirely filled. The gas is conducted under the surface of water, and as each bubble arrives in contact with the air it takes fire spontaneously, producing a bright flash and a wreath of white smoke, which enlarges as it rises in the air. 2. The same spontaneously inflammable gas is evolved when calcium phosphide is thrown into water (Fig. 69). The phos- phide of calcium is prepared by passing vapor of phosphorus over fragments of incandescent lime ; it instantly decomposes water with formation of calcium hypophosphite and sponta- neously inflammable hydrogen phosphide. However, when calcium phosphide is treated with hydro- chloric acid, hydrogen phosphide is produced, which does not take fire without the application of heat (Fig. 70). In this case, the gas is formed by double decomposition between the hydrochloric acid and the calcium phosphide ; the calcium combines with the chlorine, forming calcium chloride, and the hydrogen of the acid combines with the phosphorus. 3. In the same manner, when phosphorous acid is strongly heated in a small retort, it evolves a hydrogen phosphide which is not spontaneously inflammable. 4H 3 P0 3 = Phosphorous acid. PH 3 + 3H 3 P0 4 Phosphoric acid. COMPOUNDS OF PHOSPHORUS AND CHLORINE. 167 Properties. — The gas thus obtained is colorless, and pos- sesses a garlicky odor. It is but slightly soluble in water, but is soluble in alcohol and in ether. When it is pure it does not take fire in the air at a temperature below 100°, and then burns with a very luminous white flame. According to Paul Thenard, the spontaneous inflammability of the hydrogen phos- phide prepared by the methods first mentioned is due to the Fig. 69. Fig. 70. presence of another phosphide. P 2 H 4 ; this is a very volatile liquid, extremely inflammable, and the least trace of its vapor in hydrogen phosphide gas communicates to the latter the property of spontaneous inflammability. Hydrogen phosphide is absorbed by a solution of cupric sulphate, with the formation of black phosphide of copper; The composition of hydrogen phosphide, PH 8 , recalls that of ammonia. NH 3 , and the analogy between the two gases is further revealed by the property common to both of uniting with hydriodic acid. There is a compound of hydrogen phos- phide with hydriodic acid, a well-defined, solid body,, crystal- lizing in brilliant cubes. PH 3 .HI or PH 4 I phosphoniuin iodide. The existence of a solid phosphide of hydrogen has been demonstrated, and the formula P 2 H attributed to it. COMPOUNDS OF PHOSPHORUS AND CHLORINE. There are two chlorides of phosphorus : Phosphorus trichloride PCI 3 Phosphorus pentachloride . . -. PC1 & 168 ELEMENTS OF MODERN CHEMISTRY. There are, besides, Phosphorus oxychloride . POC1 3 Phosphorus sulphochloride PSC1 3 PHOSPHORUS TRICHLORIDE. PCI 3 When a current of dry chlorine is passed over phosphorus heated in a small tubulated retort, a liquid compound of chlo- rine and phosphorus is formed and may be condensed in a cooled receiver. This is phosphorus trichloride. It is a fuming, colorless liquid, having a density of 1.45 and boiling at 74°. If it be poured into water, it at first sinks to the bottom, and then rapidly disappears, evolving white fumes of hydro- chloric acid, and forming phosphorous acid, which remains in solution. PCP + 3H 2 = H 3 P0 3 + 3HC1 PHOSPHORUS PENTACHLORIDE. PCI 5 In contact with an excess of chlorine, phosphorus trichloride absorbs two more atoms of that gas, and condenses into a yellow crystalline solid, phosphorus pentachloride. This body is volatile, and sublimes without fusion when heated, even below 100°. When heated under pressure, it melts at 148° and boils at a slightly higher temperature. Its vapor density, taken at 336° and reduced to 0°, is equal to 3.656. This density should be double, supposing that the molecule PCI 5 occupies two volumes. The anomaly, however, is only apparent, for there are good reasons for believing that at the temperature 336° the vapor of phosphorus pentachloride no longer exists, and that the compound is decomposed or dis- sociated into a mixture of phosphorus trichloride and chlorine, a mixture which would give four volumes of vapor for one molecule of PCI 5 . ppi 5 f PCP = 2 volumes. | CI 2 =2 volumes. 4 volumes. Indeed, when the vapor density of phosphorus pentachloride is taken by diffusing it in the vapor of the protochloride, which PHOSPHORUS OXYCHLORIDE. 169 prevents the dissociation before mentioned, a figure is found which corresponds very nearly with the theoretic density 7.21 (A. Wurtz). Phosphorus pentachloride decomposes water with energy, forming hydrochloric and phosphoric acids. PCI 5 + 4H 2 = H 3 PO + 5HC1 When only a small quantity of water is present, hydrochloric acid is disengaged, by the exchange of two atoms of chlorine for one atom of oxygen, and a colorless liquid is formed which is called phosphorus oxy chloride. When heated in a current of hydrogen sulphide, phosphorus pentachloride is converted into the sulphochloride, a colorless liquid boiling at 126°. PCI 5 + H 2 = 2HC1 + POCP PCI 5 + H 2 S = 2HC1 + PSCP PHOSPHORUS OXYCHLORIDE. POCP This body is readily obtained by exposing phosphorus penta- chloride to moist air until it becomes liquid, and subsequently distilling the liquid (A. Wurtz). It is formed in a great num- ber of reactions when phosphorus pentachloride is heated with hydrated acids, such as oxalic acid, boric acid, etc., or with oxides, such as phosphoric oxide. In these cases, one atom of oxygen from the oxidized body is exchanged for two atoms of chlorine from the pentachloride (Gerhardt). Phosphorus oxy chloride is a colorless liquid, boiling at 110°. When poured into water, it sinks and is at once decomposed, hydrochloric and phosphoric acids being formed. POCP + §I}o» = ^}0 3 + 3HC1 Phosphorus oxy chloride. 3 molecules water. Phosphoric acid. COMPOUNDS OF PHOSPHORUS WITH BROMINE AND IODINE. Two bromides of phosphorus are known : Phosphorus tribromide, PBr\ a colorless liquid. Phosphorus pentabromide, PBr 5 , a yellow, crystalline mass. To the trichloride and tribromide of phosphorus there cor- responds a triiodide, concerning which but little is known. h 15 170 ELEMENTS OF MODERN CHEMISTRY. The best defined and most important combination of phos phorus with iodine is the compound P 2 P. Phosphorus Iodide, P 2 I 4 . — This body is obtained by dis- solving 26 parts of dry phosphorus in 30 or 40 times its weight of carbon disulphide, and gradually adding to the solution 203.4 parts of iodine. The liquor, at first reddish-yellow, becomes orange-yellow ; it is distilled on the water-bath to drive out a part of the carbon disulphide, and on cooling it deposits a bright-red, crystalline mass. This is the iodide P 2 P. It crystallizes in long, brilliant, flattened needles, which are flexible, and melt at 100°. On contact with water it is decom- posed, forming phosphorous and hydriodic acids, and at the same time depositing a yellow, flocculent precipitate rich in phosphorus (Corenwinder). COMPOUNDS OF PHOSPHORUS AND OXYGEN. Phosphorus combines with oxygen, forming two oxides : Phosphorus trioxide, or phosphorous oxide . . P 2 3 Phosphorus pentoxide, or phosphoric oxide . . P 2 5 Each of these oxides can combine with three molecules of water, phosphorous and phosphoric acids being thus formed. P 2 3 + 3H 2 = 2H 3 P0 3 P 2 5 + 3H 2 = 2H 3 P0 4 Besides these two acids there is another containing less oxy- gen ; it is hypophosphorous acid, whose corresponding oxide is unknown. These three acids form a series containing for three atoms of hydrogen and one atom of phosphorus regularly-in- creasing quantities of oxygen ; they may be said to constitute different degrees of oxidation of hydrogen phosphide. PH 3 hydrogen phosphide. PH 3 (missing). PH 3 2 hypophosphorous acid. PH 3 3 phosphorous acid. PH 3 4 phosphoric acid. Constitution of the Oxygen Acids of Phosphorus. — Phos- phorous and phosphoric acids are related, — the first to phos- phorus trichloride, the second to phosphorus oxychloride. In HYPOPHOSPHOROUS ACID. 171 fact, they are derived from these compounds by the action of water. P'"C1 3 phosphorus trichloride. P(OH) 3 phosphorous acid (phosphorus trihydrate). (PO)'"Cl 3 phosphorus oxy chloride (phosphoryl trichloride). (PO)" ; (OH) 3 phosphoric acid (phosphoryl trihydrate). To phosphorus pentachloride, PCI 5 , would correspond a pen- tahydrate, P(OH) 5 , which is unknown. Phosphoric acid would be derived from the latter by the loss of a molecule of water. P(OH) 5 = H 2 + (PO)(OH) 3 It is seen that in phosphorous acid, as in the trichloride, phos- phorus is regarded as playing the part of a triatomic element, while it is pent atomic in the pentachloride. In hypophosphorous acid, it must be admitted that one atom of hydrogen is united directly to the triatomic phosphorus, and its constitution is expressed by the formula F'O OH (oh hypophosphorous acid. H 3 P0 2 When phosphorus is boiled with milk of lime or with a con- centrated solution of baryta, a soluble hypophosphite is pro- duced, and on treating the solution of barium hypophosphite with sulphuric acid, a precipitate of barium sulphate and a solution of hypophosphorous acid are obtained ; they may be separated by filtration. When sufficiently concentrated, the liquor leaves a colorless and very acid syrupy residue, which constitutes hypophosphorous acid. This acid is decomposed at a high temperature, yielding phosphoric acid and hydrogen phosphide. It is gifted with energetic reducing properties : it instantly decomposes the salts of mercury and silver, setting free the metal. An excess of hypophosphorous acid added to a solution of cupric sulphate precipitates, by the aid of a gentle heat, hydride of copper, Cu 2 H 2 , which is decomposed at 100° into copper and hydrogen (A. Wurtz). 172 ELEMENTS OF MODERN CHEMISTRY. Hypophosphorous acid contains three atoms of hydrogen, only one of which is capable of being replaced by an equiva- lent quantity of a metal. The composition of the hypophos- phites is consequently expressed by the following general formula : R'HTO 2 in which R' represents a monatomic metal, such as potassium, capable of replacing hydrogen atom for atom. PHOSPHOROUS ACID. H 3 P0 3 Preparation. — Phosphorous acid results from the action of water upon phosphorus trichloride, as already seen. It may be obtained in a state of purity by evaporating the acid liquor resulting from this reaction, and heating the syrupy residue in a platinum capsule until the odor of hydrogen phosphide is perceptible. On cooling, the acid solidifies to a crystalline mass. Properties. — These crystals absorb moisture when exposed to the air, and are resolved into an intensely acid liquid ; they melt at a gentle heat, and are decomposed by a high tempera- ture into hydrogen phosphide and phosphoric acid. Like hypophosphorous acid, phosphorous acid possesses re- ducing properties. Its boiling aqueous solution reduces the salts of mercury, silver, and gold, and this reduction is favored by the presence of ammonia. It converts arsenic acid into arsenious acid. Chlorine, bromine, and iodine convert it into phosphoric acid in presence of water. H 3 P0 3 + H 2 + CP = 2HC1 + H 3 P0 4 Phosphorous acid contains three atoms of hydrogen, two of which are replaceable by an equivalent quantity of a metal. It is hence called a dibasic acid. The composition of the neutral phosphites is expressed by the general formula R' 2 HP0 3 , in which R' represents a monatomic metal like potassium or sodium. PHOSPHORIC OXIDE— PHOSPHORIC ACID. 173 PHOSPHORIC OXIDE, OR PHOSPHORUS PEXTOXIDE. (phosphoric anhydride.) p 2 Q5 This compound may be obtained by burning phosphorus in a large globe filled with dry air. A dense white smoke is pro- duced, and condenses upon the walls of the vessel in flakes like snow. This body is the anhydride of phosphoric acid. When exposed to the air, it absorbs moisture and is converted into metaphosphoric acid. P 2 5 + H 2 = 2HPO 3 When thrown into water it dissolves with a hissing noise, such as is produced by a red-hot iron. Phosphoric oxide volatilizes at a dull-red heat ; it is unde- composable by heat. It yields the oxychloride when distilled with phosphorus pentachloride. P 2 5 + 3PCP = 5POCP It also yields phosphorus oxychloride when distilled with dry common salt (Lautemann). PHOSPHORIC ACID. (ORTHOPHOSPHORIC ACID.) H3PO* Preparation. — 1. This acid may be prepared by boiling phosphorus with nitric acid. On account of the violence of the reaction the operation is difficult to regulate, and even dangerous when ordinary phosphorus is employed, but it succeeds very well with powdered amorphous phosphorus. This is heated with tolerably concentrated nitric acid in a retort, fitted with a receiver, and, when the whole of the phos- phorus has disappeared, a little nitric acid is added to the contents of the retort, and the liquid is concentrated in a platinum capsule. When the last portions of nitric acid have been driven out, a small quantity of water is added, and the syrupy liquid is placed in a bell-jar over a dish containing concentrated sulphuric acid. At the end of some time, the 15* 174 ELEMENTS OF MODERN CHEMISTRY. phosphoric acid is deposited in the form of hard, transparent, prismatic crystals. 2. A current of chlorine may be passed through warm water under which is a layer of melted phosphorus. Phosphoric acid and hydrochloric acid are formed. POP + 4H 2 = H 3 P0 4 + 5HC1 As soon as all of the phosphorus has disappeared the solution is evaporated, and the hydrochloric acid is driven out by heating the residue to 200°. The residue is dissolved in water and forms a solution which will deposit the acid in crystals when concentrated as indicated above. Properties. — When exposed to the air, these crystals attract moisture and deliquesce. Their solution is very acid. It does not coagulate white of egg, and it produces no cloud in a solu- tion of barium chloride, but it forms a white precipitate of ammonio-magnesium phosphate in a solution of magnesium sulphate on the addition of ammonia. With silver nitrate to which ammonia has been added, it gives a yellow precipitate of trisilver phosphate, Ag 3 PO. Orthophosphoric acid contains three atoms of hydrogen, each of which is replaceable by an equivalent quantity of metal. PYROPHOSPHORIC ACID. H*P 2 0* When orthophosphoric acid is heated for a long time to 213° it loses water and is converted into a new acid, which is called pyrophosphoric. Two molecules of phosphoric acid lose one molecule of water, and then unite to form a single mole- cule of pyrophosphoric acid. /OH PO^OH /OH N)|H| PO^OH = H 2 + )0 = H*P 2 T JOH PO^OH x OH PO^OH OH The residue constitutes an opaque, semi-crystalline mass, composed almost entirely of pyrophosphoric acid. METAPHOSPHORIC ACID. 175 Its aqueous solution forms a white precipitate of silver pyrophosphate in solutions of silver nitrate. H*P 2 T + 4AgN0 3 = Ag*FO T + 4HN0 3 When heated with water, pyrophosphoric acid again com- bines with one molecule of that liquid, and is converted into phosphoric acid by a reaction the inverse of that by which it is formed. METAPHOSPHORIC ACID. HPO Preparation. — When phosphoric acid is heated to redness in a platinum crucible, a hard, transparent, vitreous mass is obtained on cooling ; this is metaphosphoric acid. It is formed by the abstraction of one molecule of water from phosphoric acid. H 3 P0 4 — H 2 = HPO 3 It may also be obtained directly from calcium acid phos- phate, the preparation of which from bone-ash has already been described. A slight excess of dilute sulphuric acid is added to the concentrated solution of this salt, and the insoluble cal- cium sulphate formed is separated by nitration. Since, how- ever, the calcium sulphate is not entirely insoluble in water, the solution is concentrated, and alcohol added, which com- pletely precipitates the sulphate. The liquid is again filtered, the alcohol driven off by evaporation, and the residue heated to a temperature near redness to remove the excess of sulphuric acid. On cooling, a vitreous mass of metaphosphoric acid is ob- tained. An aqueous solution of metaphosphoric acid instantly pro- duces a precipitate of silver metaphosphate in a solution of silver nitrate. HPO 3 + AgNO 3 = AgPO 3 + HNO 3 A few drops of the acid solution added to white of egg sus- pended in water produces an abundant white precipitate. The same metaphosphoric acid is formed when phosphoric oxide is thrown into a large quantity of cold water, or when it is allowed to deliquesce in the air. Under these circumstances, ELEMENTS OF MODERN CHEMISTRY. one molecule of phosphoric oxide combines with only one molecule of water. PO 5 + H 2 = 2HP0 3 The preceding considerations establish the existence of three phosphoric acids, which differ both in composition and proper- ties. To these three acids correspond three salts of silver, and it will be seen that the latter differ from the acids only by containing silver instead of hydrogen, a substitution which takes place atom for atom. ACIDS. SILVER SALTS. H 3 P0 4 phosphoric acid (orthophos- Ag 3 P0 4 trisilver phosphate (ortho- phoric). phosphate). H 4 P 2 7 pyrophosphoric acid. Ag 4 P 2 7 silver pyrophosphate. HPO 3 metaphosphoric acid. AgPO 3 silver metaphosphate. It may be added that, independently of the acids and salts of which the composition and nomenclature have just been considered, others have been described, the most interesting of which are related to the metaphosphates, of which they con- stitute polymeric modifications. That is, two, three, four, or more molecules of metaphosphoric acid are condensed in a single molecule, forming more complicated acids. COMPOUNDS OF PHOSPHORUS AND SULPHUR. When phosphorus is heated with dry sulphur, or when a mixture of the two bodies is melted under water, they combine with a vivid combustion which is sometimes accompanied by dangerous explosions. The action is less violent with amor- phous phosphorus. According to the proportions of these bodies which are brought into contact, several combinations of phosphorus and sulphur may be obtained, among which the trisulphide, P 2 S 3 , and the pentasulphide, P 2 S 5 , correspond to phosphorous and phosphoric oxides. The pentasulphide may be obtained in pale yellow crystals. : ARSENIC. Vapor density compared to air 10.37 Vapor density compared to hydrogen .... 150. Atomic weight As = 75. Arsenic was discovered by A. Schroeder in 1694. Natural State and Extraction. — There exists in nature a ARSENIC. 177 common and abundant mineral which contains iron, sulphur, and arsenic, and which is called mispickel; it is a sulphar- senide of iron. When it is strongly heated, the arsenic is volatilized and a residue of iron sulphide remains. FeSAs = FeS + As Mispickel. Iron sulphide. The operation is conducted on the large scale in earthenware cylinders placed horizontally in a furnace. The arsenic sublimes into sheet-iron pipes fitted -to the open extremity of the cylin- ders which extend beyond the furnace. The volatilization of the arsenic is facilitated by the addition of a certain quantity of metallic iron. The arsenic of commerce may be purified by distilling it with charcoal in a stoneware retort. Properties. — Recently-sublimed arsenic presents the appear- ance of a steel-gray, crystalline mass, having a metallic lustre. Its crystalline form is an acute rhombohedron. Its density is about 5.7. Arsenic volatilizes without melting at a temperature below dull redness. Its vapor is colorless. When it is heated under strong pressure it melts to a transparent liquid. On exposure to the air it loses its lustre and assumes a black-gray color ; in this case its surface becomes covered with a thin layer of a brown-black pulverulent substance, regarded by some chemists as a suboxide of arsenic. Arsenic oxidizes when it is heated in the air or in oxygen. If a small quantity of arsenic be thrown upon a red-hot coal, white vapors are produced, and an alliaceous odor is percep- tible. A fragment of arsenic may be strongly heated in the hori- zontal branch of a tube con- taining oxygen (Fig. 71) ; the metal takes fire and burns with • bluish* flame, producing white vapors of arsenious oxide. If arsenic be preserved from the air under a layer of water, in which it is insoluble, it oxidizes slowly, in such a manner as to form a small quantity of arsenious acid, which dissolves in H* 178 ELEMENTS OF MODERN CHEMISTRY. the water. This property explains the efficacy of powdered arsenic (commercial cobalt) for poisoning flies. If powdered arsenic be sprinkled into dry chlorine, each particle burns with a bright flash. The arsenic unites with the chlorine, being converted into the trichloride AsCl 3 . It also combines directly with bromine, with iodine, and with sulphur. Arsenic is used to harden shot to prevent the leading of fowling-pieces. HYDROGEN ARSENIDE (ARSINE). Density compared to hydrogen 39. Molecular weight AsH 3 =78. Preparation. — This gas may be prepared by the action of hydrochloric acid upon zinc arsenide. Zn 3 As 2 + 6HC1 = 2AsH 3 + 3ZnCl 2 Zinc arsenide. Zinc chloride. It must be handled with prudence, as it is extremely poisonous. Properties. — Hydrogen arsenide is colorless ; its odor is penetrating and garlicky. At a red heat it is decomposed into arsenic and hydrogen. On the application of flame, it burns in the air with a bluish light, producing fumes of arsenious oxide. If the supply of air be insufficient, arsenic is deposited. With one and a half times its volume of oxygen, hydrogen arsenide forms an explosive mixture, the products of the combination being water and arsenious oxide. 2AsH 3 + O 6 = As 2 3 + 3H 2 Chlorine decomposes hydrogen arsenide with a flash of light and formation of hydrochloric acid. An excess of chlorine yields arsenic trichloride, but in the presence of water, arsenious oxide is formed. 2AsH 3 + 6C1 2 + 3H 2 = As 2 3 + 12HC1 Water dissolves about one-fifth of its volume of hydrogen arsenide. When this gas is agitated with a solution of cupric sulphate, it disappears entirely if the gas be pure, and leaves a residue of hydrogen should that gas have been present in the free state in the mixture (Dumas). 3CuSO + 2AsH 3 = Cu 3 As 2 + 3H 2 SO Cupric sulphate. Copper arsenide. # Silver nitrate solution decomposes hydrogen arsenide ; silver, is precipitated, and arsenious acid formed. AsH 3 + 6AgN0 3 -f 3H 2 = H 3 As0 3 + 6HN0 3 + Ag 6 . ARSENIC CHLORIDE. — ARSENIOUS OXIDE. 179 ARSENIC CHLORIDE. AsCl 3 Preparation. — 1. A current of dry chlorine may be passed over powdered arsenic contained in a retort, the neck of which is fitted to a cooled receiver. The chloride formed condenses as a yellow liquid, containing an excess of chlorine, front which it may be freed by distillation over powdered arsenic (Dumas). 2. A mixture of 40 grammes of arsenious oxide and 400 grammes of sulphuric acid is gently heated in a tubulated retort, and fragments of fused sodium chloride are gradually added ; arsenic chloride distils over and condenses in the receiver. 3H 2 SO + 6XaCl + As 2 3 = 3Na 2 SO + 2AsCl 3 + 3H 2 Sodium chloride. Sodium sulphate. Properties. — Arsenic chloride is a colorless, oily, and very dense liquid. It boils at 134°. Its density at 0° is 2.05. It gives off white fumes in the air, and is very poisonous. An excess of water instantly decomposes it into hydrochloric acid and arsenious oxide, which, being but slightly soluble, is precipitated. 2AsCP + 3H 2 = As 2 3 + 6HC1 ARSENIOUS OXIDE. As 2 8 Preparation. — This dangerous poison is obtained in the arts by roasting arseniferous minerals, particularly mispickel. Roasting is an operation which consists in heating a mineral in contact with air, by which the oxidizable elements present are oxidized. When arseniferous minerals are roasted, arsen- ious oxide is formed among other products, and volatilizes, and is condensed either in wide horizontal chimneys or in a large building divided into numerous communicating compartments, through which the vapor is led consecutively. It is collected in the form of a powder, and is resublimed in cast-iron pots surmounted by sheet-iron cylinders, in which it condenses. Properties. — Recently-sublimed arsenious oxide occurs as vitreous masses ; but it soon loses its transparency and becomes milk-white, presenting the appearance of porcelain. When a large piece of the opaque oxide is broken, the interior is usually found to be still transparent and vitreous. 180 ELEMENTS OF MODERN CHEMISTRY. Arsenious oxide then exists in two forms : the vitreous variety is amorphous ; the opaque is crystalline. The former variety changes into the latter by a molecular transformation which takes place in the midst of the amorphous vitreous mass. Arsenious oxide crystallizes in regular octahedra or in tetra- hedra ; sometimes, but more rarely, in right-rhombic prisms. It is dimorphous. It dissolves slowly in cold water, in which it is but slightly soluble, and in this respect there is a curious difference between the opaque and the vitreous varieties. The latter is three times more soluble than the former ; while one part of the vitreous oxide dissolves in 25 parts of water at 13°, one part of the opaque variety requires 80 parts of water for its solution at the same temperature. The aqueous solution of arsenious oxide feebly reddens blue litmus. It is almost tasteless. It may be regarded as contain- ing normal arsenious acid, H 3 As0 3 , corresponding to normal phosphorous acid, H 3 P0 3 ; but this hydrate cannot be separated from the solution. On evaporation, the oxide As 2 3 is always deposited. 2H 3 As0 3 = As 2 3 + 3H 2 The aqueous solution of arsenious oxide, neutralized with ammonia, gives a green precipitate with solution of cupric sul- phate ; this is copper arsenite, or Scheele's green. With silver nitrate it gives a canary-yellow precipitate of silver arsenite. Arsenious oxide is more soluble in hydrochloric acid than in water. If a slip of clean copper be introduced into this solu- tion, it becomes covered with a steel-gray or black coating of arsenic. Reinsch's test for arsenic consists in boiling the suspected substance with dilute hydrochloric acid and bright metallic copper. The arsenic is deposited upon the copper, and by carefully heating the latter in a small tube the arsenic vola- tilizes and is converted into arsenious oxide, which condenses in the crystalline form, easily recognizable by aid of a micro- scope. By the action of zinc the solution of As 2 3 in hydrochloric acid disengages hydrogen arsenide ; the zinc displaces the hy- drogen of the hydrochloric acid, and, by the action of this nascent hydrogen upon the arsenious oxide, water and hydro- gen arsenide are formed. As 2 3 + 6H 2 = 3H 2 + 2AsH 3 ARSENIOUS OXIDE. 181 Marsh's Apparatus.— The reducing action of nascent hy- drogen upon arsenious oxide is used for the detection of this substance by the aid of Marsh's apparatus. This consists of an apparatus for the generation of hydrogen (Fig. 72) ; it contains pure zinc and dilute sulphuric acid, and the hydrogen burns at the drawn-out jet with an almost colorless flame. If, however, a few drops of a solution of arsenious oxide be in- troduced by the fun- nel-tube, the character of the flame is at once changed ; it becomes bluish, elongated, and diffuses a white smoke, and if a white porce- lain surface be de- pressed into it, large spots of a brownish color are produced. These are composed of arsenic, which is set free in the interior of the flame by the decomposition of the hydrogen arsenide by the heat. Fig. 72. Fig. 73. Fig. 73 represents a more perfect form of Marsh's appa- ratus? The hydrogen, mixed with the hydrogen arsenide, first 16 182 ELEMENTS OF MODERN CHEMISTRY. traverses a tube, B, filled with cotton, designed to arrest the small drops of liquid which may be carried with the gas ; it then passes through a narrow tube wrapped with metallic foil and heated to redness in a tube-furnace. The hydrogen arsen- ide is decomposed into hydrogen and arsenic, and the latter is deposited as a brilliant black mirror in the cooler portion of the tube. (For distinction between arsenic and antimony by this test, see page 186.) Marsh's apparatus permits the detection of the least trace of arsenious or arsenic acid in a liquid. It is of great value in medico-legal researches, as arsenious oxide is a common and dangerous poison. ARSENIC ACID IPAsO Preparation. — When arsenious oxide is heated with nitric acid having a specific gravity of 1.35, red vapors are disen- gaged and the oxide is oxidized into arsenic acid, which may be obtained as a syrupy liquid by sufficient concentration. When left for a long time in a cool place it deposits colorless crystals, which constitute a hydrate 2H 3 As0 4 + H 2 (E. Kopp). These crystals are very deliquescent, and dissolve in water with the production of cold. They melt at 100°, losing their water of crystallization, and there remains a mass com- posed of fine needles of the normal acid H 3 As0 4 . When heated for some time to a temperature between 140 and 180°, this acid loses water, and is converted into pyro- arsenic acid, H 4 As 2 7 . 2H 3 AsO — H 2 = H 4 As 2 7 Between 200 and 206° another quantity of water is driven out, and on cooling there remains a pasty, pearly mass, which is metarsenic acid, HAsO 3 . H 3 AsO* — H 2 = HAsO 3 It will be noticed that in their modes of formation and in their constitution, arsenic, pyro-arsenic and metarsenic acids are analogous to the corresponding acids of phosphorus. When metarsenic acid is heated to dull redness, it loses all of its hydrogen in the form of water, and is converted intt arsenic oxide, As 2 5 . 2HAs0 3 — H 2 = As 2 5 COMPOUNDS OF SULPHUR AND ARSENIC. 183 At this temperature the oxide melts, and at a bright-red heat it is decomposed into arsenious oxide and oxygen. As 2 5 = As 2 3 + O 2 When exposed to the air it absorbs moisture, but very slowly, and even when treated with water it requires a certain time for solution. Ordinary arsenic acid, which may be called ortharsenic, is very soluble in water ; its solution strongly reddens blue litmus and possesses a very acid taste. It is reduced by nascent hydro- gen, like the solution of arsenious oxide. When neutralized with ammonia, it forms a bluish-white precipitate with solution of cupric sulphate, and a brick-red precipitate with silver nitrate. Hydrogen sulphide produces no immediate. precipitate. A solution of sulphurous acid reduces arsenic acid to arse- nious oxide, and then on the addition of hydrogen sulphide, a yellow precipitate of arsenic sulphide, As' 2 S 3 , is formed. COMPOUNDS OF SULPHUR AND ARSENIC. Three sulphides of arsenic are known: Arsenic disulphide, or realgar . As 2 S 2 Arsenic trisulphide, or orpiment As 2 S 3 Arsenic pentasulphide As 2 S 5 Arsenic Disulphide, As 2 S 2 . — This body occurs in nature in the form of transparent red crystals, which belong to the type of the oblique rhombic prism. It is obtained as a red mass having a conchoidal fracture by melting 75 parts of arsenic with 32 parts of sulphur. It is fusible, and may be crystallized by slow cooling. When strongly heated in closed vessels, it boils and distils without alteration, but when heated in the air, it burns into arsenious and sulphur- ous oxides. The alkaline sulphides and ammonium sulphide dissolve realgar, leaving a brown powder which has been con- sidered as a subsulphide of arsenic. Boiling solution of potas- sium hydrate also dissolves realgar, forming a mixture of potassium arsenite and sulpharsenite ; the latter is a soluble compound of arsenic trisulphide and potassium sulphide; a brown powder remains undissolved. Arsenic Trisulphide, or Orpiment, As 2 S 3 . — When a solu- tion of arsenious oxide is submitted to the action of hydrogen 184 ELEMENTS OF MODERN CHEMISTRY. sulphide, the liquid assumes a yellow color without the forma- tion of any precipitate, but if a drop of hydrochloric acid be added, a yellow, flocculent precipitate of arsenic trisulphide is formed at once. As 2 3 + 3H 2 S = As 2 S 3 + 3H 2 The composition of arsenic trisulphide corresponds to that of arsenious oxide, and is the same as that of the orpiment found in nature. It may also be obtained by fusing together arsenic and sul- phur in the proper proportions, or even arsenious oxide and sulphur; in the latter case, sulphurous oxide is disengaged, and arsenic trisulphide sublimes. Thus prepared, orpiment occurs as crystalline masses of a yellow color, bordering upon orange, and a pearly aspect. Its density is 3.459. It is fusible and volatile. Arsenic trisulphide obtained by precipitation is insoluble in cold water, and but slightly soluble in boiling water, but it is very soluble in ammonia. By continued boiling with water, it yields hydrogen sulphide and arsenious acid (de Clermont and Frommel). It is also dissolved by solutions of the alka- line sulphides with the formation of sulpharsenites, compounds of two sulphides, in which the alkaline sulphide plays the part of a base and the arsenic trisulphide the part of an acid. Orpiment also dissolves in solutions of the caustic alkalies with the formation of an arsenite and a sulpharsenite. Arsenic Pentasulphide, As 2 S 5 .— By the prolonged action of hydrogen sulphide upon a solution of arsenic acid, a pale- yellow precipitate is obtained, which is a mixture of the trisul- phide and sulphur. Arsenic pentasulphide has been obtained by fusing together • the proper proportions of sulphur and orpiment. It corresponds to arsenic oxide. As 2 5 As 2 S 5 Arsenic oxide. Arsenic sulphide. The alkaline sulphides dissolve it with the formation of sulpharsenates. Among the latter there is one having the composition K 3 AsS 4 , and which corresponds to the arsenate K 3 AsO. It is formed by the following reaction : As 2 S 5 + 3K 2 S = 2(K 3 AsS 4 ) ANTIMONY. 185 ANTIMONY. . Sb = 120 Antimony is generally classed with the metals. It indeed possesses the lustre of a metal, and it conducts heat and elec- tricity ; but in a true chemical classification these physical properties cannot overbalance the most striking chemical anal- ogies. By its affinities, and by the nature and constitution of its compounds, antimony must find a place by the side of arsenic, which must itself be classed with phosphorus and nitrogen. Metallurgy of Antimony. — The" most common ore of anti- mony, which is a sulphide, was known to the ancients. The metal is extracted from it by a very simple process. The sul- phide is first separated by fusion from the earthy materials, called gangue, with which it is associated ; it is then roasted or heated in contact with air. The sulphur is in great part expelled in the form of sulphurous oxide gas, and the antimony is converted into oxide, which still contains some undecom- posed sulphide. The whole is then pulverized, and the pow- der mixed with pulverized charcoal impregnated with sodium hydrate. This mixture is calcined in crucibles, and the anti- mony oxide and a portion of the sulphide is reduced by the charcoal ; sodium sulphide is also formed, and this dissolves a portion of the antimony sulphide, forming a flux which floats upon the molten antimony ; after cooling, the latter is found at the bottom of the crucible as a button, easy to separate from the scoriae. By another process the antimony sulphide is fused with metallic iron. Iron sulphide and antimony are formed, and the latter collects at the bottom by reason of its greater density. Perfectly pure antimony is prepared in the laboratory by reducing antimonous or antimonic oxide by charcoal. Properties. — Antimony is a brilliant white metal, having a slightly bluish lustre ; it is brittle, and has a laminated frac- ture. Its density is 6.715. It melts at about 450°, and sensibly vaporizes at a white heat. Antimony may be crystallized by allowing large masses of the fused metal to cool slowly, and decanting the liquid por- tion. Small acute rhombohedra may be obtained in this manner. 16* 186 ELEMENTS OF MODERN CHEMISTRY. When heated in contact with air, antimony is converted into antimonous o^xide, Sb 2 3 . If a fragment of antimony be introduced into a cavity scraped in a piece of charcoal, and the flame of a blow-pipe be directed upon it, it melts, becomes red-hot, and gives off white fumes. If now the molten globule be allowed to fall, it breaks up into a multitude of smaller globules on striking the floor, and each particle rebounds into the air as a brilliant spark, leaving behind it a train of smoke. Powdered antimony burns brilliantly in dry chlorine. Type metal contains twenty per cent, antimony and eighty per cent, lead; the alloy is hard, ami takes a sharp impression of the mould. HYDROGEN ANTIMONIDE. There is a compound of hydrogen and antimony which has not yet been obtained in the pure state, but which, according to all probability, is the body SbH 3 . Like its analogue, hy- drogen arsenide, it is decomposed by heat ; it can also be pre- pared in Marsh's apparatus by the action of nascent hydrogen upon a solution containing antimony, and when decomposed by heat it forms metallic rings and mirrors, which it is of im- portance to distinguish from those formed by arsenic. The following differences are sufficient for this purpose: The antimony rings are not displaced when heated in a current of hydrogen ; the arsenic rings are volatilized, and condense in a cooler portion of the tube. The spots and rings of antimony are not dissolved by a solu- tion of sodium hypochlorite (Labarraque's solution), which at once dissolves those of arsenic. The antimony spots are readily dissolved by a drop of nitric acid, and the liquid leaves on evaporation a white residue, which is not colored by the addition of a drop of silver nitrate solution. Under the same circumstances, the arsenical spots leave a white residue, which assumes a brick-red color when moistened with a solution of silver nitrate, owing to the for- mation of silver arsenate. COMPOUNDS OF ANTIMONY AND CHLORINE. Antimony trichloride SbCl 3 Antimony pentachloride SbCl 5 Antimony Trichloride, SbCl 3 .— This compound, formerly COMPOUNDS OF OXYGEN AND ANTIMONY. 187 known as butter of antimony, is formed by the action of hy- drochloric acid upon antimony sulphide. It is generally pre- pared in the laboratory from the residue from the preparation of hydrogen sulphide. This acid liquid is distilled in a retort provided with a receiver, which is changed as soon as the anti- mony chloride which distils over begins to crystallize in the neck of the retort. This chloride is solid, transparent, and colorless. It melts at 73.2°, and boils at 230°. It dissolves in water charged with hydrochloric acid, forming a colorless solution, but when this liquid is diluted with water there is formed an abundant white precipitate, long known as powder of Algaroth. It is an oxychloride of which the composition does not appear con- stant. There is one which contains SbOCl, and which can be regarded as antimony trichloride, in which two atoms of chlo- rine have been replaced by one atom of oxygen. It is formed by a double decomposition, according to the following reaction : SbCP + H 2 = 2HC1 + SbOCl Antimony Pentachloride, SbCl 5 . — This is formed by the action of an excess of chlorine upon antimony or upon the trichloride. It is a yellow liquid, giving off white fumes in the air. It is volatile, but cannot be distilled without undergoing a partial decomposition into chlorine and antimony trichloride. When exposed to the air, it absorbs moisture and is converted into a crystalline mass, which is a hydrate of the pentachloride. When treated with a large excess of water, it is decomposed with production of heat, and formation of pyrantimonic and hydrochloric acids. COMPOUNDS OF OXYGEN AND ANTIMONY. Two oxides of antimony are known, corresponding to those of phosphorus and arsenic : Antimonous oxide Sb 2 O s Antimonic oxide Sb 2 5 Normal antimonic acid, H 3 Sb0 4 , corresponding to phosphoric and arsenic acids, is not known in the free state, but a derivative of this acid exists and may be regarded as antimony ant intonate. Its composition is Sb 2 4 , and it is derived from antimonic acid 188 ELEMENTS OF MODERN CHEMISTRY. by the substitution of an atom of antimony for three atoms of hydrogen. H 3 Sb0 4 antimonic acid. SbSbO 4 antimony antimonate. There is a pyrantimonic and also a metantimonic acid, analogous to the corresponding phosphorus acids : H 4 Sb 2 7 pyrantimonic acid. HSbO 3 metantimonic acid. ANTIMONOUS OXIDE. Sb 2 3 This is obtained by oxidizing the metal in the air. The operation may be conducted in two crucibles placed one above the other, an opening being pierced in the upper one for the access of air. They are heated to redness in a furnace, and on cooling, the antimony is found to be partially converted into brilliant needles that the ancients called silver flowers of anti- mony. The crystals are right rhombic prisms, mixed with regular octahedra, for antimonous oxide crystallizes in two forms, presenting the same character of dimorphism as arsenious oxide. The two compounds are hence said to be tsodimorphous. When solution of sodium hydrate, or better, sodium carbon- ate, is poured into solution of antimony trichloride, a white precipitate of antimonous hydrate is formed, and, in the latter case, carbonic acid gas is disengaged. SbCP + 3NaOH = H 3 Sb0 3 + 3NaCl Sodium hydrate. Antimonous hydrate. Sodium chloride. This hydrate readily parts with a molecule of water, being- converted into another hydrate, HSbO 2 . H 3 Sb0 3 — H 2 = HSbO 2 ANTIMONY ANTIMONATE. Sb 2 0* This compound is formed when antimonous oxide is heated for a long time in the air, oxygen being absorbed, or when antimonic oxide is strongly calcined, oxygen being then disen- gaged. It is a white, infusible powder, undecomposable by heat and insoluble in water. ANTIMONIC OXIDE AND ACIDS. 189 ANTIMONIC OXIDE AND ACIDS. When powdered antimony is heated with concentrated nitric acid, a white powder is obtained, which is nietantimonic acid. It contains one atom of hydrogen capable of being replaced by an equivalent quantity of metal, and thus corresponds to meta- phosphoric acid. HPO 3 HSbO 3 KSbO 3 Metaphosphoric acid. Metantimonic acid. Potassium metantiinonate. When it is heated to dull redness, it loses water and is con- verted into antimonic oxide. 2HSb0 3 — H 2 = Sb 2 5 If antimony pentachloride be poured into an excess of water, a white precipitate of pyrantimonic acid is formed. It is the analogue of pyrophosphoric acid, and, like the latter, contains four atoms of hydrogen. H*P0 7 H*Sb 2 7 K 4 Sb 2 7 Pyrophosphoric acid. Pyrantimonic acid. Potassium pyrantimonate. According to Freniy, potassium pyrantimonate may be obtained by heating metantimonic acid or potassium metanti- monate with potassium hydrate, in a silver crucible. 2KSb0 3 + 2KOH = K 4 Sb 2 7 + H 2 Potassium Potassium Potassium metantimonate. hydrate. pyrantimonate. The metantimonate may be extracted by water, in which it is soluble, from the white mass, called by the ancients dia- phoretic antimony ', which is obtained by deflagrating in a red- hot crucible a mixture of 2 parts of nitre (potassium nitrate) and 1 part of powdered antimony. Cold water first dissolves potassium nitrate from this mass, and then potassium metanti- monate. The solution of the latter salt produces with hydro- chloric acid a white precipitate of metantimonic acid. SULPHIDES OF ANTIMONY. Two sulphides of antimony are known : Antimony trisulphide, or antimonous sulphide . . Sb 2 S 3 Antimony pentasulphide, or antimonic sulphide . . Sb 2 S 5 Antimonous Sulphide, Sb 2 S 3 . — This compound, ordinarily called sulphide of antimony, occurs both in the crystalline 190 ELEMENTS OF MODERN CHEMISTRY. form and amorphous. Crystallized, it exists in nature and is the mineral commonly known as stibium. It is separated from its gangue by fusion, and is thus obtained in gray masses com- posed of brilliant needles having a metallic lustre. Amorphous, it constitutes the orange-colored precipitate formed by the action of hydrogen sulphide upon a solution of antimony chloride. The precipitate is insoluble in ammonia, but dissolves in ammonium sulphide and in the alkaline sulphides. Antimony trisulphide is reduced by hydrogen at a high tem- perature ; hydrogen sulphide is formed, and antimony remains. When heated in the air, antimony sulphide is oxidized with formation of sulphurous oxide and antimonous oxide. The incompletely roasted residue melts at a red heat, and on cool- ing assumes the form of a brown vitreous mass called glass of antimony. It is an impure oxysulphide which appears to contain the compound Sb 2 S 2 = ™ « > 0. Antimony trisulphide is used in pyrotechny, adding to the brilliancy of colored fires. Antimony Pentasulphide, Sb 2 S 5 . — When finely-pulverized antimony trisulphide is digested with sulphur and a solution of sodium hydrate, or a mixture of sulphur, sodium carbonate, and lime, the antimony sulphide gradually dissolves in the liquid, combining both with sulphur and with the sodium sul- phide formed. The product of the reaction is a sulphantimo- nate of sodium, which is deposited in fine crystals from the concentrated liquid. . Sb 2 S 5 +' 3Na 2 S = 2Na 3 SbS 4 Sodium sulphide. Sodium sulphantimonate. The crystals of this compound contain 9 molecules of water of crystallization. It corresponds to the sulpharsenate already mentioned, and to trisodium phosphate, Na 3 PO. It is soluble in water, and on the addition of hydrochloric acid to its solution, hydrogen sulphide is disengaged and anti- mony pentasulphide is precipitated. 2Na 3 SbS* + 6HC1 = 6NaCl + Sb 2 S 5 -f 3H 2 S General Considerations upon the Elements of the Nitro- gen Group. — Nitrogen, phosphorus, arsenic, and antimony, and bismuth might be added, form a group of elements allied by the most striking analogies. This is made manifest by the BORON. 191 atomic composition of their compounds, as will be seen in the following synopsis : HYDROGEN COMPOUNDS. NH 3 PH 3 Ammonia. Hydrogen phosphide. AsH 3 Hydrogen arsenide. SbH 3 Hydrogen antimonide. CHLORINE COMPOUNDS. NCP Nitrogen trichloride. PCP Phosphorus trichloride. PCP AsCP Arsenic trichloride. SbCP Antimony trichloride. SbCP Phosphorus pentachloride. Antimony pentachloride. OXYGEN COMPOUNDS. N 2 3 P 2 3 As 2 3 Sb 2 3 Nitrogen trioxide. Phosphorous oxide. Arsenious oxide. Antimonous oxide. N'O* P 2 5 Asr'O 5 Sb 2 5 Nitrogen pentoxide. Phosphoric oxide. Arsenic oxide. Antimonic oxide. H 3 P0 3 Phosphorous acid. H 3 As0 3 Arsenious acid. HNO 2 Nitrous acid. H 3 PO Phosphoric acid. H*P 2 0' H 8 Sb0 3 Antimonous acid. HSbO 2 Antimonyl hydrate. H*Sb 2 0' HNO 3 Nitric acid. H 3 AsO Arsenic acid. H 4 As 2 7 Pyrophosphoric acid. Pyro-arsenic acid. Pyro-antimonic acid. HPO 3 HAsO 3 HSbO 3 Metaphosplioric acid. Metarsenic acid. Metantimonic acid. If the analogy between nitrogen and phosphorus were com- plete, there should be an orthonitric acid, H 3 N0 4 = HNO 3 -f- H 2 0, corresponding to ordinary or orthophosphoric acid. This acid is not known as a definite hydrate, but compounds exist which are derived from it. Thus, bismuth subnitrate. BiNO*, can be regarded as a salt of orthonitric acid, in which three atoms of hydrogen are replaced by one atom of triatomic bismuth. BORON. Bo = 11. Boron, the radical of boric acid, was discovered by Gray- Lussac and Thenard in 1808. It is possible that the element has not yet been obtained in a perfectly pure state. 192 ELEMENTS OF MODERN CHEMISTRY. Preparation. — 100 parts of powdered boric oxide are fused with 60 parts of sodium, in small fragments, in an iron cruci- ble ) 40 or 50 parts of sodium chloride are added, to increase the fusibility of the mixture, and the crucible is covered. The reaction yields sodium borate and boron : 2Bo 2 3 + 3Na 2 = 2Na 3 Bo0 3 + Bo 2 . Boric oxide Sodium Sodium borate. When the reaction has terminated, the still-liquid mass is poured into water acidulated with hydrochloric acid. The sodi- um borate dissolves, and the boron remains as a greenish powder. Properties. — Boron is amorphous, infusible. It must be dried at ordinary temperatures ) if heated to 300° in the air, it burns into boric oxide. When heated in a current of hydro- gen, it becomes brown and much more inalterable in the air. Its combustion in pure oxygen is very brilliant, and it possesses a singular affinity for nitrogen, with which it combines directly at a red heat, forming a nitride, BoN. When heated to dull redness in an atmosphere of nitrogen dioxide, it burns into a mixture of boric oxide and boron nitride (Wohler and Deville). Boron decomposes water at a red heat, and otherwise behaves as an energetic reducing agent. When boric oxide is fused with aluminium, boron is set free, and aluminium oxide is formed: Al 2 -f- Bo 2 3 = APO 3 -f Bo 2 . The liberated boron combines with a portion of the alu- minium, forming a compound which crystallizes in brilliant, black, square octahedra, having a density of 2.63 and almost as hard as the diamond. These crystals, which may be obtained by treating the cold fused mass successively with hydrochloric acid and potassium hydrate, were long supposed to be crystal- lized boron, but they are really a complex compound of boron and aluminium, containing also carbon, and being yellow in color if the reduction be made in a carbon crucible. BORON CHLORIDE. BoCl 3 Preparation.— This body is formed when dry, amorphous boron is heated in a current of chlorine. It may be prepared by the action of chlorine on an incandescent mixture of boric oxide and charcoal Bo 2 3 + 3C + 3CP = 2BoCP + 3CO. Bcric oxide. Boron chloride. Carbon monoxide. BORON FLUORIDE. — BORIC ACID. 193 Properties.— In a state of purity, boron chloride is a color- less, mobile, and highly-refractive liquid, boiling at 17°. It fumes in the air, and is readily decomposed by water into boric and hydrochloric acids. BoCP + 3H 2 = 3HC1 + Bo(OH) 3 BORON FLUORIDE. BoFl 3 Density compared to air 2.31 Density compared to hydrogen 34. Preparation. — Boron fluoride was discovered by Gray-Lussac and Thenard in 1810. It is prepared by heating in a glass retort an intimate mixture of one part of boric oxide and two parts of powdered calcium fluoride with twelve parts of sul- phuric acid. The gas disengaged is collected over mercury. 3CaFi 2 + Bo 2 3 + 3H 2 SO* == 3CaSO* + 3H 2 + 2BoFP Calcium Boric oxide. Calcium sulphate, fluoride. Properties. — Boron fluoride is a colorless gas, having a suf- focating odor. It produces abundant fumes in the air, and is very soluble in water, which dissolves about 800 times its volume of this gas. Its affinity for water is so great that it carbonizes paper and analogous organic substances, from which it removes the elements of water. The solution of boron fluoride in water is accompanied by a chemical reaction ; when the aqueous solution of this gas, satu- rated at the ordinary temperature, is cooled to 0°, crystals of boric acid are deposited, and a very acid liquid is obtained, known as hydrofluoboric acid ; its composition is expressed by the formula : BoFffi = BoFP.HFl BORIC ACID. H 3 Bo0 3 Preparation. — Boric acid was discovered by Homberg in 1702. It is found in the free state in the craters of certain volcanoes, and exists in solution in the lagoni of Monte- Rotondo, in Tuscany. These are muddy little lakes, through which arise the gaseous emanations from the fissures of a vol- canic soil. The gases (sujjioiii) contain sensible traces of boric i 17 194 ELEMENTS OF MODERN CHEMISTRY. acid, which is dissolved by the water of the lagoni. On evap- oration, this water furnishes the crude boric acid. Large quantities of borax (sodium borate) are obtained from Borax Lake and from Lake Clear, about two hundred and fifty miles north of San Francisco, California. Calcium borate and the principal compounds of boric acid are abundant on the Pacific slope in the United States and in Chili. In the laboratory, boric acid is prepared by decomposing a boiling saturated solution of borax or sodium borate with dilute sulphuric acid. The latter is added in small portions until the liquid strongly reddens litmus-paper ; the solution is then allowed to cool, and the boric acid separates in the crystalline form. Properties. — Pure boric acid crystallizes in pearly scales, somewhat greasy to the touch. It dissolves in 25 parts of water at 18°, and is much more soluble in boiling water. The solution is feebly acid, and changes blue litmus solution to a wine color. Boric acid dissolves in alcohol, and the solution burns with a green flame. When heated to 100° it loses one molecule of water, and is converted into metaboric acid, HBoO 2 . If the latter be main- tained for a time at a temperature of 140°, it is converted into tetraboric acid, H 2 Bo 4 7 . 4HBo0 2 = HWO 7 + H 2 When boric acid is heated in a platinum crucible to a tem- perature near redness, it loses all of its water, melts, and solidi- fies to a transparent glass on cooling. This is boric oxide. 2H 3 Bo0 3 = Bo 2 3 + 3H 2 At a red heat this body dissolves a great number of solid sub- stances, particularly the metallic oxides ; it then yields variously colored glasses on cooling. Boric oxide is not decomposed by charcoal at a red heat, but is converted into boron chloride by the simultaneous action of chlorine and. charcoal. SILICON. Si = 28. Like boron, silicon exists amorphous and in the crystalline form. It was discovered by Berzelius in 1825. Preparation. 1. Amorphous Silicon. — Dry sodio-silicon SILICON. 1 95 fluoride is heated with half its weight of metallic sodium : sodium fluoride is formed and silicon is set free. Na 2 Fl 2 .SiFl 4 + 2Na 2 = 6NaFl + Si Sodio-silicon fluoride. Sodium fluoride. On cooling, the mass is exhausted, first with cold, and after- wards with hot, water; a brown powder of amorphous silicon remains. 2. Crystallized Silicon. — Deville and Caron obtained crys- tallized silicon by projecting a mixture of 3 parts of potassium and silicon double fluoride, 4 parts of zinc, and 1 part of sodium into a red-hot crucible. Fluoride of sodium is formed, and the silicon set free dissolves in the zinc and separates in the crystalline form on cooling; it is isolated from the zinc by dissolving the button in hydrochloric acid ; the silicon remains in the form of brilliant laminae or needles. These crystals are of a dark steel-gray color, and possess a metallic lustre; they are composed of chaplets of regular octahedra. Properties. — Amorphous silicon is a brown powder, more dense than water, in which it is insoluble, and producing dark stains on the fingers. When heated in the air, it takes fire and burns with a bright light into silicic oxide, SiO 2 . Crystallized silicon has a density of 2.49. It may be heated to redness in oxygen without taking fire, but when it is calcined with potassium carbonate the latter is decomposed with a vivid emission of light, potassium silicate being formed and carbon being set free. Crystallized silicon resists the oxidizing action of both potassium nitrate and potassium chlorate, but it dis- solves slowly in a boiling solution of potassium hydrate, hydro- gen being disengaged and potassium silicate being formed. It burns when heated to redness in an atmosphere of chlorine, silicon chloride being formed. HYDROGEN SILICIDE. Probable formula SiH 4 Preparation. — This compound was discovered by Wohler and Buff in 1857. Magnesium silieide* is introduced into a two-necked bottle, which is then entirely filled with water that * Wohler prepares this silicide by fusing in a crucible a mixture of 40 parts of magnesium chloride. 35 parts of silicon and sodium double fluor- ide, and 10 parts of sodium chloride, these salts being previously mixed with 10 parts of sodium in minute fragments. 196 ELEMENTS OP MODERN CHEMISTRY. has been recently boiled. One of the necks of the bottle is fitted with a funnel-tube which passes to the bottom of the bottle, while to the other is adapted a delivery-tube leading to the pneumatic trough ; this tube also should be completely filled with water so that there is not a single bubble of air in the whole apparatus. Concentrated hydrochloric acid is then introduced by the funnel-tube, and immediately reacts with the magnesium silicide, forming magnesium chloride, which dissolves, and hydrogen silicide, which is disengaged and must be collected in jars filled with recently boiled water. Properties. — The gas thus obtained is not pure hydrogen silicide ; it contains an excess of hydrogen. It is colorless and insoluble in water from which the air has been expelled. Water containing air in solution oxidizes it. If bubbles of the gas be allowed to escape through the water of the trough, each bubble takes fire on coming to the surface, burning with a bright light and a little explosion, and producing a white smoke of silicic oxide. This smoke forms rings like those produced by hydrogen phosphide under the same circum- stances, but often colored brown by a portion of silicon set free. The incomplete combustion of hydrogen silicide is accompa- nied by a brown deposit of amorphous silicon. At a red heat, hydrogen silicide is decomposed into hydrogen and silicon. SILICON CHLORIDE. SiCl* This compound is formed when silicon is heated to dull redness in a current of chlorine, or when a current of the latter gas is passed over an incandescent mixture of charcoal and silica. SiO 2 + C 2 JL CI 4 = SiCl 4 + 2CO Silicic oxide. Carbon monoxide. Preparation. — Precipitated silica, lamp-black, and oil are intimately mixed into a stiff" paste. This paste is made into little balls, which are put into a crucible, the cover of which is then luted on, and the whole is heated to redness in a furnace. When cool, the balls are introduced into a porcelain tube or a clay retort (Fig. 74), which is then heated to bright redness, while a current of carefully-dried chlorine is passed through. The silicon chloride and the carbon monoxide formed are SILICON FLUORIDE. 197 passed through two U tubes surrounded by a mixture of ice and salt. The silicon chloride is thus condensed. Properties. — Silicon chloride is a volatile, colorless liquid, of an irritating odor. It fumes in the air. Its density is 1.52, and it boils at 59°. It is instantly decomposed by water, silicic and hydrochloric acids being formed. A part of the silicic acid is precipitated Fig. 74. in the form of a jelly, while another part remains in solution. The latter is perhaps a hydrate corresponding to the chloride. SiCl 4 + 4H 2 = 4HC1 + Si(OH)* There exists a tetrabromide of silicon, SiBr*. and a tetra- iodide, Sil 4 , both corresponding to the chloride which has just been described. Friedel has recently discovered an iodide, Si 2 I 6 , remarkable as belonging to an entirely new series. SILICON FLUORIDE. SiFl* Density compared to air 3.6 Density compared to hydrogen 52. Preparation. — An intimate mixture of silicious sand and 17* 198 ELEMENTS OF MODERN CHEMISTRY. finely-powdered calcium fluoride, or fluor spar, is introduced into a glass flask (Fig. 75), and a sufficient quantity of sul- phuric acid is added to reduce the whole to a creamy consistence. A gentle heat is applied, and the gas disengaged may be col- lected over mercury. 2CaFP + 2H 2 SO + SiO 2 = 2CaSO + SiFl 4 + 2H 2 Calcium fluoride. Silicic oxide. Calcium sulphate. Fig. 75. Properties. — Silicon fluoride is a colorless, suffocating gas, producing white fumes when allowed to escape into the air. It may be liquefied by a low temperature and a strong pressure. On contact with water it is decomposed, silicic hydrate separat- ing in gelatinous flakes, and hydrofluosilicic acid being formed. 3SiFl 4 + 3H 2 = 2(H 2 Fl 2 .SiFF) + H 2 Si0 3 Hydrofluosilicic acid. Hydrofluosilicic Acid. — A saturated, aqueous solution of this acid is a highly acid liquid, fuming in the air, and evapo- rating slowly at 40° from a platinum-dish without leaving any residue. It is prepared by passing gaseous silicon fluoride into water under which is a layer of mercury. The delivery-tube must dip beneath the surface of the mercury, so that the silicon flu- oride can only come in contact with the water after passing through the metal; otherwise the delivery-tube would become obstructed by the deposit of gelatinous silica. Hydrofluosilicic acid is employed as a reagent in the labora- tory. It precipitates the salts of potassium and sodium, form- ing insoluble fluosilicates, R 2 Fl 2 .SiFl 4 . SILICIC OXIDE AND ACIDS. 199 SILICIC OXIDE AND ACIDS. (SILICA.) Native State. — Silicic oxide is widely diffused in nature. ^ It occurs crystallized, as the different varieties of quartz ; amor- phous, as agate, chalcedony, cornelian, flint, etc. ; granulated, it is found in sandstones and the sand produced by their disaggre- gation ; in this case it is often mixed with variable quantities of alumina and oxide of iron. It has the composition SiO 2 . Rock-crystal is pure silicic oxide. It occurs as six-sided prisms, terminated by pyramids of six faces (Fig. 76). As hydrate, silica exists in various minerals, such as opal and hydrophane. It is also found in the form of pulverulent deposits and in solution in many running waters, in large proportion in the hot waters of the geysers in Iceland. Properties. — Quartz is infusible at the highest furnace heats, but undergoes a viscous fusion when introduced into the flame of the oxyhydrogen blow- pipe. Neither carbon nor potassium is capable of j^m 76 reducing it, even at the highest temperatures. It is not attacked by acids, with the exception of hydrofluoric acid. Boiling alkaline solutions scarcely affect it, but the amor- phous varieties of silica, such as flint, as well as opal and the other hydrates, dissolve more readily in boiling solutions of the alkaline hydrates. All of the varieties of silica, when heated to redness with the alkalies or alkaline carbonates, combine with the bases, forming silicates which enter into fusion at a high temperature and solidify to a vitreous mass on cooling. Potassium silicate, or soluble glass, is a transparent mass, soluble in water. When hydrochloric acid is added to this solution, potassium chloride is formed and silicic acid is precipitated as a gelatinous mass, which is not insoluble in water. An aqueous solution of silicic acid may be obtained. If hydrochloric acid be added to a dilute solution of potas- sium silicate, the liquid remains transparent although it contains silicic acid. It may be poured into a dialyser. composed of a piece of parchment-paper stretched over a wooden or glass ring, and floated on the surface of pure water contained in another vessel. The potassium chloride gradually passes through the 200 ELEMENTS OF MODERN CHEMISTRY. membrane, as would any crystallizable body, and the silicic acid remains alone dissolved in the water in the dialyser, as all other amorphous bodies which are soluble in water would do. Graham gave the name dialysis to this separation of crys- tallizable bodies, which he named crystalloids, from uncrystal- lizable bodies, which he named colloids, by means of certain membranes. The former bodies pass through the membranes, which are, however, impermeable to the colloids. The silicic acid which remains in solution probably consti- tutes normal silicic acid, H 4 Si0 4 = SiO 2 + 2H 2 0. Glass is a mixture of potassium or sodium silicate with cal- cium silicate, and generally contains aluminium silicate. It is made by the prolonged fusion of potassium or sodium carbon- ate with pure quartz sand and lime. Flint glass contains lead, introduced in the form of red lead. Colored glasses are ob- tained by adding metallic oxides to the above ingredients. Cuprous oxide gives red glass; cupric oxide, green; cobalt oxide, blue, etc. Soda glass is more fusible than potash glass. Uses. — Silica is largely employed in all of its various forms. Crystallized quartz, or rock crystal, is used for the manufacture of ornaments, spectacle-glasses, and lenses. Chalcedony, onyx, and opal are sought for by the lapidary and engraver. Agate, which is very hard, is used for the manufacture of mortars, etc. Sandstones serve for building purposes and for grindstones; sand, for mortars and the manufacture of glass and pottery. CARBON. C = 12 Natural State and Varieties. — The carbon of chemists pure charcoal. This substance is known to all ; black, friable, light, absolutely fixed, inalterable by the air at ordinary tem- peratures, but combustible when heated in the air, it results from the calcination of organic matters, and particularly wood, in closed vessels. But carbon by no means always reveals these same properties. It occurs in nature under forms so different that it is impossible to apply a general description to all of its known varieties. What could be more different, as far as physical properties are concerned, from the soot deposited by a smoky flame, or the light, porous, and opaque charcoal, than the hard, dense, and transparent substance found in nature CARBON. 201 in the form of diamond ? Nevertheless, these bodies are com- posed of one and the same substance, carbon ; alike, they all burn in oxygen at a high temperature, producing carbonic acid gas. Among the various forms which carbon assumes, and which constitute one of the most curious examples of dimorphism, the following may be described : Diamond. — This is the hardest of all bodies ; it scratches all others, and can only be trimmed by grinding with its own dust. It is found crystallized in the. form of the regular octahe- dron and the modifications thereof, among which must be men- Fig. 77. tioned the polyhedra of twenty-four and forty-eight faces. The faces are .generally convexly curved (Fig. 77). The density of the diamond is between 3.50 and 3.55. It is a bad conductor of heat and electricity ; it strongly refracts and disperses light. From this latter fact Newton first divined its combustible nature, which was proved, in 1694, by the Floren- tine academicians of del Cimento, who burned a diamond in the focus of a concave mirror. Lavoisier and Davy repeated this celebrated experiment. Exposed to the high temperature of the voltaic arc between two carbon poles in a vacuum, the dia- mond swells up, blackens, and is converted into a substance analogous to coke ( Jacquelain). Graphite, or Plumbago. — This is a crystalline variety of carbon, which is found in primitive rocks in brilliant steel-gray foliated masses. It sometimes occurs in hexagonal laminae. It can be scratched with the finger-nail, and leaves a black trace when drawn over paper. Its density is 2.2, and it con- ducts heat and electricity. It burns only at very high tem- peratures; ordinarily, it contains from one to two per cent, of foreign matters, i* 202 ELEMENTS OF MODERN CHEMISTRY. It has been obtained artificially. Melted iron possesses the property of dissolving carbon at a very high temperature, and again depositing if on cooling in the form of hexagonal scales of graphite. Plumbago is used for the manufacture of lead-pencils and crucibles, and is called black lead. There are other natural varieties of carbon, but they are far from presenting the same degree of purity as diamond or graphite. They are: Anthracite, a hard and compact variety of carbon containing from 8 to 10 per cent, of earthy matters. Bituminous coal, a brilliant, black variety, strongly impreg- nated with bituminous and earthy matters. It has been pro- duced by the slow decomposition of vegetable matters buried in the earth in the early geological ages. This origin is indi- cated by the impressions of leaves, stems, and fruits, which are evident in certain specimens of this coal. It contains only from 75 to 88 per cent, of carbon. When it is calcined in closed vessels, it disengages combustible gases and products which may be condensed in the liquid form and then separate into two layers. One is aqueous and ammoniacal, while the other is composed of tar. The residue of the distillation of bituminous coal is coke. The interior walls of the cast-iron vessels in which coal is distilled become covered with a com- pact layer of a gray, dense, hard and sonorous carbon, which is a good conductor of heat and electricity. This is the carbon of gas-retorts, and is produced by the igneous decomposition of hydrocarbons rich in carbon, which are disengaged during the calcination of the coal. Fat coals are those which burn with a long flame, softening in burning ; dry coals burn with a short flame which produces less heat than the preceding. Lignite is a combustible mineral containing less carbon, and more impure than bituminous coal ; it is found in the lower tertiary formations. Natural jet, which is employed for the manufacture of ornaments, is a variety of lignite. Among the artificial carbons, independently of coke, may be mentioned wood charcoal, lamp-black, and animal char- coal. Wood Charcoal. — When wood is calcined in closed vessels it leaves a residue which is ordinary charcoal. It is prepared on the large scale by two processes, carbonization in stacks, ■ CARBON. 203 which is carried on in the forests, and distillation in closed vessels. Charcoal is amorphous, brittle, and sonorous, a bad conductor of heat and electricity. Its density does not exceed 1.57. The lighter varieties are the more combustible. Its combustion leaves a residue of one or two per cent, of cinders, formed principally of mineral salts, among which the most abundant are the carbonates of calcium and potassium. Fig. 78. Lamp-black is produced by the incomplete combustion of organic substances rich in carbon. When rosin or tallow is burned, a dense smoke is produced which is composed of par- 204 ELEMENTS OF MODERN CHEMISTRY. tides of carbon that have escaped combustion. In the arts, lamp-black is procured by burning rosin in cast-iron pots, C (Fig. 78), heated by a fire, F. The vapors given off are ig- nited, and the smoke is conducted into a chamber, A, the walls of which are hung with canvas. On this the lamp-black is de- posited, and is detached by lowering the cone B, which acts as a scraper. Lamp-black is not pure carbon. It contains tarry and oily matters, from which it may be freed by calcination in a covered crucible. It is used for the manufacture of printing- inks. Animal charcoal is produced by calcining animal matters, such as blood, the debris of skin, horn, bone, etc., in closed vessels. Bone-black or ivory-black contains the calcareous salts, calcium phosphate and carbonate, which form the base of the osseous tissue. The carbon is consequently disseminated through a porous mass. These salts may be extracted by treating the bone-black with dilute hydrochloric acid, by which they are dissolved. The residue, washed with water and dried, is known as washed or purified animal charcoal. Absorbent Properties of Charcoal. — The amorphous and porous varieties of carbon, of which several forms have been described, possess the property of absorbing and retaining in their pores, gases, liquid and solid bodies. It is to this absorp- , tive faculty that are due the decolorizing and disinfecting properties of charcoal, which are made use of to a large extent in the arts. If a piece of incandescent charcoal be plunged into mercury that it may cool out of contact with the air, and then be intro- duced into a small jar filled with ammonia or hydrochloric acid over the mercury-trough, the gas is at once absorbed and the mercury rises in the jar. The following table, by Th. de Saussure, indicates the quan- tities of several gases which are absorbed by one volume of charcoal : 1 volume of charcoal absorbs 90 volumes of ammonia. 85 " hydrochloric acid. 65 " sulphurous oxide. 55 " hydrogen sulphide. 40 " nitrogen monoxide. 35 " carbon dioxide. 9.42 " carbon monoxide. 9.25 " oxygen. 7.50 " nitrogen. 1.75 " hydrogen. CARBON. 205 Charcoal increases in weight when exposed to the air, for it absorbs and condenses the atmospheric moisture. When plunged into water charged with a small quantity of hydrogen sulphide, it absorbs that gas and removes the odor of the water. The disinfecting properties of charcoal are thus easily explained. It is well known that charcoal will remove the unpleasant odor of corrupted waters, of meats slightly spoiled, and in general of organic matters in a state of putrefaction. A layer of char- coal between two layers of sand is an excellent filter for the clarification of drinking waters. The decolorizing properties of charcoal are another mani- festation of this general faculty of absorption, which is pos- sessed in the highest degree by animal charcoal. If litmus solution or red wine be agitated with a sufficient quantity of animal charcoal and subsequently filtered, the liquids pass through colorless. This property of animal charcoal is largely applied in the arts, particularly for decolorizing sugars and syrups. Chemical Properties. — Carbon is distinguished by its powerful affinity for oxygen, an affinity which is not, however, 18 206 ELEMENTS OF MODERN CHEMISTRY. exercised except at high temperatures. It only combines with oxygen at a red heat, and remains incandescent as long as com- bination goes on, the heat produced by the combination being sufficient to maintain the incandescence. In pure oxygen it burns with a brilliant light. The product of the combustion is carbonic acid gas. By the aid of heat, carbon decomposes a great number of oxygenized compounds, removing and combining with the whole or a part of their oxygen. This decomposition takes place at comparatively low temperatures when the oxygenized body does not strongly retain its oxygen ; in this case, carbon dioxide is formed, and the reduction of cupric oxide by char- coal furnishes an example. In the contrary case, the reduction, that is, the decomposition of the oxidized body, requires a very high temperature ; carbon monoxide is then formed. The re- duction of zinc oxide by charcoal is an example. If an incandescent charcoal be rapidly plunged under a bell- jar filled with water on the pneumatic trough, bubbles of gas arise and collect in the jar (Fig. 79). They are formed of a mixture of hydrogen, carbon monoxide, and a small quantity of carbon dioxide. These gases are produced by the decom- position of the water by the charcoal, which was red-hot at the moment of contact with the liquid. C -f H 2 = H 2 + CO carbon monoxide. Carbon combines directly with sulphur at a high tempera- ture, forming carbon disulphide. COMPOUNDS OF CARBON AND OXYGEN. Two compounds of carbon and oxygen are known : Carbon monoxide CO Carbon dioxide, or carbonic acid gas CO' 2 The latter body, which has long been known as carbonic acid, is the oxide corresponding to the true carbonic acid, which would be CO 2 + H 2 = H 2 C0 3 This normal carbonic acid is as yet unknown : it is doubtless too unstable to exist in the free state. However, its existence CARBON MONOXIDE. 207 may be admitted, for a corresponding compound is known in sulphocarbonic acid H 2 CS 3 . CAEBON MONOXIDE. Density compared to air 0.967 Density compared to hydrogen 14. Molecular weight CO . =28. Preparation. — 1. An intimate mixture of zinc oxide and charcoal may be calcined in a clay retort, ZnO + C = CO + Zn 2. A convenient method of preparing carbon monoxide con- sists in heating oxalic acid with an excess of sulphuric acid in a glass flask. The oxalic acid loses the elements of water, which it yields to the sulphuric acid, and breaks up into carbon dioxide and carbon monoxide. C 2 H 2 4 = CO + CO 2 + H 2 Oxalic acid. Carbon monoxide. Carbon dioxide. 9 The mixture of the two gases is passed through a wash-bottle, B (Fig. 80), containing a solution of potassium hydrate, by 208 ELEMENTS OF MODERN CHEMISTRY. which the carbon dioxide is absorbed, potassium carbonate being formed. Carbon monoxide alone passes through, and may be collected over water. Properties. — Carbon monoxide is a colorless, odorless gas. It is neutral, and does not trouble lime-water, which distin- guishes it from carbon dioxide. It extinguishes burning bodies, but is combustible itself, burning in the air with a blue flame, and forming carbon dioxide. It is not only unfit for respira- tion, but is very poisonous, combining with and profoundly altering the red corpuscles of the blood. Composition. — If two volumes of carbon monoxide be mixed with one volume of oxygen in an eudiometer, and a . spark be passed, complete combustion takes place, and the three volumes of the primitive mixture are reduced to two volumes of carbon dioxide. This can be verified by passing into the eudiometer a solution of potassium hydrate, which will completely absorb the new gas. It hence follows that two volumes of carbon monoxide con- tain the same quantity of carbon as two volumes of carbon dioxide. Knowing from other circumstances that two volumes of carbon dioxide contain two volumes of oxygen, it follows that two volumes of carbon monoxide contain one volume of oxygen. Its composition is then expressed by the formula CO — 2 volumes. Carbon monoxide undergoes dissociation at a very high tem- perature. Under special conditions, H. Sainte-Claire Deville succeeded in resolving it into carbon and oxygen. It is almost insoluble in water, but is absorbed by a solution of cuprous chloride in hydrochloric acid (Doyere and F. Le Blanc). Advantage is taken of this property in volumetric analysis to separate carbon monoxide from certain other gases. When heated for a long time to 100°, in sealed tubes with potassium hydrate, it combines with the alkali, forming potas- sium formate (Berthelot). CO + KOH == KCHO 2 Potassium hydrate. Potassium formate. It is a beautiful synthesis of formic acid, so named because it exists in ants. Action of Chlorine upon Carbon Monoxide— Under the influence of sunlight, carbon monoxide combines directly with chlorine, forming a gas which is known as chloro-carbonic oxide, CARBON DIOXIDE. 209 or carbonyl chloride. It was formerly called phosgene gas. One volume of carbon monoxide combines with one volume of chlorine to form one volume of carbonyl chloride, so that the density of the latter is equal to the sum of the densities of carbon monoxide and chlorine. Compared to Hydrogen. Compared to Air. Density of carbon monoxide . . 14. 0.967 Density of chlorine 35.5 2.44 Density of carbonyl.chloride . 49.5 O.407 At ordinary temperatures, carbonyl chloride is a colorless gas, having a suffocating odor that provokes tears. At a low temperature, it condenses to a colorless liquid, boiling at 8.2° (Emmerling and Lengyel). It is instantly decomposed by water, with the formation of carbon dioxide and hydrochloric acid. COCP + H 2 = 2HC1 + CO 2 Its mode of formation, its composition, and its properties indicate its relations to carbon dioxide. 2 volumes CO absorb 2 volumes of chlorine to form 2 volumes CO. CI 2 2 volumes CO absorb 1 volume of oxygen to form 2 volumes CO.O It is seen that carbon monoxide plays to a certain extent the part of a radical; it combines directly with oxygen or with chlorine to form either oxide or chloride of carbonyl. It is seen also that carbonyl chloride represents carbon dioxide in which one atom of oxygen is replaced by two atoms of chlorine. CARBON DIOXIDE. Density compared to air 1.529" Density compared to hydrogen 22. Molecular weight CO 2 =44. This gas was discovered by Black in 1648, and its composi- tion was recognized by Lavoisier in 1776. It is one of the constituents of the atmosphere, and is the product of a great number of reactions which take place on the earth's surface, such as the combustion of carbon and organic matters, respira- tion, and the phenomena of putrefaction and fermentation. It issues from the soil of volcanic countries. 18* 210 ELEMENTS OF MODERN CHEMISTRY. Fig. 81. Preparation. — Fragments of marble, which is calcium car- bonate, are intro- duced into a two- necked bottle fitted with a delivery- tube and a safety- tube (Fig. 81). The bottle is half- filled with water, and hydrochloric acid is gradually added by the fun- nel-tube. An ef- fervescence imme- diately takes place, due to the disen- gagement of car- bon dioxide. CaCO 3 + 2HC1 -C0 2 + CaCP + H 2 Calcium carbonate. Calcium chloride. The gas is most conveniently collected by dry downward displacement, like chlorine. Composition. — 1. If carbon be burned in oxygen, the latter is converted into carbon dioxide without changing its volume. Hence two volumes of carbon dioxide contain two volumes of oxygen. These two volumes of oxygen, which represent two atoms, are combined with one atom of carbon, and the compo- sition of a molecule of carbon dioxide is hence expressed by the formula CO 2 = 2 volumes. 2. Dumas and Stas determined the centesimal composition of carbon dioxide by burning a known weight of diamond in oxygen, and carefully weighing the carbon dioxide produced. By subtracting the weight of the diamond burned from that of the carbon dioxide, the weight of the oxygen was determined. The apparatus employed is represented in Fig. 82. The increase in weight of the tubes L, M, N, 0, P indicates the quantity of carbon dioxide formed. Dumas and Stas thus found that 100 parts of carbon dioxide contain Carbon 27.27 Oxygen 72.73 100.00 CARBON DIOXIDE. 211 212 ELEMENTS OF MODERN CHEMISTRY. a centesimal relation which is expressed more simply by the numbers Carbon . 12 Oxygen 32 44 12 being the weight of one atom of carbon, and 32 the weight of two atoms of oxygen. Physical Properties. — Carbon dioxide is colorless ; it has a feeble, somewhat pungent odor. A litre of this gas at 0°, and under the pressure of 760 millimetres, weighs 1.966 grammes. Fig. 83. It is not permanent. Faraday succeeded in liquefying it at a temperature of 0°, under a pressure of 36 atmospheres. The apparatus which is now used for its liquefaction is represented in Fig. 83. It is composed of two reservoirs, A and B, com- CARBON DIOXIDE. 213 niunieating by the metallic tube i. furnished with a stop-cock at each end. The cylinders are made of heavy cast-iron, and are further strengthened by forged iron bands forced over their circumference. Each cylinder is movable on a horizon- tal axis, h. B is the generator: into it are introduced 1800 grammes of sodium dicarbonate. and a cylindrical copper tube. I), containing 1000 grammes of ordinary sulphuric acid. The cylinder is then closed by a strong screw plug, and a few oscil- lating movements are given to it in order that the sulphuric- acid may gradually run out upon the sodium dicarbonate. Carbon dioxide is disengaged and is liquefied by its own press- ure as it accumulates in the apparatus. By the effect of the chemical action the temperature is raised to 30 or 40°, and. • communication being established between the two cylinders, the carbon dioxide distils rapidly into the receiver, the tem- perature of which is about 15°. The operation is repeated several times, that one or two kilo- grammes of the liquid may accumulate in the receiver. A tube passes to the bottom of this vessel, and on opening the stop-cock which closes the superior extremity of this tube, a jet of the liquid is thrown out with force ; it is received tangentially in a metallic box. A, A' (Fig. 8-1). having very thin sides. In this a portion of the oxide solidifies by reason of the great depression of temperature produced by the change of another portion into the gaseous state. A glittering-white, flaky mass collects in the receiver, having the appear- ance of snow. This is solid carbon dioxide. It is a bad conductor of heat and electricity, and can be ex- "~~Fig 84 posed to the air for a few minutes before it disappears. In reassuming the gaseous form, it pro-, duces an intense cold. If it be mixed with ether, the mixture, which is less porous and a better conductor of heat, can produce a lowering of temperature as great as — 90°. By pouring it upon mercury, large masses of that metal may be frozen. Drion and Loir have recently succeeded in collecting and maintaining carbon dioxide in the liquid state. It is colorless and mobile; has a density of 0.72 at -{-21°, and 0.98 at — 8°. 214 ELEMENTS OF MODERN CHEMISTRY. This considerable difference between the densities is due to the enormous dilatation which the liquid undergoes between these limits of temperature. Indeed, ten volumes of liquid carbon dioxide at 0° occupy fourteen volumes at 30°. The coefficient of dilatation of the liquid is then superior to that of the gas. Carbon dioxide is incombustible, and extinguishes burning bodies. If carbon dioxide be poured from one vessel into another containing a lighted candle, it falls upon the flame like water, extinguishing it at once (Fig. 85). Lime-water poured into a jar of carbon dioxide becomes clouded, owing to the formation of insolu- ble calcium carbonate. These experiments permit the easy recognition of carbon dioxide from carbon monoxide. Carbon dioxide dissolves in its own volume of water at 15° under the normal pressure. If the press- ure be increased, the solubility of the gas is increased in the same proportion. Thus, under a press- ure of ten atmospheres one litre of water will dissolve ten litres of carbon dioxide ; but it must be remembered that under a press- ure of ten atmospheres these ten litres are reduced to one litre. Thus, one litre of water, which dissolves one litre of carbon dioxide at the ordinary pressure, dissolves also one litre under a pressure of ten atmospheres, and it may be said that water always dissolves its own' volume of carbon dioxide, whatever may be the pressure. Water saturated with carbon dioxide under strong pressure, disengages a portion of the gas as soon as the pressure is removed. Such water is universally known and consumed in large quantities under the name of gaseous water or soda water. The solution of carbon dioxide exercises a much more ener- getic solvent action upon certain substances than pure water. It dissolves calcium carbonate, forming a soluble dicarbonate; it is even capable of dissolving calcium phosphate, transform- ing it into acid phosphate, which is soluble. Carbon dioxide is more soluble in alcohol than in water. Fig. 85. CARBON DISULPHIDE. 215 It is undecomposable by heat alone, but may be decomposed or reduced at high temperatures by contact with bodies avid of oxygen. Such substances are hydrogen and carbon. With the latter body the reduction takes place at a red heat, giving rise to the formation of carbon monoxide, the volume of which is double that of the carbon dioxide employed. CO 2 + C = 2CO Carbon dioxide (2 vols.). Carbon monoxide (4 vols.). CARBON DISULPHIDE. CS 2 This body is prepared by passing sulphur vapor over incan- descent charcoal. In the arts, the operation is conducted in cylindrical, cast-iron vessels, filled with charcoal and heated to redness, into which sulphur is introduced. The carbon disul- phide distils, and is condensed in a suitable cooling apparatus. Carbon disulphide is a colorless, very mobile, and highly-re- fracting liquid. Its odor is usually strong and unpleasant, but is rather agreeable when the compound is perfectly pure. Its- density at 15° is 1.271, and it boils at 46°. It is very inflam- mable, and burns with a blue flame, producing sulphurous oxide and carbon dioxide. CS 2 + O 6 = 2S0 2 + CO 2 Its vapor, mixed with oxygen, explodes when heated. Carbon disulphide corresponds in composition to carbon dioxide. CO 2 carbon dioxide. CS 2 carbon disulphide. It is also analogous to the latter body in its chemical func- tions. While carbon dioxide combines with metallic oxides, forming carbonates, carbon disulphide combines with 'metallic sulphides, forming sulphocarbonates. CO 2 + Xa 2 = XaTO 3 corresponding to H 2 C0 3 Sodium oxide. Sodium carbonate. Carbonic acid (hypothetical). CS 2 + >VS = Na'CS 8 corresponding to H 2 CS 3 Sodium sulphide. Sodium sulphocarbonate. Sulphocarbonic acid. Sodium carbonate and sulphocarbonate possess the same con- stitution. By the action of strong acids they should give anal- ogous products : the one, carbonic acid. H 2 C0 3 ; the other, 216 ELEMENTS OF MODERN CHEMISTRY. sulphocarbonic acid, H 2 CS 3 . The latter body is indeed formed under such circumstances, but normal carbonic acid, if it exist, possesses no stability, and at once decomposes into carbon diox- ide and water. H 2 C0 3 = CO 2 + H 2 Carbon disulphide is employed in the arts in the manufac- ture of vulcanized caoutchouc, and as a solvent for caoutchouc in the fabrication of goods impermeable to water by the deposit of a thin layer of that substance. It is also employed as a solvent for, and in the extraction of, fats and oils. CARBON OXYSULPHIDE. Density compared to air 2.1046 Density compared to hydrogen 30.4 Molecular weight CSO =60.. This body was discovered by de Than in 1867. It is inter- mediate between carbon dioxide and carbon disulphide. COO carbon dioxide. CSO carbon oxysulphide. CSS carbon disulphide. Preparation. — It is prepared by decomposing potassium sul- phocyanate by dilute sulphuric acid. Potassium sulphate and sulphocyanic acid are formed, and the latter, in the presence of an excess of sulphuric acid and water, decomposes into am- monia and the gas carbon oxysulphide, which may be collected over mercury ; the ammonia remains combined with the sul- phuric acid in the form of sulphate. CSNH + H 2 = NH 3 + CSO Sulphocyanic acid. Carbon oxysulphide. Properties. — Carbon oxysulphide is a colorless gas, having an odor like that of carbon disulphide, but also recalling that of hydrogen sulphide. On contact with an incandescent body, even a match pre- senting a spark of fire, it takes fire, burning with a blue flame, and depositing sulphur if the supply of air be insufficient. With one and a half times its volume of oxygen it constitutes an explosive mixture. 2 volumes of carbon oxysulphide . . = CSO mixed with 3 volumes of oxygen = O 3 yield 2 volumes of carbon dioxide . . . . = CO 2 and 2 volumes of sulphur dioxide . . . . = SO 2 COMPOUNDS OF CARBON AND HYDROGEN. 217 Water dissolves about its own volume of carbon oxysulphidc. but the solution decomposes in a few hours, with the formation of hydrogen sulphide and carbon dioxide. CSO + H 2 = CO 2 + H 2 S Carbon oxysulphide is absorbed completely, but more slowly than carbon dioxide, by solutions of the alkaline hydrates ; by a reaction analogous to the preceding, a sulphide and a carbonate are formed. COMPOUNDS OF CARBON AND HYDROGEN. These compounds are numerous and important. Carbon unites with hydrogen, in different proportions, and the atoms of carbon and hydrogen may accumulate in considerable numbers in the molecules of their compounds. These combinations are called hydrocarbons or carbides of hydrogen. Hydrogen mono- carbide, or marsh gas, contains only one atom of carbon com- bined with four atoms of hydrogen ; its molecule is therefore represented by the formula CH 4 . In olefiant gas, or ethylene, two atoms of carbon are united with four atoms of hydrogen; in the volatile liquid known as benzine or benzol, which is ob- tained in large quantities from coal-tar, six atoms of carbon are combined with six atoms of hydrogen. Lastly, the molecule of oil of turpentine contains ten atoms of carbon and sixteen of hydrogen. Hence these substances give us the following formulae : CH 4 methane, or marsh gas. C 2 H* ethylene,. or olefiant gas. C 6 H 6 benzine. C 10 H 16 turpentine. These examples, which might be indefinitely multiplied, show : 1st. That the atoms of carbon unite in various proportions with the atoms of hydrogen to constitute the molecules of the hydro- carbons. 2d, That they accumulate in greater or less numbers to form molecules more and more complex, that is. containing an increasing number of atoms of carbon and hydrogen. All of these bodies must be considered among the organic compounds ; indeed, the latter are nothing more than the com- pounds of carbon, and carbon monoxide and dioxide may also be properly considered as the most simple organic combinations. k 19 218 ELEMENTS OF MODERN CHEMISTRY. Hence if the most strictly rigorous method were adhered to, the description of the compounds of carbon and oxygen would be followed by that of all the other compounds of this element, that is, of all the organic compounds. However, for the pur- poses of study it is advantageous to treat the latter bodies separately, and they will be so considered in this work. The following experiments will expose some of the general proper- ties of the hydrocarbons which have been mentioned : 1. If a lighted taper be applied to a jar of methane, which is also called marsh gas, because it is disengaged from the muddy bottoms of marshes, the gas takes fire and burns with a lumi- nous flame. 2. If the same experiment be repeated with ethylene gas, which contains for the same proportion of hydrogen twice as much carbon as marsh gas, a still more luminous flame results. 3. It is well known that benzine and turpentine take fire when lighted, and burn with bright flames ; but it is also known that their flames are smoky. The hydrocarbons are then combustible; and how could they be otherwise, since they contain only two combustible elements, carbon and hydro- gen? The products of the combustion are water and carbon dioxide, and the forma- tion of the latter gas may be proved by agitating the con- tents of the jars in which tne combustion has taken place with lime-water; the latter immediately becomes milky by the precipitation of calcium carbonate. This combustion is more or less complete ; when the gas or vapor which burns contains a large amount of combustible elements, the oxygen of the air may not be present in sufficient quantity to burn them all, that is, to oxidize them completely. Under these conditions it is the hydrogen which is burned by preference, and the carbon partly escapes combustion. STRUCTURE OF FLAME. 219 A flame is a gas or vapor in combustion. This combustion is an oxidation, and it is the oxygen of the air which is the agent. In order that it may take place, it is generally neces- sary that the combustible gas shall be brought to a high tem- perature; but once commenced, the combustion continues of itself, because the heat disengaged by the oxidation is sufficient to maintain the phenomenon. But if a flame be suddenly cooled, the combustion is at once arrested. A flame may be cooled by depressing into it a piece of fine wire gauze. The incandescent gases cannot pass through the meshes of the gauze without being- cooled by contact with the metal, which is a good conductor of heat. For this reason, no combustion takes place above the gauze (Fig. 86). If a piece of wire gauze be held over an escaping jet of gas. the latter may be ignited above the gauze, and will burn without the combustion being propagated to the gas below ; the gauze acts as a screen, separating the jet into two portions, the lower cold and invisible, the upper in combustion and luminous. Sir Humphry Davy made a happy ap- plication of these facts in the construction of the miner's safety-lamp. This is an ordinary lamp surrounded by a cylinder of wire gauze (Fig. 87). Such a lamp gives less light than one not protected by an envelope, but it re- moves the danger of explosions of fire- ^-- i damp, for when an explosive mixture is p IG g-^ formed in the galleries of a mine, the gas may penetrate to the interior of the lamp and take fire there, but the flame cannot pass through the cooling envelope of wire gauze. The safety-lamps are now constructed with the lower part of the cylinder of glass, so that there is no diminution in the amount of light given. As the oxidation of combustible elements is the source of heat, it is evident that the different parts of a flame cannot be 220 ELEMENTS OF MODERN CHEMISTRY. uniformly hot, for the oxygen of the surrounding air cannot equally attain all portions. The exterior borders are the most intensely heated; they are surrounded by air, and constitute the seat of combustion. From them the heat is radiated not only externally, but also to the interior of the flame, where it produces interesting phenomena. These may be studied by analyzing a flame, that is, considering separately the different parts of which it is composed. If the flame of a can- dle be examined, it will be found to present three distinct layers, or cones (Fig. 88). 1 . A dark central part, a, which surrounds li III A tne w i c k- This is known as the obscure cone, or cone of generation; its temperature is not high. 2. A luminous part, bb\ surrounding the ob- scure cone. This is the centre from which the light is emitted. It is known as the luminous cone, or cone of decomposition. 3. An exterior envelope, cc\ thin, and pro- ducing but little light, yellow towards the sum- mit, e, and bluish towards the base, dd! . It is the cone of complete combustion, and its temperature is the highest. It is easy to account for these phenomena. The material of the candle is melted by the heat Fig. 88. °f the flame, the liquid is drawn up into the wick by capillarity, and arrives at the incan- descent summit. There it is decomposed, producing gases and vapors rich in carbon and hydrogen, and which rise around the wick, forming an irregular cone. The gaseous products consti- tuting this cone do not present the same composition through- out. They have been analyzed by H. Sainte-Claire Deville, by the aid of very ingenious processes. The obscure cone is formed of gaseous products holding in suspension finely-divided carbon, which has not yet arrived at incandescence. These products become heated on reaching the more central portions of the flame. Then the carbon, which is set free by the decomposition of gases rich in carbon, is brought to bright incandescence, but it is completely burned only when it reaches the exterior envelope, where the oxygen is in excess. A simple STRUCTURE OF FLAME. 221 experiment will demonstrate that the most luminous portion of the flame holds in suspension finely-divided and incandes- cent carbon. If a porcelain saucer be depressed into this portion, the carbon will be deposited on the vessel in the form of soot. It is this solid and incandescent carbon which causes the luminosity of the flame. The flame of hydrogen, which con- tains only gaseous products, is pale. In the calcium or Drum- mond light it produces great brilliancy because a solid body, lime, is heated to bright incandescence. When the carbon suspended in a flame is in excess in proportion to the supply of oxygen, it is incompletely burned, and is carried into the air. The flame then smokes. At the base of the cone, carbon monoxide and methane, the first products of the decomposition of the candle, burn on con- tact with the air at dd! with a bluish flame. According to recent experiments, the density of a burning gas is not without influence upon the lustre of the flame. The flame of hydrogen is luminous when that gas is burned under strong pressure (Frankland). Illuminating gas is a mixture of hydrogen with various gas- eous hydrocarbons and a small proportion of carbon monoxide. It is manufactured by the destructive dis- tillation of bituminous coal. The aqueous products containing ammonia, and the tarry matters formed during the distilla- tion are condensed, and the gas is purified by washing with water and passage over slaked lime to remove sulphur and other impurities. Illuminating gas forms an explosive mixture with air, but if the mixture be burned as it is formed, the resulting flame will be almost colorless and will deposit no soot, the whole of the carbon coming in contact with sufficient oxygen for its complete combustion. These conditions are fulfilled in the Bunsen burner (Fig. 89). In this burner, the force of the escaping gas-jet draws in air through holes immediately oppo- site the jet in a wider tube, at the end of which the mixture is burned. 19* Fig. 89. 222 ELEMENTS OF MODERN CHEMISTRY. GENERAL NOTIONS UPON THE METALLOIDS. THEORY OF ATOMICITY. From a consideration of the facts acquired in the study of the elements known as metalloids, we may deduce certain gen- eral consequences, and while looking back on the field over which we have passed, we may at the same time fix certain landmarks for the remainder of our course. The elements which we have studied are not alike in their aptitude to enter into combination, nor in the general characters of their compounds. In this respect, analogies and differ- ences have been established between them, and these have become the basis of a rational classification. Following the example of Dumas, we have arranged these elements in groups or families, uniting in the same group those which are related by their chemical functions. For this reason boron has been separated from silicon and carbon, since it differs from them so far as concerns the composition of their compounds. The groups thus formed are as follows : HYDROGEN. OXYGEN. NITROGEN. BORON. SILICON SULPHUR. PHOSPHORUS. CARBON FLUORINE. SELENIUM. ARSENIC. CHLORINE. TELLURIUM. ANTIMONY. BROMINE. IODINE. In order to account for the chemical functions of all these bodies, that is, for the parts which they play in their combina- tions, we must first consider their hydrogen compounds. They constitute the following series : HH H 2 H 3 N H*Si Hydrogen. Water. Ammonia. Hydrogen silicide. HCl H 2 S H 3 P H 4 C Hydrochloric acid. Hydrogen sulphide. Hydrogen Hydrogen phosphide. carbide. HBr H 2 Se H 3 As Hydrobromic acid. Hydrogen selenide. Hydrogen arsenide. HI H 2 Te H 3 Sb Hydriodic acid. Hydrogen telluride. Hydrogen antimonide. HFl Hydrofluoric acid. THEORY OF ATOMICITY. 223 It is seen that the preceding groups are characterized by the composition of their hydrogen compounds. While the bodies of the first group combine with hydrogen atom for atom, those of the second group require two atoms of hydrogen, those of the third three, and those of the fourth four, to form hydrogen compounds. Hence we may draw the conclusion that the atoms ,'of these metalloids are far from being equivalent in their power of combination with hydrogen. The atoms of chlorine, bromine, and iodine are equivalent to each other in this respect, for each requires but one atom of hydrogen. The atoms of oxygen, sulphur, etc., are equivalent to each other, for each combines with two atoms of hydrogen. The atoms of nitrogen, phosphorus, arsenic, and antimony are equivalent to each other, for each of them unites with three atoms of hydrogen. Lastly, the atoms of carbon and silicon are equivalent, for each can unite with four atoms of hydrogen. But, on the other hand, it is evident that the atoms of chlo- rine, oxygen, nitrogen and carbon are not equivalent to each other, as regards their power of combination with hydrogen, since each of them unites with a different number of atoms of that body. In this respect it may be said that 1 atom of chlorine is equivalent to 1 atom of hydrogen. 1 atom of oxygen " 2 atoms " 1 atom of nitrogen " 3 atoms " 1 atom of carbon u 4 atoms " It is evident that the capacity of combination which resides in the atoms of simple bodies and by which they attract the atoms of hydrogen, is unequal. Leaving aside its intensity, this force is exerted in different degrees, for it determines the union of 1 atom of chlorine, oxygen, nitrogen, or carbtfn, with 1, 2, 3, or 4: atoms of hydrogen. This number of hydrogen atoms is the measure of the degree of force which resides in the atoms, — of the capacity of combi- nation which they possess for each other. Hence we conclude that The atoms of chlorine and- its associates are monatomic or univalent. The atoms of oxygen " " diatomic or bivalent. The atoms of nitrogen " " triatomic or trivaleat. The atoms of carbon " " tetr atomic or quadrivalent. 224 ELEMENTS OF MODERN CHEMISTRY. The capacity of combination which resides in the atoms, and which is exerted in such different manners according to the nature of the atoms, is called atomicity. Atomicity is the relative equivalence of the atoms; it is simple or multiple, and if we consider it in its first degree, we may say that the atoms of chlorine and the atoms of hydrogen are so constituted that a single atom of one attracts a single atom of the other. When they combine, they exchange in some manner a unit of satura- tion, and in the combination of chlorine and hydrogen two of these units of force are neutralized ; two units of saturation or two atomicities are exchanged: the atoms of chlorine and of hydrogen are univalent. The force which resides in an atom of oxygen is more com- plex. It attracts two atoms of hydrogen, and represents the second degree of capacity of combination, and we may say that in each atom of oxygen reside two atomicities, which are satis- fied and exchanged when this atom combines with two atoms of hydrogen. Hence, four atomicities are satisfied by the com- bination. Following the same reasoning, we consider that a triple capa- city of combination is active in an atom of nitrogen when this atom unites with three atoms of hydrogen ; and that six atom- icities are satisfied by the combination. Lastly, tetratomic carbon is provided with four atomicities, which are satisfied by the four atomicities which reside in four atoms of hydrogen. If this neutralization or exchange of two units of saturation be represented by a hyphen, we will have the following formulae : H-Cl H-O-H H H Hydrochloric acid. Water. i i N H-C-H /\ i H H H Ammonia. Hydrogen monocarbide It is seen that in the formulae for water, ammonia and hydro- gen monocarbide, the polyatomic elements, oxygen, nitrogen and carbon, constitute, as it were, the nuclei around which the other atoms are symmetrically grouped. A great many other bodies present the same constitutions as the preceding ; it is evident that a given element in any com- pound may be replaced by another element having the same atomicity, without disturbing the equilibrium of the atomicities. THEORY OF ATOMICITY. 225 Indeed, if we suppose the chlorine, oxygen, nitrogen, and carbon to be replaced by elements of corresponding atomicities, we will have the series of hydrogen compounds already con- sidered. All of the bodies which are classed together in the series belong to the same type. Each contains an equal num- ber of atomicities for the same number of atoms. According to the principle of substitution announced above, it is evident that the hydrogen in each of the hydrogen com- pounds under consideration may be replaced by another mon- atomic element, and the compounds thus formed will still belong to the primitive types. So considered, a great number of compounds possess the same constitution, — that is, the same molecular structure, — as hydrochloric acid, water, ammonia, and methane or hydro- gen monocarbide. Such are those arranged in vertical columns in the following table : Type HC1 Type IPO Type NH3 Type CH* Cl-Cl H-O-H K CI Free chlorine. Water. i 1 N Cl-C-Cl /\ 1 H H CI Potassium amide. Carbon tetrachloride. K-Cl Cl-O-Cl CI Cl rtassium chloride. Hypochlorous oxide. i i P Cl-Si-Cl y\ i CI CI Cl Phosphorus trichloride. Silicon tetrachloride. K-I H-O-K CI H stassium iodide. Potassium hydrate. 1 i • Sb • H-Si-H /\ I Ag-I Ag-O-Ag CI CI H Silver iodide. Silver oxide. Ant imony trichloride Hydrogen silicide. All of these bodies belong to the respective types HC1, H 2 0, NH 3 , CH 4 , the first three of which were established by Grer- hardt, and have their existence explained by the atomicity of the elements ; that is, by the varying equivalence of their atoms, measured, in the present examples, by the number of hydrogen atoms with which they combine. One atom of oxygen is equivalent to two atoms of hydrogen 226 ELEMENTS OF MODERN CHEMISTRY. or two atoms of chlorine. Hence, in the preceding combina- tions, two atoms of chlorine may be replaced by one atom of oxygen without changing the equilibrium of the atomicities. Thus, the oxides SiO^CO 2 , correspond to the chlorides SiCl 4 , CC1 4 , and belong to the same type. The four atomicities of an atom of silicon or carbon are saturated by the four atomici- ties of two atoms of oxygen. The trichlorides of phosphorus and antimony, PCI 3 and SbCP, which will be found in the preceding table, require an impor- tant remark. They are not saturated with chlorine, and each may combine with two more atoms of that element, producing the compounds PCI 5 and SbCl 5 . Thus, while phosphorus exhausts its power of combination with hydrogen in uniting with three atoms of that element in PH 3 , its capacity of combination with chlorine is only exhausted when it has combined with five atoms ; while it plays the part of a triatomic element in hydrogen phosphide, it is pentatomic in phosphorus pentachloride. From these facts it follows that it is often difficult to meas- ure in an absolute manner the capacity of combination which resides in an atom ; for that capacity varies according to the nature of the elements upon which it is exerted. Affinity is an elective force. A given element does not attract all of the other elements with equal facility ; it selects certain ones by preference, and neglects the others. With one, it may form but a single compound; with another, it may form several. Nitrogen forms with hydrogen but one combination, ammo- nia, NH 3 , which cannot fix any more atoms of hydrogen. Sat- urated with hydrogen in ammonia, nitrogen manifests in con- tact with that element but three atomicities. But let ammonia be brought in contact with a body other than hydrogen, hydro- chloric acid, for example, and it will combine with it, forming ammonia hydrochloride, or ammonium chloride. If its ca- pacity of combination is exhausted for hydrogen, HH, it is not exhausted for hydrogen combined 'with chlorine, HC1. Thus, an atom of nitrogen possesses other affinities than those which it manifests for hydrogen in ammonia. While nitrogen is triatomic in ammonia because it is united with three mon- atomic atoms, it behaves as a pentatomic element in ammonium chloride. The parts which polyatomic elements play in their compounds may be expressed by accents marking the number of atomici- THEORY OF ATOMICITY. 227 ties or the quantivalence of the element, as shown in the following formulae : 0"H 2 N'"H 3 N V H*C1 P"C1 3 P V CP C iv O" 2 Water. Ammonia. Ammonium Phosphorus Phosphorus Carbon chloride. trichloride, pentachloride. dioxide. In these compounds, as has been remarked before, the poly- atomic elements form, as it were, the nuclei around which the other elements are grouped. This is an important idea, since it leads to the determination of the constitution of the mole- cules, that is, the arrangement of their atoms. The considera- tions just presented concerning the functions of the elements in compounds alone permit the resolution of this question ; they alone lead to the discovery of the relations existing be- tween the atoms in their combinations, and to the determina- tion of their relative positions, in a word, to the revelation of the molecular structure. The following developments will demonstrate this fact. We will reconsider certain of the combinations above men- tioned, which have been taken as types. In water, an atom of diatomic oxygen fixes two atoms of hydrogen. One atom of oxygen can fix two atoms of any monatomic element, forming compounds belonging to the same type as water ; but it cannot at the same time fix a monatomic element and a diatomic element. In other words, an atom of hydrogen in water may be replaced by an atom of chlorine, bromine, iodine, or potassium, but not by an atom of oxygen ; and if a second atom of the latter element be joined to the oxygen of water, it will be seen that there remains a free affin- ity which may be satisfied by hydrogen. Hydrogen dioxide would result. H-0"-H H-0"-0"-H Water. Hydrogen dioxide. Hence, we draw the conclusion that in hydrogen peroxide, the two atoms of oxygen are combined with each other, and that in uniting together each atom loses one atomicity, the two others being satisfied by hydrogen. The same considerations are applicable to the compounds of chlorine and oxygen. Hypochlorous acid may be regarded as composed of an atom of chlorine united to the group hydroxyl. Cl-0"-H = Cl(OH)' Hypochlorous acid. "228 ELEMENTS OF MODERN CHEMISTRY. In this compound the chlorine exchanges one unit of satu- ration with the oxygen of the group OH, just as it exchanges one with hydrogen in hydrochloric acid : it is monatomic or univalent. In chloric acid it is combined with two atoms of oxygen and one group, OH. It exchanges 4 atomicities with oxygen, and one with the group OH : Cl v O" 2 (OH/ Chloric acid. Chlorine thus manifests 5 atomicities in chloric acid; but it has 7 in perchloric acid. Cl vii 3 (OH)' Perchloric acid. Without dwelling on these considerations, we will take one more example. In hydrogen phosphide, one atom of phosphorus is combined with three atoms of hydrogen ; it manifests but three atomici- ties, and these could not neutralize those which reside in three atoms of oxygen, since the latter possess six atomicities. If, then, three atoms of diatomic oxygen were united with one atom of triatomic phosphorus, it is clear that three affinities would remain free, one in each of the three atoms of oxygen. In phosphorous acid, these three affinities of the oxygen atoms are satisfied by three atoms of hydrogen. We may suppose that in the molecule of this compound, the phosphorus is the nucleus around which are grouped three atoms of oxygen, each of which is joined also to one atom of hydrogen. This atomic grouping is indicated in the following formulae : H i P /\ H H Hydrogen phosphide. OH i P HcfoH Phosphorous acid. This hydrogen, combined with the oxygen in all of the oxy- gen acids, plays invariably the same part: it saturates the one atomicity which remains free in one atom of oxygen. The oxygen thus combined with an atom of hydrogen, has lost one of its atomicities by the fact of this combination ; it still retains one in the group OH, which represents, as it were, water less one atom of hydrogen. HOH — H = (OH)' THEORY OF ATOMICITY. 229 This group is named hydroxyl, and it is evident that, although it cannot exist by itself, it may play the part of a monatomic element, for it retains one free atomicity. It may then replace a monatomic element, such as hydrogen or chlo- rine. Indeed, it plays an important part in the constitution of acids. If we consider the examples which have already been dis- cussed, we will notice that it is this hydroxyl which, by com- bining with an element or group of elements capable of forming acids, confers upon them "the characters of acids. So consid- ered, hypochlorous acid is formed by the union of hydroxyl with an atom of chlorine. Cl(OH)' Hypochlorous acid. Sulphuric acid is formed by the union of two hydroxyl groups with sulphurous oxide, and represents in a manner sulphuryl chloride in which the two atoms of chlorine are replaced by two hydroxyl groups. SO 2 1 C1 SO 2 1 (° H )' feU (CI bU {(OH)' Sulphuryl chloride. Sulphuric acid. Phosphorous acid is formed by the union of three hydroxyl groups with one atom of phosphorus. fCl f(OH)' F"-|C1 F"4(OH)' (CI ((OH)' Phosphorus trichloride. Phosphorous acid. Lastly, phosphoric acid results from the union of three hy- droxyl groups with one atom of phosphorus already combined with one atom of oxygen (phosphoryl) (Cl ((OH)' , 0"F i Cl 0"P T I (OH)' (Cl ((OH)' Phosphoryl trichloride. Phosphoric acid. Such, according to the theory of atomicity, are the relations existing between the atoms of certain acids ; such, in other words, is the constitution of these acids. It would be easy to extend these considerations to other bodies, but the examples we have chosen are sufficient to indicate the importance of the idea of atomicity, when it is applied to the discovery and definition of 20 230 ELEMENTS OF MODERN CHEMISTRY. the part played by each element in a given compound. By supposing the capacities of combination of chlorine, oxygen, sulphur, and phosphorus to be known, we have been able to follow these bodies in their most important combinations, we have seen how they attract and group around themselves other elements. We have thus been able to penetrate the atomic structure of the molecules, and have built up as it were the molecular edifice. It must be remembered, however, that the preceding formulae do not in any manner represent the real positions of the atoms in space. Their sole object is to indi- cate the points of attachment of the affinities, and consequently the mutual relations between the atoms. CHEMICAL ENERGY— THERMOCHEMISTRY. The study of the elements and compounds already described has shown that combination is usually accompanied by a more or less intense development of energy, while in some cases energy is developed by decomposition. Ws have seen that many compounds are dissociated or separated into their elements by temperatures more or less elevated, and it is not difficult to understand that the amount of energy developed or absorbed in the formation of a compound, is the exact measure of the energy required or developed in its decomposition. The determination of the precise amount of energy developed or absorbed in any chemical reaction is the object of thermo- chemistry. In order to simplify and harmonize results for com- parison, the kilogramme degree is selected as the unit of energy, representing the quantity of heat necessary to raise the tem- perature of one kilogramme of water through one degree centi- grade. This unit is termed a calorie, and the heat of formation or decomposition of a compound is expressed by the number of calories produced by the formation or decomposition of one molecule of the substance, the atom of hydrogen being supposed to weigh one gramme. Thus the heat of formation of carbon dioxide will be the number of calories produced by the perfect combustion of twelve grammes of carbon. When practicable, the heat of formation is determined by the energy of combus- tion. As a general formula, we may consider that the com- bining atoms possess energy in some form, chemical, physical, CHEMICAL ENERGY — THERMOCHEMISTRY. 231 or mechauieal, which energy we may call m. The product of the reaction will possess m ± n energy, ± n being the energy disengaged by the reaction. It has been found that the amount of energy developed by the formation of any compound from its elements is precisely the same whether the body is formed at once or by several stages. Thus, the heat of formation of CO 2 is the same whether it be formed by C + O 2 = CO 2 , or by G + = CO and CO + = CO 2 . In the oxidation of a combustible compound which has been formed with disengagement of energy, less heat should be pro- duced than by the direct oxidation of the constituent elements, since part of their atomic energy has already been disengaged by their combination. Thus, the energy of formation of CH 4 should be represented by the difference between the heat pro- duced by the combustion of CH 4 , and that produced by the combustion of C plus that of H 4 (H = 1 gramme). The energy of formation of CO will be the difference between the energy of combustion of C and that of CO. Direct and indirect methods of reasoning of this kind have enabled the calculation of the energy of formation of a large number of compounds. The physical state of the reacting bodies and of the product is necessarily an important factor in thermo-chemical consider- ations. If the product be gaseous while the reacting bodies be liquid or solid, a certain amount of energy will be required to maintain the matter in the gaseous form, and this quantity must be calculated and added to that actually resulting from the reaction. If, on the contrary, the bodies entering into combination be liquid or gaseous while the result is solid, the direct energy of combination will be lower than the heat de- veloped by the reaction. While the laws governing chemical energy are as yet unde- veloped, it is not difficult to understand the cause of the phe- nomena in which heat is disengaged or absorbed. We must believe that the atoms of any element are endowed with motion, and chemical energy then becomes atomic motion. If the atomic motion be arrested, the energy appears as heat, molecu- lar motion, or in some other form. When two elements manifest energetic affinities for each other, it is because their atoms are moving in such a manner that a portion of the 232 KLE.MF.N Mr.MlSTKV. atomic motion may be mutually arrested ; this atomic en is then transformed into heat energy or molecular motion. While all chemical action most the manner of that motion cannot at present be fully undev- stood. Atomic energy, thai is, affinity, musl be a Function of temperature, since the atomic vibrations of the - may be so varied by an absorption rf energy from external sources that, on one hand, the motions of atoms manifesting little affinity for each other may be bo In mbination must take place, and, on the other, the harmonious movements of unlike atoms ma] be rendered so incompatible that atom- will separate, fin I .ore stable equilib- rium in molecules of the elementary substances. In this manner are can readily interpret those cases in which decomposition is attended b; lopmenl y, as with hydrogen dioxide, nitrogen iodide, and many other oompoonds. In the formation of nitrogen iodide by the action of ammonia on iodine 15 . ammonium iodid IN ll r 3P = NT + :;mi 1 Ammonium iodide is formed with dig 'it of en but in the aboi ome apparent ; the liquid does not become warm ; t ; j which disaj from the atoms in the ammonium iodide is transferred to the atoms of nitrogen and iodine, and enal mbine, forming nitrogen iodide. Th as then possess gr energy than when in in of nitrogen and iodine, and on the least disturbance of the unstable equilibrium the niti iodide i- decomposed; the atom- of nitrogen combine, forming molecules of nitrogen, and the atom- of iodine form mole of iodine. Part of the atomic' motion being thufl 1. the energy of formation of ammonium iodide reappears and be- comes external in the form of enemy of formation of mole, of nitrogen on one hand, and of iodine on the other. These principles are capable of extended application. They have been developed by the labors of Favre and Silberman, Julius Thomson, Berthelot, Tommassi, and others. METALS. The metals are elements which are good conductors of heat and electricity, and are endowed with a peculiar lustre, which is called the metallic lustre. This definition, it will be ob- served, is founded upon certain physical characters rather than upon chemical properties. It is unsatisfactory and wanting in exactness, for it is applicable to bodies which are properly con- sidered as metalloids. Such is antimony, which has already been described, and bismuth, which should be placed beside antimony. Indeed, the distinction between the metals and metalloids is not so well marked that a line which shall sepa- rate these two classes of simple bodies may be sharply drawn. Physical Properties of the Metals. — These will be found in the table on page 232, but the indications there given may be completed by certain other developments. The metals are opaque, but their opacity is not absolute. A sheet of gold-leaf pressed out between two plates of glass allows the passage of a green light. Gold possesses a brilliant lustre and .a yellow color, but it loses this lustre when it is reduced to a minute powder. When, however, this powder is rubbed with a hard body, when, for example, it is triturated in an agate mortar, or passed under the burnisher, it acquires a certain degree of cohesion, and again assumes its lustre. It is thus with all the metals. They lose their metallic lustre when finely divided and reassume it on burnishing. The yellow color of gold is not its true color ; the rays which reach the eye are the result of but one reflection, but if light be successively reflected from ten surfaces of gold, the metal will appear of a bright-red color. Under the same circum- stances, copper will appear scarlet, zinc indigo, iron violet, and silver pure yellow (B. Prevost). Most of the metals may be crystallized. Bismuth is the most striking example. If a few kilogrammes of pure bismuth be fused, and the liquid mass be allowed to cool slowly, the 20* 233 234 ELEMENTS OF MODERN CHEMISTRY. "eg a 1-8 3 fl II ll c o a o - a 3 S o £ o < N !C O s-a lO 2 *"* -* • O 00 OS £- o OS s j w « s is* c a & 2, § .g §■ a a § •d » fl ft . •- -d o o o o © © a iO iO W ifl iO S5 95 M M 0©©©00©0©© ©©©©©©©©©© .3 - B « O *g o .3 o eg > 2 .2 * a •* io ©© I + 8 2 ,§>© a r) a >> a 3 3 o '* a T! a a 3 ■rt rt Oh yj H pq J CJ S3 <5 «* a" -a • « © * © § J" '■a ^ Ill ■§ a - si I p 3 § NftOft««3aoH( oo t— «Ot-r-CMC<)CM©c iMMHoaooooooi o o IS 0) S - •- O « O g ^1 1?*! £ 1 S 1 S 1 1 a S | .3|5.Sa5'g?2 H^OtS3<5 ewelr ? {Copper' 250-80 a ., . (Silver 900 Silver coin < „ - AA ( Copper 100 ■**»■- (copTer : : : : : : : "S —j-* |S£- :::::: ::Z f Copper ....... 93.5-95 Bronze medals < Tin 6-4 ( Zinc 0.5-1 ««— {Srr ::::::: '5 Beii-etai { gw« ;;;;;;; g | Copper ....... 67 Speculum-metal ] T Aluminium bronze j °°PP er . • • • • • • »0-85 ( Aluminium 10-O Red brass ( !>P er ?» ( Zinc 10 White brass { °°PP er f { Zinc 3d f Copper 50 German silver 1 Zinc 25 (Nickel ....... 25 T ^- tai lemony :::::: 11 ("Tin 100 Britannia-metal \ Antimony Bismuth 1 [ Copper 4 Hard P e - ter &: ::::::: 9 i Soft pewter \ Plumbers* solder Tin 82 Lead 18 {Tin 66 {Lead 33 240 ELEMENTS OF MODERN CHEMISTRY. METALLIC OXIDES AND HYDRATES. Formation of Metallic Oxides.— The metals absorb oxygen with very unequal energy. Many of them become oxidized when exposed to the air at temperatures more or less elevated. In this respect it is important to distinguish the action of dry air from that of moist air. Potassium is the only metal that absorbs dry oxygen at ordi- nary temperatures. All of the other metals, with the excep- tion of silver, gold, and platinum, only become oxidized in the air at very high temperatures. Melted lead absorbs oxygen. Mercury becomes oxidized at about 350° ; copper at a dull-red heat. The combination often takes place with the production of luminous heat. Iron burns in oxygen, but it is necessary that the metal be first heated to bright redness that the combustion may take place. However, the finely-divided iron that is obtained by reducing oxide of iron in a current of hydrogen at a comparatively low temperature, will take fire when exposed to the air at ordi- nary temperatures. It is pyrophoric, and the fine state of division of the metal favors the oxidation. If the powder be projected into the air, each particle takes fire and burns with a bright flash. A bright sheet of iron will indefinitely preserve its brilliant surface in dry air, but if a drop of water be placed upon it, or if it be exposed to the action of a moist atmosphere, rust makes its appearance in a short time. This rust is ferric hydrate, for the metal has at the same time absorbed oxygen and water. It is generally admitted that it is the oxygen of the air dis- solved in the water that first fixes upon the metal, and that the combination is favored by the presence of carbon dioxide. However it may be, the spot of rust once formed constitutes a Voltaic couple with the iron itself, and the current so estab- lished decomposes the water. The oxidation then proceeds rapidly, the oxygen of the decomposed water combining with the metal. It is possible that hydrogen dioxide may play a part in oxi- dations ; it may be formed as a secondary product during the . METALLIC OXIDES AND HYDRATES. 241 decomposition of the water, and fix directly upon the metals, converting them into hydrates (TVeltzien). Fe 2 + 3H 2 2 = Fe 2 6 H 6 Iron. Hydrogen dioxide. Ferric hydrate. Mg + H 2 2 = Mg0 2 H s Magnesium. Magnesium hydrate. Indeed, the oxidation of metals in moist air always produces hydrates and not oxides. Composition and Classification of the Oxides. — It has already been remarked that the metals differ as to the number of oxygen atoms with which they combine ; besides this, the same metal may form several compounds with oxygen ; differ- ent degrees of oxidation. Hence the oxides present different compositions, and the differences are important, since they exer- cise a marked influence upon the properties of the compounds. 1. Certain oxides present the same atomic constitution as water. Two atoms of metal are combined with one atom of oxygen. K 2 potassium oxide. Na 2 sodium oxide. Li 2 lithium oxide. T1 2 thallium oxide. Ag 2 silver oxide. 2. One atom of certain metals can combine with one atom of oxygen ; the oxides of the general formula 310 result. BaO barium oxide. SrO strontium oxide. CaO calcium oxide. MgO magnesium oxide. MnO manganous oxide. FeO ferrous oxide. ZnO zinc oxide. PbO lead oxide. CuO cupric oxide. HgO mercuric oxide. SnO stannous oxide. The metallic oxides containing but one atom of oxygen are generally energetic bases ; that is. they react energetically with the acids, forming salts. They are sometimes called basic oxides. 3. The sesquioxides are those which contain two atoms of metal and three atoms of oxygen. Such is antimony oxide, that has already been studied; the oxides of bismuth, gold, etc 3 present an analogous composition. l 21 242 ELEMENTS OF MODERN CHEMISTRY. Sb 2 3 antimony sesquioxide. Bi 2 3 bismuth sesquioxide. Au 2 3 gold sesquioxide. Fe 2 3 ferric oxide. Mn 2 3 manganic oxide. Cr 2 3 chromic oxide. A1 2 3 aluminium oxide. 4. A large number of oxides contain two atoms of oxygen. BaO 2 barium dioxide. SrO 2 strontium dioxide. MnO 2 manganese dioxide. PbO 2 lead dioxide. SnO 2 stannic oxide. The first four dioxides are incapable of uniting with acids to form corresponding salts. Dumas called them singular oxides. When manganese dioxide is heated with sulphuric acid, oxygen is disengaged, and manganous sulphate is formed, which corre- sponds not to the dioxide, but to manganous oxide. H 2 S0 4 + MnO 2 = MnSO + H 2 + Sulphuric acid. Manganese dioxide. Manganous sulphate. Under the same circumstances, the other singular oxides act in the same manner. As to stannic oxide, it is the anhydride of a metallic acid. SnO 2 + H 2 = H 2 Sn0 3 Stannic acid. 5. The oxides which contain three atoms of oxygen possess acid characters still more marked than stannic oxide. Man- ganese trioxide, MnO 3 , is known. Ferric and chromic anhy- drides present the same composition. MnO 3 manganese trioxide, or manganic anhydride. CrO 3 chromium trioxide, or chromic anhydride. FeO 3 iron trioxide, or ferric anhydride. 6. There is a class of oxides still more complex than the preceding; they can be regarded as formed by the union of two oxides, and they have been named saline oxides. Such are Manganoso-manganic oxide Mn 3 4 = Mn 2 3 -f MnO, or red oxide of manganese. Dipluuiboso -plumbic oxide Pb 3 4 = PbO 2 + 2PbO, or red oxide of lead. The first contains one molecule of a sesquioxide, combined with one molecule of a monoxide ; the second, one molecule of a dioxide and two molecules of a monoxide. METALLIC OXIDES. 243 Chemical Properties of the Oxides. — Some of the oxides are fixed, that is, undecomposable by heat; others lose the whole or a part of their oxygen at temperatures more or less elevated. The oxides of the noble metals, such as silver, gold, and platinum, are decomposed by heat alone into metal and oxygen. We have seen that mercuric oxide is decomposed by a dull-red heat. Many of the oxides that contain two or three atoms of oxygen lose a part of the latter element when heated to redness. Such are the dioxides of manganese, lead, and barium. The oxides containing but one atom of oxygen are among the most stable. Some of them absorb oxygen when they are heated in contact with air, forming higher oxides. Among these are manganous, ferrous, plumbous, and stannous oxides. Hydrogen reduces the greater number of the oxides at tem- peratures more or less elevated ; water is formed, and the metal is set at liberty. If a current of dry hydrogen be passed over ferric oxide heated in a glass bulb (Fig. 92), the oxide is reduced, and a Fig. 92. black powder is obtained which is finely divided and pyropho- ric iron. Vapor of water escapes at the same time by the drawn-out point of the bulb. Fe 2 3 + 3H 2 = 3H 2 + 2Fe Ferric oxide. Iron. 244 ELEMENTS OF 310DERN CHEMISTRY. The ferric oxide may be replaced by cupric oxide, CuO. If this oxide be heated in a current of hydrogen, it is reduced, and the action is so energetic that it gives rise to the produc- tion of luminous heat. Carbon reduces the greater number of the oxides with for- mation of either carbon dioxide or monoxide. It is even more energetic in its action than hydrogen, for it decomposes oxides which are irreducible by the latter element, such as those of potassium and sodium. The oxides of calcium, barium, stron- tium, magnesium, and aluminium are irreducible by carbon. The other oxides require for reduction a temperature more or less elevated, according to the force with which they retain their oxygen. If the reduction be difficult, a high temperature is required, and carbon monoxide is formed ; otherwise carbon dioxide is the product. A small quantity of cupric oxide may be reduced by char- Fig. 93. coal by heating the mixture in a glass tube by the aid of a spirit-lamp (Fig. 93). Carbon dioxide is disengaged. 2CuO + C = 2Cu + CO 2 Cupric oxide. Copper. But to reduce zinc oxide by charcoal, the mixture must be METALLIC OXIDES. 245 heated to bright redness in a clay or iron retort, and in this case carbon monoxide is evolved. ZnO + C Zinc oxide. Zn + CO Zinc. Chlorine decomposes nearly all of the oxides at a high tem- perature. It drives out the oxygen and combines with the metal, forming a chloride. Some of the oxides are irreducible by carbon, and resist also the action of chlorine. Such an oxide is aluminium oxide-, or alumina. But if these oxides be submitted to the simultaneous » action of chlorine and carbon at a high temperature, they are converted into chlorides, and carbon monoxide is disengaged. An intimate mixture of alumina and charcoal may be intro- duced into a porcelain tube, BB (Fig. 94), which is heated to Fig. 94. bright redness, and a current of dry chlorine then passed through. In this case, carbon monoxide is disengaged, while aluminium chloride is formed and volatilizes and may be con- densed in a cooled receiver. Sulphur decomposes all of the oxides except alumina and its analogues. The reaction takes place at a high temperature, and gives rise to the formation of a sulphide and sulphurous oxide, or a sulphide and a sulphate if the latter be not decom- posable by heat. 21* 246 ELEMENTS OF MODERN CHEMISTRY. If sulphur be heated with cupric oxide, cupric sulphide is formed and sulphurous oxide is evolved. 2CuO + 3S = 2CuS + SO 2 Cupric oxide. Cupric sulphide. However, if calcium oxide (lime) or lead oxide, PbO, be heated with sulphur, a sulphate and a sulphide are formed. 4CaO + 2S 2 = 3CaS + CaSO* Calcium oxide. Calcium sulphide. Calcium sulphate. Action of Water upon the Oxides — Metallic Hydrates and Acids. — If some fragments of barium oxide (baryta) be sprinkled with cold water, an energetic reaction immediately takes place. The water unites with the metallic oxide with so much energy that the heat disengaged is sufficient to convert a portion of the water into vapor. The barium oxide is con- verted into hydrate. BaO + H 2 = Ba(OH) 2 Barium oxide. Barium hydrate. In the same manner, the oxides of potassium and sodium energetically absorb the elements of water, being converted into hydrates. K 2 + H 2 = 2KOH Potassium oxide. Potassium hydrate. The hydrates of potassium and sodium are soluble in water and their solutions are caustic, changing tincture of violet to a green color and restoring the blue color to reddened litmus solution. These hydrates constitute the alkalies. The hydrates of barium, strontium, and calcium are likewise soluble in water to a certain extent, and their solutions are also somewhat caustic. Other hydrates are insoluble ; they may be obtained by double decomposition by precipitating the corresponding salts with an alkali. If a solution of potassium hydrate be poured into a solution of cupric sulphate, a light-blue precipitate of cupric hydrate is formed. CuSO 4 + 2KOH = K 2 SO + Cu(OH) 2 Cupric sulphate. Potassium hydrate. Potassium sulphate. Cupric hydrate. But if this precipitate be heated, even in the liquid in which it was formed, it changes brown, and is converted into oxide by losing its water. Cu(OH) 2 — H 2 = CuO SULPHIDES. 247 A great number of metallic hydrates undergo the same decomposition when they are heated. There are true metallic acids which contain the elements of an oxide plus the elements of water. Such are H 2 CrO = CrO 3 + IPO Chromic acid. Chromium trioxide. HOInO 4 = MnO 3 + H 2 "Manganic acid. Manganese trioxide. As far as their constitution is concerned, these metallic acids may be compared to sulphuric acid. EPSO 4 == SO 3 + H 2 They also resemble sulphuric acid in their chemical func- tions ; each contains two atoms of basic hydrogen, that is. two atoms of hydrogen which are replaceable by a metal. SULPHIDES. Sulphur has a great tendency to unite with the metals, and the union often takes place with a vivid evolution of heat. Copper-turnings and iron-filings burn in the vapor of sulphur. The phenomena which favor or determine, and those which accompany this combination, have already been indicated, and we have seen that the presence of a small quantity of water favors chemical union in a mixture of sulphur and iron-filings. Certain metals, such as aluminium, zinc, and gold, resist the action of sulphur even at high temperatures. In composition the sulphides are analogous to the oxides. The more important of the transformations which they may undergo are the following: Oxygen decomposes all of the sulphides at a temperature more or less elevated. Finely-divided potassium sulphide, obtained by calcining the sulphate with an excess of charcoal, is a black powder, but it becomes incandescent on contact with oxygen, and if thrown into the air it produces a shower of sparks. It is known as Gay-Lussac's pyrophorus. Its fine state of division favors the absorption of oxygen, and the latter converts it into sulphate. *K? S j_ o = K 2 SO Potassium sulphide. Potassium sulphate. Dry oxygen acts in the same manner upon all the sulphides 248 ELEMENTS OF MODERN CHEMISTRY. when the corresponding sulphates are stable at high tempera- tures. In the contrary case, sulphurous oxide is formed, and a residue of oxide or even of metal is obtained, if the oxide be decomposable by heat. If zinc sulphide be roasted, it is converted into zinc oxide, and sulphurous oxide is evolved ; but if sulphide of mercury be heated in a current of air, metallic mercury is obtained. HgS + O 2 = Hg + SO 2 Mercuric sulphide. Mercury. Moist oxygen acts upon the sulphides more readily than the dry gas. It unites with them at ordinary temperatures, form- ing sulphates. FeS + O = FeSO Sulphide of iron. Ferrous sulphate. , Chlorine attacks all of the sulphides, forming metallic chlo- rides and sulphur chloride, if the dry method be employed, or with deposition of sulphur if the reaction take place in presence of water. Water dissolves the alkaline sulphides as well as those of cal- cium, barium, and strontium ; the sulphides of the other metals are insoluble in water. Hydrogen sulphide combines with certain sulphides, convert- ing them into sulphydrates. The analogy will be noticed be- tween this reaction and that of water upon the oxides. K 2 S + H 2 S = 2KSH Potassium sulphide. Potassium sulphydrate. K 2 + H 2 = 2KOH Potassium oxide. Potassium hydrate. CHLORIDES. Chlorine, bromine, and iodine form with the metals com- pounds which possess the appearance and certain properties of salts. Indeed, common salt, or sodium chloride, has given the name to the entire class of saline compounds. Hence Berze- lius named chlorine, bromine, and iodine the halogen bodies, and called their combinations with the metals the haloid salts. Thus he admitted the relation between these compounds and the true salts, while at the same time distinguishing them by a particular name, for while they resemble the salts in their prop- erties, they differ from them in composition. This subject will be more fully considered farther on. CHLORIDES. 249 Composition. — All of the metals, with the exception of plat- inum, combine directly with free chlorine, but all do not com- bine with it in the same atomic proportions, and often the same metal forms several distinct combinations with this element. Hence the differences in the composition of the chlorides. They are formed by the union of an atom of metal with one, two, three, four, five, or six atoms of chlorine. KCl Potassium chloride. CaCP Calcium chloride. SbCP Antimony trichloride. SnCl* Tin tetrachloride. SbCP Antimony pentachloride. Mod 6 Molybdenum hexachloride. NaCl Sodium chloride. FeCT Ferrous chloride. Bid 3 Bismuth trichloride. TiCP Titanium tetrachloride. • AgCl Silver ZnCP Zinc And 3 Gold PtCP Platinum chloride. chloride, trichloride, tetrachloride. To these chlorides must be added those which are formed by the union of two atoms of metal with two or six atoms of chlorine. Cu 2 CP Cuprous chloride. Hg^CP Mercurous chloride. APCP Aluminium chloride. Cr 2 CP Chromic chloride. Fe 2 CP Ferric chloride. Cuprous chloride and mercurous chloride contain for the. same quantity of chlorine twice as much metal as cupric chlo- ride, CaCP, and mercuric chloride, HgCP. In the first, two atoms of copper or mercury are combined together to fix two atoms of chlorine, and these two atoms of metal remain thus associated in all the cuprous and mercurous compounds. It is the same in the chloride of aluminium, and in chromic and ferric chlorides. Each of them contains two atoms of metal intimately associated, and combined as a whole with six atoms of chlorine. The same metal may form several combinations with chlorine. Thallium combines with one or three atoms of chlorine. Tin and platinum combine with two or four atoms of chlorine. Antimony combines with three or five atoms of chlorine. Physical Properties of the Chlorides. — Most of the chlo- rides are solid and possess the aspect, color, and physical prop- erties of the salts of the same metal. Nearly all are crystalline and soluble in water. Only the chloride of silver, mercurous L* 250 ELEMENTS OF MODERN CHEMISTRY. and cuprous chlorides are insoluble ; plumbic chloride and thal- lous chloride are but slightly soluble in water. Certain metallic chlorides are liquid at ordinary tempera- tures. Such are the tetrachlorides of tin and titanium. Some, like the chlorides of zinc and bismuth, are solid, but fusible at low temperatures. These latter were formerly designated as metallic butters. Most of the chlorides are fusible at high temperatures, and many of them are volatile and can be distilled without altera- tion. It is thus with the liquid chlorides, with the chlorides of zinc, bismuth, mercury, etc. Chemical Properties. — As a rule, the chlorides are very stable. Only the chlorides of certain of the precious metals, as those of gold and platinum,", are entirely decomposed by a high temperature. Some of the higher chlorides lose chlorine when calcined, and are converted into lower chlorides. Thus, cupric chloride is converted into cuprous chloride when heated out of contact with. air. A great number of the chlorides are reduced when they are heated in a current of hydrogen. In this case, hydrochloric acid is disengaged, and the metal remains. Thus, hydrogen removes the chlorine from the chlorides of silver and iron. These decompositions are determined by the powerful affinity of chlorine for hydrogen. The action of the metals upon the chlorides gives rise to interesting phenomena which are worthy of study. If corrosive sublimate, which is mercuric chloride, be mixed with powdered tin and the mixture be heated in a small glass retort provided with a receiver, a liquid will soon collect in the latter which diffuses thick vapors in the air. It is the tetra- chloride of tin, called by the ancient chemists " fuming liquor of Libavius." It is formed by the decomposition of the mer- curic chloride, which gives its chlorine to the tin, metallic mercury being at the same time set free. Bismuth decomposes mercuric chloride in the same manner when the two substances are heated together. These experi- ments are conducted in the dry way. They may be modified by operating in the presence of water, in which we have re- marked that most of the chlorides are soluble ; it is thus with mercuric chloride. If a plate of copper be plunged into a solution of this body, it at once becomes covered with a layer of metallic mercury. CHLORIDES. 251 That metal is displaced from its combination by the copper, which combines with the chlorine : cupric chloride is formed, and after the lapse of some time, the liquid will contain only that compound. It becomes green, and if a plate of zinc be plunged into it, the copper will be precipitated in its turn, and the zinc will combine with the chlorine and enter the solution ; the liquid then contains zinc chloride. Thus, the metals reciprocally displace each other from their solutions, according to the energy of their affinities. In this case it is the possession of the chlorine for which they antago- nize each other, the stronger driving out the weaker. It must be remarked that in this respect the chlorides behave in the same manner as the oxygen salts. This analogy is continued in innumerable reactions. Solu- tions of the chlorides enter into double decompositions like solutions of the true salts. If potassium hydrate be added to a solution of either cupric sulphate or cupric chloride, in each case a light-blue precipitate of cupric hydrate is obtained. CuSO + 2KOH = K 2 SO + Cu(OH) 2 Cupric sulphate. Potassium hydrate. Potassium sulphate. Cupric hydrate. CuCP + 2KOH = 2KC1 + Cu(OH) 2 Cupric chloride. Potassium chloride. But cupric chloride resembles the sulphate in still another property. When perfectly pure it is yellowish. If it be moist- ened with water, it becomes heated and assumes a green color. It has combined with water, and will dissolve if enough of that liquid be added. A green liquor is thus obtained, which de- posits, by spontaneous evaporation, magnificent green prisms. These crystals are hydrated cupric chloride. They contain water of crystallization, and can only exist on that condition. It is the same with the crystals of cupric sulphate. Thus, certain chlorides are capable of taking water of crys- tallization like the true salts. We may complete the analogy by one more characteristic. 1. If a solution of aluminium sulphate be added to a con- centrated solution of potassium sulphate, and the mixture be agitated, an abundant crystalline deposit is obtained. This is a double salt, — potassium and aluminium sulphate, or alum. 2. If a solution of platinic chloride be added to a concen- trated solution of potassium chloride, a yellow precipitate is 252 ELEMENTS OF MODERN CHEMISTRY. formed at once. It is the double chloride of potassium and platinum, which contains all of the elements of two molecules of potassium chloride and one molecule of platinic chloride. This example shows that the chlorides can combine together, forming double chlorides, just as the true salts may combine together to form double salts. SALTS. Definition. — The salts are formed by the substitution of metal for the hydrogen of the acids, and they result from the action of the acids upon the metallic oxides or hydrates. The name acid applies to two classes of compounds : the first are formed by the union of hydrogen with a strongly electro-nega- tive element, such as chlorine or bromine ; these are the liy- dracids. Such are hydrochloric acid, HC1, and hydrobromic acid, HBr. The acids of the other class are more complicated, contain- ing hydrogen united with a strongly electro-negative oxidized group, that is, a group of atoms formed by oxygen and another element; these are the oxacids. Such are nitric acid, HNO 3 , and sulphuric acid, H 2 SO*. These two classes of acids behave in the same manner in contact with bases, that is, with metallic oxides or hydrates. 1. If hydrochloric acid be gradually added to a concentrated solution of potassium hydrate, the liquid becomes heated, and, as it is neutralized by the acid, a white crystalline de- posit separates and augments on cooling : it is potassium chloride. 2. If sulphuric acid diluted with its volume of water be cautiously and gradually added to a concentrated solution of potassium hydrate, the liquid becomes heated, and, as it is neutralized by the acid, a white crystalline deposit separates and increases on cooling : it is potassium sulphate. The analogy between the two reactions is marked. In each case a powerful base, potassium hydrate, has been neutralized by an energetic acid ; the reaction has been accompanied by the production of heat, and has given rise to the formation of a saline matter which has been deposited. The part of the reaction which is invisible is the formation of water. This formation of water, which always accompanies the generation SALTS. 253 of a salt in the ordinary manners, is expressed in the following equations : KOH + HC1 = KC1 + H 2 Potassium hydrate. Potassium chloride. 2KOH + H-SO = K 2 SO + 2H 2 Potassium sulphate. These reactions, it will be seen, consist in an interchange of elements, a double decomposition. The hydrogen of the acid is exchanged for the metal of the potassium hydrate and by the exchange the potassium hydrate is convert ed into water,, while the acid, that is, the salt of hydrogen, is converted into a salt of potassium. All hydrogen compounds capable of thus exchanging their hydrogen for an equivalent quantity of metal, fill the functions of acids, and these acids become salts when their hydrogen is thus replaced by a metal. It may then be seen what an important part hydrogen plays in the formation of salts. From whence comes this property, this capacity for such exchanges, and of replacement by metals ? Without doubt from the element or group with which the hydrogen is united in the acids ; and in this respect chlorine and sulphur play the same parts in hydrochloric and sulphydric acids that the oxidized groups play in nitric, sulphuric, and phosphoric acids. HC1 H 2 S Hydrochloric acid. Sulphydric acid. H(X0 3 ) H 2 (SO :! ) H 3 fP0 8 ) Nitric acid. Sulphurous acid. Phosphorous acid. H(C10 3 ) IT-\S0 4 ) H 3 (PO) Chloric acid. Sulphuric acid. Phosphoric acid. This property is characterized by saying that the elements or groups, to which the hydrogen is united, are strongly electro- negative, or add, in opposition to the hydrogen, which is strongly electro-positive, or basic. When such an acid reacts upon an oxide, or upon a hydrate, an interchange of elements takes place, and a salt and water are formed ; the latter is a constant product necessary to the reaction. Other examples may be added to those already given. If a current of hydrogen sulphide be passed into a solution of potassium hydrate until no more is absorbed, potassium sulphydrate and water are formed. H 2 S + KOH = KSH + H 2 Potassium sulphydrate. 22 254 ELEMENTS OF MODERN CHEMISTRY. If an excess of dilute sulphuric acid be poured into a solu- tion of potassium hydrate, potassium acid sulphate and water are formed. H 2 SO + KOH = KHSO + H 2 Potassium acid sulphate. Lastly, if cupric oxide be heated with dilute sulphuric acid, it dissolves, coloring the liquid blue. Cupric sulphate and water are formed. H 2 SO + CuO == CuSO -f H 2 Cupric oxide. Cupric sulphate. Neutral, Acid, and Basic Salts. — If the salts result from the substitution of the metals for the basic hydrogen of acids, it is evident that their composition must be related to that of the acids from which they are derived. We know that the latter contain one, two, or three atoms of hydrogen, capable of being replaced by an equivalent quantity of metal : they are monobasic, dibasic, and tribasic. It is evident that the salts must present analogous differences in their composition, accord- ing as they are derived from a monobasic, a dibasic, or a tribasic acid. A salt is neutral when the basic hydrogen has been entirely replaced by an equivalent quantity of metal. But the substi- tution may be only partial, for when an acid contains two atoms of basic hydrogen, only one of these atoms may be replaced by one atom of metal ; there will then remain in the salt thus formed one atom of basic hydrogen. When an acid contains three atoms of basic hydrogen, it may happen that only one is replaced by one atom of metal ; there will then remain in the salt two atoms of basic hydrogen ; or it may be that two atoms of hydrogen are replaced by an equivalent quantity of metal, and there will then remain in the salt a single atom of basic hydrogen. Whenever basic hydrogen thus remains in a salt, the satura- tion of the acid is said to be incomplete. The salt formed ordinarily retains the characters of an acid; it is an acid salt. The following table indicates the possible cases of complete or incomplete saturation which may be presented by a mono- basic, a dibasic, and a tribasic acid : HNO 3 H 2 SO* H 3 PO Nitric acid. Sulphuric acid. Phosphoric acid. SALTS. . . 2aa KNO 3 § j SO 4 | 2 1 PO Potassium nitrate. Potassium acid sulphate. Monopotassiuru phosphate. K 2 S0 4 g | PO Potassium sulphate. Dipotassium phosphate. K 3 PO Tripotassium phosphate. Certain neutral salts possess the property of combining with the hydrates or the oxides. The compounds so formed contain all of the elements of the neutral salt, plus those of the hydrate or oxide ; they are called basic salts. Thus, the oxides of lead and copper may combine with the various salts of lead and copper, forming basic salts of those metals. Richter's Laws. — Towards the close of the last century fruitful investigation was made into the phenomena of neu- tralization or saturation of acids by bases. We know that a given weight of acid requires for its neutralization a fixed and absolutely invariable quantity of a given base. Thus, for the conversion of 1000 grammes of sulphuric acid into neutral potassium salt, a quantity of potassium hydrate corresponding to 961 grammes of potassium oxide, K 2 0, is required. To saturate these 1000 grammes of sulphuric acid, it is necessary to take weights of the oxides which are invariable for each one separately, but which vary among themselves. Thus, 1000 grammes of concentrated sulphuric acid are neu- tralized by the following quantities of the oxides named : Potassium oxide 961 grammes. Sodium oxide 632 " Barium oxide 1561 " Calcium oxide 571 " Zinc oxide . 866 " Cupric oxide 811 M Mercuric oxide 2201 " Silver oxide 2367 " ' Again, to neutralize 1000 grammes of the most concentrated Ditric acid, the following quantities of the same oxides are required : Potassium oxide 747 grammes. Sodium oxide 492 " Barium oxide 1214 " Calcium oxide 444 " Zinc oxide 651 " Cupric oxide 631 " Mercuric oxide 1714 " Silver oxide 1841 " ELEMENTS OF MODERN CHEMISTRY. Ricliter was the first to remark that these latter quantities are precisely in the same ratio to each other as the quantities of oxides which neutralize 1000 grammes of sulphuric acid. Thus, 961 747 632 _ 492 961 __ 747 1561 ""1214 ^ H 7 , etc. 571 444 In other words, the quantities of oxides which neutralize a given weight of one acid are proportional to the quantities of the same oxides ichich neutralize the same weight of another acid. This law of the composition of salts was discovered, towards the close of the last century, by Richter, a chemist of Berlin. Berzelius quoted another German chemist, Wenzel, as the author of this law of proportion, and his error has appeared in all of the treatises on chemistry during the last fifty years. Richter also studied the phenomenon of the precipitation of metallic solutions by the metals. It is known that when a piece of iron is plunged into a solution of cupric sulphate, the iron dissolves, displacing a certain quantity of copper, without other change. Since the new salt formed, ferrous sulphate, ex- ists in the solution in the same conditions of neutrality as the cupric sulphate, the quantities of metal which thus displace each other are equivalent. As neither oxygen nor acid is set at liberty, it must be admitted that the respective quantities of the metals, in the salts successively formed, are united to the same quantity of oxygen. It has even been supposed that in the salts which, like the sulphates, contain four atoms of oxygen, the metal is in intimate relation with one of these atoms, which is precisely sufficient to constitute the metal in the state of monoxide. CuSO 4 = CuO,S0 3 FeSO 4 = FeO,S0 3 If this were so, it is evident that when cupric sulphate is decomposed by iron, the quantity of metal which enters into solution would combine or enter into relations with precisely the quantity of oxygen abandoned by the copper. This quantity of oxygen being constant, the quantities of the metals which com- SALTS. 257 bine successively with it, differ, but are equivalent to each other, and it is evident that the oxides thus formed would be more rich in oxygen as the weight of metal which enters into solution is less considerable ; in other words, the richness of all these oxides in oxygen is inversely proportional to the weights of the metals which successively become dissolved ; it was in this form that Bichter announced the second law of the com- position of salts. It will be seen that this law is implied in the first, and that both are but particular cases and natural con- sequences of the theory of equivalents, as it is understood at present and as it has already been explained (page 23). General Properties of Salts. — The salts present very differ- ent colors. Those which are formed by an acid possessing a color are themselves colored ; such are the chromates, manga- nates, and permanganates. Most of the colored oxides form salts presenting various colors. , Ferrous salts are bluish-green. Ferric salts are yellow or yellowish-brown. Manganese salts are rose-colored. Chromium salts are dark green. Nickel salts are green. Cobalt salts are currant-red or blue. Cupric salts are blue or green. Gold salts are yellow. It is to be remarked that these various colors are only devel- oped, as a rule, when the salts are hydrated, that is, combined with water of crystallization. The taste of the salts depends upon their solubility ; it is wanting altogether or but slightly marked in the insoluble salts ; more or less pronounced and very diverse in the soluble salts. The salts of magnesium are bitter ; the aluminium salts are astringent ; those of iron astrin- gent, with a metallic after-taste ; the salts of lead are at the same time sweet and astringent ; the salts of copper, antimony, and mercury have an acrid metallic taste, which is nauseous, and is called styptic. The salts generally present regular forms, more frequently occurring in crystals. Some of them are obtained as amor- phous precipitates, but in nature even these may assume the crystalline state. Isomorphism. — Certain salts which possess similar atomic compositions crystallize in identical or nearly identical forms; they are called isomorphous. It is thus with the double sul- 22* 258 ELEMENTS OF MODERN CHEMISTRY, phates, which are called alums, and of which ordinary alum or aluminium and potassium sulphate is the type. These alums are formed by the union of a sulphate, R 2 (S0 4 ) 3 , with a sul- phate, M 2 S0 4 , and they all contain 24 molecules of water of crystallization. Thus, ordinary alum, A1 2 (S0 4 /.K 2 S0 4 + 24H 2 Aluminium and potassium double sulphate. is isomorphous with chrome alum and iron alum. Cr 2 (SO/.K 2 SO + 24H 2 Chromium and potassium double sulphate. Fe 2 (S0 4 ) 3 .K 2 S0 4 + 24H 2 Iron and potassium double sulphate. All of these alums crystallize in regular octahedra. Further, a solution containing two alums, for example, aluminium and potassium sulphate and aluminium and ammonium sulphate, deposits on concentration crystals in which the two salts are mixed. Such is the character of isomorphous bodies ; crystal- lizing in the same form, they may mix together and replace each other in all proportions in the same crystal. Many exam- ples of isomorphism will be cited in the course of this work. It will now be sufficient to add that this idea of isomorphism has rendered valuable service to chemical theory by permitting the grouping together of bodies similar both in crystalline form and atomic constitution, and by furnishing in such cases useful indications for the determination of the atomic weights. It is evident that when two similar combinations, two sulphates, for example, are recognized to be isomorphous, it is necessary to represent their constitutions by analogous formulae, and the latter can only be possible under the condition that the atomic weights of the metals contained in these sulphates have known values. Action of Water upon the Salts. — If water be poured upon and agitated with powdered chalk, a white, cloudy liquid is obtained. The chalk is suspended in the water without being- dissolved ; it is simply held up in the form of minute particles, and if the liquid be allowed to stand, the precipitate is de- posited, and clear water again appears above the deposit. However, if saltpetre, or potassium nitrate, be agitated with water, a colorless, transparent liquid is obtained. The saltpetre is dissolved in the water; it has disappeared as a solid body. SALTS. 259 It is melted by the water, as is commonly said, and is uniformly diffused through the liquid. It has itself become liquid, and this is the phenomenon of solution. It is accompanied by a production of cold, that is, an absorption of heat; for in assum- ing the liquid state and becoming diffused throughout the water, the saltpetre must absorb heat. If the introduction of powdered nitre into the solution be continued, the solid still disappears, but a time arrives when the salt introduced ceases to dissolve ; for water at a given tem- perature can only dissolve a fixed quantity of a salt, and when this limit is attained, the solvent force of the water upon the salt- petre is exhausted. The water is then said to be saturated with the salt, and any excess of the latter remains in the solid state. But if now the solution be heated, this excess is in its turn dissolved, for the solubility augments with the temperature, and as the latter is elevated, a larger quantity of the salt is dis- solved. When the liquid begins to boil, the temperature and the solubility of the salt have reached their extreme limit. If the boiling saturated solution be allowed to cool, it depos- its a large portion of the salt in the form of crystals. In this manner voluminous, colorless, and transparent prisms are ob- tained which fill the vessel, and which are surrounded by a solution of saltpetre, saturated at the temperature to which the liquid has been cooled. This liquid is called the mother-liquor of the crystals. It is thus that soluble salts are crystallized by cooling their hot saturated solutions. Generally the same facts are observed for other soluble salts. Their solubility increases with the temperature; there are, however, some exceptions to this rule. Sodium chloride is not more soluble in hot than in cold water, and gypsum, or calcium sulphate, is sensibly more soluble in cold than in hot water; for, while 500 parts of boiling water are requisite to dissolve one part of gypsum, only 460 parts of cold water are necessary to dissolve the same quantity. The maximum solu- bility of sodium sulphate is between 32 and 33°. Crystals of nitre may be obtained by another process. We may expose the cold saturated solution to the air at the ordi- nary temperature, or, better still, place it in a bell-jar over a vessel containing sulphuric acid. The water of the solution slowly disappears, and, as it is dissipated in vapor, a portion of the dissolved salt separates in the solid form. The crystals thus formed by spontaneous evaporation are generally very regular. 260 ELEMENTS OF MODERN CHEMISTRY. But water exerts another and a different action upon the salts. Perfectly dry cupric sulphate, CuSO, is a white powder. If water be poured upon it, it becomes blue and dissolves, com- municating to the liquid a blue color and notably raising its temperature. On evaporation, this liquid deposits crystals of blue vitriol, and if these be compared with the dry white pow- der with which we started, they will be found to differ from it by the water they contain. We have employed the anhydrous salt, and have hydrated it. In fact, the sulphate, CuSO 4 , has absorbed five molecules of water, with which it has combined, and this combination, like all others, has taken place with the production of heat. The water which is thus absorbed by cer- tain salts, and which combines with them in definite propor- tions, is necessary to the formation of their crystals ; it is called water of crystallization. It is not necessary to the constitution of the salts them- selves ; they can exist without it, and generally lose it when they are heated to a temperature more or less elevated, without undergoing any other decomposition. Certain salts abandon their water of crystallization with such facility that they give it up to the surrounding air when the latter is not saturated with moisture. They then become opaque and lose their forms, for crystals cease to exist when their water of crystalli- zation is disengaged. These salts become covered with a dry powder in the air and are called efflorescent salts. It is seen by the example just cited that the phenomenon of solution of salts in water, which depends upon a physical action, upon a change of state, is often complicated with a true combination of the salt with water, that is, a chemical action which disengages heat. The latter is generally more energetic than the physical action, and the difference between the two effects is then manifested by an elevation of temperature. But the physical phenomenon is produced alone when the salt which dissolves is incapable of combining with water of crystallization. A depression of temperature is then observed, as we have seen in the case of nitre, the crystals of which are anhydrous; but another example will more clearly illustrate this important phenomenon. If water be poured upon recently fused and powdered calcium chloride, the salt dissolves with production of heat. It changes not only its state but its composition ; it combines energetically SALTS. 261 with the water, and this combination produces more heat than is absorbed by the change of state. Hence there is an eleva- tion of temperature. If calcium chloride, combined with its water of crystalliza- tion, be rapidly mixed with snow, the salt is so soluble in water that it causes the snow to melt at the same time that it becomes liquid itself. Here there is no combination, no chemical action, and no heat is disengaged. It is a double physical phenome- non? — fusion of the snow and fusion of the calcium chloride, — and neither of these bodies can undergo a change of state with- out absorbing heat, Hence there is a depression of tempera- ture which may reach — 40°. A mixture of snow and calcium chloride is a freezing mix- ture. A mixture of equal parts of common salt and broken ice or snow is frequently used for the production of cold. The phenomenon of the solution of salts in water presents none of the characteristics of a chemical action ; it does not take place in definite proportions. In fact, a soluble salt requires for its complete solution a quantity of water, which is always the same for a certain weight of the salt at a given temperature ; but there exists no atomic relation between this quantity of water and the weight of the salt which is dissolved. Further, although the solubility of a salt presents for each temperature a maximum limit, that is, although a given weight of a salt requires for its solution a quantity of water which is invariable and which cannot be diminished, when the solution has been accomplished an indefinite quantity of water may be added, and the liquid will still remain perfectly homogeneous. Supersaturation. — We have seen that a saturated solution of a salt at a given temperature generally deposits a part of that salt on cooling. This is not always the case ; it sometimes happens, if the cooling take place under certain conditions, that a portion of the salt, which the difference in temperature should reduce to the solid state, still remains in solution. The solu- tion is then said to be supersaturated. Sodium sulphate and alum have a great tendency to form such solutions. A hot, saturated solution of sodium sulphate is contained in the tube A (Fig. 95). It is heated to boiling, so that the vapor escapes by the drawn-out extremity. By the aid of a blow- pipe, the tube is then sealed at C, before the vapor can con- dense, and is then allowed to cool. A vacuum is formed above 262 ELEMENTS OF MODERN CHEMISTRY. the solution, for the air has been driven out by the vapor. The cold liquid remains limpid ; it deposits no crystals. But the instant the drawn-out point of the tube is broken off, the air enters and crystallization at once commences at the surface and Fig. 95. proceeds throughout the entire mass, which becomes solid ; at the same time an elevation of temperature may be observed. 100 grammes of water and 200 grammes of crystallized so- dium sulphate may be heated to ebullition in a narrow-necked flask, and as soon as vapor begins to issue from the mouth, the latter may be covered with a watch-glass and the whole allowed to cool tranquilly. The salt remains dissolved, and the solution contained in the flask is supersaturated; but as soon as the watch-glass is removed the liquid becomes a solid mass of crys- tals (Loewel). In the first experiment it is the sudden entry of the air which determines the crystallization ; in the second, it is the free access of air, and it may be admitted that in each case the air acts by the corpuscles which it holds in suspension, and which, falling into the solution, determine the crystallization. Indeed, Loewel has shown that air which has been filtered SALTS. 263 through cotton-wool has lost the property of causing supersat- urated solutions to crystallize. But what i§ the nature of these particles which by falling upon the surface of supersaturated solutions occasion crystalli- zation ? The researches of Gernez have thrown great light upon this question. According to him, they are saline particles simi- lar to the salt dissolved. The sodium sulphate is deposited in the preceding experiments because the entry of the air has allowed an imperceptible particle of sodium sulphate to fall upon the surface of the -liquid, and around this particle the crystallization begins immediately and is propagated through- out the entire mass of the supersaturated liquid. The air then contains a trace of sodium sulphate, as it contains a trace of common salt and of carbonate and sulphate of calcium. These particles are suspended in the air in a state of extreme division, and are carried from great distances by the winds. A boiling saturated solution of sodium hyposulphite may be allowed to cool in a carefully-corked flask. When cold, it is so concentrated that it possesses an oily consistency. The flask may be carefully uncorked and the surface of the liquid touched with a rod to the end of which a small particle of sodium hy- posulphite has been made to adhere. Crystallization at once commences at the spot where the rod touches the liquid, and in a few seconds the whole mass becomes solid. There is at the same time a notable disengagement of heat (Gernez). The crystallization will also take place if a particle of sodium sulphate be allowed to fall into the solution, for the latter salt possesses the same crystalline form as sodium hyposulphite, and an analogous constitution. Ebullition of Saline Solutions. — Aqueous solutions of the salts generally possess a boiling-point higher than that of water. Thus, a saturated solution of common salt boils at 108.4° ; a saturated solution of potassium nitrate boils at 115.9?; and a saturated solution of calcium chloride boils only at 179.5°. Action of Heat upon the Salts. — The hydrated salts lose their water when they are heated. Ordinarily, a temperature of 100° is sufficient to expel the water of crystallization. Cer- tain salts melt in this water before losing it ; they are so soluble in hot water that they dissolve in the water which at a lower tem- perature constitutes them in the crystalline state. This is called aqueous fusion. A great number of anhydrous salts melt when they are exposed to intense heat; this is called igneous fusion. 264 ELEMENTS OF MODERN CHEMISTRY. Heat exerts a decomposing action upon many salts. Upon this point it is difficult to give general laws. It can only be said that the stability of a salt depends upon three conditions, namely, the fixedness of the corresponding acid, the stability of the corresponding oxide, and the energy of the affinity with which the two react together to form the salt. Thus the salts of acids decomposable by heat are themselves decomposed at an elevated temperature. It is thus with the chlorates, the perchlorates, and the nitrates. Among the sul- phates, some are decomposable, others are fixed. The latter are those of potassium, sodium, barium, strontium, calcium, mag- nesium, lead, etc. The corresponding oxides of potassium, sodium, barium, etc., are fixed bases, and possess a powerful affinity for sulphuric acid. Hence their sulphates are stable. Most of the carbonates are decomposable by heat; indeed, the affinity of carbonic acid for the bases is as a rule feeble. It is exceptionally strong for the alkaline bases ; hence the alka- line carbonates and barium carbonate resist the action of heat. Action of Electricity upon the Salts. — When an electric current traverses the aque- ous solution of a salt, the latter is decomposed. The metal separates at the neg- ative pole, and the other element of the salt at the positive pole. This other element may be an elec- tro-negative element, such as chlorine, or an oxidized group, that is, a group of atoms, one or more of which is oxygen. The electrolysis of a salt may be effected as follows : An U tube ( Fig. 96) contains a solution of cupric chloride. In each branch a plate of platinum dips into the liquid, and these plates, connected by conducting wires with the two poles of a battery, constitute the positive and negative electrodes. As soon as the current SALTS. 265 passes, the electro-positive element of the salt, the copper, is deposited upon the electro-negative electrode, and the chlorine, which is electro-negative, is disengaged at the positive electrode. A part of this chlorine combines with the platinum electrode by a secondary reaction, forming platinum chloride, but the principal action, that is, the decomposition of cupric chloride by electrolysis, is represented by the following equation: CuCP = Cu + CI 2 Cupric chloride. . Copper. Chlorine. If the cupric chloride be replaced by cupric sulphate, the current will decompose this salt into copper, which deposits upon the negative electrode, and into SO*, which possesses no stability, and consequently breaks up at the positive electrode into SO 3 , which combines with the water to form sulphuric acid, and 0, which is disengaged at the positive electrode. The decomposition of the SO 4 is a secondary action. The principal action accomplished by the work of the current is expressed by the following equation : CuSO 4 = Cu + SO* Cupric sulphate. Copper. Oxidized group. The secondary reactions are as follows : S0 4 = S0 3 + SO 3 + H 2 = H 2 S0 4 The experiment may be repeated upon potassium sulphate, and a solution of this salt colored by the syrup of violets is in- troduced in the U tube. As soon as the current passes, bub- bles of gas are seen to arise from each electrode. Free oxygen appears at the positive electrode, as in the preceding case, and at the same time the liquid filling this branch of the tube as- sumes a red color. This is the evidence of the presence of sulphuric acid formed at the positive electrode. The gas disengaged at the negative electrode is hvdroiren, which is produced by a secondary action of the water upon the potassium which is removed from the salt at the negative pole. Potassium hydrate is thus formed, and the syrup of violets in this branch of the tube is colored green. The principal ac- tion accomplished by the current is expressed, as in the pre- ceding cases, by the equation K 2 S0 4 = K 2 + SO 4 Potassium sulphate. Potassium. Oxidized group. M 23 266 ELEMENTS OF MODERN CHEMISTRY. The metal, which is electro-positive, is carried to the nega- tive pole ; the oxidized group to the positive pole. But the two elements thus separated have provoked or undergone sec- ondary actions independent of the work of the current. The potassium has decomposed the water, the oxidized group has been broken up, as explained in the preceding case. It will be understood from these reactions that all of the salts, whatever may be their nature, undergo the same kind of decomposition when submitted to the action of an electric cur- rent. They are separated into two elements. The one is elec- tro-positive, and is liberated at the negative pole ; this is always the metal. The other is electro-negative and goes to the posi- tive pole, whether it be a simple body, such as chlorine, or an oxidized group, such as SO 4 . It will also be seen that such groups occupy in the oxidized salts the same position held by chlorine in the chlorides. Such is the principal action, that is, the decomposition, accomplished by the action of the electric current, a decomposition which is called electrolysis. Action of the Metals upon the Salts. — The metals may displace each other in their saline solutions. If a plate of copper be plunged into a solution of silver nitrate, the copper enters into solution in the form of cupric nitrate, displacing and precipitating the silver. Cu + 2AgN0 3 = Cu(N0 3 ) 2 + Ag 2 Silver nitrate. Cupric nitrate. If a piece of iron be introduced into a solution of cupric sulphate, the iron instantly becomes covered with a layer of metallic copper, .precipitated by a portion of the iron which enters the solution. Fe + CuSO 4 = Cu + FeSO Cupric sulphate. Ferrous sulphate. If a strip of zinc around which some brass wires have been twisted be suspended in a dilute solution of plumbic acetate, the zinc will slowly displace the lead, which will be deposited in brilliant scales upon the brass wires. The latter gradually assume the appearance of fern-leaves, and the experiment constitutes the formation of the lead-tree. Richter, of Berlin, was the first to remark (1792) that the metals displace each other in their saline solutions without the neutrality of the latter being disturbed. When a neutral salt is precipitated by a metal, a new neutral salt results. The BERTHOLLET S LAWS. 267 ferrous sulphate formed by the action of iron upon cupric sul- phate is neutral like the latter. It may be further stated that in this respect the chlorides behave like the oxygen salts. Iron displaces copper from cu- pric chloride as from the sulphate. In the first case it com- bines with CI 2 , in the second with SO 4 , and in this circumstance again the latter group acts in the same manner as chlorine. CuCP + Fe = FeCP + Cu Cupric chloride. Ferrous chloride. Cu(S0 4 ) + Fe = Fe(S0 4 ) + Cu Cupric sulphate. Ferrous sulphate. The following table indicates the order in which the metals precipitate saline solutions : SALTS OF WHICH THE METALS ARE PRECIPITATED BY CERTAIN METALS. Salts of tin . . , Salts of antimony Salts of bismuth . Salts of lead . . Salts of copper . Salts of mercury- Salts of silver . Salts of platinum Salts of gold . . reduced by iron, zinc, and all the preceding metals reduced by iron, zinc, manganese, cobalt, and all the preceding metals . reduced by iron and zinc. BERTHOLLET'S LAWS. To conclude this general study of the salts, it only remains to indicate the actions exerted upon them by the acids and the bases, and the reciprocal actions of the salts themselves. These facts have been established and discussed principally by Ber- thollet, who demonstrated the influence of physical conditions, such as insolubility and volatility, upon the direction of chem- ical decompositions. Action of Acids upon the Salts. — When an acid, that is, a salt of hydrogen, is added to a metallic salt, the former tends to exchange elements with the latter, in such a manner as to form a new salt and a new acid. If sulphuric acid be added to powdered potassium nitrate, 268 ELEMENTS OF MODERN CHEMISTRY. the latter partially dissolves without the aid of heat, and potassium acid sulphate and nitric acid are formed. KNO 3 + H 2 S0 4 = HNO 3 + KHSO 4 Potassium nitrate. Sulphuric acid. Nitric acid. Potassium acid sulphate. But this reaction is by no means complete. Powerful as are its affinities, the sulphuric acid cannot decompose the whole of the potassium nitrate unaided by heat ; a portion of the latter salt remains unaltered in presence of the excess of sulphuric acid, so that the resulting thick and fuming liquid really con- tains two acids and two salts, namely : Sulphuric acid. Nitric acid. Potassium acid sulphate. Potassium nitrate. The reaction takes place as if two acids were in presence of a single base. There is a conflict between the acids, and they tend to divide the base, which is potassium, in such a manner that each acid may saturate a portion. Hence the decomposition of potassium nitrate is not com- plete, and it is arrested as soon as the nitric acid set free can dispute with the sulphuric acid the possession of the base. There is then established a state of equilibrium between the two acids, both remaining in presence of the two salts. But this equilibrium is unstable and may be deranged by various circumstances. If the acid mixture be heated, abundant white vapors are disengaged. It is the nitric acid which volatilizes. But the sulphuric acid becomes thus preponderant in the liquid and decomposes another portion of potassium nitrate, and, if the volatilization of the nitric acid set free be not arrested by the removal of the heat, it is evident that nothing can prevent the complete decomposition of the potassium nitrate by the sul- phuric acid. The nitric acid, which by its presence alone prevented this total decomposition, is rendered powerless. Such is the influence of volatility or the gaseous state upon the progress of decompositions ; it is manifested in the highest degree in acids more volatile than nitric acid, such as carbonic and sulphurous acids. We have already seen that the carbon- ates and sulphites are easily and entirely decomposed by the energetic acids. While the volatility of acids favors the decomposition of their salts, insolubility may play an analogous part. berthollet's laws. 269 If hydrochloric acid be added to a solution of potassium sili- cate, a gelatinous precipitate of silicic acid is at once produced, and at the same time potassium chloride is formed. The de- composition is complete, for the silicic acid is insoluble. If sulphuric acid be poured into a solution of barium nitrate, a precipitate of barium sulphate is immediately formed, while at the same time nitric acid is set free. Ba(N0 8 ) 2 + H 2 S0 4 = 2HX0 3 + BaSO Barium nitrate. Sulphuric acid. Mtric acid. Barium sulphate. In this case also the decomposition is complete, for the ba- rium sulphate is insoluble. In these two reactions, the division of thebase between the two acids cannot take place, since one of the products is imme- diately removed from the sphere of action by its insolubility. In the first case, it is the newly-formed acid which is precipi- tated ; in the second, it is the newly-formed salt which is de- posited in the insoluble state. Influence of Mass. — One other circumstance can influence the extent of these decompositions: it is the relative masses of the bodies which are in presence of each other. In the first experiment, it was supposed that an amount of sulphuric acid had been added to potassium nitrate sufficient to produce the double decomposition. If a large excess had been employed, it is evident that it would have become preponderant in the mixture, and that it would have displaced a more con- siderable portion of nitric acid. The influence of mass is manifested in the case of very feeble acids, and permits them to displace stronger acids. If a small quantity of tricalcic phosphate be introduced into water charged with carbonic acid, the latter, compensating by its mass for its deficiency in energy, will remove from the phosphate a portion of its base. Calcium dicarbonate and calcium acid phosphate are formed, both of which are soluble. Such, according to Berthollet, is the influence of insolubility and volatility upon the phenomena of double decomposition ; such, on the other hand, is the influence of mass. The same conditions intervene, and in the same manner, in the reactions which we are about to study. Action of Bases upon the Salts. — We will here consider only the action of the soluble bases, that is, the alkaline hy- drates. 23* 270 ELEMENTS OF MODERN CHEMISTRY. If a solution of potassium hydrate be poured into a solu- tion of sodium sulphate, no apparent change takes place; but, according to the principle which has just been announced, it is probable that the potassium hydrate has liberated a portion of sodium hydrate. Na 2 SO* + 2KOH = K 2 SO + 2NaOH Sodium sulphate. Potassium hydrate. Potassium sulphate. Sodium hydrate. But this decomposition cannot be complete, and the liquid must contain four bodies, namely : Sodium sulphate. Potassium sulphate. Sodium hydrate. Potassium hydrate. If potassium hydrate be added to a solution of cupric sul- phate, a light-blue precipitate of cupric hydrate is obtained. In this case the decomposition is complete, owing to the insol- ubility of the cupric hydrate which cannot dispute with the potassium hydrate the possession of the acid. CuSO 4 + 2KOH = K 2 S0 4 + Cu(OH) 2 Cupric sulphate. Potassium hydrate. Potassium sulphate. Cupric hydrate. If a solution of barium hydrate be poured into a solution of potassium sulphate, a precipitate of barium sulphate is pro- duced, and potassium hydrate remains in solution. In this case again, the decomposition is complete, by reason of the in- solubility of the barium sulphate. The potassium cannot di- vide the acid with the barium, for the latter escapes with all of it in the form of insoluble sulphate. K 2 S0 4 + Ba(OH) 2 = BaSO 4 + 2KOH Potassium sulphate. Barium hydrate. Barium sulphate. Potassium hydrate. Action of the Salts upon each other. — The action of salts upon each other is what would naturally follow from the prin- ciples exposed in treating of the action of acids upon salts. Indeed, the latter possess the same constitution as the acids, and in their reactions upon salts should give rise to phenomena of the same order. These are exchanges of elements, double decompositions, which take place and are more or less complete, according to the physical conditions of the bodies which are produced, and also according to the relative masses of the re- acting bodies. In the first place, we must consider the reciprocal actions of the soluble salts. berthollet's laws. 271 If a solution of cupric sulphate be treated with a solution of sodium chloride, no precipitate is formed, but the blue color of the liquid is changed to green. This color is that of cupric chloride, and it may be supposed that the latter salt is formed by the reciprocal action of the sodium chloride and cupric sulphate. CuSO 4 ' + 2NaCl = : Na 2 SO* + CuCP Cupric sulphate: Sodium chloride. Sodium sulphate. Cupric chloride. But this interchange of elements between the cupric sulphate and the sodium chloride is arrested before the decomposition of the two salts is complete. A part of each remains unaltered in the presence of the other and of the two new salts which are formed. Consequently, the green liquor obtained in this experiment contains four salts, namely : Cupric sulphate. Sodium chloride. Sodium sulphate. Cupric chloride. The respective proportions in which these salts exist in the mixture depend upon several circumstances. Malaguti has shown that in cases of this kind it is the energy of the affinity of the acids for the bases which governs the decomposition. The most energetic acid tends to combine with the most power- ful base, and the proportion of the salt thus formed predomi- nates in the mixture. Thus there is set up, as it were, between the elements in presence a sort of conflict, in which the stronger are victorious, while the weaker are not altogether annihilated. The result is a state of equilibrium which is only disturbed in case one of the products is by reason of its insolubility removed from the sphere of action of the other. The latter condition is realized in the following experiments. When barium chloride is added to the blue solution of cupric sulphate, a precipitate of barium sulphate is immediately formed, and cupric chloride remains in solution, coloring the liquid green. CuSO + Bad 2 = BaSO + CuCl 2 Cupric sulphate. Barium chloride. Barium sulphate. Cupric chloride. In this case the decomposition is complete, owing to the in- solubility of the barium sulphate. That salt is removed by cohesion from the sphere of action of the compounds which remain in solution. The portions first formed, and thus with- 272 ELEMENTS OF MODERN CHEMISTRY. drawn, are replaced by others, and the reaction once commenced is finished in the same manner, so that the whole of the cupric sulphate is converted into barium sulphate. A concentrated solution of common salt produces no precipi- tate in a concentrated solution of magnesium sulphate. How- ever, we must admit that there is an interchange of elements, and that the liquid contains four salts, namely : * Magnesium sulphate. Sodium chloride. Sodium sulphate. Magnesium chloride. If this solution be exposed to an intense cold, it deposits crystals of sodium sulphate, while magnesium chloride remains in solution (Balard). Of the four salts which are in presence of each other, the sodium sulphate is the least soluble ; it is therefore deposited, and the double decomposition continues in the same manner until the greater part of the magnesium sulphate has been decomposed. The subject could be further developed by other examples. Those which have been given are sufficient to expose the true principle of double decomposition. We may add that if the operations be conducted in the dry way and at a high temperature, the volatility of the products which may be formed exerts an influence upon the reactions analogous to that which has been established for insolubility. If an intimate mixture of mercuric sulphate and sodium chloride be heated in a glass matrass, a sublimate of mercuric chloride is formed. HgSO 4 + 2NaCl = Na 2 S0 4 + HgCP Mercuric sulphate. Sodium chloride. Sodium sulphate. Mercuric chloride. Action of Soluble Salts upon Insoluble Salts. — The study of double decomposition may be concluded by a summary ex- position of the action of soluble salts upon insoluble salts. It is analogous to that which has just been studied, that is, it is characterized by a tendency to an interchange of elements. A single example will be sufficient. If a solution of sodium carbonate be boiled for a long time with barium sulphate, it is found that the latter salt has under- gone a partial decomposition. It is partially converted into barium carbonate, insoluble like the sulphate, and the liquid becomes charged with a certain quantity of sodium sulphate. BaSO 4 -f Na 2 CO s = Na 2 S0 4 + BaCO 3 Barium sulphate. Sodium carbonate. Sodium sulphate. Barium carbonate. NITRATES. 273 This decomposition is more complete as the proportion of sodium carbonate which reacts upon the barium sulphate is increased. Here, as in some of the preceding experiments, the influence exerted by the greater mass is very appreciable. This study may be aptly terminated by summary indications upon the composition and properties of the more important classes of salts, which are the nitrates, sulphates, and carbonates. NITRATES. Composition. — Nitric acid containing HNO 3 , the nitrates contain the group NO 3 combined with a metal which replaces the hydrogen of the acid. Consequently they contain one or more groups, NO 3 , according to the nature of the metal which has neutralized the nitric acid. Thus, 1. KOH + HNO 3 = KNO 3 -f H 2 Potassium hydrate. Nitric acid. Potassium nitrate. 2. PbO + 2HN0 3 = Pb(N0 3 ) 2 + H*0 Plumbic oxide. Plumbic nitrate. 3. h 3 }° 3 + 3HX ° 3 = Bi(N0 3 ) 3 + 3H 2 Bismuthic hydrate. Bismuth trinitrate. With these few examples, we may conclude : 1. That potassium, which unites with one atom of chlorine to form potassium chloride, KC1, unites also with one group, NO 3 , to form potassium nitrate. 2. That lead, which unites with two atoms of chlorine to form plumbic chloride, PbCP, unites also with two groups, NO 3 , to form plumbic nitrate. 3. That bismuth, which unites with three atoms of chlorine to form bismuth trichloride. BiCl 3 , unites also with three groups, NO 3 , to form bismuth trinitrate. In the chloride K'Cl potassium is monatomic. In the chloride Pb"Cl 2 lead is diatomic. In the chloride Bi"'Cl 3 bismuth is triatomic. In the nitrates, these three metals play the same parts as in the chlorides; and we may say, in a general manner, that the metallic nitrates contain a metal united with as many times NO 3 as the metal possesses atomicities. In K'(N0 3 ) monatomic potassium is united with NO 3 In Pb"(N0 3 ) 2 diatomic lead is united to 2X0 3 In Bi"'(N0 3 ) 3 triatomic bismuth is united to 3X0 3 Such is the law of the composition of the nitrates. M* 274 ELEMENTS OF MODERN CHEMISTRY. Properties. — All of the nitrates are soluble in water. Some of them are deposited from their solutions in the form of hy- drated crystals. Such is cupric nitrate, which crystallizes with six molecules of water at a low temperature. Others separate in anhydrous crystals. Such are the nitrates of potassium, sodium, silver, barium, and lead. All of the nitrates are decomposable by heat, and the pro- ducts of the decomposition vary with the nature of the nitrate and with the temperature. Thus, potassium nitrate is first converted into nitrite, and this is finally decomposed into nitrogen, oxygen, and potassium oxide. The nitrates of barium and lead yield nitrogen peroxide, oxygen, and a residue of oxide. Silver nitrate yields nitrogen peroxide, oxygen, and a residue of metal. 2AgN0 3 = N 2 + O 2 + Ag 2 All of the nitrates liberate oxygen when they are heated; rich in oxygen, they constitute an abundant source of that element, and they are also easily reduced by bodies possessing a strong affinity for it. Sulphur, charcoal, phosphorus, and certain metals are ener- getically oxidized when heated with the nitrates. If sulphur be heated with potassium nitrate, potassium sulphate is formed, and sulphurous oxide and nitrogen are disengaged. 2KN0 3 + S 2 = K 2 S0 4 + SO 2 + N 2 Potassium nitrate. Potassium sulphate. When powdered potassium nitrate is thrown upon burning charcoal, the salt melts and increases the combustion of the charcoal, producing a vivid deflagration. Potassium carbonate is formed and carbon dioxide and nitrogen are disengaged. 4KN0 3 + 5C = 2K 2 C0 3 + 3C0 2 + 2N 2 Potassium nitrate. Potassium carbonate. Distinctive Characters. — All of the nitrates deflagrate when thrown upon incandescent charcoal. With concentrated sulphuric acid they evolve white vapors of nitric acid in the cold, and more abundantly when the reaction is aided by heat. When mixed with copper-filings and treated with concentrated sulphuric acid, they disengage red vapors. When the solution of a nitrate is mixed with its own volume of concentrated sulphuric acid, and a crystal of ferrous sulphate is introduced into the liquid, the crystal very soon assumes a 1 SULPHATES. 275 brown color which is communicated to the liquid. In this very delicate reaction the nitric acid is reduced by the ferrous sulphate to nitrogen dioxide, which colors the excess of ferrous sulphate brown (page 154). The solution of a nitrate, when treated with sulphuric acid, will decolorize solution of sulphate of indigo when the liquid is heated to boiling. SULPHATES. Composition. — Sulphuric acid. IPSO 4 , contains two atoms of hydrogen capable of being replaced by a metal. When both are replaced by an equivalent quantity of metal, a neutral sul- phate is formed. An acid sulphate is formed when a single one of these atoms of hydrogen is replaced by a single atom of metal. The hydrogen of the acid is removed by the oxygen of the metallic oxide or hydrate which more or less completely saturates the sulphuric acid. Several cases may be presented. 1. K'OH + IPSO 4 = g | SO 4 + H 2 Potassium hydrate. Potassium acid sulphate. 2. 2K'OH + H 2 S0 4 — K'-SO 4 + 2H 2 Potassium sulphate. 3. Pb"0 + H 2 S0 4 = Pb"S0 4 + H 2 Plumbic oxide. Plumbic sulphate. r h 2 so 4 ( so 4 4. (A1 2 )"0 3 + 1 H 2 S0 4 = (AFT ] SO 4 + 3H 2 (H 2 S0 4 (SO 4 Aluminium oxide. 3 molecules. Aluminium sulphate. These examples show that all of the sulphates contain the group SO 4 , which in sulphuric acid is united with two atoms of hydrogen. This group is diatomic; it is necessary, then, that in the sulphates it shall be united with a quantity of metal equivalent to two atoms of hydrogen. 1 . In the acid sulphates it is united with an atom of hydro- TV 1 gen and an atom of a monatomic metal, tt [ SO 4 . 2. It is united with two atoms of a monatomic metal in the neutral sulphates ITSO 4 . 3. With one atom of a diatomic metal in the neutral sul- phates M"SO\ These cases are very simple. It is not so, however, with 276 ELEMENTS OF MODERN CHEMISTRY. the fourth, in which we consider the saturation of sulphuric acid by an oxide R 2 3 , such as ferric oxide or aluminic oxide. Each of the three atoms of oxygen of the oxide R 2 3 removes H 2 from a molecule of H 2 S0 4 , and it results that the metal which was combined with 30", combines with 3(S0 4 )". The two atoms of metal which are substituted for 3H 2 in three mol- ecules of H 2 S0 4 are then equivalent to 6 atoms of hydrogen. They are hexatomic, as is marked by the index vl . Properties. — The sulphates are nearly all soluble in water. Those of barium, strontium, and lead are insoluble. The sul- phates of calcium and silver, and mercurous sulphate are but slightly soluble. The alkaline sulphates, and those of calcium, barium, stron- tium, magnesium, and lead, are undecomposable by heat. The others are decomposed at a high temperature. A residue of oxide generally remains, while sulphurous oxide and oxygen are disengaged. The sulphates of zinc and copper are thus decomposed at a high red heat. CuSO 4 = SO 2 + + CuO Cupric sulphate. Cupric oxide. In case the oxide is reducible by heat, the residue consists of metal. HgSO = Hg + SO 2 + O 2 Mercuric sulphate. Mercury. The sulphates R 2 (S0 4 ) 3 are decomposed at a comparatively low temperature, disengaging vapor of sulphur trioxide and leaving a residue of sesquioxide. Fe 2 (S0 4 ) 3 = Fe 2 3 + 3S0 3 Ferric sulphate. Ferric oxide. Sulphuric oxide. The sulphates are easily reduced by bodies avid of oxygen, such as charcoal. If an intimate mixture of potassium sulphate with an excess of charcoal be heated to bright redness, and allowed to cool out of contact with the air, a black powder is obtained, which pro- duces a shower of sparks when projected into the air. It is the pyrophorous of Gay-Lussac. It owes its spontaneous in- flammability on contact with the air to finely-divided potassium sulphide which it contains, and which attracts oxygen with great avidity. The sulphide is formed according to the following reaction : K 2 S0 4 + 4C = 4C0 + K 2 S Potassium sulphate. Potassium sulphide. CARBONATES. 277 In the same manner barium sulphate and calcium sulphate are converted into sulphides by the action of charcoal at a high temperature. The other sulphates are also reduced under the same circum- stances, but the products vary; carbon dioxide or carbon mon- oxide and sulphurous oxide are disengaged, and the residue consists of either oxide or metal. Distinctive Characters. — When treated by sulphuric acid, the sulphates do not evolve any gas. They do not deflagrate when thrown upon burning charcoal. Their solutions give a white precipitate of barium sulphate with barium nitrate, which is insoluble in nitric acid. When this precipitate is washed, dried, and calcined with an excess of charcoal, it leaves a resi- due of barium sulphide, and when this is moistened with hy- drochloric acid, it evolves hydrogen sulphide, which is easily recognized by its odor. CARBONATES. Composition. — Carbonic acid is dibasic, like sulphuric acid. It is not known in the state of hydrate, and the carbonates are formed by the direct union of carbon dioxide with the metallic oxides or hydrates. When freshly-burnt lime is exposed to the air, it attracts at the same time the moisture and the carbonic acid gas of the air 3 and is converted into carbonate. CO 2 + CaO = CaCO 3 Calcium oxide. Calcium carbonate. The carbonates then contain the group CO 3 combined with a metal. In carbonic acid, this group would be united with two atoms of hydrogen. The composition of the more simple car- bonates is expressed by the following formulae: H 2 C0 3 carbonic acid (unknown). tt f CO 3 acid carbonates (dicarbonates). E/ 2 C0 3 neutral carbonates. M"C0 3 neutral carbonates. In these formulae. E/ represents a monatomic metal, such as potassium, which is equivalent to one atom of hydrogen. M" represents a diatomic metal, such as calcium, which is equiva- lent to two atoms of hydrogen. Properties. — Only the alkaline carbonates are soluble in pure 24 278 ELEMENTS OF MODERN CHEMISTRY. water. The others are insoluble, but they dissolve in water charged with carbonic acid. The soluble carbonates possess an alkaline reaction. It is the same with the acid carbonates of the alkaline metals, which are ordinarily called bicarbonates, such as potassium dicarbonate KHCO 3 . All of the carbonates except the alkaline carbonates are de- composable by heat. In this decomposition carbon dioxide is disengaged, and there remains a residue of oxide, or of metal in case the oxide be reducible by heat. Thus, the carbonates of magnesium, calcium, zinc, lead, and copper leave a residue of oxide after calcination ; silver carbonate leaves a residue of metal. Barium carbonate is but slowly decomposed at a white heat ; its decomposition is facilitated by heating it in a current of steam. Bodies avid of oxygen act upon the carbonates as upon the oxides ; the metal is reduced if the base be reducible. Char- coal acts in this manner upon the carbonates. If cupric carbonate be heated with charcoal, carbon dioxide is disengaged, and metallic copper remains. 2CuC0 3 + C = 3C0 2 + 2Cu Cupric carbonate. Copper. In this experiment carbon dioxide is disengaged, for cupric oxide is easily reducible by charcoal. It is not the same with potassium oxide ; hence potassium carbonate is only reduced by charcoal at a very high temperature with disengagement of carbon monoxide. K 2 C0 3 + 2C = 3CO + K 2 When barium carbonate is heated with charcoal, carbon monoxide is disengaged in the same manner, but there remains a residue of barium oxide, for the latter is irreducible by char- coal. BaCO 3 + C = 2CO + BaO Phosphorus decomposes all of the carbonates. A small piece of phosphorus may be placed at the bottom of a small test-tube, and the latter then nearly filled with well- dried sodium carbonate. The part of the tube containing the carbonate being heated to redness, the phosphorus may be heated so that its vapor will pass over the incandescent car- CLASSIFICATION OF THE METALS. 279 bonate. The latter will be decomposed with the formation of sodium phosphate and a deposition of carbon. After cooling. the contents of the tube will be black. The experiment may be repeated upon calcium carbonate. The phosphorus is placed in a small crucible, which is then introduced into a larger one. The calcium carbonate (chalk) is then placed upon the lid of the smaller crucible, which is pierced with holes. The arrangement is heated upon a double grate, so that when the chalk has been brought to incandes- cence, the vapor of phosphorus may be caused to pass through it by placing some hot coals upon the lower grate. The chalk is rapidly decomposed, carbon monoxide is disengaged, and a mixture of calcium phosphate and phosphide is formed. This mixture serves for the preparation of hydrogen phosphide. Distinctive Characters. — When treated with sulphuric acid, the carbonates disengage a colorless, incombustible gas, which extinguishes burning bodies and produces a milkiness when agitated with lime-water. CLASSIFICATION OF THE METALS. In the preceding pages we have studied the composition and the general properties of metallic compounds. This study has revealed the fact that the metals possess very different aptitudes to form compounds, and various capacities of combination, which are manifested by the greater or less number of other atoms which the atoms of these metals can attract. In this respect, the differences existing between the metals are analogous to those which we have already remarked between the metalloids. On comparing the metals among themselves, some are discov- ered which resemble each other in the general structure of the compounds which they are capable of forming, and such can naturally be classed in the same group. On this plan the metals are divided into several families analogous to those first proposed by Dumas for the metalloids, and it will be seen that the general composition of the metallic compounds furnishes the elements for a natural classification of the metals. While this principle is excellent, its application is attended with some difficulties which chemistry has not yet been able to solve. Consequently, this chapter must be limited to summary indi- cations upon the subject. Some of the metals are incapable of combining with more 280 ELEMENTS OP MODERN CHEMISTRY. than a single atom of chlorine, bromine, or iodine. The com- pounds thus formed correspond in their atomic constitution to hydrochloric, hydriodic, and hydrobromic acids. On comparing potassium chloride or silver chloride to hydrochloric acid, it will be seen that an atom of potassium or an atom of silver occupies in them the place occupied by the hydrogen of the acid. The atoms of potassium and of silver 1 are therefore equivalent to the atoms of hydrogen as far as their capacity of combination is concerned. The other alkaline metals, such as sodium and lithium, are similar and belong to the same group. Their chlorides, bromides, and iodides, which are arranged in the following table, present analogous compositions : Monatomic Metals. Monatomic Chlorides. Monatomic Bromides. Monatomic Iodides. Potassium K' H'Cl EBr HI KC1 KBr KI Sodium Na' NaCl NaBr Nal Lithium Li' LiCl LiBr Lil Silver Ag' AgCl AgBr Agl These metals form oxides whose atomic constitutions corre- spond to that of water, each containing two atoms of metal for one of oxygen. Their sulphides correspond to hydrogen sul- phide, containing two atoms of metal for one of sulphur. With the oxides and sulphides we may group the hydrates and sulphydrates, which possess analogous atomic constitutions. Type H20. Type H2S. MONOSULPHIDES. SlTLPHYDRATES. K2S KSH Na2S NaSH Ag^S The same analogy is continued between the salts of these 1 Wislicenus has shown that the constitution of certain double salts of silver can be understood only by considering that this metal is diatomic, and that its compounds are analogous to the cuprous compounds. For convenience of study it is preferable to consider silver as a monatomic ele- ment, and its compounds then become analogous in structure to those of potassium and sodium. Moreover, this classification is in a measure justi- fied by the isomorphism of corresponding compounds of silver and potassium. Oxides. Hydrates. K 2 KOH Na20 NaOH Ag2Q CLASSIFICATION OF THE METALS. 281 metals, as will be seen from the nitrates and sulphates which we take as examples. Nitric Acid, HNO 3 . Sulphuric Acid, H2S0 4 . Nitrates. Sulphates. Acid Sulphates. KNO 3 K 2 SO± KHSO* NaNO 3 Na 2 SO± NaHSO* AgNO 3 Ag2SO* It is seen that in all of these compounds the metals under consideration replace hydrogen atom for atom ; each of them possesses the same capacity of combination as that gas. They are said to be monatomic. Certain other metals manifest a double capacity of combina- tion; one atom of any of these is capable of replacing two atoms of hydrogen, consequently it can combine with two atoms of chlorine, bromine, or iodine, or with one atom of oxygen or sulphur. In the chlorides of these metals, the two atomicities of the metal are satisfied by the two atomicities of two atoms of chlorine. In their oxides, the two atomicities of the metal are satisfied by the two atomicities or bonds of affinity which reside in one atom of oxygen. These metals are then diatomic. They are quite numerous and can be divided into several groups, one of the most natural of which com- prises barium, strontium, calcium, and lead. The following table shows the constitution of the principal compounds of these metals : Diatomic Metals. i Chlorides. Oxides. Nitrates. Sulphates. Barium Ba" . Strontium Sr" . Calcium Ca" . Lead Pb" . . 2HC1 H 2 2HN0 3 H2SO* BaC12 SrCP CaCl 2 PbCl 2 BaO SrO CaO PbO Ba(N0 3 ) 2 Sr(NX) 3 )2 Ca(N0 3 ) 2 Pb(N0 3 ) 2 BaSO* SrSO± CaSO* PbSO* The metals of this group combine with oxygen in two pro- portions, forming not only the monoxides, RO, but also the dioxides, RO 2 . They thus form two oxides, while they are capable of forming but one chloride, RC1 2 . Thus, barium forms a monoxide, BaO, a dioxide, BaO 2 . and a dichloride, 24* 282 ELEMENTS OF MODERN CHEMISTRY. BaCl 2 ; but no tetrachloride of barium is known, and it is nut probable that barium can act as a tetratomic element. How is it, then, that in the dioxide this metal can combine with two atoms of oxygen, while it cannot combine with four atoms of chlorine, which are equivalent to two atoms of oxygen ? In other words, what is the atomicity of barium in the dioxide which would seem to correspond to a tetrachloride? It is undoubtedly diatomic in the dioxide as it is in the monoxide, and the constitution of barium dioxide is analogous to that of hydrogen dioxide, which has already been indicated. The two atoms of oxygen mutually satisfy two of their atomicities by combining together, and they retain two which are neutral- ized in combining with the diatomic atom of barium. Thus, in barium monoxide one atom of oxygen is joined to one atom of barium by both of its atomicities ; in the dioxide two atoms of oxygen are united to one atom of barium, each by one atom- icity. If we represent the saturation of two atomicities by a straight line, as has before been explained, we will have the following formulae : Ba=0 Ba ium monoxide. /\ 0-0 Barium dioxide Iii this manner, theory enables us to fix the relations existing between the atoms in a given body. The comparison may be continued between the other diatomic metals. Magnesium, the radical of magnesia, somewhat resem- bles calcium in its relations, and forms, as it were, the centre of a group including magnesium, zinc, cobalt, and nickel, and which is called the magnesium group. Manganese and iron, on one hand, and copper, on the other, seem to join this group by certain of their characteristics. In their most stable and gen- erally their most important compounds, these metals act as diatomic elements. All form the dichlorides KCr 2 and the oxides RO. But in other compounds, manganese and iron seem removed from the metals of this group, and resemble chromium and aluminium. Copper, which resembles magne- sium in the series of cupric compounds, approaches mercury in the cuprous series. Bismuth, which might be classed with antimony, and gold are triatomic in. their most important combinations. They form the chlorides Bid 3 and AuCP. CLASSIFICATION OF THE METALS. 283 A certain number of the metals may be grouped together as tetr atomic, since they manifest four atomicities in their principal combinations. They are tin, titanium, and zirconium. They form the chlorides RC1* and the oxides RO 2 . In stannic chlo- ride, SnCl*, the tin is saturated with chlorine, of which it cannot combine with more than four atoms ; it is tetrafomic in this saturated compound. But it may combine with only two atoms of chlorine, thus forming the chloride SnCl 2 , which is not saturated, for it can still fix two more atoms of chlorine. Tin only manifests two atomicities in the dichloride. In the same manner, ferrous chloride, FeCl 2 , can absorb chlorine, becoming ferric chloride. The latter contains two atoms of iron and six of chlorine. These two atoms of iron exist in all the ferric compounds ;" together they manifest six atomicities, for in ferric chloride they are united with six atoms of chlorine. They constitute a hexatomic couple. Compounds. Chlorides. Oxides. Sulphates. Ferric Manganic Chromic Aluminic Fe2Cl 6 Mn2Cl6 Cr2Cl 6 A12C1 6 Fe203 Mn20 3 Cr203 A1203 Fe 2 (S0 4 ) 3 Mn2(S0 4 ) 3 Cr2(S0±) 3 A1 2 (S0±) 3 The following table gives a resume of the constitution of the principal metallic combinations. The metals there chosen as examples have different atomicities. The hexatomic couple, consisting of two atoms of iron, may for convenience be called ferricum. Metals. Chlorides. Oxides. Nitrates. Sulphates. Monatomic metal — Potassium K' . KC1 K20 KN03 K2SO* Diatomic metal — Barium Ba" . . . BaC12 BaO Ba(N03)2 BaSO* Triatomic metal — Bismuth Bi w . . BiC13 Bi203 Bi(N03)3 Bi?(S04)3 Tetratomic metal — Tin Sniv . . . SnCH Sn02 Hexatomic group — Ferricum (Fe2)vi Fe2C16 Fe20 3 Fe2(N03)6 Fe2(SO*)3 284 ELEMENTS OF MODERN CHEMISTRY. Such are the principles furnished by the theory of atomicity for a rational classification of the metals. Mendelejeff's Theory. Within recent years the labors of a Russian chemist, Men- delejeff, have developed interesting relations between the atomic weights and properties of the elements. He has shown that the properties are functions of the atomic weights, and that the functions are periodic. This relation is not applicable to a limited group of elements, but extends throughout the whole series, and consists not in certain analogies, but in the general physical and chemical properties taken together. If the elements be arranged in the order of their atomic weights, it will be noticed that these latter increase gradually by only a few units, and also that the properties of the elements are gradually modified with the increase in atomic weights. The modifications are not, however, continually progressive, but are developed in several series. The differences between the atomic weights of neighboring elements are not equal, but are sensibly so, and where these differences are excessive it is probably owing to the existence of undiscovered elements. Mendelejeff predicted the existence of several such elements, and at least two of the lacunae have since been filled by the discovery of gallium and scandium. The hypothesis is then certainly worthy of serious consideration in all attempts to classify the elements. The theory may be best explained by considering an example of the periodicity on which it rests. Let us study the first fourteen elements after hydrogen in the order of their atomic weights. Li =7. Gl=9.4. Bo = 11. C = 12. N = 14. 0=16. Fl = 19. Na = 23. Mg=24. Al = 27.3. Si = 28. P = 31. S = 32. CI = 35.5. We have here two groups, in each of which the change in physical and chemical properties is markedly progressive with the increase in atomic weight. The densities gradually increase to the middle of each series, and then decrease to the end. The atomic volumes, which are the quotients of the atomic weights by the densities, gradually decrease to the middle of the series, and then augment. The volatility also diminishes from sodium to silicon, and again increases to the end of the series. CLASSIFICATION OF THE METALS. 285 Na. Mg. Al. Si. P. S. CI. Densities 0.97 1.75 2.67 2.49 1.84 2.06 1.38 Atomic volumes ... 24 14 10 11 16 16 27 The atomicity, or combining capacity, as indicated by the number of atoms of hydrogen or chlorine with which one atom of the elements combines, displays a similar periodicity. LiCl. G1C1 2 . BoCl 3 . CH*. NH 3 . OH 2 . F1H. NaCl. MgCl 2 . A1C1 3 . (?) SiCl 4 . PH 3 . SH 2 . C1H. The oxygen compounds show a similar progression. Li 2 G1 2 2 Bo 2 3 C 2 4 N 2 5 Na 2 Mg 2 2 A1 2 3 Si 2 4 P 2 5 S 2 6 CPO 7 The number of oxygen atoms with which a constant number of atoms of elements of these series can combine, regularly increases, and the properties of the oxides undergo a gradual modification. Those at the beginning of the series form pow- erful bases ; the intermediate oxides are indifferent, while the latter members form strong acids. That which characterizes these variations is that they occur in the same manner in the two groups, so that the first member of the first series (Li) corresponds to the first member of the second. These two series form the first two periods of Men- delejeff, who has shown that these series or periods can be ex- tended throughout the whole list of elements, and that the properties of the elements are in periodic relations with their atomic weights. While this statement is true in a general manner, and while the discovery has greatly aided in the classification of some of the elements, the progressive variations in the properties of the elements forming a period are by no means uniform, and it is to be remarked that the same irregularity exists in the pro- gressive increase in atomic weights. Indeed, while the atomic weights of a few of the elements are almost identical, others which follow in order are far separated. A great lacuna be- tween two neighboring atomic weights seems to indicate the existence of an unknown element, and, as we have seen, two such lacunae have already been filled. It is probable that new discoveries will lead to the correction, as well as to the further development, of MendelejeflF's theory. It must be remembered, however, that the atomicity of the 286 ELEMENTS OF MODERN CHEMISTRY. elements is not absolutely fixed, but depends upon the nature of the atoms which are combined, and we must classify each element according to the chemical analogies of its more ordinary and more general combinations. Thus, lead is undoubtedly tetratomic in many compounds, among which is a chloride PbCl 4 , but its more ordinary compounds PbO, PbCl 2 , etc., jus- tify its consideration with diatomic elements. Wislicenus has shown that some of the compounds of silver can be understood only by considering silver as a diatomic metal, in which two atoms form a couple that always enter together into combina- tions ; thus, -Ag-Ag-. But it is more satisfactory to con- sider this element as monatomic, as indicated by its analogies with the group of alkaline metals. 'The metals will be considered in the following order, and may be arranged in a number of groups, the members of each group being related by the physical and chemical analogies of their compounds. POTASSIUM. SODIUM. LITHIUM. CESIUM. RUBIDIUM. SILVER. CALCIUM. STRONTIUM. BARIUM. GLUCINUM. MAGNESIUM. ZINC. CADMIUM. LEAD. COPPER. MERCURY. ALUMINIUM. LANTHANUM. CERIUM. DIDYMIUM. SCANDIUM. SAMARIUM. HOLMIUM. ERBIUM. THULIUM. YTTRIUM. GALLIUM. IRON. COBALT. NICKEL. MANGANESE. URANIUM. CHROMIUM. MOLYBDENUM. TUNGSTEN. VANADIUM. NIOBIUM. TANTALUM. INDIUM. GOLD. THALIUM. BISMUTH. TIN. TITANIUM. ZIRCONIUM. THORIUM. PLATINUM. RHODIUM. RUTHENIUM* PALLADIUM. IRIDIUM. OSMIUM. POTASSIUM. 287 < POTASSIUM. K=r39.1. Potassium was discovered by Sir Humphry Davy in 1807. It ordinarily occurs in commerce in gray, globular masses, readily yielding to the pressure of the nail. It has a dull, tarnished appearance, but when freshly cut it exposes a brilliant surface. It is the metallic radical of potash. If a fragment of this metal be thrown into water, it at once takes fire and rushes about on the surface of the liquid, burn- ing with a violet flame. Finally, it disappears with a little explosion. This brilliant phenomenon is due to the energy with which potassium decomposes water. 2H 2 + K 2 = 2KOH + H 2 The hydrogen which is disengaged is inflamed by the incan- descent metal. The potassium hydrate formed ultimately dis- solves in the water, but its temperature being very high at the moment of its solution, and its combination with the water also producing heat, there results a sudden formation of steam, which gives rise to the little explosion. Preparation and Properties. — Potassium is prepared by decomposing potassium carbonate by carbon at a high tempera- ture. KTO 8 + 2C = SCO + K 2 Potassium carbonate. Carbon monoxide. The mixture is heated to whiteness in an iron retort and the vapors are passed into a copper receiver. The potassium dis- tils and condenses in globules or irregular masses, still contain- ing charcoal and a black substance. It is purified by redistilla- tion in an iron retort, and is condensed in a copper receiver filled with naphtha. The manufacture of potassium is- a dan- gerous operation. It is accompanied by the formation of various accessory products, among which is a black substance which sometimes explodes spontaneously on contact with the air. Potassium melts at 62.5° (Bunsen). It boils at a red heat, and its vapor is green. When exposed to the air, it rapidly absorbs oxygen and at the same time decomposes the atmos- pheric moisture. It inflames at a temperature but slightly elevated and becomes converted into oxide. 288 ELEMENTS OF MODERN CHEMISTRY. POTASSIUM OXIDES. Potassium monoxide, K 2 0, is, formed when thin pieces of the metal are abandoned to the action of dry air, or when potassium hydrate is heated with potassium. 2K0H + K 2 = 2K 2 + H 2 It is a grayish-white substance which unites with water with extreme violence, forming potassium hydrate. K 2 + H 2 = 2K0H A tetroxide of potassium, K 2 4 , is formed when potassium is heated in an excess of oxygen, but it is little known. POTASSIUM HYDRATE, OR CAUSTIC POTASSA. KOH This important compound is prepared by boiling 1 part of potassium carbonate with 12 parts of water, and gradually add- ing milk of lime to the boiling liquid. The lime combines with the carbonic acid forming an insoluble carbonate, while the potassa remains in solution. K 2 C0 3 + Ca(OH) 2 = CaCO 3 + 2KOH Calcium hydrate. Calcium carbonate. When the decomposition is finished the liquid is allowed to settle, and the clear solution decanted and rapidly evaporated. The residue is melted in a silver dish and poured out upon flat stone slabs or cast in cylindrical metallic moulds (Fig. 97). This product is known as potash by lime. It is impure. By treating it with alcohol, which dissolves only the potassium SULPHIDES OF POTASSIUM. 289 hydrate, it may be purified from lime, and the salts of potas- sium it may contain, and especially the carbonate, which is formed by the absorption of carbonic acid gas from the air during the evaporation. The clear alcoholic solution is decanted, and after the alcohol has been expelled by distillation, the resi- due is evaporated to dryness and fused in a silver dish. It is known as potash by alcohol. Recently-fused potassium hydrate occurs as opaque, white fragments having a short fibrous fracture and a density of 2.1. It melts at a red heat and volatilizes at whiteness ; it is not decomposed by heat. When exposed to the air, it absorbs moist- ure and carbonic acid gas, and deliquesces. It is very soluble in water, and produces heat in dissolving. A hydrate, KOH -f- 2H 2 0, is deposited from its hot and very concentrated solu- tion in acute rhombohedra. Potassium hydrate is decomposed by iron at a white heat : oxide of iron is formed, and hydrogen and potassium vapor are disengaged. Gray-Lussac and Thenard founded a process for the preparation of potassium on this decomposition. Until then the metal had only been obtained in small quantities by Davy by the electrolysis of potassium hydrate. Potassium hydrate is very caustic. It softens and destroys the skin, and for this purpose is employed in surgery as a caustic. It manifests the properties of an alkali in the highest degree ; these are its solubility in water, its power to neutralize the acids and decompose a great number of metallic solutions, and its corrosive action on the tissues. This alkalinity may be shown by the energy with which the most feeble solutions of potassa restore the blue color to reddened litmus, and change to green the tincture of violets. SULPHIDES OF POTASSIUM. Potassium will burn in vapor of sulphur. It unites' with the latter body in five different proportions, forming the sul- phides K 2 S, K 2 S 2 , K 2 S 3 , K 2 S 4 , and K 2 S 5 . Potassium monosulpliide is formed when potassium sulphate is heated to redness in a current of hydrogen, or in a brasqued l and covered crucible with charcoal. 1 A brasqued crucible is a clay crucible into which powdered charcoal moistened with gum-water has been strongly pressed, and afterwards cal- cined. The substance to be reduced is placed in a cavity hollowed out in the charcoal. n 25 290 ELEMENTS OP MODERN CHEMISTRY. K 2 SO* + 4C = 4CO + K 2 S Potassium sulphate. Potassium monosulphide. A reddish, deliquescent, and caustic mass is thus obtained. When a mixture of sulphur and potassium carbonate is fused, carbon dioxide is disengaged, and a brown mass is obtained on cooling, which is known as liver of sulphur. It is a mixture of potassium poly sulphide with un decomposed carbonate and potassium sulphate or hyposulphite, according to the tempera- ture and the proportions of sulphur which have been employed. With an excess of sulphur, potassium pentasulphide is obtained. Liver of sulphur dissolves in water with a brown-yellow color. Potassium pentasulphide and hyposulphite are also formed when potassium hydrate is boiled with an excess of flowers of sulphur. The filtered solution is brown. When treated with hydrochloric acid, it evolves hydrogen sulphide, and finely- divided, yellowish, pulverulent sulphur is deposited. K 2 S 5 + 2HC1 = 2KC1 + EPS + S 4 POTASSIUM CHLORIDE. KC1 This salt is found crystallized in cubes in the neighborhoi of certain fissures of Vesuvius, and in thin layers in the saline deposits at Stassfurth, Prussia, and in other localities. At Stassfurth there is found a double chloride of potassium and magnesium, KCl,MgCP + 6H 2 0. When this double salt is dissolved in hot water, the greater part of the potassium chloride is deposited on cooling while the magnesium chloride remains in solution. Potassium chloride crystallizes in cubes, but it sometimes separates in octahedra from solutions containing free potassa. It is unaltered by the air. Its taste is analogous to that of sodium chloride ; it is more soluble in water than the latter, and produces a greater depression of temperature in dissolving. 1 part of chloride of potassium dissolves in 3 parts of water at 17.5°. 100 parts of water at 0° dissolve 29.23 parts of potassium chloride and 0.2738 additional for each degree of temperature. POTASSIUM IODIDE. KT This compound is quite important on account of its use in medicine. It is obtained by adding powdered iodine to solution ood POTASSIUM NITRATE. 291 of potassium hydrate until the latter is completely neutralized. Potassium iodide and iodate are formed, the latter being pre- cipitated. The whole is evaporated to dryness, and the residue heated to redness, by which the iodate is converted into iodide. The mass is redissolved in boiling water and the solution con- centrated ; fine cubical crystals of potassium iodide are obtained on cooling. These crystals are opaque and anhydrous. They melt at a red heat without decomposition ; their taste is salty and some- what bitter. 100 parts of- water at 18° dissolve 143 parts of potassium iodide. A solution of potassium iodide dissolves iodine abundantly, assuming a dark-brown color. If nitric acid be added to a solution of potassium iodide, iodine is at once deposited and red vapors are disengaged if the solution be concentrated (page 131). This decomposition of potassium iodide takes place even in very dilute solutions. It may serve for the detection of the smallest trace of this salt if a solution of starch be previously added to the liquid ; in this case a blue color will be produced. Potassium bromide is prepared by a process similar to that which yields potassium iodide. It crystallizes in cubes which are soluble in about 1.5 parts of cold water. POTASSIUM NITEATE. KN03 This important salt, long known as nitre and saltpetre, im- pregnates the soil and sometimes effloresces upon its surface in certain regions of India, Egypt, Persia. Hungary, and Spain. In the United States, it is found in many localities, generally in caverns in limestone rock, called saltpetre caves. It is obtained by lixiviating the earthy matters containing it and evaporating the solution. It is less abundant in northern climates. It is formed wherever nitrogenized organic substances decompose in pres- ence of potassa. Thus, it exists in small quantities in the soil of cellars, in moist walls, and in the debris of demolitions. In these cases it is mixed with a certain quantity of sodium nitrate and a large excess of calcium and magnesium nitrates. Formerly such materials were lixiviated to obtain the nitrates, all of which were then converted into potassium nitrate. Nitre is also manufactured artificially by exposing to the air mixtures 292 ELEMENTS OF MODERN CHEMISTRY. of animal matters with wood-ashes and lime which are fre- quently moistened with stale urine or stable-drainings. How- ever, a great part of the potassium nitrate employed in the arts is now obtained from the natural sodium nitrate of Peru. Two processes are employed. One consists in adding the sodium nitrate to a concentrated boiling solution of potassium carbonate : sodium carbonate being less soluble than the latter, is precipitated and continues to deposit during the concentration ; it is removed, and the potassium nitrate, which is very soluble in hot water, crystal- lizes out on cooling. The second process consists in decomposing the sodium nitrate with potassium chloride. The saturated and boiling mixture of the two solutions deposits sodium chloride, which is sepa- rated, and the potassium nitrate crystallizes on cooling. Properties. — This salt crystallizes from its aqueous solution in long, six-sided prisms, terminated by six-sided pyramids. Gen- erally these crystals are grooved or striated. They belong to the right rhombic system. Their taste is cooling and slightly bitter. Potassium nitrate melts at about 350°; at a higher tem- perature it disengages oxygen and is converted into potassium nitrite, KNO 2 , which is in its turn decomposed at a red heat, leaving a mixture of oxide and peroxide of potassium. Potassium nitrate is very soluble in hot water : 100 parts of water at 0° dissolve only 13.32 parts of the salt, but at 18° they dissolve 29 parts ; at 97°, 236 parts ; and at 100°, 246 parts. The facility with which potassium nitrate parts with its oxy- gen, of which it contains nearly half its weight, renders it an energetic oxidizer of many bodies. If a small quantity of pulverized saltpetre be thrown upon glowing coals, the salt melts and decomposes, increasing the combustion at the point of contact with the fuel : it is said to deflagrate. The nitrate becomes converted into carbonate. Gunpowder is an intimate mixture of about seventy-five parts of saltpetre, fifteen of charcoal, and ten of sulphur. As is well known, the combustion of this substance is instantaneous, and gives rise to the sudden formation of gaseous products. The decomposition may be expressed geuerally by stating that the charcoal combines with the oxygen of the nitre to form carbon dioxide and carbon monoxide ; the nitrogen is liberated, and the sulphur combines with the potassium, forming potassium sulphide. As the mixture contains all of the oxygen neces- POTASSIUM SULPHATE— POTASSIUM CHLORATE. 293 sary for its own combustion, the latter can be effected in a limited and closed space. It can readily be understood that the explosive energy of the powder is due to a sudden evo- lution of gas occupying many times the volume of the pow- der, and of which the volume is still further augmented by the high temperature. POTASSIUM SULPHATE. K 2 SO* This salt is obtained as a by-product in various industrial operations. It deposits from the mother-liquors of the soda from sea-weed when these are exposed to low temperatures. It may be made by saturating with potassium carbonate the potas- sium acid sulphate which is formed in the preparation of nitric acid by the decomposition of potassium nitrate with sulphuric acid, a process which is now but little employed. It crystallizes in four-sided prisms or in double, six-sided pyramids belonging to the orthorhombic system. These crys- tals are hard, anhydrous, unaltered by the air, and melt at a red heat without decomposition. They are but slightly soluble in water and insoluble in absolute alcohol. 100 parts of water at 0° dissolve 8.36 parts, and 0.1741 part for each additional degree of heat. POTASSIUM ACID SULPHATE. |}S0* This salt may be obtained by fusing 13 parts of the neutral sulphate with 8 parts of concentrated sulphuric acid. The saline mass is dissolved in boiling w r ater, and the solution when properly concentrated deposits rhombic octahedra or tabular crystals belonging to the orthorhombic system. Potassium acid sulphate is much more soluble in water than the neutral salt ; its solution is acid. When strongly heated, it first gives up water and then sulphuric oxide, leaving a resi- due of neutral sulphate. POTASSIUM CHLORATE. KC103 This salt is formed, together with potassium chloride, by the action of chlorine upon a concentrated solution of potassium hydrate or carbonate : 6C1 + 6KOH = KCIO 3 + 5KC1 + 3H 2 25* 294 ELEMENTS OF MODERN CHEMISTRY. It is less soluble than the chloride, and is consequently de- posited in great part as the solution becomes saturated with chlorine. It is purified by several recrystallizations. In the arts, it is obtained by the action of chlorine upon a mixture of lime, potassium chloride, and water, heated in closed vessels. Chlorate and chloride of calcium are formed, and in presence of the potassium chloride, a double decomposition takes place, potassium chlorate and calcium chloride, which is very soluble, being formed. The liquid is filtered hot, and the potas- sium chlorate crystallizes out on cooling. KC1 + 3CaO + 3d 2 = KCIO 3 + 3CaCP Calcium oxide. Calcium chloride. Potassium chlorate crystallizes in colorless, rhomboidal tables. When very thin they present an iridescent reflection. It melts at 400°, and at a higher temperature is decomposed into oxygen and chloride and perchlorate of potassium, the latter of which is also decomposed when the temperature is raised still further. 2KC10 3 = KC1 + KCIO 4 + O 2 KCIO 4 = KC1 + O 4 Potassium chlorate deflagrates when thrown upon hot coals ; when mixed with sulphur, it explodes by friction or percussion ; the detonation becomes dangerous if the sulphur be replaced by phosphorus. It is not very soluble in cold water. 100 parts of water at 0° dissolve 3.3 parts, and at 24°, 8.44 parts. It is much more soluble in boiling water. POTASSIUM PERCHLORATE. KCIO* This salt is formed by the action of either heat or sulphuric acid upon potassium chlorate (page 124). It is but slightly soluble in water, requiring 65 parts at 15° for its solution. It crystallizes in anhydrous and transparent right rhombic prisms. Above 400° it decomposes into potassium chloride and oxygen. POTASSIUM CARBONATES. Potassium Neutral Carbonate, K 2 C0 3 . — This carbonate is found in commerce under the simple name potash, and is known according to its source as Russian or American potash. POTASSIUM CARBONATES. 295 It is obtained by lixiviating wood ashes ; that is, exhausting them with water, evaporating the solution to dryness, and cal- cining the residue in the air. The potash thus obtained is impure carbonate mixed with other salts of potassium, princi- pally the chloride and sulphate, and small quantities of silicate. It contains from 60 to 80 per cent, of carbonate. Potassium carbonate is now manufactured from the native chloride, Stassfurth salt, by a process similar to that which will be described for the manufacture of sodium carbonate from common salt. Pure potassium carbonate may be prepared by calcining potas- sium acid tartrate, or cream of tartar, at a red heat. A black mass is thus obtained from which water dissolves pure potas- sium carbonate, and the solution is evaporated to dryness. Neutral potassium carbonate is very soluble in water, and absorbs moisture from the air. 1 part of the anhydrous salt dissolves in 1.05 parts of water at 3°, and in 0.49 parts at 70° (Osann). The solution has a decided alkaline reaction. A very concentrated hot solution deposits rhombic octahedra containing K 2 C0 3 + 2H 2 on cooling. Potassium Acid Carbonate, KHCO 3 . — When a current of carbonic acid gas is passed into a concentrated solution of potas- sium neutral carbonate, the gas is absorbed, and crystals of potassium acid carbonate, ordinarily known as bicarbonate of potassa, are formed. It represents carbonic acid in which a single atom of hydro- gen is replaced by an atom of potassium. CO 2 + H 2 0*= H 2 C0 3 carbonic acid (hypothetical). K "I CO 2 + KHO = -n- y CO 3 potassium acid carbonate. CO 2 + K 2 = K 2 C0 3 potassium carbonate. Potassium acid carbonate readily crystallizes in oblique rhom- bic prisms. It is much less soluble in water than the neutral carbonate, and its solution disengages carbonic acid gas on boiling. Its reaction is alkaline. Characters of Potassium Salts. — The salts of potassium communicate a violet tint to flame. Their solutions are not precipitated either by hydrogen sulphide, ammonium sulphide, or sodium carbonate. Perchloric acid occasions a white precipitate of potassium perchlorate. 296 ELEMENTS OP MODERN CHEMISTRY. Platinum tetrachloride produces a yellow, crystalline precipi- tate of platinum and potassium double chloride, 2KCl.PtCl 4 . Hydrofluosilicic acid forms a white, gelatinous precipitate consisting of potassium fluosilicate. SODIUM. Na = 23 Sodium was discovered by Sir Humphry Davy in 1807. It is made by decomposing sodium carbonate with charcoal, a certain proportion of chalk being added to render the mixture infusible. The operation is conducted in large cast-iron cylin- Fm. 98. ders covered with a refractory luting to enable them to resist the high temperature required to effect the decomposition. The vapor passes into a flattened receiver in which the sodium condenses, and from which it runs into appropriate vessels (Fig. 98). sodium. 297 silvery lustre, melts at 90.6°, and distils at a red heat. It is not as avid of oxygen as potassium ; it can be melted in the air without taking fire. When thrown upon water, it melts and runs around on the surface, producing a hissing noise. The water is decomposed with disengagement of hydrogen and the formation of sodium hydrate. The reaction is analogous to that of potassium upon water, but is less energetic; fre- quently, however, it terminates by an explosion. If sodium be thrown upon hot water, or water which has been thickened with gum or starch, so that the consistence of the liquid may prevent the globule from moving rapidly, the latter becomes sufficiently heated to ignite the hydrogen evolved, which then burns with a yellow flame. The compounds of sodium are widely diffused in nature, and generally present great analogies with the corresponding potas- sium compounds. OXIDES AND HYDRATE OF SODIUM. Two oxides of sodium are known, a monoxide, Na 2 0, and a dioxide, Na 2 2 . Sodium hydrate, NaOH, is frequently employed in the lab- oratory and in the arts under the name caustic soda. It is prepared by decomposing a rather dilute, boiling solution of so- dium carbonate by milk of lime, in the manner described for the preparation of potassium hydrate (page 283). It occurs as a white solid, which attracts moisture and carbonic acid from the air, and finally becomes transformed into a dry mass of carbonate. Sodium hydrate is freely soluble in water, and is very caustic. It is known in commerce as concentrated lye. SODIUM SULPHIDE AND SULPHYDRATE. Sodium sulphide, Na 2 S, is prepared by the following pro cess: A concentrated solution of sodium hydrate is divided into two equal parts; one part is then saturated with hydrogen sulphide, sodium sulphydrate being formed. NaOH + H 2 S = NaSH + H 2 Sodium hydrate. * Sodium sulphydrate. N* 298 ELEMENTS OF MODERN CHEMISTRY. To this sulphydrate the other portion of sodium hydrate is added, and the solution is concentrated out of contact with the air. Hydrated crystals of sodium sulphide are deposited. NaSH + NaOH = H 2 + Na 2 S These crystals are rectangular prisms terminated by four- faced points. When pure, they are colorless; they are very soluble in water. SODIUM CHLORIDE. NaCl This body is common salt, or sea-salt. It is widely diffused in nature. It is found in the solid state, as rock-salt, in large deposits in many countries. Sea-water contains a large proportion of sodium chloride, and this salt also exists in a number of mineral waters, of which it forms the most abundant constituent. In France, the greater portion of the salt delivered to com- merce is obtained by the evaporation of sea-water in the salt- marshes near the ocean, and the salt-basins along the Mediter- ranean. These are extensive basins into which the water is led from the sea, and where it forms a shallow layer, which is continually swept by the summer winds. It thus becomes con- centrated, and the concentration is favored by the water being continually kept in motion from one basin to another, until it arrives in the areas where the salt is deposited. The mother- liquors, from which the sodium chloride is separated, and which are still saturated with that salt, contain, in addition, magne- sium sulphate and salts of potassium. By cooling them to a low temperature sodium sulphate is obtained, being formed by a double decomposition between the sodium chloride and the magnesium sulphate. The new mother-liquor then deposits, first, potassium and magnesium double sulphate, and after- wards, magnesium and potassium double chloride (Balard). It was in the latter of these liquors that Balard discovered bro- mine in 1826. Sodium chloride is also obtained by the evaporation of the waters of salt springs. The operation is conducted in large sheet-iron boilers ; the salt crystallizes from the hot liquid, and a double sulphate of calcium and sodium, which is but slightly soluble, deposits in the basins in the course of time. SODIUM SULPHATE. 299 Sodium chloride crystallizes from its aqueous solution in cubes. The crystals are generally small, and a great number of them frequently become agglomer- ated in symmetrical hopper-like masses (Fig. 99). These crystals are anhy- drous, but contain a small quantity of interposed water ; when heated they decrepitate, because this water is vola- tilized and suddenly separates the crys- Fig. tals. Rock-salt is sometimes found in transparent cubes, sometimes in octahedra and intermediate forms. Sodium chloride fuses at a red heat and solidifies to a crystalline mass on cooling. It volatilizes at a white heat. It is very soluble in water, and its solubility does not increase with the temperature. According to Gay-Lussac, 1 part of common salt dissolves in 2.78 parts of water at 14° a u a 2.7 " " 60° u u a 2.48 " " 109.7° The saturated solution boils at 109.7° ; its density at 8° is 1.205. Sodium chloride is insoluble in absolute alcohol. SODIUM SULPHATE. Na 2 SO This salt is obtained in the arts by decomposing common salt with sulphuric acid (page 117). This' operation, which constitutes the first step in the manu- facture of sodium carbonate, is conducted in a reverberatory furnace, connected with a suitable apparatus for the condensa- tion of the hydrochloric acid which is disengaged. Sodium acid sulphate is first formed, and at a higher temperature this reacts upon another molecule of sodium chloride. ^JSO 4 + NaCl = Na 2 SO* -f HC1 Sodium acid sulphate. Sodium sulphate. Sodium sulphate is now extensively produced by subjecting the mother-liquors from the manufacture of salt from sea-water to intense cold. It crystallizes from water in four-sided, oblique rhombic prisms, containing 10 molecules of water of crystallization; 300 ELEMENTS OP MODERN CHEMISTRY. these crystals effloresce in the air. They possess a bitter, salty, and disagreeable taste. They are very soluble in water, and the temperature of their maximum solubility is 33°. Accord- ing to Gay-Lussac, 100 parts of water at 0° dissolve 12 parts of sodium sulphate. <( u 130 u 43 a n « « 25° " 100 " " « *< 33° " 332.6 " " « « 50° " 263 " u When the solution saturated at 33° is heated, it deposits an- hydrous sodium sulphate in orthorhombic octahedra, analogous to the anhydrous sodium sulphate found in nature (thenar dite). Sodium Acid Sulphate, ^ } SO 4 .— This salt may be ob- tained by dissolving in water the requisite proportions of so- dium neutral sulphate and sulphuric acid. On cooling the saturated solution, oblique rhombic prisms are obtained, which, according to Mitscherlich, contain two molecules of water of crystallization. These crystals are very soluble in water, and have an acid taste. Alcohol decomposes them into sulphuric acid, which dissolves, and neutral sulphate, which precipitates. SODIUM CARBONATE. Na 2 C03 This important salt, known also as soda and sal-soda, is manufactured on an immense scale in the arts. It is used in the manufacture of soap and glass, for washing, and many other purposes. It was formerly obtained from the ashes of fuci, algae, and other sea-plants which furnished Alicant soda. It is now most generally prepared from sodium chloride, and the process, which is due to Le Blanc, consists of three distinct operations : 1st, the transformation of the sodium chloride into sulphate by sulphuric acid ; 2d, the conversion of the sul- phate into carbonate by calcination with a mixture of chalk and coal ; 3d, lixiviation of the calcined mass and evaporation of the solution. Only the latter two operations need be de- scribed here : they are conducted in reverberatory furnaces, of which the doubly-arched roofs are licked by the flame of the combustible (Fig. 100). SODIUM CARBONATE. 301 A mixture of 1000 parts of sodium sulphate, 1040 parts of chalk, and 580 parts of coal, is first introduced into compart- ment B of the furnace, where it is dried. It is then transferred to compartment A, where the temperature is very elevated, and where the sodium sulphate is reduced to sulphide by the Fig. 100. coal. The sodium sulphide and chalk react upon each other, forming sodium carbonate and calcium sulphide (Kolb). The results of the reaction may be expressed by the follow- ing equation : Na 2 SO + CaCO 3 + C* = Xa 2 C0 3 + CaS + 4CO. There are, however, certain secondary reactions which take place at the same time ; thus, a certain quantity of sodium oxide is formed by the action of the coal upon the carbonate. Na 2 C0 3 + C = 2CO + Na 2 "When the incandescent mass has become pasty, it is removed from the furnace, reduced to powder, and thoroughly lixiviated. The water dissolves the sodium carbonate, and leaves the in- soluble calcium sulphide, which remains mixed with the lime produced by the decomposition of the excess of chalk employed (Gossage, Scheurer-Kestner). The solutions are concentrated in the boiler D. heated by the waste heat from the soda fur- nace. Finally, they are drawn off into the compartment C, where they are evaporated to dryness. The sal-soda of com- merce is thus obtained. When the properly-concentrated solu- tion is allowed to cool, the crystallized soda of commerce is deposited. Another process, proposed by Schloesing and Rolland, is also used for the fabrication of sodium carbonate. 26 302 ELEMENTS OF MODERN CHEMISTRY. It depends upon the double decomposition which takes place between ammonium acid carbonate and sodium chloride in concentrated aqueous solution. Nad + (NH 4 )HC0 3 = NH 4 C1 + NaHCO 3 The sodium acid carbonate, which is but slightly soluble, is precipitated ; it is collected and converted into the neutral car- bonate by the action of heat. 2NaHC0 3 = Na 2 C0 3 + CO 2 + H 2 It thus loses half of its carbonic acid, which is utilized for the preparation of a new quantity of ammonium acid carbonate. The other portion of the carbonic acid necessary for this oper- ation is produced by the calcination of lime-stone (calcium car- bonate), which at the same time yields the lime necessary for the liberation of the ammonia contained in the mother-liquor in the form of ammonium chloride. A considerable quantity of sodium carbonate is also manufac- tured from cryolite, which is a double fluoride of sodium and aluminium, and of which large deposits exist in Greenland. The mineral is calcined with lime, calcium fluoride and alunii- nate of soda being formed. APFF,6NaFl + 6CaO = 6CaFP + Al 2 3 ,3Na 2 Cryolite. Calcium fluoride. Aluminate of soda. The latter compound is dissolved out by water and decom- posed by carbonic acid gas, aluminium oxide being precipitated and sodium carbonate remaining in solution. Sodium carbonate crystallizes in oblique rhombic prisms, containing 10 molecules of water of crystallization. When heated, they fuse in this water of crystallization, which they then abandon ; they also lose it by efflorescence when exposed to the air. Sodium carbonate is very soluble in water, and the solution has a strongly alkaline reaction. According to Poggiale, 100 parts of water at 0° dissolve 7.08 parts of sodium carbonate. 10° " 16.06 " " 20° " 25.93 « " 25° " 30.83 " " 30° " 35.90 " " 104.6° " 48.5 « " The saturated solution boils at 104.6°. Sodium carbonate is insoluble in alcohol. SODIUM BORATE. 303 Sodium Acid Carbonate, XaHCO 3 . — When carbonic acid gas is passed into a solution of sodium carbonate or over crystals of that salt, the gas is absorbed and sodium acid car- bonate, commonly called bicarbonate of soda, is formed. This salt crystallizes in oblique, four-sided prisms, shortened into the form of tables. Its taste is salty and slightly alkaline. It is less soluble in water than the neutral carbonate. It restores the blue color to reddmed litmus; its solution does not pre- cipitate that of magnesium sulphate. When boiled, it loses carbonic acid, neutral carbonate being formed. PHOSPHATES OF SODIUM. There are three phosphates of sodium derived from ordinary or otho-phosphoric acid. H) Na} Na) Nal H [ PO* H I PO 4 + 2H20 Xa [ PO± + 12H20 Xa \ PO± + 12H20 Hj HJ Hj XaJ Phosphoric Monosodium Disodium phosphate. Trisodium phosphate, acid. phosphate. Monosodium phosphate is acid, the disodium is neutral, and the trisodium has an alkaline reaction. Disodium phosphate, or, as it is frequently called, common or neutral phosphate of soda, is the most important. It is prepared by neutralizing the cal- cium acid phosphate, obtained by digesting bone-dust with dilute sulphuric acid and filtering, with sodium carbonate. Tricalcium phosphate is precipitated, and disodium phosphate remains in solution. By evaporation of the filtered liquid, the salt may be obtained in voluminous, transparent, oblique rhombic prisms, containing 12 molecules of water of crystallization. Mono- sodium phosphate exists in urine, and is the cause of the normal acidity of that excretion. SODIUM BORATE, OR BORAX. . Na 2 Bo 4 07 This salt corresponds to tetraboric acid, containing 2Bo 2 3 + H 2 = H 2 Bo 4 7 . It results from the action of one molecule of sodium oxide upon two molecules of boric oxide. 2(Bo 2 3 ) + Na 2 = Na 2 Bo 4 7 It crystallizes with either 10 or 5 molecules of water. Borax was formerly obtained from Asia, where it exists in solution in the waters of certain lakes. By the evaporation 304 ELEMENTS OF MODERN CHEMISTRY. of these waters a product known as tinkal was obtained ; this is natural borax; it crystallizes in oblique rhombic prisms. Borax is found in abundance in certain lakes in California. A great part of the borax of commerce is obtained by satu- rating the boric acid of Tuscany with sodium carbonate, and causing the solution to crystallize below 56°. If the boiling solution be very concentrated, it deposits between 79 and 56° crystals which are octahedral and contain only 5 molecules of water of crystallization. The two varieties of borax, the prismatic and the octahedral, differ then in their proportions of water of crystallization. When borax is heated, it melts in its own water, swells up and becomes dry, and then undergoes igneous fusion. Melted borax dissolves a great number of oxides and forms with them variously-colored glasses on cooling. It dissolves in 12 parts of cold and 2 parts of boiling water ; the solution has a faint alkaline reaction. Characters of Sodium Salts. — Sodium salts are not pre- cipitated from their solutions by either hydrogen sulphide, ammonium sulphide, sodium carbonate, or platinic chloride. Hydrofluosilicic acid forms with them a white precipitate. A solution of potassium antimonate produces a white precipitate of sodium antimonate (Fremy). Sodium salts impart a yellow color to flames. A small quantity of alcohol may be ignited in a saucer and will burn with an almost colorless flame, but the introduction of a small quantity of sodium hydrate, chloride, or any other sodium compound, at once colors the flame bright yellow. This character is very sensitive, and the smallest trace of sodium may thus be recognized by introducing a platinum wire, dipped into the substance to be tested, into the colorless flame of the blow-pipe or of a Bunsen burner. LITHIUM, Li = 7 In 1817, Arfvedson, a Swedish chemist, discovered a new alkali, lithia, which is the hydrate of lithium, LiOH, analogous to potassium hydrate, KOH. To this hydrate corresponds an oxide, Li 2 0, and a chloride, LiCl. Bunsen was the first to ob- tain the metal lithium, which he prepared by electrolysis of the CESIUM AND RUBIDIUM. 305 fused chloride. It is a silvery-white metal, but its surface rap- idly tarnishes in the air. It is the lightest of the solid ele- ments, its density being between 0.578 and 0.589. It melts at 180°. It is less oxidizable than either sodium or potassium. When heated above its point of fusion in the air or in oxygen, it burns with a brilliant white flame. It decomposes water at ordinary temperatures, but without melting like sodium. The salts of lithium are soluble in water, but the carbonate and phosphate only slightly so. There exists also a double phosphate of sodium and lithium, which is but slightly soluble. The salts of lithium communicate a red color to the flame of alcohol or of the Bunsen burner. The compounds of lithium are generally prepared from the native silicate known as lepidolite. CLESIUM AND RUBIDIUM. SPECTRUM ANALYSIS. Cassium and rubidium are two alkaline metals discovered by Kirchhoff and Bunsen in 1860-61, by the aid of a new method of analysis. This method consists in the examination of spectra ; hence the name spectrum analysis. The solar spectrum formed upon a screen which intercepts a beam of solar light refracted by passage through a prism, con- sists of a series of colored bands. The different simple rays of which white light is composed are unequally refracted by the prism, and separate from each other on their emergence. The violet rays, which are farthest turned from their primitive direction, form the most deviated extremity of the spectrum. The red rays, which are the least refracted, form the least de- viated extremity. The visible spectrum of solar light presents not only a succession of variously-colored bands ; when it is closely examined by the aid of magnifying instruments, it is found that the succession is not continuous, but that the lumi- nous bands are traversed by dark lines. These lines, which were discovered by Wollaston and studied by Fraunhofer, are very numerous, and are irregularly distributed throughout the spectrum, from the red to the violet, but each one of them occupies a definite position, and for the principal lines that position has been determined by exact measurements. Fraun- 26* 306 ELEMENTS OF MODERN CHEMISTRY. hofer designated them by the letters A, B, C, D, E, F, Gr, H. The D line is the most distinct of all : its place is in the yel- low. Other lights, the stars, for example, give similar discon tinuous spectra. On the contrary, an incandescent platinum wire, or any other luminous source which contains no volatile matter, gives a continuous spectrum. Very interesting facts are observed when the sources of light are flames into which the vapors of volatile substances, par- ticularly the metallic salts, are introduced. The spectra of such flames are formed exclusively of brilliant lines (see plate). If a platinum wire which has been dipped into a solution of sodium chloride be introduced into the colorless flame of a Bunsen burner, the flame will assume a yellow color, and will give a visible spectrum, but one which is very incomplete, since it consists of a single yellow line. It has been found that this line exactly coincides with the dark line D, existing in the yellow of the solar spectrum. This line characterizes sodium in all of its compounds : it is the spectrum of sodium. In the same manner, a flame into which a compound of potas- sium, lithium, barium, calcium, or other volatile metal is intro- duced, will give for each metal a particular spectrum formed of variously-colored lines. Each is perfectly characterized by the number, color, and position of the lines. Barium give s the most numerous and the widest lines ; other metals give more compli- cated spectra. That of iron is composed of 70 brilliant lines. Kirchhoff and Bunsen, who discovered these facts, made a happy application of them to analysis. To detect the presence of a metal in a compound or even in a mixture, a small portion of the substance is introduced into a colorless gas flame, and the spectrum then given by the flame is observed by the aid of an instrument called a spectroscope. The light to be examined is caused to pass through a narrow rectangular slit before falling on the prism. The image of the slit is then refracted to its own peculiar place in the spectrum. The method is so sensitive that xwu\ To o" of a milligramme of sodium chloride will render the yellow sodium line distinctly visible. The discovery of two new metals, caesium and rubi- dium, crowned the brilliant researches of KirchhofF and Bunsen. Since then, three other new metals have been discovered by the aid of spectrum analysis : thallium, which gives a green line, indium, which gives an indigo-blue line, and gallium, which gives two violet lines very close together. Thallium was SILVER. 307 discovered by Crookes and Lamy, indium by Reich and Richter, and gallium, the discovery of which was most remarkable of all, by Lecoq de Boisbaudran. SILVER. Ag(Argentum) = 108 Natural State. — Silver is found native and in combination in many minerals. Among these are the sulphide, the sulph- antimonides and sulpharsenides, the antimonide, chloride, bro- mide, iodide, selenide, telluride, and lastly an amalgam of silver. It is found in small proportions in many galenas and copper pyrites. Treatment of Silver Ores. — The silver is extracted from galena by first reducing the lead, and then submitting the argentiferous lead obtained to cupellation (page 359). Silver ores free from lead are treated by a peculiar process called amalgamation , since it is based upon the employment of metallic mercury which dissolves silver; the amalgam of silver formed is decomposed by heat. Several processes are employed for the chlorination and amalgamation of silver. Freiberg Amalgamation Process. — The Freiberg silver ore is poor, containing only two or three thousandths of silver in the form of sulphide, disseminated through iron and copper pyrites. The ore is pulverized, mixed with one-tenth its weight of common salt, and roasted in a reverberatory furnace. The sulphides are oxi- dized, with . disengagement of sul- phurous acid gas and formation of sulphates. The latter react upon the sodium chloride, forming sodium sulphate and metallic chlorides : all of the silver is thus converted into chloride. The product of the roast- ing is reduced to powder, washed, and introduced, together with water and scrap-iron, into amal- gamation barrels, which are rotated by water-power (Fig. 101). When the mixture has become homogeneous, mercury is added 308 ELEMENTS OF MODERN CHEMISTRY. Fig. 102. and dissolves the silver set free by the action of the iron upon the silver chloride ; it also dissolves a small quantity of copper formed by the reduction of cuprous chloride present. After the barrels have been rotated for some hours, the amalgam is collected and compressed in canvas bags, through which the excess of mercury, alloyed with a very small quantity *of foreign metals, passes, while a pasty amalgam of silver and copper remains in the bags. This amalgam is put into iron cups, bb (Fig. 102), set upon an iron rod on a tripod base, a, standing in a vessel of water. The whole is cov- ered with a bell-shaped iron hood which dips into the water, and the upper part of. which is surrounded by burning coals. The mercury volatilizes and condenses in the cold water, and an alloy of silver and copper, containing about 28 per cent, of the latter metal, as well as small quantities of lead, antimony, etc., remains in the cups. It is purified either by cupellation or by refining. Oupeilation consists in melting the impure silver with lead, as will be described on page 335. In refining, the silver i* melted in a hemispherical iron vessel lined with a thick layer of marl and wood ashes. It is a porous cupel, which absorbs the oxides formed by the action of the air upon the lead and copper alloyed with the silver ; the latter remains in the cupel at the close of the operation in a pure state. Mexican Amalgamation Process. — American silver ore con- sists of sulpharsenide and sulphantimonide of silver, mixed with silver chloride and native silver, the whole being disseminated in silica, calcium carbonate, and ferric oxide. In Mexico, the following primitive process is still used. The finely-pulverized ore is mixed with two per cent, of common salt and thrown into circular areas paved with flag-stones, where it is rendered homogeneous by being trodden for several hours by mules. About one per cent, of copper pyrites which has been roasted in the air and contains cupric sulphate is then added. The latter salt reacts with the sodium chloride, forming sodium sul- phate and cupric chloride, which latter decomposes the silver sulphide, forming silver chloride and cupric sulphide. Mer- SILVER. 309 eury is then added and reduces the silver chloride, with for- mation of chloride of mercury and metallic silver. During the whole time the mass is continually trodden by the mules, and the mercury comes in contact with the disseminated silver : the amalgam formed solidifies in about a fortnight. A second and finally a third addition of mercury is then made until 7 or 8 parts of that metal have been employed for one part of silver to be extracted. After a few months, the operation is termi- nated, and the mass is washed with large quantities of water to remove the earthy and salty matters. The amalgam remains, and is heated in order to extract the silver. American Process. — The above method of extraction is too slow to be employed for the vast quantities of silver ore that are mined on the Pacific Slope. The ore is there crushed and roasted with sodium chloride and a small proportion of cupric sulphate, in furnaces of a peculiar construction. By this meaos all of the silver is converted into chloride. The mass is made into a pulp with water and agitated with mercury in large tanks or vats. The silver chloride is reduced as before, and the amalgam obtained is first squeezed out and afterwards heated in iron retorts to expel the mercury. Properties. — Silver is the whitest and most brilliant of all the ordinary metals. Next to gold, it is the most malleable and the most ductile. Its density is 10.5. It melts towards 1000°, and when fused has the curious property of dissolving oxygen, of which it absorbs 22 times its volume. On solidifying, it again disengages the gas ; this phe- nomenon, which occasionally causes the projection of portions of silver, is called spitting. Silver volatilizes at the high tem- perature of the oxyhydrogen blow-pipe. It is unaltered by the air. It absorbs ozone, being converted into the dioxide Ag 2 2 . It combines with hydrogen dioxide, forming argent ous and argentic hydrates (Weltzien). It decomposes concentrated solution of hydriodic acid, dis- engaging hydrogen and forming silver iodide (Deville). Hy- drochloric acid only attacks it superficially. Hydrogen sulphide blackens it, forming a pellicle of silver sulphide. Its best sol- vent is nitric acid which attacks it in the cold, yielding silver nitrate and disengaging red vapors. The alkalies have no action upon silver ; for this reason, silver vessels are used for fusing potassium hydrate and concentrating its solution. 310 ELEMENTS OF MODERN CHEMISTRY. SILVER OXIDE. Ag20 The only important oxide of silver is the monoxide, which is precipitated in the anhydrous state when potassium hydrate, free from chloride, is added to a solution of silver nitrate. It forms an olive-brown, flocculent deposit which yields a brown powder on drying. Silver oxide is readily decomposed by heat into silver and oxygen. It is reduced by hydrogen at a temperature below 100°. When recently precipitated, it is slightly soluble in water. It is an energetic base, perfectly neutralizing the acids, and displacing cupric oxide from the cupric salts. When oxide of silver is digested with ammonia it is con- verted into a very explosive, black powder, known as fulmi- nating silver. Its composition is not yet well known. SILVER SULPHIDE. Ag 2 S To the oxide of silver corresponds the sulphide Ag 2 S, which occurs native, crystallized in regular octahedra, ordinarily mod- ified by facettes. It is soft and can be scratched by the finger- nail. Silver and sulphur also combine readily by the aid of heat. SILVER CHLORIDE. AgCl This body is found native and is known to mineralogists as horn-silver. It is sometimes found crystallized in cubes and octahedra. It is formed directly when silver is heated in chlo- rine gas, and is prepared by double decomposition by adding hydrochloric acid or a solution of sodium chloride to solution of nitrate of silver. A white, curdy precipitate is thus obtained, which assumes a violet tint when exposed to the action of light. The change of color is due to partial decomposition. Silver chloride melts at about 260°, and solidifies on cooling to a gray, horn-like mass that can be cut with a knife. If recently precipitated and moist silver chloride be placed upon a sheet of zinc, in a short time a dark color will appear on the borders of the chloride, and the whole of that body will SILVER IODIDE — SILVER NITRATE. 311 soon be converted into a dark-gray powder of finely-divided silver. Zinc chloride is at the same time formed. This reaction takes place much more rapidly if the silver chloride be moistened with hydrochloric acid. In this case the reduction is effected by nascent hydrogen produced by the action of the hydrochloric acid on the zinc. When silver chloride is fused with the alkaline hydrates or carbonates, it is reduced to metallic silver : oxygen is disen- gaged, and an alkaline chloride is formed. Recently-precipitated silver chloride dissolves readily in aque- ous ammonia. When dry, it absorbs ammonia gas abundantly, and Faraday employed this compound for the preparation of liquid ammonia. Silver chloride dissolves also in solutions of the alkaline hyposulphites. SILVER IODIDE. Agl Silver iodide is obtained as a yellow precipitate by adding potassium iodide to a solution of silver nitrate. It blackens on exposure to light. It is but very slightly soluble in ammo- nia, a property which distinguishes it from silver chloride. SILVER NITRATE. AgNO 3 This salt is prepared by dissolving silver in nitric acid. If the metal be pure, a colorless solution is obtained which after concentration and cooling deposits large, colorless tables of an- hydrous silver nitrate. If silver coin be employed, the solution will be blue, containing, independently of silver nitrate, cupric nitrate. The latter may be removed by evaporating the residue to dryness and carefully heating it, so that the salt may remain fused for some time. The cupric nitrate is decomposed, while the silver nitrate remains mixed with cupric oxide, from which it may be freed by solution and filtration. Fused silver nitrate constitutes lunar caustic. This salt dissolves in its own weight of cold, and in half its weight of boiling water. The solution is neutral to test-paper. When exposed to the air, it blackens, as do also the crystals and the fused salt, by reason of a partial reduction due to the organic matters suspended in the air. 312 ELEMENTS OF MODERN CHEMISTRY. It blackens the skin from a similar cause. Hydrogen slowly reduces the solution of silver nitrate with deposition of metallic silver (Beketoff). Characters of Silver Salts. — Solutions of the silver salts are precipitated black by hydrogen sulphide and by ammonium sulphide. Potassium hydrate forms an olive-green precipitate of silver oxide, insoluble in excess. Ammonia does not precipitate them. Hydrochloric acid and the soluble chlorides form a white precipitate of silver" chloride, insoluble in either cold or boiling nitric acid, but soluble in ammonia. Potassium iodide gives a yellow precipitate, almost insoluble in ammonia. Silvering. — This operation consists in covering the common metals or glass with a coating of silver more or less thick. The metals are silvered by either amalgamation or galvanic deposition. In the latter and preferable operation, a solution of the double cyanide of silver and potassium is generally used. Mirrors and glass articles in general are silvered by the re- duction of a silver salt by aldehyde, glucose, or tartaric acid. The following receipt is given by Liebig: a solution of 10 grammes of silver "nitrate is supersaturated with ammonia and rendered strongly alkaline by caustic soda. The volume of the liquid should be 1450 c.c. Another solution is prepared by dissolving 1 part of milk sugar in 10 parts of water. The latter solution is mixed with its own volume of the first solu- tion, and the glass to be silvered is washed with alcohol and immersed in the liquid. The reduction of the silver salt begins immediately, and does not require the aid of heat. The experiment may easily be made in a glass flask, the interior of which will be uniformly silvered. Assaying of Silver. — This name is applied to the methods which serve for the analysis of alloys of silver and copper, such as coin, medals, silverware, and jewelry. The assay may be conducted by the dry way or by the wet way. The dry assay consists in the operation called cupellation (Fig. 118). A certain quantity of metallic lead is melted in a cupel of bone-ash in a reverberatory furnace, and a weighed quantity of the alloy of silver and copper, carefully wrapped in a small piece of paper, is placed upon the fused metal. The silver dissolves in the melted lead, and a ternary alloy is thus obtained which is exposed to the action of air at a red heat. ASSAYING OF SILVER. 313 Under these conditions, the lead and copper become oxidized ; the oxide of lead fuses, and the melted litharge, which should be in great excess in proportion to the oxide of copper, dis- solves the latter, and with it is absorbed by the porous cupel. The phenomenon of brightening (page 336) indicates the ter- mination of the process. Fig. 103. The wet assay, invented by G-ay-Lussac, consists in adding to a solution in nitric acid of a known weight of the alloy of silver and copper, a titered solution of sodium chloride, that is. a solution containing an exactly known weight of salt in one litre of water. This solution is cautiously added until it no longer precipitates silver chloride, and the quantity of silver present is calculated by the volume of the titered solution that has been required to completely precipitate the silver in the form of chloride. As the latter readily deposits from a liquid that is carefully agitated, it is easy to catch the termination of the operation, that is, the precise moment when all of the silver is precipitated and the addition of the titered liquid must be arrested. o 27 314 ELEMENTS OF MODERN CHEMISTRY. Process. — Two titered solutions are used to precipitate the silver : 1st, a normal solution, containing 0.5417 gramme of sodium chloride per decilitre, a quantity sufficient to precipitate one gramme of silver ; 2d, a decinormal solution, that is, one containing the same quantity of sodium chloride per litre, so that 1 c.c. of this liquid will precipitate one milligramme of silver. To analyze an alloy of silver, a coin, for example, such a quantity is weighed as would contain one gramme of silver, if the proportion of silver were a little less than the extreme limit allowed. If the alloy ought to contain 900 thousandths of pure silver, with a tolerance of 2 thousandths, it would be rejected should it contain only 897 thousandths. We suppose, however, that the latter is its quality, and weigh a quantity of the alloy which would then contain one gramme of pure silver, that is, 1.1148 grammes. This alloy is dissolved in nitric acid, and one decilitre of the normal solu- tion is added. All of the silver should not be precipitated, for the standard of the alloy should be above 897. This is deter- mined by adding to the clarified liquid one or more cubic cen- timetres of the decinormal solution, until the liquid ceases to be troubled by a fresh addition. As each cubic centimetre of this solution corresponds to one milligramme of silver, we must add to the gramme of silver at first precipitated as many milligrammes as we have added cubic centimetres of the deci- normal solution, the last cubic centimetre added counting for only half a milligramme. Knowing the quantity of pure silver contained in 1.1148 grammes of the alloy analyzed, the standard of the latter is determined by a simple calculation. CALCIUM. Ca = 40 Lime, which is universally known, is the oxide of a metal called calcium. According to Lies-Bodard and Jobin, calcium may be obtained by decomposing calcium iodide with sodium in an iron crucible. Matthiessen obtained it by decomposing fused calcium chloride by the voltaic current. Calcium has a yellow color when freshly filed, but it tarnishes rapidly in moist air and becomes covered with a grayish layer of hydrate. When heated upon platinum-foil, it takes fire and OXIDE AND HYDRATE OF CALCIUM. 315 burns with a dazzling flame. It decomposes water at ordinary temperatures. OXIDE AND HYDRATE OF CALCIUM. Lime, or calcium oxide, CaO. is obtained by calcining the carbonate in peculiar furnaces, which are called lime-kilns. It occurs as large, compact, and hard grayish masses, which con- stitute quick-lime. It is infusible, even at the highest temperatures. When exposed to the air, it attracts moisture and carbonic acid, aug- ments in volume, and is finally converted into a white powder. a mixture of calcium hydrate and carbonate. When lime is sprinkled with water, it absorbs the liquid without giving rise to any particular phenomenon ; but in a little while, the pieces saturated with water become hot. give off steam, and then they split and increase in volume. If enough water be used, the quick-lime will be converted into a white powder, which is called slaked lime; it is calcium hydrate. CaO + H 2 = Ca0 2 H 2 = Ca(OH) 2 When slaked lime is suspended in water, a white, creamy liquid is obtained that is called milk of lime. If this be fil- tered or allowed to settle, the clear, limpid liquid resulting will have an alkaline reaction, for it contains a small quantity of calcium hydrate in solution : it is lime-water. Calcium hydrate is more soluble in cold than in hot water. Employment of Lime in Constructions. — Lime is largely employed for building purposes in both ordinary and submarine constructions. The limestone which is used for the preparation of lime is rarely pure, and consequently the product of its cal- cination presents different qualities, according to the propor- tions of foreign matters which remain in the lime, and which consist of a small quantity of magnesia, oxide of iron, and especially clay. Fat limes are those produced by the calcina- tion of almost pure limestones; they develop much heat, and swell up very much on slaking. Such lime forms an unctuous and binding paste with water, and forms ordinary mortar when mixed with sand. Impure limestones yield lean lime, contain- ing magnesia, oxide of iron, and clay. It is gray, and develops but little heat and increases but slightly in volume on slaking. The calcination of limestone containing from 10 to 30 per cent. 316 ELEMENTS OF MODERN CHEMISTRY. of clay produces hydraulic lime. Such lime sets under water, that is, the mortar solidifies after a few days, and becomes very hard, even when immersed in water. On account of this curious property it is used in submarine constructions. Such lime is yellow ; slaking it produces but little heat, and scarcely any in- crease in volume. The hydraulic mortar formed by its mix- ture with sand will harden under water. Mortars possessing this property may also be prepared by mixing lime with baked argillaceous materials, such as powdered tiles, pottery, bricks, etc. Certain argillaceous rocks of volcanic origin, the pozzolana so abundant near Vesuvius, for example, yield an excellent hydraulic lime when mixed with fat lime. Cement is a variety of lime resulting from the calcination of limestones containing from 40 to 50 per cent, of slate. When mixed with water, such cement sets in a few minutes in a solid mass like plaster. Vicat has shown that the different varieties of hydraulic lime and cement can be prepared by properly calcining carbonate of lime, or chalk, with various proportions of clay. According to him, ordinary mortar sets because the lime gradually absorbs carbonic acid gas from the air, forming a carbonate which hardens and binds together the grains of sand. The hardening of hydraulic lime and mortar is due to another cause : the clay which they contain in the anhydrous state tends to become hydrated and to form a double silicate of calcium and aluminium, or a silicate and aluminate of calcium, insoluble compounds, which become very coherent on contact with water. CALCIUM CHLORIDE. CaCl 2 This salt is prepared by dissolving white marble or chalk in hydrochloric acid. When the solution is concentrated it deposits large, six-sided prisms, containing 6 molecules of water of crys- tallization. They are very deliquescent and produce a depres- sion of temperature when they are dissolved in water. If they be mixed with their own weight of snow or powdered ice, a cold of — 45° may be produced. When they are heated, they melt in their water of crystalliza- tion, of which they lose 4 molecules at 200°, and the remainder at a red heat ; at the latter point the mass enters into igneous fusion. On cooling, the fused calcium chloride solidifies to a CALCIUM NITRATE — CALCIUM CARBONATE. 317 white, crystalline mass, in which form it is ordinarily employed for the desiccation of gases. Calcium chloride dissolves readily in alcohol. CALCIUM NITRATE. Ca(NOV 2 + 4H 2 This salt is formed naturally in the neighborhood of dwell- ings, in the soils of cellars, and in damp walls. It is contained in what are known as saltpetre materials ; it exists in certain spring and well waters. It may be made by saturating nitric acid with calcium carbonate. It is very soluble in water and in alcohol. It crystallizes with difficulty in six-sided, oblique rhombic prisms, which contain -I molecules of water of crys- tallization : they are deliquescent. CALCIUM CARBONATE. (CARBONATE OF LIME.) CaCO 3 Calcium carbonate is found in great abundance in nature, and under different forms. It exists crystallized as Iceland spar and aragonite ; the former crystallizes in colorless, trans- parent, and doubly refracting rhoinbohedra ; the latter in right rectangular prisms. Marble, the various limestones, and chalk, constitute other varieties of natural calcium carbonate. Pure water dissolves but feeble traces of this salt ; water charged with carbonic acid dissolves a larger quantity, converting it into dicarbonate. It is in this state that it is contained in hard waters. Calcium carbonate may be prepared by double decomposition between solutions of sodium carbonate and calcium chloride. When heated to bright redness, it is completely decomposed into lime and carbonic anhydride. 27* 318 ELEMENTS OF MODERN CHEMISTRY. CALCIUM SULPHATE. CaSO* This salt exists in two states in nature : anhydrous, it con- stitutes the anhydrite of mineralogists ; combined with two molecules of water of crystallization, it forms gypsum or plas- ter stone. Gypsum sometimes occurs in lance-head-shaped crystals, grouped together ; they are divisible into thin, trans- parent layers, easily scratched by the finger-nail. Certain varieties of gypsum constitute alabaster. All the forms of hydrated calcium sulphate contain 21 per cent, of water. AVhen heated to 80° in the air, or to 115° in closed vessels, the sulphate, CaSO 4 -f- 2 IPO, abandons its water of crystalli- zation and is converted into the anhydrous sulphate. Between 120 and 130°, this dehydration is rapid and complete. It is operated on the large scale in plaster furnaces. In this state calcium sulphate will readily recombine with its water of crystallization. If the plaster be calcined at too high a tem- perature it will not again become hydrated. If powdered plaster of Paris be mixed with enough water to form a creamy liquid, it may be poured into a mould, and in a few minutes will harden to a compact mass, completely filling every cavity of the mould. In becoming hydrated, the particles of calcium sulphate assume the crystalline form and increase in volume. These properties render plaster of Paris valuable in building operations. It is also employed to a large extent in agriculture. Calcium sulphate is but slightly soluble in water. 1000 parts of boiling water dissolve a little more than 2 parts of the salt; at 35° they dissolve 2.64 parts; at 20°, 2.05 parts. CHLORINATED LIME. (BLEACHING-POWDER.) This substance is largely employed in the arts under the name chloride of lime, and is obtained by exposing well-slaked lime to the action of chlorine. Its constitution is not perfectly understood; it was long regarded as a mixture of calcium tie . 3d CHLORINATED LIME. 319 chloride and calcium hypochlorite, CaCl 2 -f Ca(ClO) 2 , but re- cent researches have shown that it does not contain calcium hypochlorite already formed. The formation of the alkaline hypochlorites by the action of chlorine on a solution of an alkaline hydrate is explained on page 123. With the hydrates of diatomic metals like calcium the action is more complicated, and is probably expressed by the equation Ca(OH) 2 + CP = Ca(OCl)Cl + H 2 Its manufacture is conducted by passing a current of chlorine over slaked lime placed in layers upon shelves arranged in the walls of masonry chambers (Fig. 104). The product always contains a certain proportion of lime which cannot possibly be chlorinated. Fig. 104. Chlorinated lime is an energetic bleaching agent ; under the influence of acids it is decomposed, chlorine being set free. A solution of the compound is decomposed by the more feeble acids, even by carbonic acid gas, and decomposes spontaneously in a short time into calcium chloride and calcium hypochlorite. 320 ELEMENTS OF MODERN CHEMISTRY. Inasmuch as the substance is a mixture, and not a definite compound, its reactions may be interpreted in several different manners. It always contains water, calcium hydrate and a proportion of calcium chloride, and its active principle is probably expressed by one, or perhaps both, of the following formulae : Ca pb = pb tetratomic in a series of compounds in which two atoms com- bined together form a hexatomic couple (R-R) vi , as has been indicated on page 283. The chlorides of this series conse- quently present the general formula R 2 C1 6 , while the oxides are represented by R 2 3 . In addition, iron, nickel, cobalt, and manganese form series of compouuds in which the metal appears to be diatomic ; as types of these compounds we may consider ferrous oxide, FeO, and ferrous sulphate, FeSO*. The oxides of this latter class are strongly basic ; the sesquioxides are also basic, but in the presence of more energetic bases may act as weak acids. Iron and manganese also form oxides of the composition FeO 3 and MnO 3 , which act as the anhydrides of acids. Uranium is related to manganese and iron by certain com- pounds, and there are others which relate it to chromium, mo- lybdenum, and tungsten. The latter three elements combine with oxygen, forming the anhydrides of energetic acids, and their atoms mav be regarded as hexatomic. ALUMINIUM. Al = 27 5 This metal long remained a chemical curiosity, and has only become common within a few years. It was discovered in 1827 by Wohler. and in 1854, H. Saint-Claire Deville succeeded in producing it on the large scale. It is obtained by decom- posing aluminium and sodium double chloride by sodium. APCl 6 ,2XaCl + 3Na 2 = 8NaCl + AP In the arts, a mixture of sodium, aluminium and sodium double chloride, and cryolite, is projected into a reverberatory furnace heated to bright redness. The cryolite acts as a flux : it is a double fluoride of sodium and aluminium, found native in Greenland. Aluminium is a white metal, and has a somewhat bluish lustre when polished. It is ductile, malleable, very sonorous, and a good conductor of heat and electricity. It is as light as glass and porcelain, its density being only 2.56. 372 ELEMENTS OF MODERN CHEMISTRY. Aluminium is unaltered by the air, even by moist air. When heated in thin sheets in a current of oxygen, it burns and is converted into alumina. Nitric and sulphuric acids scarcely attack it. Hydrochloric acid dissolves it rapidly, disengaging hydrogen. It is immediately attacked by boiling solutions of potassium or sodium hydrates; hydrogen is disengaged and alkaline aluminates are formed. ALUMINIUM OXIDE, OR ALUMINA. A1 2 0* Corundum, a very hard precious stone, consists of anhydrous alumina. It is named oriental ruby when it has a red color ; sapphire when it is blue, and oriental topaz when it has a yellow tint. Emery is a sort of opaque corundum ; it is gran- ular and colored by a small quantity of oxide of iron. When ammonium carbonate is added to a solution of alum, carbon dioxide is evolved, and a gelatinous precipitate of hy- drated alumina is formed. The precipitate dissolves readily in caustic potassa. When heated, it loses water and is converted into anhydrous alumina ; the latter is undecomposable by heat ; it fuses only in the flame of the oxyhydrogen blow-pipe. Gaudin has succeeded in pro- ducing fine precious stones that cannot be cut by the file, and at least as hard as rock-crystal, by melting Limoge emerald (anhydrous alumina) with various substances, such as sand, kaolin, talc, and lime, which are added as fluxes. Alumina cannot be reduced by charcoal at the highest tem- peratures ; it can only be reduced by the joint action of char- coal and chlorine ; aluminium chloride is then formed. ALUMINIUM CHLORIDE. A1 2 C1 6 When a current of chlorine is passed over an incandescent mixture of alumina and charcoal, aluminium chloride and carbon monoxide are formed (Oersted). APO 3 + 3C + CI 6 = 3CO + APC1 6 Aluminium chloride thus formed is a white, crystalline sub- stance, sometimes having a light-yellow color. It is fusible, and ALUMINIUM SULPHATE — ALUM. 373 volatilizes in the air at a temperature little above 100°. When exposed to the air it gives off white fumes and attracts moist- ure. It dissolves in water with production of heat. A solution of aluminium chloride may be obtained by dis- solving gelatinous alumina in hydrochloric acid. When this solution is evaporated, it decomposes as soon as it attains a certain degree of concentration, disengaging hydrochloric acid. and leaving alumina. Aluminium chloride readily combines with sodium chloride, forming a double chloride. APCl 6 .2XaCl, fusible towards 200°. ALUMINIUM SULPHATE. Al 2 (SO)3 + 18H 2 This is obtained in the arts by decomposing non-ferruginous clays with sulphuric acid. It crystallizes with difficulty in needles and in thin, pearly scales. In this state it contains 18 molecules of water of crystallization. It dissolves in 2 parts of cold water. When heated, it first loses its water, and at a higher temperature it gives off sulphuric anhydride, leaving a residue of alumina. AP(SO) 3 = 3S0 3 + APO 3 It is seen that aluminium sulphate represents 3 molecules of sulphuric acid, in which the 6 atoms of hydrogen have been replaced by the hexatomic couple AP. H 2 SOM fSO 4 H 2 SO V + APO 3 = 3H 2 + (Al 2 )* ] SO 4 H 2 S0 4 ) (SO 4 ALUMINIUM AND POTASSIUM DOUBLE SUL- PHATE, OK ALUM. Al 2 (SO±) 3 .K 2 SO* -f 24H 2 If a concentrated solution of aluminium sulphate be added to a concentrated solution of potassium sulphate, and the mix- ture be stirred with a glass rod. a crystalline deposit soon forms from the union of the two salts to form a double sulphate which is alum. This salt is not very soluble in cold water, but dissolves abundantly in boiling water, and is deposited on cooling in 32 374 ELEMENTS OF MODERN CHEMISTRY. voluminous, transparent octahedra. When heated, these crys- tals melt in their water of crystallization (24 molecules), and in losing this water, the melted mass swells up considerably. Alum may be obtained crystallized in cubes, and it is prepared in this form in the neighborhood of Civita-Vecchia by working a mineral which contains the elements of alum with a large excess of alumina. The mineral is known as aliiminite, and the cubical alum is called Roman alum. This cubical variety may be prepared in the laboratory by adding a small quantity of potassium carbonate to a hot solu- tion of ordinary alum, so that the precipitate first formed will be redissolved on agitating the liquid. On cooling, cubical crystals are deposited which are ordinarily opaque. These are formed under the influence of a small quantity of basic sul- phate (aluminium sulphate combined with an excess of alu- mina) contained in the liquid, and which probably enters into the constitution of the crystals. With this slight difference, octahedral alum and cubical alum present the same composi- tion, which is expressed by the formula A1 2 (S0 4 ) 3 .K 2 S0 4 -|- 24H 2 0. Ammonia alum is obtained by adding ammonium sulphate to solution of aluminium sulphate. It possesses a constitution analogous to that of ordinary alum, with which it is isomor- phous. It contains A1 2 (S0 4 ) 3 .(NH 4 ) 2 S0 4 + 24H 2 It is often substituted in the arts for potassium alum, being cheaper than the latter. When strongly calcined, it leaves a residue of pure alumina. Other alums are known in which iron, manganese, and chro- mium play the part taken by aluminium in ordinary alum. These alums are all isomorphous (Mitscherlich). By the ac- tion of sulphuric acid on the sesquioxides of the above metals, sulphates are formed analogous to aluminium sulphate, and of which the composition is expressed by the general formula (B/ 2 ) vi (S0 4 ) 3 . With the sulphates JYFSO 4 , they form alums, all of which crystallize in regular octahedra, and which can be mixed in one and the same crystal without the form of the latter being affected by the mixture. The following are the most important of these compounds : Manganese alum .... Mn 2 (SO*) 3 .K 2 S0 4 + 24H 2 Iron alum Fe 2 (S0 4 ) 3 .K 2 S0 4 + 24H 2 Chromium alum .... Cr 2 (S0 4 ) 3 .K 2 S0 4 + 24H 2 ALUM. 375 It is seen that each of these presents an atomic composition similar to that of ordinary alum. The aluminium compounds are widely disseminated in nature. Feldspar is a double silicate of aluminium and potassium. The latter metal is replaced by sodium in albite. and by calcium in labradorite.- Many other minerals contain aluminium silicate combined with alkaline or earthy silicates: such are granite, idiocrase. mica, etc. The zeolites are silicates of aluminium containing water of crystallization. Clay is a hydrated silicate of aluminium ; it results from the disintegration of feldspar by the action of water and air. the alkaline silicate being gradually dissolved and eliminated. The purest clay is kaolin, or porcelain clay ; it contains alumina, silica, and water in the proportions indicated by the formula 2Si0 2 ,AP0 3 ,2H 2 0. Plastic clays are those which form a binding paste when mixed with water, and acquire great hardness after being baked, without fusing. They are used for the manufacture of pottery, refractory fire-bricks, and crucibles. Fuller s earth is a clay which forms with water a paste that is but slightly adhe- rent ; it is employed in scouring and fulling cloth. Marls are intimate mixtures of clay and chalk ; they are employed in agriculture. Pottery. — Clay is the basis of all pottery. Other matters, such as sand, powdered feldspar or quartz, etc., are generally added, for while they diminish the plasticity of the clay, they also diminish its shrinkage on baking. Pottery is classified as semivitrifiecl pottery, such as porcelain and stoneware ; porous pottery, such as faience and bisque ; and common pottery or terra-cotta. Porcelains. — These are manufactured from kaolin, to which sand is added to prevent shrinkage, and feldspar, which causes the ware to undergo a partial fusion, and renders it translucent. These materials are finely pulverized, mixed with water, and the paste is kneaded for a long time in order to render it homo- geneous. Pieces fashioned in this paste are submitted to a pre- liminary baking, which gives them a certain degree of coherence. The porous porcelain thus obtained must be coated with a var- nish which will melt and spread upon its surface : this glaze is 376 ELEMENTS OF MODERN CHEMISTRY. formed of a mixture of quartz and kaolin reduced to an impal- pable powder ; the latter is suspended in water, into which the pieces are dipped. They are then subjected to a second baking in ovens where the temperature is sufficiently elevated to fuse the glaze and partially vitrify the paste. Ceramic Stonewares. — These are manufactured from the same materials as porcelain, but less pure ; they are therefore slightly colored. They are baked at a high temperature, and are glazed by throwing common salt upon the incandescent objects in the furnace ; hydrochloric acid is disengaged, and a double silicate of aluminium and sodium is formed, which fuses and spreads upon the surface of the ware. Faiences are made from plastic clay mixed with quartz re- duced to an impalpable powder. Articles formed of this paste are submitted to a preliminary baking, and are then coated with a fusible glaze, composed of quartz, potassium carbonate, and oxide of lead. A second baking causes the pieces to become covered with an impermeable, vitreous layer of silicate of lead and potassium. This glaze is transparent ; for ordinary ware it is rendered opaque by the addition of oxide of tin. It is a true enamel. Common pottery , which serves for culinary purposes, is made from ferruginous clay, mixed with sand and marl. The glazing is composed of a double silicate of aluminium and lead. LANTHANUM, DIDYMIUM, AND CERIUM. These three rare metals are found associated as silicates in the minerals cerite, euxenite, gadolinite, etc. Their separation is a matter of some difficulty. The mineral is treated with sul- phuric acid, by the aid of heat, and the solution obtained after filtering from the separated silica, is precipitated by ammonium oxalate. A mixture of the three oxides is obtained when the oxalates are calcined, and from this mixture very dilute nitric acid dissolves only the cerium. The didymium and lanthanum in the residue may be separated by taking advantage of the action of heat on solutions of the sulphates. The latter are quite soluble in cold water, but lanthanum sulphate is deposited when the solution is heated to 30°, while the didymium sul- phate remains in solution. METALS NOT YET ISOLATED. 377 Tbe metals have been isolated by decomposing their chlorides by electricity. They possess about the hardness of lead, and a color and lustre resembling iron : didymium is rather more yellow. Their den- sity is comprised between 6.05, that of lanthanum, and 6.7, of cerium. They are readily oxidized, and burn brilliantly when heated in the air. They appear to be tetratomic, combining in hexatomic couples, like aluminium and iron. Their oxides are strongly basic, per- fectly neutralizing the acids and forming crystallizable salts. Lanthanum oxide has the composition La 2 3 . Didymium forms two oxides, Di 2 3 , and another to which has been assigned the formula Di 4 9 . Cerium has two oxides, Ce 2 3 and CeO 2 , and forms two corresponding series of salts. The chlorides of the metals have the general composition R 2 C1 6 . The eerie salts are white or yellowish. Didymium salts are rose-colored or rose-violet. The other salts are colorless. Closely related to these three metals are the following METALS NOT YET ISOLATED. As early as 1794, Gadolin, a Finn, discovered in the mineral gadolinite, which bears his name, an oxide, which he named yttria. In 1843, Mosander concluded from researches on this earth that it contained at least three oxides, the metallic radi- cals of which were introduced into the list of elements under the names erbium, terbium, and ytterbium, or yttrium. Until recently very little has been actually known concerning these oxides, but the investigations of Delafontaine, Lawrence Smith, Marignac, Cleve, and Nilson have shown that the earths formerly known as erbine and yttria are much more complex than was supposed. It seems that the oxides of at least six metals have been isolated, and it is possible that the series may be completed by the separation of others. These elements exist in gadolinite, euxenite, orthite, thorite. and particularly in the samarskite of North Carolina, in which they occur as niobates and tantalates. Their quantity is so small, and the separation of their oxides is attended by so great difficulty, that the elements have not yet been isolated. Their oxides, and in some cases a number of salts, have been exam- ined, and spectroscopic analysis has aided in setting aside all doubt as to the existence of the elements. It is to be remarked that at least one of these elements, scan- 32* 378 ELEMENTS OF MODERN CHEMISTRY. dium, fills a position designated as vacant by Mendelejeff in his classification of the elements. It appears probable that they are all tetratomic, and combine in hexatomic couples, like aluminium and iron. The general formula of the oxides would then be R 2 3 ; the atomic weights are calculated to agree with this composition. The following are the names which have been given to these elements : Scandium, discovered by Nilson, and studied by Cleve, has an atomic weight of 44 or 45 ; the oxide is white. Samarium. — Atomic weight = 150. This element was named by Lecoq de Boisbaudran, and appears to be identical with decipium, of which Delafontaine announced the existence in 1878 ; its oxide is white. Holmium. — Atomic weight about 162 (Cleve) ; has a yellow oxide. Erbium. — Atomic weight = 166 ; forms a rose-colored oxide and red salts (Cleve). Thulium. — Atomic weight = 170.4 ; a white oxide. Yttrium, or Ytterbium.— "Atomic weight = 172.5 ; oxide white. GALLIUM. Ga = 69.9 This metal was discovered in 1876 by Lecoq de Boisbaudran. It is contained in small quantity in certain blendes. One of the richest, found in Westphalia, contains only one sixty-thou- sandth of its weight. In order to extract the gallium, the ore is roasted, and the product dissolved in sulphuric acid. An acid liquor is thus obtained, containing principally sulphate of zinc, with sulphates of iron, aluminium, indium, etc., and a trace of gallium sul- phate. The following reactions are employed by Lecoq de Bois- baudran and Jungfleisch for the separation of the gallium : 1. When the liquid is neutralized, the ferric oxide, alumina, and gallium oxide, which is a sesquioxide, are precipitated. The precipitate is redissolved in sulphuric acid, and the same operation repeated after converting the ferric oxide into ferrous oxide, which remains dissolved in the neutral liquid. By this means the greater part of the iron is removed. 2. G-allium oxide dissolves, like alumina and zinc oxide, in an excess of potassium hydrate ; when this solution is saturated iron. 379 with hydrogen sulphide, the zinc is precipitated as sulphide, while the gallium and aluminium remain in solution. The greater part of the zinc is thus separated. 3. When water is added to a boiling solution of gallium sulphate, the latter is precipitated as subsulphate, while alumi- nium sulphate remains in solution. 4. Gallium oxide dissolves in an excess of ammonia ; alumina does not. 5. Gallium separates in the metallic state when a voltaic current is passed through an alkaline solution of gallium oxide. Physical Properties. — Gallium has a metallic lustre recalling that of nickel. It readily crystallizes in forms derived from a right rhombic octahedron, generally in magnificent laminae. Its density is 5.96. It melts at 29.5°. and has a tendency to re- main in a state of superfusion. It is not volatile. This collection of properties gives to gallium a special place among the metals. It is one of the most remarkable of recent discoveries. Chemical Properties. — These are but little known at present. Gallium is oxidized but little, if at all, when heated in the air or in oxygen. It forms a sesquioxide, Ga 2 3 , which resembles alumina in that it forms alums. Gallium alum w^as obtained by Lecoq de Boisbaudran. Gallium combines directly with chlorine, forming a solid, crystalline, and very volatile chloride. IRON. Fe(Ferrum) = 56 Natural State and Metallurgy.— Iron is the most impor- tant of the metals. Its preparation and working are difficult, therefore it was not the first metal used by civilized man. The bronze age preceded the iron age, and those who first employed the latter metal probably extracted it from the masses which fall from time to time upon the surface of the earth, and are known as meteorites. Their principal constituent is metallic iron, which is alloyed with nickel, cobalt, and chromium. Iron is employed in three principal forms : soft or malleable iron, cast iron, and steel. Soft iron is almost pure iron ; cast iron is a combination of iron with carbon and silicon ; steel also contains carbon, but in smaller proportion than cast iron. The principal ores of iron are the magnetic, or black oxide, 380 ELEMENTS OP MODERN CHEMISTRY. Fe 3 4 , red hematite, Fe 2 3 , and spathic iron or ferrous carbon- ate, FeCO 3 . The various hydrates of the sesquioxide {oolitic iron, brown hematite, etc.) and ferrous carbonate mixed with clay (bog-iron ore), are more abundant than the preceding, but are not as rich and are less valuable. All of these minerals are oxidized. If the ore contain sul- phur, that element is first driven out by roasting. The metal- lurgy of iron then consists in reducing the oxide with carbon, and separating the reduced iron from the earthy matter, which is generally silicious. Two methods are employed for this purpose. The first consists in heating the rich ores with charcoal alone ; part of the oxide of iron then combines with the gangue, forming a very fusible slag (double silicate of aluminium and iron). This is the Catalan method. The other consists in mixing the ore with coal and calcium carbon- ate ; the gangue then com- bines with the lime, forming a double silicate of lime and aluminium, which fuses only at a very high temperature. Under these conditions the iron unites with a portion of the carbon, forming cast iron. This is the blast-fur- nace method. Catalan Method. — This is only applicable to very rich ores and in countries where combustibles are expensive, as in Spain, the Pyrenees, and in Corsica. Fig. 116 represents a sec- tion of a Catalan furnace ; it is a trough-shaped masonry furnace with a hearth. The materials are placed in two piles, side by side, upon a layer of well-ignited charcoal ; one pile consists of charcoal and is next the tuyere ; the other is the ore, equal to half the quantity of charcoal, and is placed oppo- site. The combustion is sustained by the blast from a tuyere, D, which reaches the border of the hearth. The carbon dioxide here formed is converted into carbon monoxide by the IRON. 381 mass of incandescent charcoal, and the latter gas reduces the ore. again passing into the state of dioxide. Metallic iron is thus formed, and at the same time a portion of the ferric- oxide is reduced to ferrous oxide, and combines with the o-ano'ue. forming a double, alumino-ferrous silicate, which is very fusible and constitutes the slag. The reduced iron collects in the bottom of the hearth in the form of a spongy mass, which is agglutinated anc j forced under the hammer. Fig. 117. Blast-furnace Process.— All iron ores may be treated by this method. They are crushed and introduced with alternate layers of limestone and coal into the blast-furnace (Fig. 117). The latter has the form of two cones, the bases of which are 382 ELEMENTS OF MODERN CHEMISTRY. joined together. It is closed at the bottom, and hot air is in- jected through tuyeres to sustain the combustion. It is open at the top, where it is continually charged with fresh materials, as the incandescent mass sinks in the furnace and the molten mate- rials are drawn off below. The latter first collect in a cavity placed below the vent of the tuyere, and separate on this hearth into metal, which sinks to the bottom, and slag, which floats and flows over the edge. When the crucible is full of molten metal, the latter is run off into channels made in sand upon the floor of the casting-room. In these rough moulds it solidifies in bars having a semicircular section, which are called pigs. The reactions which take place in the blast-furnace are of great interest. At the lower part, where the temperature is the highest, carbon dioxide is produced by the combustion of the coal ; farther up, in the widest portion, this gas is reduced to carbon monoxide by the incandescent coal ; still higher, where the furnace begins again to contract, and where the temperature is dull red, the carbon monoxide reduces the oxide of iron, and a spongy mass of metallic iron is there formed. In descending, this iron unites with part of the carbon, and at the same time the silica of the gangue combines with the lime, forming a silicate which fuses and constitutes the slag. A small quantity of silica is reduced in the hottest part of the furnace, and the silicon formed combines with the cast iron. Cast iron is converted into soft iron by refining ; this opera- tion consists in removing from the cast iron the greater part of its carbon. . For this purpose it is melted in contact with the air ; the carbon, silicon, and a small proportion of iron are oxidized, forming a basic silicate, of which the excess of oxide is finally reduced by the carbon of the cast iron. The latter thus becomes less fusible, and is converted into a spongy mass of soft iron. Several of these masses are united and the scoriae expressed from them by the blows of a steam-hammer. Or the metal is melted on the hearth of a reverberatory furnace under a layer of ferruginous scoriae and scales of oxide of iron ; the oxygen of these materials burns the carbon out of the cast iron, the whole mass being vigorously stirred. The latter operation is called puddling. Preparation of Pure Iron. — Pure iron may be obtained by reducing ferric oxide by hydrogen at a temperature near red- ness, or by passing hydrogen over anhydrous ferrous chloride ' iron. 383 contained in an incandescent porcelain tube. Hydrochloric acid is formed and evolved, and the iron remains as a gray, spongy mass, having a metallic lustre where it has been in contact with the porcelain (Peligot). Properties of Soft Iron. — Forged, or bar iron, is not chem- ically pure. It contains a small quantity of carbon, and traces of silicon, sulphur, and phosphorus, and even nitrogen. The purest soft iron is that used for the teeth of carding-machines and for piano-strings. The density of forged iron varies from 7.4 to 7.9. It is very tenacious, ductile, and malleable. When rolled out, it is called sheet iron. Tin plate is sheet iron covered with a layer of tin. Galvanized iron is coated with a surface of zinc. Iron melts only at the highest heats of a wind-furnace. When softened by a white heat, it may be soldered to itself, or welded, a very important property for the working of the metal. Iron is attracted by the magnet ; it is magnetic ; but it is not, like steel, capable of retaining magnetism when removed from the magnetic influence. It is not altered by dry air at ordinary temperatures, but at a red heat it absorbs oxygen and is converted into scales of black oxide of iron. Iron may be obtained as an impalpable powder by reducing finely-divided ferric oxide by a current of hydrogen at as low a temperature as possible. In this state it takes fire when ex- posed to the air at ordinary temperatures : it is pyrophoric. Iron rapidly becomes oxidized in moist air ; it becomes cov- ered with a layer of rust, which is ferric hydrate. It is con- sidered that the oxidation of iron moistened with water is first set up by the oxygen dissolved in the water; it continues with greater energy as soon as a light coat of ferric hydrate has been formed on the metal. The hydrate forms a voltaic couple with the iron itself, by which the water is decomposed ; part of the hydrogen displaced by the iron combines with the nitrogen of the air, forming ammonia; indeed, rust always contains a small proportion of ammonia. Iron decomposes water at a red heat, setting free the hydro- gen. It dissolves readily in hydrochloric acid, liberating impure and fetid hydrogen. Its oxidation by nitric acid is attended by curious phenomena. If dilute nitric acid be poured upon iron tacks, the metal is at once attacked with an abundant disengagement of red vapors. 384 ELEMENTS OF MODERN CHEMISTRY. On the other hand, the same metal is not attacked by very concentrated nitric acid (monohydrated), and after having been exposed to the strong acid, the tacks may be put into dilute acid, and the latter will then be found to have no effect. By the action of the concentrated acid, the iron becomes passive; its surface is covered with a thin layer of gas which protects it. But if it be touched at any point with a copper wire while in the dilute acid, chemical action will instantly be re-established. Cast Iron and Steel. — The properties and appearance of cast iron differ with the proportions of carbon and silicon which it contains. The iron does not form definite compounds with these bodies; they seem to be dissolved by the cast iron when it is liquid. When cast iron containing much carbon is quickly cooled, it becomes hard, brittle, whiter than soft iron, and seems homogeneous. This is ivhite iron. When slowly cooled, a large proportion of the carbon is deposited as laminae of graphite, and the less homogeneous iron then possesses a certain degree of malleability : it is gray iron. Some cast irons contain traces of sulphur and phosphorus; they remain white even after very slow cooling. Others are lamellar and glittering; they contain manganese and are rich in carbon. The proportion of carbon contained in cast iron varies from 2 to 5.5 per cent. Steel contains less carbon, from 0.7 to 2 per cent. The quantities of carbon contained in steel and even in cast iron render it difficult to suppose that these products are veritable carbides of iron. Steel may be obtained by a partial decarbonization of cast iron. Manganiferous iron is especially applicable for this prep- aration. It is submitted to a partial refining, being maintained in the liquid state for some hours under a layer of scoriae rich in oxide of iron. A part of the carbon is burned out by the oxygen of this oxide : natural steel is thus obtained. Soft iron may be converted into steel. The operation is con- ducted in cases of refractory fire-clay, into which bars of iron, and charcoal-powder, mixed with a small quantity of ashes and common salt, are introduced in alternate layers. The bars being thus isolated in a bed of charcoal, the cases are closed and heated to redness in a furnace. The incandescent metal absorbs carbon, and at the termination of the operation is found con- verted into steel by cementation. IRON. 385 The most homogeneous and most valuable steel is cast steel. It is obtained by fusing crude steel in crucibles in a wind-fur- nace. Bessemer has introduced an important improvement in the manufacture of steel. His process, which bears his name, con- sists in adding variable quantities of a properly-constituted cast iron to molten and perfectly refined soft iron. \ In this process, the iron to be converted into steel is decar- bonized by a current of air which is forced through the molten metal by strong press- ure. The operation is conducted in an appa- ratus represented in Fig. 118, which is called the converter. It has an ovoid form, is constructed of strong plate iron, and is well- lined with refractory fire-bricks. It is ar- ranged on trunnions, so that an oscillating move- ment may be given to it. The air arrives under pressure by the tuyeres which open into the bot- tom of the converter. The latter is first filled with incandescent coke, which is brought into active combustion by the blast. When the interior of the converter is heated to whiteness, the coke is emptied out and replaced by the molten cast iron, the con- verter being inclined to prevent the entrance of the metal into the tuyeres. The blast is then again turned on, and the com- pressed air bubbling through the molten metal burns out all of the carbon. A flame of great brilliancy rushes from the orifice of the apparatus, and the aspect of this flame indicates precisely the progress of the operation and its termination. At this moment the apparatus is inclined, the blast arrested, and a sufficient quantity of melted cast iron or spiegeleisen, a crystalline cast iron rich in carbon, is added to the now refined iron to convert the whole into steel; about 7 per cent, of spie- R 33 Fig. 118. 386 ELEMENTS OF MODERN CHEMISTRY. geleisen is required. The steel is then run out into suitable moulds. The valuable qualities of steel are well known. It is suscep- tible of a high polish ; it is ductile and malleable like iron, and can also be forged. At the temperature at which malleable iron becomes soft, steel melts. It becomes hard and brittle when it is suddenly cooled after having been heated to redness. This operation, which is called tempering, develops new quali- ties in the steel, — elasticity and hardness. It assumes these properties in different degrees, according to the rapidity of the cooling, and the difference between the temperature to which it has been heated and that to which it is cooled. The greater this difference, and the more rapid the cooling, the harder will the steel become. After a slow cooling, it is soft and mallea- ble like iron. When tempered steel is heated, and allowed to cool slowly, it partly or entirely loses its hardness. It loses it entirely if it be heated to the temperature to which it was exposed before tempering. Its temper is drawn incompletely, that is, it re- tains a certain amount of hardness and elasticity, if it be re- heated to inferior temperatures. The qualities which it will assume after cooling may be predicted from the various tints developed on its surface during the heating. Each of these tints corresponds to a determined temperature. Straw-yellow corresponds to 220° Brown " 255° Light blue " 285-290° Indigo-blue " 295° Sea-green " 331° OXIDES OF IRON. Three oxides of iron are known : Ferrous oxide FeO Ferric oxide Fe 2 3 Ferroso-ferric oxide Fe 3 4 Fremy has also discovered the existence of a ferric acid, of which the composition is not certainly established. Ferrous Oxide, FeO. — Debray has obtained this oxide by partially reducing ferric oxide. The latter is heated in a cur- rent of gas formed of equal volumes of carbon monoxide and carbon dioxide. A black powder remains, which is ferrous oxide. Fe 2 3 + CO = 2FeO + CO 2 OXIDES OF IRON. 387 Ferric Oxide, Fe 2 3 . — This is found anhydrous in nature in red hematite and specular iron. It may be prepared by calcining ferrous sulphate, or green vitriol. This salt first loses its water, and then at a red heat decomposes into sul- phuric anhydride, sulphurous oxide, and ferric oxide. 2FeS0 4 = SO 3 + SO 2 + Fe 2 3 A red powder is thus obtained, which is known as colcothar, or jeweller* s rouge. This oxide is amorphous, while red hematite is crystallized in acute rhombohedra. H. Deville has succeeded in converting the amorphous oxide into the crystallized by heating the former to redness in a very slow current of hydrochloric acid. Kust is ferric hydrate, a combination of ferric oxide with water, and ordinarily presents the composition 2Fe 2 8 + 3H 2 Such a hydrate is also encountered in nature as brown hematite. Another natural hydrate, containing Fe 2 8 + H 2 0, is known under the name of g&thite. Ammonia or potassium hydrate will at once produce a volu- minous and flocculent. rust-colored precipitate in a solution of ferric chloride. This precipitate constitutes a ferric hydrate. But if an excess of tartaric acid be added to the solution of a ferric salt, the liquid may be saturated with potassium hy- drate and will still remain clear, no precipitate of ferric hydrate being formed. Advantage is taken of this property in analysis for the sepa- ration of ferric oxide from other oxides which tartaric acid does not retain in solution in an alkaline liquid. If a solution of ferric acetate be poured into a dialyser (page 199), and the water in the exterior vessel be frequently changed, the salt will finally be entirely decomposed. Acetic acid will pass through the membrane, while ferric hydrate will remain dissolved in the water in the dialyser (Graham). Ferroso-ferric Oxide, Fe : W. — This compound, also called magnetic oxide of iron, constitutes the black scales which form upon the surface of iron when it is heated to redness in the air ; it may be regarded as a compound of ferrous and ferric oxides. FeO + Fe 2 3 = Fe 3 4 . 388 ELEMENTS OF MODERN CHEMISTRY. SULPHIDES OF IRON. Several sulphides of iron are known. The disulphide, or pyrites, FeS 2 , a largely-diflu&ed mineral, is the most important of these sulphides. It occurs in two distinct forms : Yellow pyrites, which crystallizes in cubes. It occurs as brilliant cubes, or dodecahedra, having a yellow color and a metallic lustre. White pyrites, which forms rhombic prisms, variously modi- fied, and presents a dull, greenish-yellow color. This variety is much more alterable than the other, and possesses a great tendency to attract oxygen from the air and become converted into sulphate. When heated in closed vessels, pyrites loses a part of its sulphur. A combination of monosulphide and sesquisulphide of iron is encountered in nature ; it crystallizes in regular hexagonal prisms and is called magnetic pyrites. Monosulphide of Iron, FeS, is found in small quantity in many meteorites. It is ordinarily obtained by heating to red- ness in a covered crucible a mixture of three parts of iron- filings and two parts of sulphur. When the mixture has fused, it is poured out and solidifies to a brittle, blackish mass, having a metallic reflection. In this state, it is used for the preparation of hydrogen sulphide. CHLORIDES OF IRON. Ferrous Chloride, Fed 2 , is obtained anhydrous by the action of dry hydrochloric acid gas upon metallic iron. It forms white pearly scales. When iron is treated with aqueous hydrochloric acid, it dissolves, and hydrogen is disengaged. The green, filtered liquid deposits, when sufficiently concentrated, bluish- green, oblique rhombic prisms. This is hydrated ferrous chlo- ride, FeCl 2 + 4H 2 0. Ferric Chloride, Fe 2 Cl 6 , is formed when a current of chlorine is passed over iron-turnings heated in a glass or poreclain tube. The two bodies combine with incandescence, and if the chlorine be in excess, ferric chloride will be obtained as a brilliant black, crystalline sublimate. FERROUS SULPHATE. 389 This body is very soluble in water and forms a yellow-brown solution. The latter may be obtained by dissolving ferric oxide, such as powdered hematite, in hot hydrochloric acid, or by passing chlorine into a solution of ferrous chloride. Ferric chloride is also soluble in alcohol. FERROUS SULPHATE. FeSO* - 7H 2 This salt has long been known under the names green vitriol and copperas. It is obtained by exposing iron pyrites to the air. or roasting that mineral at a moderate heat. It is generally prepared by dissolving iron in dilute sulphuric acid, and it is a residue from the preparation of hydrogen sulphide by means of iron sulphide and dilute sulphuric acid. It crystallizes in oblique rhombic prisms, containing 7 mol- ecules of water of crystallization. When exposed to the air, these crystals effloresce slightly, and at the same time their surface becomes yellow from absorption of oxygen and the formation of ferric subsulphate. 2FeSO* + = Fe 2 (\SO) 2 = Fe 2 3 .2S0 3 When heated, they lose their water, of which six molecules are disengaged at 114°. and the seventh only at 300°. At a higher temperature the salt decomposes into sulphurous oxide, and a ferric subsulphate different from the preceding. 2FeSO = SO 2 + (Fe 2 2 )SO The crystals of ferrous sulphate are freely soluble in water. 100 parts of the salt dissolve in 164 parts of water at 10°. and in 30 parts of boiling water. The green solution absorbs oxy- gen from the air, becomes troubled, and deposits yellow ferric subsulphate. Other hydrates of ferrous sulphate are known. According to Mitscherlich. a saturated boiling solution of the salt deposits at 80° crystals containing four molecules of water. According to Marignae. when a solution of ferrous sulphate containing free sulphuric acid is evaporated in a vacuum, crystals are first deposited which contain 7 molecules of water, then a sulphate FeSO - 5H 2 0. and finally. FeSO 4 - 4EPO. The sulphate FeSO 4 + 5H'0. is isomorphous with crystal- lized cupric sulphate (blue vitriol), and like it crystallizes in dissvmetric prisms. 33* 390 ELEMENTS OF MODERN CHEMISTRY. FERRIC SULPHATE. Fe 2 (SO±) 3 This salt is obtained by heating ferrous sulphate with nitric and sulphuric acids; the brown solution is evaporated, and the residue well dried. 2FeS0 4 + H 2 S0 4 + = H 2 + Fe 2 (S0 4 ) 3 Ferric sulphate is a slightly-yellowish, white mass, which dissolves completely, but very slowly, in water. The solution is yellow-brown, and has an acid reaction. When concentrated by evaporation, it deposits a deliquescent, yellowish, crystalline mass, which constitutes hydrated ferric sulphate. There are several ferric sub sulphates ; those which have been mentioued above result from the action of one molecule of ferric oxide upon one or two molecules of sulphuric acid, the neutral sulphate resulting from the action of one molecule of ferric oxide upon three molecules of sulphuric acid. IPSO 4 + Fe 2 3 = H 2 + (Fe 2 2 )"SO* Ferric monosulphate. h!? + Fe2 ° 3 = 2H2 ° + ( Fe2 °) iv { so* - Ferric disulphate. H 2 S0 4 + Fe 2 3 = 3H 2 + (Pe 2 )" \ SO 4 H 2 S0 4 ( SO 4 Ferric trisulphate (normal sulphate). FERROUS CARBONATE. FeCO 3 Spathic iron ore, which crystallizes in rhombohedra, is fer- rous carbonate. When a solution of sodium carbonate is added to a solution of ferrous sulphate, a greenish-white precipitate is obtained, which rapidly becomes colored in the air, absorb- ing oxygen and losing carbonic acid. When recently precipi- tated, it dissolves in a large excess of carbonic acid. Characters of Ferrous Salts. — The solutions of these salts are green , they are not precipitated by hydrogen sulphide, but ammonium sulphide forms a black precipitate of ferrous sul- phide. Potassium hydrate or ammonia produces a greenish - white precipitate of ferrous hydrate, insoluble in an excess of COBALT. 391 the reagent, and rapidly becoming colored in the air. Potas- sium ferrocyanide (yellow prussiate of potash) forms with fer- rous salts a light-blue precipitate. Potassium ferricyanide (red prussiate) forms a dark-blue precipitate. Solution of gall-nuts does not color ferrous salts. Characters of Ferric Salts. — Hydrogen sulphide produces a precipitate of sulphur, reducing the salts to the ferrous state. Ammonium sulphide precipitates them black. Potassium hy- drate and ammonia form red-brown precipitates of ferric hy- drate, insoluble in an excess of the reagent. Potassium ferro- cyanide forms a dark-blue precipitate which is Prussian blue. Potassium ferricyanide produces a dark-brown color without precipitation. Potassium sulphocyanate gives a blood-red color. Solution of gall-nuts forms a bluish-black precipitate which constitutes ink. COBALT. Co= 59 Cobalt was discovered by Brandt in 1753. It is found prin- cipally in the state of arsenide, CoAs 2 , and as sulph-arsenide, CoAsS (gray cobalt). Its ores are worked principally for the production of a dark-blue, vitreous mass, a combination of cobalt silicate and potassium silicate, known as smalt or azure blue The metal is prepared in the laboratory by calcining its oxa- late in a covered crucible. CoC 2 4 = Co + 2C0 2 Cobalt oxalate. Carbon dioxide. It may be obtained as a metallic button by heating the pul- verulent metal in a lime crucible in a wind-furnace. The lime crucible is placed in another crucible of refractory clay, and the space between the two is filled up with fragments of quick- lime (H. Sainte-Claire Deville). Pure cobalt is silvery- white. It is very malleable ; its den- sity is 8.6, and it is magnetic. At ordinary temperatures it is unaffected by the air, but at a red heat it is converted into oxide. Oxides of Cobalt. — A monoxide, CoO, and a sesquioxide, Co 2 3 , are known, and several intermediate oxides. The monoxide may be obtained by calcining cobalt carbonate in close vessels. It is a greenish-gray or olive-green powder, which is reduced by hydrogen, charcoal, and carbon monoxide at a red heat. 392 ELEMENTS OF MODERN CHEMISTRY. When heated with borax before the blow-pipe, it dissolves, forming a blue glass. It is used for giving a blue color to glass and porcelain. When an excess of potassium hydrate is added to the solu- tion of a salt of cobalt, a rose-red precipitate of cobalt hydrate, Co(OH) 2 , is formed. Cobalt sesquioxide, Co 2 3 , is prepared by passing a current of chlorine through water, holding in suspension the rose- colored hydrate above mentioned. 2CoO + H 2 + CI 2 = Co 2 3 + 2HC1 The sesquioxide is deposited as a black powder, which may be dried by carefully heating it. Cobalt Chloride, CoCl 2 . — When pulverulent cobalt is heated in a current of chlorine, it takes fire and is converted into a chloride, which sublimes in blue scales. A solution of this chloride may be obtained by dissolving either monoxide or car- bonate of cobalt in hydrochloric acid. The neutral solution is currant-red, and on evaporation deposits hydrated crystals of the same color. But when it is concentrated, after having added hydrochloric or sulphuric acid, it becomes blue. This change of color, due to the formation of anhydrous chloride even in the midst of the hot liquid, has caused the employ- ment of cobalt chloride as a sympathetic ink. Characters traced with the dilute solution, which is rose-colored, are invisi- ble on white paper, and appear blue only when the paper is warmed, again becoming invisible on cooling, by the absorption of atmospheric moisture. Cobalt Sulphate, CoSO 4 + 7H 2 0.— This salt is found in nature, crystallized in oblique rhombic prisms. It may be ob- tained by dissolving the oxide or carbonate in dilute sulphuric acid and concentrating the red solution. At ordinary temper- atures, the latter deposits red crystals, isomorphous with ferrous sulphate. Between 20 and 30°, it yields right rhombic prisms, containing 6 molecules of water, and isomorphous with magne- sium sulphate. Characters of Cobalt Salts. — The cobaltous salts are the more important. Their solutions are rose or currant-red, but when concentrated and hot they become blue, especially when an excess of acid is present. Hydrogen sulphide does not pre- cipitate solutions of cobalt salts. Ammonium sulphide forms a black precipitate. Potassium hydrate gives a blue precipitate NICKEL. 393 of a basic salt, which, in presence of an excess of potassa, is converted into hydrate of cobalt, having a dirty rose color. Ammonia forms a blue precipitate, soluble in an excess of the reagent. When heated with borax in the blow-pipe flame, the salts of cobalt yield beads of a pure blue color. NICKEL. "Ni = 59 This metal was discovered by Cronstedt in 1751. Natural State and Extraction. — Nickel is found as arsen- ide, NiAs 2 , in hupfemichel or nickeline. In the preparation of smalt from the ores of cobalt, which always contain nickel, the latter metal combines with the arsenic and a certain proportion of sulphur, forming a metallic-looking mass known as speiss. In the arts, nickel is extracted from kupfernickel or from speiss. In the laboratory it is prepared by reducing the oxide in a brasqued crucible, or by calcining the oxalate out of con- tact with the air. When heated to whiteness in a lime cruci- ble the nickel melts to a metallic button. Properties. — Pure nickel is grayish- white. It is malleable, ductile, and very tenacious. Its density is 8.279, and may be increased to 8.666 by hammering. Next to manganese, it is the hardest of the metals. It is less fusible than iron and more fusible than manganese. It is magnetic at ordinary tempera- tures, but loses this property at about 250°. It is unaltered by the air at ordinary temperatures, but absorbs oxygen at a red heat. It dissolves slowly in dilute sulphuric and hydrochloric acids, rapidly in nitric acid. In contact with concentrated nitric acid it becomes passive like iron. Nickel is used in the arts, in the manufacture of an alloy known as German silver, which contains 50 per cent, of copper, 25 of nickel, and 25 of zinc. Nickel may be deposited as a brilliant metallic layer by the electrolysis of a solution of nickel and ammonium double sul- phate (A. C. and E. Becquerel). Adams made an application of this property to the nickel-plating of various objects by electro-metallurgy, and the process is now largely employed. Oxides of Nickel. — A monoxide, NiO, and a sesquioxide, Ni 2 3 , are known. The anhydrous monoxide is an ash-gray powder. It is 394 ELEMENTS OP MODERN CHEMISTRY. obtained by strongly calcining the nitrate or carbonate. On adding potassium hydrate to a nickel salt, an apple-green pre- cipitate of nickel hydrate, Ni(OH) 2 , is formed. Nickel sesquioxide may be obtained by moderately calcining the nitrate. It is black. When chlorine gas is passed into water holding nickel hydrate in suspension, a dark-brown pow- der is obtained, which is a hydrate of the sesquioxide. This hydrate may also be made by precipitating a nickel salt with potassium hydrate mixed with an alkaline hypochlorite. When strongly calcined, nickel sesquioxide abandons part of its oxygen and is changed into monoxide. Treated with hydro- chloric acid, it yields nickel chloride, and chlorine is disengaged. Ni 2 3 + 6HC1 = 2NiCP + 3H 2 + CI 2 Nickel Chloride, NiCl 2 . — This salt may be obtained anhy- drous by the action of chlorine on nickel-filings ; it is volatile at a dull-red heat, and sublimes in golden-yellow scales. The hydrated chloride is formed by the action of boiling water on the anhydrous salt, or by the action of hydrochloric acid on the oxide or carbonate. Its solution is green, and after proper concentration deposits beautiful green crystals which contain NiCl 2 + 9H 2 0. Nickel Sulphate, NiSO + 7H 2 0.— The sulphate is depos- ited in fine, emerald-green, orthorhombic prisms, isomorphous with magnesium sulphate, when its solution is allowed to evap- orate spontaneously below 15°. There is another hydrate con- taining 6H 2 0, which is dimorphous. When deposited between 20 and 30°, it crystallize in square octahedra, but when its solution is made to crystallize between 60 and 70°, right rhom- bic prisms are obtained, isomorphous with the corresponding sulphates of magnesium, zinc, and cobalt. Nickel sulphate dissolves in 3 times its weight of water at 10°. Characters of Nickel Salts. — The nickel salts when hy- drated or in solution have a fine emerald-green color. When anhydrous they are yellow. Hydrogen sulphide does not precipitate them from acid solu- tions. Ammonium sulphide throws down a black precipitate. Potassium hydrate and potassium carbonate form apple-green precipitates. In neutral solutions, ammonia gives a green precipitate of nickel hydrate, which dissolves in an excess of ammonia, form- ing a blue solution. MANGANESE. 395 MANGANESE. Mn = 55 This metal has been obtained as a coherent, very hard mass, by reduction of either manganous carbonate or red oxide of manganese with charcoal or sugar in a lime crucible at the highest heat of a wind-furnace (H. Deville). It is whitish-gray, and almost as infusible as platinum. Its density is 7.2. Its powder decomposes warm water. MANGANESE OXIDES. Manganese forms six compounds with oxygen : Manganous oxide MnO Manganoso-manganic oxide Mn 3 4 Manganic oxide Mn 2 3 Manganese dioxide MnO 2 Manganic anhydride MnO 3 Permanganic anhydride Mn 2 7 Manganous oxide is formed when manganous carbonate is strongly heated in a current of hydrogen. Carbon dioxide is evolved, and a green powder, which is manganous oxide, re- mains. It takes fire on contact with an incandescent body, and is converted into a brownish-red powder, which is red oxide of manganese. 3MnO -f = Mn 3 The latter body is also formed by the calcination of the diox- ide. It is analogous to the magnetic oxide of iron, and con- stitutes the mineral known as hausmannite. Manganic oxide ) Mn 2 3 , occurs in nature in the crystallized state as braunitc. It is isomorphous with alumina and ferric oxide. MANGANESE DIOXIDE. (binoxide or peroxide of manganese.) MnO 2 This important body is found abundantly in nature ; it con- stitutes the mineral pyrolusite. It may be obtained pure and anhydrous by exposing a concentrated solution of manganous nitrate to heat and gradually raising the temperature to 155°. 396 ELEMENTS OF MODERN CHEMISTRY. Nitrous vapors are evolved, and a brilliant brown-black mass is obtained, which is the dioxide. Mn(N0 3 ) 2 = MnO 2 + 2N0 2 It loses one-third of its oxygen when heated to redness, and is converted into the red oxide. When heated with concen- trated sulphuric acid, it loses half of its oxygen, manganous sulphate being formed, MnO 2 + H 2 S0 4 = MnSO 4 + H 2 + With hydrochloric acid it yields water, chlorine, and manga- nous chloride. A hydrate of manganese dioxide is formed when an excess of chlorine is directed into water holding in suspension man- ganous hydrate or carbonate. This hydrate is a dark-brown powder. Manganese dioxide is largely employed for the preparation of oxygen and chlorine. It is used to decolorize glass black- ened by carbonaceous matters or rendered green by a trace of iron. MANGANIC ACID. When manganese dioxide is heated with potassium hydrate in a silver crucible, and the calcined mass is exhausted with water, the latter dissolves out potassium manganate. A dark- green liquor is thus obtained which, when evaporated in vacuo, deposits a crystalline mass. These crystals may be drained on a porous porcelain plate, and green needles of potassium man- ganate, K 2 MnO*, remain. The salt is isomorphous with the sulphate K 2 SO\ When the green solution is boiled, it becomes red and deposits brown flakes of hydrated manganese dioxide : the red liquor is a solution of potassium permanganate, this salt being formed at the expense of the manganate, which breaks up into hydrated dioxide, potassium hydrate, and permanganate. 3K 2 MnO -f 3H 2 = K 2 Mn 2 8 + MnO'.EPO + 4KOH Potassium Potassium Hydrated manganese manganate. permanganate. dioxide. An analogous decomposition takes place when an acid is added to the green solution of manganate ; a manganous salt and permanganic acid are formed, and the latter colors the liquid red. PERMANGANIC ACID — MANGANOUS SULPHATE. 397 PERMANGANIC ACID. Potassium permanganate, K 2 Mn 2 8 , is an important salt. It may be prepared by introducing into an iron crucible 5 parts of caustic potassa with a small quantity of water, then a mix- ture of 3 i parts of potassium chlorate and 4 parts of finely- powdered manganese dioxide. The mixture is heated and continually stirred, until the mass becomes dry and the tem- perature has reached dull redness. After cooling, the product- is pulverized and introduced into 200 parts of boiling water. When the liquid has assumed a purple color, it is allowed to stand, decanted, and after neutralization by nitric acid, is evaporated at a gentle heat. On cooling, it deposits crystals that may be dried on a porous tile. Potassium permanganate crystallizes in almost black needles, having a metallic reflection. It dissolves in 15 or 16 parts of cold water, and its solution has a magnificent, intense purple color. If solution of sulphurous acid be added to potassium per- manganate solution, the latter is instantly decolorized, and the liquid contains only potassium sulphate and manganese sulphate. If a drop of the solution of potassium permanganate be placed upon a sheet of paper, it loses its color and a brown stain of hydrated manganese dioxide is produced. These experiments indicate the oxidizing properties of the permanganate. In the first, sulphurous acid was oxidized ; in the second, it was paper, of which the carbon and hydrogen removed the oxygen from the permanganate, which was thus reduced to dioxide. MANGANOUS SULPHATE. MnSO* + 7H 2 This salt may be prepared by dissolving manganous carbon- ate in sulphuric acid. The properly concentrated rose-colored solution deposits, between and 6°, oblique rhombic prisms, isomorphous with green vitriol and containing 7 molecules of water. Between 7 and 20°, manganous sulphate crystallizes with 5 34 398 ELEMENTS OF MODERN CHEMISTRY. molecules of water, like eupric sulphate, with which it is then isomorphous. Between 20 and 30°, it is deposited in oblique rhombic prisms, according to Marignac, which contain only 4 molecules of water. All of these crystals are rose-colored, and their color is deeper as they contain more water of crystallization. They are very soluble in water. MANGANOUS CAKBONATE. MnCW The residues from the preparation of chlorine may be used for making this salt. They are evaporated, without filtering, in a porcelain capsule, with frequent stirring, and the dry residue is calcined with an excess of manganese dioxide. The ferric chloride which was mixed with the manganous chloride is decomposed or volatilized during this operation. Ferric oxide remains, mixed with the excess of manganese dioxide and the manganous chloride, which resists the heat. The latter is extracted by exhausting the mass with boiling water. A rose-colored solution is thus obtained which often contains a small quantity of cobalt chloride. The latter is precipitated as sulphide by adding little by little a solution of sodium sul- phide. As soon as the precipitate, which is at first blackish, begins to assume a flesh tint, the liquid is filtered and precipi- tated by sodium carbonate. Manganese carbonate constitutes a white powder with a pale rose tint. When heated in contact with air, it gives up car- bonic acid gas and is converted into red oxide of manganese. Characters of Manganese Salts. — The salts of manganese are colorless or have a light rose color. Their solutions are not precipitated by hydrogen sulphide. Ammonium sulphide gives a flesh-colored precipitate ; sodium carbonate, a dirty white. Potassium hydrate produces a dirty white precipitate of manganous hydrate, which rapidly becomes brown by ab- sorbing oxygen from the air. When heated in the blow-pipe flame with a small quantity of potassium hydrate or nitrate, the salts of manganese give a bead which dissolves in water with a green color (manganate). URANIUM. 399 URANIUM. U = 120 1 Uranium is not found in abundance, although it is widely distributed. It occurs in pitchblende, a uranoso-uranic oxide, uranite, a calcium urano-phosphate, and in other minerals, asso- ciated with copper, bismuth, niobium, and tantalum. Euxenite contains niobate and titanate of uranium. The metal may be prepared by the action of sodium on a mixture of uranium chloride, UC1 2 , and potassium chloride, the latter being employed as a flux. The operation is conducted in a porcelain crucible contained within a plumbago crucible, and a high heat is necessary to fuse the reduced uranium. So obtained, uranium is of an iron or nickel color, not quite as hard as steel, and has a density of 18.4. When heated in the air, it is oxidized with incandescence. It does not decom- pose water, but dissolves in dilute acids/disengaging hydrogen. Uranium Oxides. — The principal oxides are UO, and IPO 3 , besides which there exist several intermediate oxides, and prob- ably a uranic oxide UO 5 . Uranium Monoxide, UO, was at first believed to be the free metal. It is a brown powder, and may be obtained by strongly heating the sesquioxide with charcoal, or in a current of hydro- gen. Prepared in the latter manner, the monoxide is pyro- phoric. A corresponding hydrate is formed when solutions of* uranous salts are precipitated by alkaline hydrates. Uranic Oxide, U 2 3 , is obtained as a light-brown powder by heating uranyl nitrate to 250°. When heated to redness, it is converted into green uranoso-uranic oxide U 3 4 . Uranic oxide combines with bases forming a series of salts of the general formula R 2 U 4 7 , in which R is one atom of a monatomic metal. The uranates are yellow, insoluble in water, but soluble in. acids. The alkaline uranates may be obtained by precipitating a uranyl salt (see farther on) with an excess of alkaline hydrate. Sodium Uranate, Na 2 U 4 7 , is known in commerce as uranium yellow, and is used for painting on porcelain, and for coloring a yellow glass which is highly fluorescent. It is prepared in 1 Within recent years many chemists have adopted 240 as the atomic ■ weight of uranium. The arguments in favor of this change are hardly more forcible than those which can be advanced for the retention of the number 120. Indeed, the specific heat of uranium is 0.0619, and this mul- tiplied by 240 would give the inexplicably anomalous atomic heat 14.86. 400 ELEMENTS OF MODERN CHEMISTRY. the arts by heating in a reverberatory furnace a mixture of lime and pitchblende. The calcium uranate so formed is decom- posed by sulphuric acid, and the uranyl sulphate obtained is treated with sodium carbonate. On adding very dilute sul- phuric acid, uranium yellow is precipitated. Uranium Chlorides. — There are three chlorides, tPCl 6 , UCP, UC1 5 , and an oxychloride U 2 2 CP. The dichloride is formed by the action of chlorine on a heated mixture of char- coal and any oxide of uranium. It is a very deliquescent body, crystallizing in black or dark-green regular octahedra having a metallic lustre. It reduces the salts of gold and silver, and converts ferric into ferrous chloride. When heated in hydro- gen, it is converted into the chloride U 4 C1 6 . Salts of Uranium. — There is a series of uranous salts, and a series formed by the radical TJO, which has received the name uranyl and appears to be monatomic. The former salts are green, and are readily converted by oxidizing agents into the corresponding uranyl salts which are yellow. Uranyl nitrate, UO.NO 3 , which may serve as a starting-point for the preparation of uranium compounds, may be made from pitchblende. The latter is pulverized, roasted, and treated with nitric acid. The solution is evaporated to dryness, the residue exhausted with water, and the liquid filtered. The yellowish- green filtrate is concentrated, and the confused crystalline mass 'which separates on cooling is drained and recrystallized from hot water. The new crystals are dried and submitted to a re- crystallization from ether, which dissolves the uranyl nitrate without dissolving the impurities. Uranyl nitrate forms large, canary yellow, orthorhombic prisms, very soluble in water, and soluble also in alcohol and ether. Heat converts it into uranium sesquioxide. CHROMIUM. Cr = 52.5 Chromium was discovered in 1797, by Vauquelin, in a min- eral formerly known as red lead of Siberia, and which is chromate of lead. It forms one of the elements of chrome iron, a combination of chromium oxide with ferrous oxide, Cr 2 3 .FeO, which corresponds to magnetic oxide of iron, Fe 2 3 .FeO. COMPOUNDS OF CHROMIUM AND OXYGEN. 401 H. Deville isolated the metal by calcining chromium oxide with charcoal and linseed oil in crucibles of lime and charcoal. Thus prepared, chromium forms grayish- white, metallic grains, which are brittle, as hard as corundum, and have a density of 5.9. This metal does not oxidize in the air at ordinary tempera- tures. At a red heat, it is converted into the oxide Cr 2 3 . When thrown into potassium chlorate in a state of fusion, it burns with a dazzling white flame, a chromate being formed. It burns in the same manner in chlorine gas, being transformed into a violet chloride. It dissolves in hydrochloric acid, disen- gaging hydrogen. COMPOUNDS OF CHROMIUM AND OXYGEN. There are two well-defined compounds of chromium and oxygen, the green oxide of chromium, Cr 2 8 , and chromic anhydride, CrO 3 . Chromium Oxide, CrO 3 , is a green powder; it may be obtained by calcining mercurous chromate, 2Hg*CrO* = 4Hg + O 5 + Cr 2 3 Another process consists in heating in a crucible a mixture of 2 parts of potassium dichromate with a little more than 1 part of flowers of sulphur. After cooling, the mass is treated with water, which dissolves out potassium sulphate and leaves chromium oxide. Eremy obtained it in small crystals by passing chlorine gas over potassium chromate heated to redness, and exhausting the cooled mass with water. Chromium oxide is undecomposable by heat, and melts only at the temperature of the forge. It forms several different hydrates. When ammonia is added to the green solution of chromic chloride, a green, flaky precipitate of chromic hydrate is formed ; it is soluble in acids and in potassium hydrate. Chromic Anhydride, CrO 3 , is prepared by gradually adding to a cold saturated solution of potassium dichromate 1J times its volume of sulphuric acid. The chromic anhydride, ordina- rily called chromic acid, set free separates in needle-shaped crystals of a dark-red color, which should be drained and re- crystallized in a small quantity of warm water. It is deliquescent; its aqueous solution has a dark yellow- 34* 402 ELEMENTS OF MODERN CHEMISTRY. brown color. It is an energetic oxidizing agent. Hydrochlo- ric acid converts it into chromic chloride, with evolution of chlorine. 2Cr0 3 + 12HC1 = Cr 2 Cl 6 + 6H 2 + 3CP If a concentrated solution of sulphurous acid be added to a solution of chromic acid, the liquid immediately becomes green from the formation of chromic sulphate. Chromates. — The most important chromates are those of potassium and lead. Potassium neutral chromate, K 2 Cr0 4 , crystallizes in lemon- yellow, right rhombic prisms, isomorphous with potassium sul- phate. It is very soluble in water, to which it communicates an intense yellow color. So great is its coloring property, that one part of chromate will sensibly color 40,000 parts of water. Potassium dichromate, K 2 Cr 2 7 , is prepared by heating to redness 2 parts of chrome iron with 1 part of nitre. The mass is exhausted with water, which dissolves out potassium neutral chromate; acetic acid is added to this solution, precipitating the silica, which is derived from the crucible and remains in the solution as silicate, and removing one-half of the potassium from the chromate, thus converting it into the dichromate. The latter crystallizes out on evaporation. Potassium dichromate is a beautiful salt of an orange-red color. It crystallizes in quadrangular tables derived from a dissy metric prism. It dissolves in 8 or 10 parts of cold water and in a much less quantity of boiling water. A strong heat decomposes it into neutral chromate, chromium oxide and oxygen. 2K 2 Cr 2 7 = 2K 2 Cr0 4 + Cr 2 3 + O 3 When heated with sulphuric acid, it loses oxygen and is converted into chromic sulphate and potassium sulphate. K 2 CV0 7 + 4H 2 SO = Cr 2 (S0 4 ) 3 + K 2 SO + 4H 2 -f O 3 The residue when exhausted with water yields a green solu- tion, which deposits on evaporation beautiful octahedral crystals of a violet-black color, constituting chrome alum. Cr 2 (S0 4 ) 3 .K 2 S0 4 + 24H 2 COMPOUNDS OF CHROMIUM AND CHLORINE. 403 Sulphurous acid reduces potassium dichrornate iu the cold, also yielding chrome alum if sulphuric acid be added. KWO 7 + 3S0 2 + H 2 SO = Cr 2 (SO*) 3 .B?S0 4 + H 2 The. constitution of potassium dichrornate is represented by the formula KOCrO 2 > KOCrO 2 COMPOUNDS OF CHROMIUM AND CHLORINE. Several combinations of chromium and chlorine are known The most important is the violet chloride. Cr 2 Cl 6 , correspond- ing to aluminium chloride and ferric chloride. It is prepared by passing chlorine gas over an intimate and perfectly dry mixture of chromium oxide and charcoal, heated to redness in a porcelain tube ; carbon monoxide is disengaged, and chromic chloride sublimes into the cooler portion of the tube in brilliant peach-blossom-colored scales. These crystals are almost insoluble in cold water, and dis- solve but slowly in boiling water. Hydrogen reduces them at a red heat, with formation of hydrochloric acid, and a chloride, Cr 2 CP, which crystallizes in white scales (Peligot). CrCl 6 + H 2 = 2HC1 -f CrCP If a small quantity of the chloride Cr 2 CP. be added to hot water, holding in suspension the violet chloride. CVC1 6 , the latter will be instantly dissolved, forming a green solution. Chlorochromic anhydride. Cr0 2 CP. is obtained by heating a previously fused mixture of common salt and potassium di- chrornate with sulphuric acid ; abundant red vapors are disen- gaged, and condense to a blood-red liquid. This body boils at 116.8°. Its density at 25° is 1.920 (Thorpe). On contact with water it decomposes into hydrochloric acid and chromic- anhydride. Cr0 2 Cl 2 + H 2 = CrO 3 + 2HC1 404 ELEMENTS OF MODERN CHEMISTRY. MOLYBDENUM. Mo = 96 This metal is prepared by reducing molybdic oxide, MoO 3 , by a current of hydrogen at a high temperature. It is a white, very hard, and almost infusible metal, having a density of about 8.6. It forms five oxides, MoO, Mo 2 3 , MoO 2 , Mo 2 5 , and MoO 3 , and a chloride,, which seems to have the composition MoCl 5 . Molybdic Oxide, MoO 3 , is obtained by roasting the native sulphide, molybdenite, MoS 2 , which occurs in black foliated masses closely resembling graphite, and capable of marking paper in the same manner. The roasting is conducted at a temperature not above redness, and the resulting oxide is dis- solved in ammonia, and the solution filtered. On evaporation and cooling, crystals of ammonium molybdate are obtained which yield molybdic oxide when calcined in the air. Molybdic oxide is a white, fusible, and volatile powder; it is but slightly soluble in water ; the solution, however, being acid. It is the anhydride of an acid which forms a somewhat complicated series of salts, one of the most important being a molybdate of ammonium having the composition Mo 7 24 (NH 4 ) 6 +4H 2 = 3(NH 4 ) 2 Mo0 4 +4H 2 Mo0 4 . This is the compound which is formed when a solution of mo- lybdic oxide in ammonia is evaporated. It is employed in the laboratory as a test for phosphorus. When its solution in nitric acid is added to a warm solution containing phosphoric acid, a yellow precipitate containing molybdic acid, ammonia, and phos- phoric acid, is thrown down. This precipitate is insoluble in nitric acid, but soluble in ammonia. TUNGSTEN. W (Wolframium) == 184 Tungsten occurs in a number of minerals, associated princi- pally with tin ores. Wolfram is tungstate of iron and manga- nese. Scheelite is calcium tungstate ; stolzite or scheelitine is tungstate of lead. The metal may be obtained by calcining tungstic oxide, WoO 3 , intimately mixed with charcoal, in a brasqued crucible or in a TUNGSTEN. 405 current of hydrogen. It has been obtained only as a highly refractory, grayish powder, having a density of about 19. It is not readily oxidized directly, except at high temperatures. It forms chlorides, WCP, WC1 4 , WC1 5 , and WC1 6 , and oxides, WO 2 , W0 3 : and W 2 5 . Tungstic Oxide, WO 3 , occurs native in a yellow powder called wolframine. It may be prepared from scheelite or from wolfram. The mineral is treated with nitro-muriatic acid, and the undissolved residue, consisting of tungstic oxide, is dissolved in ammonia. The filtered solution is evaporated to dryness, and on calcination the ammonium tungstate leaves tungstic oxide as pale yellow scales. It is fusible at a high temperature, insoluble in water and acids, soluble in alkaline solutions with formation of tungstates. Tungstic oxide is the anhydride of several acids forming well-marked salts. Normal tungstic acid, H 2 W0 4 , is precipitated as an insolu- ble yellow powder when the solution of a tungstate is decom- posed by an excess of hot acid. The alkaline normal tungstates have the general formula RrWO 4 . Besides these, there are highly complicated salts derived from the condensation of several molecules of the normal salts. One of these, known as sodium paratungstate, is prepared on a large scale by roasting wolfram with sodium hydrate and exhausting the mass with water. Its composition is Na 10 W 12 O 41 : it is used as a mordant in dyeing, and has been recommended for rendering fabrics of vegetable origin non- inflammable. The goods are treated with a solution containing twenty per cent, of sodium tungstate and three per cent, of socium phosphate. The remaining elements are tetratomic, some of them at the same time forming unsaturated compounds in which the me- tallic atom may be diatomic, as in the oxides of tin, Sn iv 2 and Sn"0. Or t#vo atoms of the metal may form a hexatomic couple, as in titanium sesquioxide, Ti 2 3 . Tin, titanium, zirconium, and thorium form a group of which the chemical analogies become evident in a comparison of the composition and relations of similar compounds, while platinum is the most important member of another group of metals which are associated together in nature, and which are related by certain chemical and physical properties. 406 ELEMENTS OP MODERN CHEMISTRY. TIN. Sn (Stannum) = 118 Natural State and Extraction. — The only mineral of tin which is worked is the dioxide (cassiterite). It is found in veins in the oldest formations, or disseminated in sand produced by their disaggregation. The principal tin mines are in India, in Malacca and the island of Banca, in Wales and in Saxony. Tin ore generally occurs mixed with various other minerals, such as sulphide and sulph-arsenide of iron, sulphides of copper and tin, etc. It is crushed and washed in order to remove light, earthy matters, and then roasted. The sulphides and sulph-arsenides are thus oxidized and disintegrated, and the product is submitted to a sec- ond washing which removes the lighter oxides, leaving the cassiterite. The latter is then heated with charcoal in a cupola-furnace, represented in Fig. 119; it is a sort of pris- matic furnace, having a hearth at the bottom where the melted metal collects. Air is blown in through the tuyere D. Car- bon monoxide is formed, and this reduces the stannic oxide ; the tin collects on the hearth, from which it is drawn into the basin I, where it is stirred with rods of green wood. The steam and gases produced by the carbonization of the wood, agitate the melted mass and bring to the surface the foreign matter or dross, which is removed. The tin is then run into moulds. Thus obtained, tin generally contains small quantities of copper, iron, lead, antimony, and arsenic. It is purified by slowly heating it on the hearth of a reverberatory furnace; the pure tin melts first and runs out of the furnace, while the less fusible alloys remain upon the hearth. This method of purification is called liquation. Properties. — Pure tin is a white metal, resembling silver in Fig. 119. tin. 407 its color and lustre. It melts at 228°, and crystallizes when slowly cooled. Crystals of tin, belonging to the type of the right square prism, may also be obtained by galvanic precipi- tation of the metal. Their density is 7.178. That of the fused and slowly-cooled metal is 7.373 (H. Deville). Tin is ductile and malleable. When a bar of tin is bent, it produces a peculiar noise called the cry of tin. The metal is unaltered by the air, but when fused, rapidly becomes covered with a grayish pellicle of oxide. Tin dis- solves in concentrated hydrochloric acid, disengaging hydrogen. The action is rapid when heat is applied. If ordinary nitric acid be poured upon granulated tin, an energetic action takes place immediately. The tin is converted into a white powder of dioxide, and torrents of red vapors are evolved. Very dilute nitric acid attacks tin almost without disengage- ment of gas. After some time the liquid will be found to con- tain a small quantity of tin nitrate and ammonium nitrate. The ammonia is formed by the simultaneous reduction of water and nitric acid by the tin. HNO 3 + H 2 = 20 2 + NH 3 When tin is heated with a concentrated solution of either potassium or sodium hydrate, hydrogen is disengaged, and an alkaline st annate is formed. Uses of Tin. — Tin enters into the composition of bronzes; it is made into dishes and covers, and the thin foil in which various substances, such as chocolate and tobacco, are enveloped. Tinning of kitchen vessels consists in covering them with a thin coating of tin. This protects the copper or iron from the action of the acids which enter into the composition of various articles of food. The objects to be tinned are first well cleaned by rubbing them with sand, and are then dipped into melted tin. After separating the excess of metal, they are polished by rubbing with cloths dipped in sal ammoniac. Tin-plate is sheet-iron covered with a thin layer of tin. The iron is first dipped into dilute sulphuric acid to remove the oxide; it is then rubbed with sand, and afterwards plunged successively into a bath of melted tallow and a bath of tin covered with tallow. On contact with the iron, the tin-enters into com- bination, forming a true alloy, which becomes covered with a coating of pure tin. 408 ELEMENTS OF MODERN CHEMISTRY. When the surface of tin-plate is washed with a mixture of hydrochloric and nitric acids, the superficial coat of tin is dis- solved, and the crystallized alloy of tin and iron is exposed. This is called crystallized tin-plate. COMPOUNDS OF TIN AND OXYGEN. Tin forms two compounds with oxygen, stannous oxide, SnO, and stannic oxide, SnO 2 . The first is of but little importance. It is obtained by precipitating a solution of stannous chloride by potassium hydrate, and boiling the precipitate, by which the white, stannous hydrate first formed is converted into a black crystalline powder of stannous oxide. When this substance is heated to 250°, it decrepitates, increases in volume, and becomes converted into an olive-brown powder, which is a dimorphous modification of the black oxide. STANNIC OXIDE. SnO 2 This body is found in nature in the form of beautiful, hard, transparent crystals of a yellowish-brown color, belonging to the type of the square prism. The white powder obtained when the metal is treated with nitric acid is a stannic hydrate, which plays the part of an acid, and was named by Fremy metastannic acid. He attributes to it the composition 5(H 4 Sn0 4 ). It would be a polymere of normal stannic acid. ^J0 4 = (0H) 4 Sn h When heated to 100°, this hydrate loses half of its water; at a -red heat, it loses the remainder and is converted into stannic oxide. When ammonia is added to an aqueous solution of stannic chloride, a white, gelatinous precipitate is formed, constituting a hydrate. H 2 Sn0 3 = S j£ | : This is the stannic acid of Fremy. It dissolves readily in hydrochloric acid, and the solution behaves as would an aqueous solution of stannic chloride. H 2 Sn0 3 + 4HC1 = SnCl* + 3IP0 SULPHIDES OF TIN — STANNOUS CHLORIDE. 409 It reacts with the bases, forming stannates of which the general composition is expressed by the formula: R 2 Sn0 3 = |* | O 3 When heated to 140°, or even when dried for a long time in a vacuum, it becomes insoluble in acids. SULPHIDES OF TIN. Two sulphides of tin are known : a monosulphide, SnS, and a disulphide, SnS 2 . The first is obtained by heating tin-filings with flowers of sulphur : the product still contains an excess of tin, and it is necessary to again heat it with a fresh quantity of sulphur. It is a crystalline, lead-colored mass. Tin disulphide or stannic sulphide is prepared by first making an amalgam of 12 parts of tin and 6 parts of mercury ; this is pulverized and the powder is mixed with 7 parts of flowers of sulphur and 6 parts of sal-ammoniac. The mixture is intro- duced into a matrass of green glass and gradually heated to dull redness on a sand-bath. Sulphur, sal-ammoniac, sulphide of mercury, and stannous sulphide are condensed in the upper part of the matrass, of which the interior becomes covered with a yellow crystalline mass of stannic sulphide. The presence of sal-ammoniac and mercury, which volatilize in this opera- tion, prevents an elevation of temperature, which would decom- pose the stannic sulphide. The latter is carried with their vapors, and condenses in brilliant, gold-like scales, which are greasy to the touch. This body is known as mosaic gold. It is decomposed by a red heat into stannous sulphide and sul- phur. It is used for coating the cushions of electric machines. STANNOUS CHLORIDE. SnCl 2 This compound may be prepared anhydrous by heating tin in hydrochloric acid gas. Hydrogen is evolved, and a white or grayish mass remains, which has a greasy appearance, and is almost transparent. It fuses at 250°. This is stannous chloride. When tin is dissolved in hot, concentrated hydrochloric acid and the limpid solution is evaporated and allowed to cool, beautiful transparent crystals are obtained, which contain s 35 410 ELEMENTS OF MODERN CHEMISTRY. SnCP + 2H 2 0. This is known in commerce as tin salt or tin crystals. The crystals of stannous chloride dissolve in a small quan- tity of water, forming a limpid liquid, but when treated with a large quantity of water, they yield a cloudy liquid, which holds in suspension a small quantity of white oxy chloride. The atmospheric oxygen dissolved in the water takes part in this decomposition of stannous chloride, from which it removes part of the metal, a corresponding quantity of stannic chloride (tetrachloride) being formed. Stannous chloride reduces many oxygenized and chlorinated compounds. It decomposes the salts of silver and mercury, setting free the metal. It instantly decolorizes the purple solution of potassium permanganate. If a solution of stannous chloride be added to a solution of corrosive sublimate (mercuric chloride), a white precipitate of calomel (mercurous chloride) is instantly formed. By adding an excess of stannous chloride, all of the chlorine may be re- moved from the mercuric chloride, and a gray precipitate of metallic mercury will be formed. Stannous chloride is employed as a mordant in dyeing. STANNIC CHLORIDE (TETRACHLORIDE OF TIN). SnCl* If thin tin-foil be thrown into a jar of chlorine gas, the metal will take fire, and in presence of an excess of chlorine will be converted into anhydrous stannic chloride. This is liquid, and gives oif white fumes in the air. It was formerly known as fuming liquor of Libavius. It is prepared by passing dry chlorine upon tin contained in a small retort. The anhydrous chloride condenses in the re- cipient in the form of a yellow liquid. It may be decolorized by rectification with a small quantity of mercury, which removes the excess of chlorine. Tin tetrachloride boils at 120°. Its density is 2.28. A small quantity of water added to it is absorbed with a hissing noise, and the formation of a crystalline deposit of a hydrate, SnCl 4 + 5H 2 0. These crystals may also be obtained by dissolving tin in aqua regia and evaporating the solution, or, again, by passing chlo- TITANIUM. 411 rine into a solution of stannous chloride and concentrating the solution. The crystals of hydrated stannic chloride dissolve in water, forming a clear solution. Characters of Stannous Solutions. — Brown precipitates are formed by both hydrogen sulphide and ammonium sulphide ; the precipitate dissolves in an excess of the latter reagent. Potassium hydrate forms a white precipitate, soluble in an excess of potassa ; ammonia yields a white precipitate, insoluble in excess. An excess of stannous chloride produces a gray precipitate of metallic mercury in a solution of mercuric chloride. Chloride of gold gives a purple precipitate (purple of Cas- sius) in dilute stannous solutions. Characters of Stannic Solutions. — Hydrogen sulphide and ammonium sulphide form yellow precipitates, soluble in a large excess of the latter reagent. Potassa, soda, and ammonia, all form white precipitates, disappearing in an excess of the reagent. Chloride of gold does not precipitate stannic solutions. A sheet of iron or zinc will precipitate the tin from either stannous or stannic solutions in gray scales, which assume the metallic lustre when burnished. TITANIUM. Ti = 50 Titanium exists in rutile, anatase, and brookite, which con- stitute three varieties of titanic oxide, and associated with iron in titaniferous iron ores. Cubical copper-colored crystals of a nitro-cyanide of titanium are frequently found in the cinders of blast-furnaces in which titaniferous ores are reduced. The metal can be obtained only with great difficulty, and then in the form of powder. It manifests a remarkable affinity for nitrogen. Titanium forms three chlorides, TiCP, Ti 2 Cl 6 , and TiCl 4 ; there are two well-defined oxides, Ti 2 3 and TiO 2 , and possibly a third, TiO. These compounds sufficiently characterize the element as a chemical analogue of tin. Titanium Dioxide, TiO 2 , as before mentioned, occurs in three different crystalline forms in nature ; as square prisms in 414 ELEMENTS OF MODERN CHEMISTRY. independently of 73 to 86 per cent, of platinum, various other metals, such as indium, palladium, rhodium, osmium, ruthenium, gold, iron, and copper-; an alloy of osmium and iridium, and various minerals, such as titaniferous iron, chrome iron, pyrites, etc. The ore is well washed to remove the sand, and treated with dilute aqua regia which dissolves the gold, iron, and cop- per ; it is then heated with concentrated hydrochloric acid and nitric acid is gradually added. The aqua regia dissolves the platinum and certain of its accompanying metals, leaving the osmium and iridium. The solution is neutralized with sodium carbonate and treated with a solution of cyanide of mercury, which precipitates palladium cyanide. A solution of ammo- nium chloride is added to the filtered liquid, and forms an abundant precipitate of ammonium and platinum double chlo- ride, which is generally mixed with a small quantity of ammo- nium and iridium double chloride. This precipitate is calcined at a dull-red heat, and leaves a dull-gray, spongy residue. It is spongy platinum. It contains a small quantity of iridium. To give coherence to this sponge and convert it into a mal- leable and ductile metal, it is reduced to powder in a wooden mortar and triturated with enough water to convert it into a perfectly homogeneous paste. This paste is introduced into a slightly-conical cylinder of brass or iron, and compressed first with a wooden piston, then by a steel rod. The compression is finished by the aid of a hydraulic press, and the slightly- conical cylinders so formed are heated to whiteness and forged under the hammer, as iron is forged. H. Sainte-Claire Deville and Debray have recently extracted the metal by simple fusion of the ore. The fusion is effected in a lenticular cavity cut in two large masses of quick-lime, placed one above the other. A current of illuminating gas is directed into this furnace, and the combustion is supported by a continual supply of oxygen. Properties of Platinum. — Platinum has a grayish-white lustre. It melts only at the highest attainable temperatures. The density of the cast metal is 21.1 ; that of the forged metal 21.5. It softens at a white heat, and can then be forged and welded like iron. The experiments of H. Deville and Troost have shown that a red-hot platinum tube allows hydrogen to pass through its pores. Platinum has the curious property of condensing gases on its surface, and this property is the cause of certain chemical phe- CHLORIDES OF PLATINUM. 415 nomena that were formerly attributed to mere contact of the metal. If a morsel of platinum-sponge be introduced into a small jar filled with an explosive mixture of oxygen and hydrogen, the gases will combine instantly, with explosion. This property is most highly developed in platinum-black. for in this form the metal exists in an extreme state of division. It may be prepared by reducing a solution of platinic chloride by zinc; or platinum dichloride may be boiled with potassium hydrate, and alcohol or a solution of sugar gradually added to the liquid, which must be continually stirred. The platinum is precipitated as a black powder. Platinum is unaltered by the air. It is not attacked by either nitric, hydrochloric, or sulphuric acids, even boiling. It dissolves in aqua regia. The alkaline hydrates attack it at high temperatures on contact with the air. It is the same with the alkaline nitrates. There are two oxides of platinum, a monoxide, PtO, and a dioxide, PtO 2 . CHLORIDES OF PLATINUM. These are the more important compounds of platinum. There are two. a dichloride, PtCP, and a tetrachloride, PtCP. Platinum dichloride is obtained by cautiously heating the tetrachloride to 200°. Chlorine is disengaged, and after cool- ing, the residue is exhausted with boiling water, which leaves an olive-green powder, constituting the dichloride. When ammonia is added to a solution of platinum dichloride in hydrochloric acid, a green, crystalline powder separates after some time. It is called green salt of llagnus, and contains PtCP + 2NH 3 It maybe regarded as the dichloride of platinoso-diammonium. Pt" H 2 H 2 H 2 It is derived from two molecules of ammonium chloride by the substitution of an atom of diatomic platinum for two atoms of hydrogen. Platinum tetrachloride, or platinic chloride, PtCP. is r 2 f N 2 .CP 416 ELEMENTS OF MODERN CHEMISTRY. formed when platinum is dissolved in aqua-regia. A red- brown solution is obtained, which, after concentration and cool- ing, deposits red-brown needles of hydrated platinic chloride. The crystals lose their water when heated, and are converted into a dark, red-brown mass, which constitutes the anhydrous chloride PtCl*. This body absorbs moisture when exposed to the air. It is very soluble in water, alcohol, and ether. If a solution of ammonium chloride be added to a solution of platinic chloride, a yellow, crystalline precipitate of plati- num and ammonium double chloride is immediately formed. This body is but little soluble in cold water, but more soluble in boiling water, from which it is deposited in microscopic, regular octahedra. It is almost insoluble in alcohol. It contains PtCl*.2NH 4 Cl A yellow, crystalline precipitate of double chloride of plati- num and potassium is obtained, in the same manner, on adding a solution of platinic chloride to a solution of a potassium salt, if the liquids be not too dilute. PtCl 4 .2KCl OTHER METALS OF THE PLATINUM GROUP. Rhodium, ruthenium, palladium, iridium, and osmium are associated with native platinum, and are usually extracted from platinum residues. They are fusible with great difficulty, and not readily attacked by acids. Their separation from each other is accomplished by tedious and complicated reactions, but, with the exception of ruthenium and rhodium, they possess certain valuable properties which have found for them applications in the arts. They combine with oxygen, forming a series of feeble bases, and a series of acid oxides. With the exception of the volatile oxides of ruthenium and osmium, these compounds are decomposed by heat into metal and oxygen. Rhodium is less fusible than platinum, and almost insoluble in aqua-regia, which, however, dissolves it if it be alloyed with the baser metals. Its specific gravity is 12.1. It forms oxides RhO, Rh 2 3 , and RhO 2 , and a chloride Rh 2 Cl 6 . Ruthenium is a hard metal, having a density of 12.26 at OTHER METALS OF THE PLATINUM GROUP. 417 0°, and is more infusible than iridium. It is hardly attacked by boiling aqua-regia. One of its most interesting compounds is a volatile oxide RuO. Its chloride has the composition Ru 2 Cl 6 . Palladium has the lowest melting-point of the group of platinum metals, fusing at about the same temperature as wrought iron. Its specific gravity at ordinary temperatures is 11.4. When a bright piece of*the metal is heated in the air, its surface becomes tarnished from the formation of a film of oxide, but at a higher temperature this oxide is again reduced to metal. The remarkable facility with which palladium ab- sorbs hydrogen has already been mentioned (page 51). Pal- ladium forms three oxides, Pd 2 0, PdO, and PdO 2 , and two chlorides, PdCl 2 and PdCl 4 . Iridium occurs with the platinum ores in grains of platin- iridium and osmiridium. Its fusing-point is the highest after osmium and ruthenium. It is very hard, and next to osmium it has the highest specific gravity of any substance known, its density being 22.38. An alloy of platinum and iridium con- taining ten per cent, of the latter metal is as hard and elastic as steel, unalterable in the air, and less fusible than platinum. It is used for the points of gold pens. Iridium forms two oxides, lr 2 3 and IrO 2 , and two chlorides, Ii 2 Cl 6 and IrCl 4 . Osmium has been obtained in cubical or rhombohedral crystals having a density of 22.48. It is infusible, and when strongly heated in the air burns into a volatile oxide, OsO 4 , which is dangerously poisonous. The native alloy, osmiridium, is used for the points of gold pens. s* 416 ELEMENTS OF MODERN CHEMISTRY. formed when platinum is dissolved in aqua-regia. A red- brown solution is obtained, which, after concentration and cool- ing, deposits red-brown needles of hydrated platinic chloride. The crystals lose their water when heated, and are converted into a dark, red-brown mass, which constitutes the anhydrous chloride PtCl*. This body absorbs moisture when exposed to the air. It is very soluble in water, alcohol, and ether. If a solution of ammonium chloride be added to a solution of platinic chloride, a yellow, crystalline precipitate of plati- num and ammonium double chloride is immediately formed. This body is but little soluble in cold water, but more soluble in boiling water, from which it is deposited in microscopic, regular octahedra. It is almost insoluble in alcohol. It contains PtCl 4 .2NH 4 Cl A yellow, crystalline precipitate of double chloride of plati- num and potassium is obtained, in the same manner, on adding a solution of platinic chloride to a solution of a potassium salt, if the liquids be not too dilute. PtCl 4 .2KCl OTHER METALS OF THE PLATINUM GROUP. Rhodium, ruthenium, palladium, iridium, and osmium are associated with native platinum, and are usually extracted from platinum residues. They are fusible with great difficulty, and not readily attacked by acids. Their separation from each other is accomplished by tedious and complicated reactions, but, with the exception of ruthenium and rhodium, they possess certain valuable properties which have found for them applications in the arts. They combine with oxygen, forming a series of feeble bases, and a series of acid oxides. With the exception of the volatile oxides of ruthenium and osmium, these compounds are decomposed by heat into metal and oxygen. Rhodium is less fusible than platinum, and almost insoluble in aqua-regia, which, however, dissolves it if it be alloyed with the baser metals. Its specific gravity is 12.1. It forms oxides RhO, Rh 2 3 , and RhO 2 , and a chloride Rh 2 Cl 6 . Ruthenium is a hard metal, having a density of 12.26 at OTHER METALS OF THE PLATINUM GROUP. 417 0°, and is more infusible than iridium. It is hardly attacked by boiling aqua-regia. One of its most interesting compounds is a volatile oxide RuO. Its chloride has the composition Ru 2 Cl 6 . Palladium has the lowest melting-point of the group of platinum metals, fusing at about the same temperature as wrought iron. Its specific gravity at ordinary temperatures is 11.4. When a bright piece of * the metal is heated in the air, its surface becomes tarnished from the formation of a film of oxide, but at a higher temperature this oxide is again reduced to metal. The remarkable facility with which palladium ab- sorbs hydrogen has already been mentioned (page 51). Pal- ladium forms three oxides, Pd 2 0, PdO, and PdO 2 , and two chlorides, PdCl 2 and PdCl 4 . Iridium occurs with the platinum ores in grains of platin- iridium and osmiridium. Its fusing-point is the highest after osmium and ruthenium. It is very hard, and next to osmium it has the highest specific gravity of any substance known, its density being 22.38. An alloy of platinum and iridium con- taining ten per cent, of the latter metal is as hard and elastic as steel, unalterable in the air, and less fusible than platinum. It is used for the points of gold pens. Iridium forms two oxides, Ir^O 3 and IrO 2 . and two chlorides, Ii 2 Cl 6 and IrCh Osmium has been obtained in cubical or rhombohedral crystals having a density of 22.48. It is infusible, and when strongly heated in the air burns into a volatile oxide, OsO 4 , which is dangerously poisonous. The native alloy, osmiridium, is used for the points of gold pens. s* ORGANIC CHEMISTRY. GENERAL IDEAS UPON THE CONSTITUTION OF ORGANIC COMPOUNDS. Organic chemistry studies the history of the compounds of carbon. The most simple of these are the gases carbon monoxide and carbon dioxide ; each contains but a single atom of carbon. In this respect they resemble the inflammable gas which is disengaged from the mud of marshes ; it contains one atom of carbon combined with four atoms of hydrogen. The gas hydrogen dicarbide or ethylene, which has already been mentioned, contains two atoms of carbon united with four atoms of hydrogen. A great number of compounds are known which contain only carbon and hydrogen, and they are called hydrocarbons or carburetted hydrogens. The atoms of carbon are aggregated in them, together with the atoms of hydrogen. Other elements are often added to the preceding, forming molecules more or less complex. The carbon atoms form as it were the framework, and the carbon compounds possess pecu- liar properties precisely on account of the easy facility with which the atoms of carbon accumulate in one and the same molecule, and link themselves in some manner one to another. The following developments will give some idea of the mode of generation and the structure of organic molecules. The most Simple Organic Compounds. — Their Composi- tion proves Carbon to be a Tetratomic Element. — The most simple of the hydrocarbons is marsh gas. When this gas is submitted to the action of chlorine, one or more atoms of hydrogen may be removed from it ; they com- bine with the chlorine and are disengaged in the form of hy- drochloric acid gas. The curious fact, first noticed by Dumas, is then observed, that each atom of hydrogen which is removed is replaced by an atom of chlorine. This substitution 418 INTRODUCTION TO ORGANIC CHEMISTRY. 419 rise to a series of chlorinated compounds, which present the most simple relations with marsh gas. The latter contains only carbon and hydrogen. The chlorine compounds derived from it by substitution, form with it the following series : CH* marsh gas, or methane. CH 3 C1 monochloromethane (methyl chloride). CH 2 C1 2 dichloromethane (methylene chloride). CHC1 3 trichloromethane (chloroform). CC1 4 tetrachloromethane (carbon tetrachloride). In each of these compounds a single atom of carbon is united with four monatomic atoms. We have seen that the atoms of chlorine and hydrogen are equivalent as regards their power of combination. In the preceding compounds, the sum of the atoms of hydrogen and chlorine which are combined with one atom of carbon is invariably four, and this number cannot be exceeded. But two atoms of a monatomic element may be re- placed by one atom of a diatomic element. One atom of car- bon, which unites with four atoms of hydrogen or chlorine, may unite with two atoms of oxygen to form carbon dioxide CO" 2 and this compound is saturated like those preceding, for one atom of oxygen is equivalent to two atoms of hydrogen or chlorine. In carbon monoxide, CO' 7 , the affinity of carbon is not satisfied ; hence this gas will unite directly with an atom of oxygen to form carbon dioxide, or with two atoms of chlo- rine to form chloro-carbonic gas. CO"CP In ammonia, one atom of nitrogen is combined with three atoms of hydrogen ; nitrogen is triatomic ; hence it may replace three atoms of hydrogen. A body is known which represents marsh gas, in which three atoms of hydrogen are replaced by one atom of nitrogen. This is the dangerous poison known as prussic or hydrocyanic acid, and the composition of which is represented by the formula CN'"H In all of the compounds which have just been mentioned a single atom of carbon is invariably united to a number of ele- ments of which the united atomicities is always four, and never more nor less than that number. It is then reasonable to conclude that in them carbon plays the part of a tetr atomic 420 ELEMENTS OF MODERN CHEMISTRY. element. This important fact, first exposed by Kekule, can be clearly understood if we represent the preceding atomic formulae in a graphic manner, that is, by symbols so arranged as to show the reciprocal relations of the atoms and their mutual satura- tion. In these formulae a saturated atomicity is indicated by a line of union, two atomicities by two lines, etc. H H H CI H-C-H H-C-Cl Cl-C-Cl Cl-C-Cl H H 6l CI Marsh gas. Monochloro Trichloromethane. Carbon methane. (Chloroform.) tetrachloride. ci 0=C=0 C1-C=0 H-CzN Carbon dioxide. Chlorocarbonic gas. Hydrocyanic acid. There exists a very volatile, ethereal liquid, which represents marsh gas, in which one atom of hydrogen is replaced by iodine. It is the body known as methyl iodide, CH 3 I. If this body be heated for a long time in a sealed tube with a solution of potassium hydrate, potassium iodide will be grad- ually formed, and the solution will contain a volatile, spirituous liquid which can easily be separated by distillation, for it boils at 66°. It is the same body which constitutes the most vola- tile of the liquids which are formed in the destructive distilla- tion of wood ; it is called wood spirit, and its chemical name is methylic alcohol. The reaction by which it is formed is very simple. The iodine of the methyl iodide combines with the potassium ; but when this iodine is removed, the carbon remains united to but three atoms of hydrogen. It is no longer saturated, and it therefore combines with the oxygen and hydrogen which were united with the potassium in the potassium hydrate. CH 3 I + KOH = CH 3 .OH + KI It will be seen that the atom of oxygen alone does not com- bine with the group CH 3 , which is called methyl. It is accom- panied by an atom of hydrogen, with which it remains united in the new compound which is called methyl hydrate or methylic alcohol. As has been said, this oxygen replaces the iodine in the iodide of methyl, but as it possesses two atomici- ties, and the carbon already united with H 3 has only one free atomicity, the atom of oxygen can only fix upon the carbon by INTRODUCTION TO ORGANIC CHEMISTRY. 421 one of its atomicities ; the other remains saturated by the atom of hydrogen. The latter is then drawn into the combination, and is united, not to the carbon, but to the oxygen. The reaction takes place as if the atom of iodine were replaced by the group liy- droxyl (OH) which is monatomic. Hence the relations between the atoms in methyl hydrate are represented by the formula H H-C-(OH)' H If we compare the constitution of the three bodies CH 3 C1, CH 3 I, CH 3 (OH), we notice that they contain a common ele- ment, namely, the group CH 3 , which is united to chlorine, to iodine, or to hydroxyl. Besides this, experiment has shown us that methyl iodide can be transformed into hydrate. The group methyl hence presents a certain stability and can pass from one combination to another. This is expressed by saying that it is a radical. If methyl iodide be heated with an aqueous solution of ammonia, among the products formed will be found the hydri- odide of a base which represents ammonia in which one atom of hydrogen is replaced by the group methyl. Potassium hydrate sets this base at liberty. At ordinary temperatures and pressures, it constitutes a gas, very soluble in water and possessing a strong ammoniacal odor. It is methylamine. The reaction by which it is formed is as follows : the iodine with- draws one atom of hydrogen from the ammonia, which atom of hydrogen is replaced by the group CH 3 . CH 3 I + NH 3 = CH 3 (NH 2 ).HI. Methylamine hydriodide. In methylamine then, the fourth atomicity of the carbon atom is saturated by nitrogen, but as this element is triatomic it brings into the combination two atoms of hydrogen which saturate its two other atomicities. It may then be said that in methylamine the fourth atomicity of carbon is saturated by the group NH 2 . This is expressed in the following formulae. H H H-C-N=H 2 = H-C!-(NH 2 )' A i Methylamine. 36 422 ELEMENTS OP MODERN CHEMISTRY. I Generation of Hydrocarbons containing Several Atoms of Carbon. — The preceding compounds contain but a single atom of carbon, but starting with one of these compounds we may produce more complicated organic molecules containing several carbon atoms. If methyl iodide be heated with sodium in sealed tubes, sodium iodide is formed, and a gas, a hydrocarbon, is confined under great pressure in the tubes. This gas escapes, and may be collected, when the drawn-out points of the tubes are opened in the blow-pipe flame. It is dimethyl, and has been formed according to the following reaction : 2CH 3 I + Na 2 = C 2 H 6 + 2NaI Methyl iodide. Dimethyl, or ethane. Two molecules of methyl iodide have entered into the reac- tion, and the whole of the carbon of these two molecules is found in one molecule of the hydrocarbon, C 2 H 6 = (CH 3 ) 2 , which results. On losing their iodine the two methyl groups combine to- gether. One of the carbon atoms attracts the other, exchanging with it the fourth atomicity set free by the loss of the iodine. Hence the iodine of one of the molecules of methyl iodide has been replaced by the carbon of the other, which fixes upon the group CH 3 by a single one of its atomicities, and at the same time brings into the combination the three atoms of hydrogen which saturate the other three atomicities. This is expressed in the following formulae : H H H H H-C-H H-C-I H-C-C-H i i ii H H HH Methane (methyl hydride). Methyl iodide. Dimethyl (ethyl hydride or ethane). The mode of generation of this new hydrocarbon, which contains two atoms of carbon, is worthy of consideration. It results from the substitution of a methyl group for one atom of hydrogen in methyl hydride. One atom of carbon, accompa- nied by three atoms of hydrogen, fixes upon another atom of carbon of which it completes the saturation. By this exchange of atomicities each of the carbon atoms retains only three affin- ities which are satisfied by three atoms of hydrogen. The two methyl groups, CH 3 -f- CH 3 = C 2 H 6 , are then united by their carbon atoms, and are held together by the affinity of INTRODUCTION TO ORGANIC CHEMISTRY. 423 carbon for carbon. In methyl hydrate the group hydroxyl is bound to the group CH 3 by the affinity of carbon for oxygen. In methylamine, the group NH 2 is united to the group CH 3 by the affinity of carbon for nitrogen. In dimethyl, it is carbon which is united to carbon. This has before been expressed by saying that the atoms of this element possess a faculty to accu- mulate in one and the same molecule. It is in this curious property that must be sought the reason for the existence of those innumerable compounds, more or less rich in atoms of carbon, which constitute the immense field of organic chemistry. But it is important to study by new examples this mode of formation of organic compounds. Dimethyl, which we have seen is produced by the action of sodium upon methyl iodide, is also known as ethyl hydride. If one of its atoms of hydrogen be replaced by an atom of chlo- rine, ethyl chloride, C 2 H 5 C1, is obtained. Ethyl iodide, C 2 H 5 I, represents ethyl hydride, in which one atom of hydrogen has been replaced by iodine. If a mixture of methyl iodide and ethyl iodide be heated with sodium, among the products of the reaction will be found a gas containing C 3 H 8 ; it is the methylide of ethyl, resulting from the combination of methyl, CH 3 , with the group ethyl, C 2 H 5 . It represents ethyl iodide in which the atom of iodine has been replaced by a methyl group, the carbon of the latter group being fixed by one of its atomicities to one of the carbon atoms of the group C 2 H 5 . In the same manner, by heating a mixture of propyl iodide, C 3 H 7 I, and methyl iodide with sodium, we may add to the propyl group, C 3 H 7 , a new atom of carbon escorted by its three atoms of hydrogen. HH HHH HHHH ii ill i i i i H-C-C-I H-C-C-C-H H-C-C-C-C-H, etc. ii ill i i i i HH HHH HHHH Ethyl iodide. Methyl-ethyl (propane). Methyl-propyl (butane). Nothing prevents the continuation of these additions of car- bon to incomplete hydrocarbons, that is, to the residues of the subtraction of iodine from the saturated iodides, of which the following are the names and formulae : CH 3 I C 2 H 5 I C 3 H 7 I C 4 H 9 I C 5 H n I, etc. Methyl iodide. Ethyl iodide. Propyl iodide. Butyl iodide. Amyl iodide. 424 ELEMENTS OF MODERN CHEMISTRY. The following hydrocarbons would then be formed succes- sively : CH3-CH3 C 2 H5-CH3 C 8 IF-CH3 C*H 9 -CH3 C 5 H n -CH 3 , etc. Methyl-methyl Methyl-ethyl Methyl-propyl Methyl-butyl Methyl-amyi (Ethane). (Propane). (Butane). (Pentane). (Hexane). In all of these cases, the atoms of carbon united together form, as it were, a continued chain, and the atoms of hydrogen are grouped around them as satellites. Homologous Bodies.: — Very simple relations exist between the hydrocarbons of which we have just studied the mode of formation. They form a series of which each member differs from the preceding by the addition of CH 2 . These relations will appear clearly if the formulae already given be replaced by the crude formulae : C H 4 methane. C 2 H 6 ethane. • C 3 H 8 propane. C 4 H 10 butane. C 5 H 12 pentane. This group of hydrocarbons constitutes what is called the homologous series of marsh gas, or the series C n H 2n+2 . Many other series are known, the terms of which are related to each other in the same manner, and the bodies which form part of them may present the greatest differences in composition. Sometimes they contain only carbon and hydrogen. Again, they may contain oxygen or nitrogen in addition to these ele- ments ; in this case the former elements are united to carbon by one or more of their atomicities, as has already been indicated. In any organic body whatever, if an atom of hydrogen united with carbon be replaced by a methyl group, CH 3 , the superior homologue of that body is obtained, that is, the compound which differs from the original body by the addition of CH 2 . There is a great resemblance in physical and chemical properties between such homologues. Some of these homologous series will be indicated farther on. Immediate Principles and Chemical Species. — The four elements, carbon, hydrogen, oxygen, and nitrogen, are the more ordinary elements of organic compounds. Those which are found in nature in the organs of plants and animals, and which have been called by Chevreul immediate principles, contain no others, excepting sulphur, which exists in certain of them. ELEMENTARY ANALYSIS. 425 But nearly all of the other elements can be introduced artificially into organic compounds ; it is thus with bromine, iodine, phos- phorus, arsenic, boron, silicon, and a great number of the metals. In uniting with carbon, in different manners and in various proportions, these elements form an innumerable multitude of compounds, each of which has a fixed composition and definite properties. These bodies constitute the chemical species, so to say. When submitted to the action of reagents, all may be modified in a thousand manners, and transformed into each other. Sometimes their composition is simplified, one or more carbon atoms being removed from the chain. Sometimes it is complicated by the addition of new atoms of carbon. All of these bodies contain carbon, and are distinguished from each other : 1. By the number of carbon atoms contained in the molecule. 2. By the nature and arrangement of the other atoms com- bined with the carbon. 3. By the arrangement of all of the atoms in the molecule. The facts relative to the atomic composition of organic com- pounds are obtained by elementary analysis and by the deter- mination of the molecular weight. ELEMENTARY ANALYSIS. The object of elementary analysis is the determination of the nature and proportion of the elements contained in any given organic body. We can give here but a summary descrip- tion of the processes employed, considering only those which have for object the determination of carbon, hydrogen, and ni- trogen. These, together, with oxygen, are the more ordinary elements of organic combinations. In a substance containing carbon, hydrogen, and oxygen, the first two elements are determined directly in the same operation ; the oxygen is determined by difference. When, in addition to the former elements, the body contains nitrogen, the determination of this requires a separate operation. Determination of Carbon and Hydrogen. — To determine the proportion of carbon and hydrogen contained in 100 parts of any given organic substance, the carbon is converted into car- bon dioxide, which is collected and weighed, and the hydrogen into water, which is condensed and weighed. These operations are conducted according to the processes indicated by Liebig. 36* 426 ELEMENTS OF MODERN CHEMISTRY. For this end, the organic matter, previously dried with care, is burned with an excess of cupric oxide. The operation is exe- cuted in a combustion-tube of hard glass, which is wrapped with a spiral of metallic foil to prevent it from bending and swell- ing under the influence of the heat. Well-dried cupric oxide is introduced into the tube, then an intimate mixture of the substance to be analyzed with a large excess of the same oxide, and the remainder of the tube is filled with pure cupric oxide. The tube is then placed in a combustion furnace, and its open extremity is put in communication with (1) an U tube, jg (Fig. 120), containing fragments of calcium chloride in the first branch, and pumice-stone impregnated with sulphuric acid in the second; (2) a tube with five bulbs, h, called Liebig's potash bulbs, containing a concentrated solution of potassium hydrate, and followed by a small U tube, % containing pumice-stone im- pregnated with potassium hydrate in the first branch, and frag- ments of potassium hydrate in the second. These different tubes have first been accurately weighed. When the appa- ratus is arranged, the combustion- tube is slowly heated, com- mencing at the extremity B, and gradually extending the heat so that each part of the tube is successively heated to redness. The water formed by the combustion is collected in the fir&t U tube, the carbon dioxide is absorbed by the potassium hy- drate in the bulbs. When the operation is terminated, the drawn-out point of the combustion-tube is broken, and con- nected by means of a caoutchouc tube with a gasometer con- taining oxygen. An excess of the latter gas is then passed through the combustion-tube, in order to drive out the traces of carbon dioxide and aqueous vapor which it contains at the end of the combustion. It is then only necessary to weigh the water tube and the carbon dioxide tubes. The increase in weight which is found indicates, on one hand, the quantity of water, and on the other the quantity of carbon dioxide, pro- duced by the combustion of the organic matter. The compo- sition of water and of carbon dioxide being known, it is easy to deduce from the weight of these two bodies the quantities of hydrogen and carbon contained in the analyzed substance, and consequently the proportion of these two elements con- tained in 100 parts of that substance. Fig. 120 represents the operation towards its close : the combustion-tube is in the gas-furnace, B, and communicates, on the right with the tubes ^, h, % destined to receive the pro- ELEMENTARY ANALYSIS. 427 428 ELEMENTS OF MODERN CHEMISTRY. ducts of the combustion, on the left with two large -U tubes, the first of which is filled with pumice-stone impregnated with potassium hydrate to absorb traces of carbon dioxide, the second with pumice-stone saturated with sulphuric acid to absorb moisture. Through these tubes is passed the oxygen, at the close of the operation, to expel the last portions of carbon dioxide and vapor of water. When the substance contains carbon, hydrogen, and oxygen, the proportion of oxygen is the difference between the total percentage of carbon and hydrogen found and 100. Fig. 121. Determination of Nitrogen. — Nitrogen may be determined by two processes. The first consists in burning a given weight of the nitrogenized substance with an excess of cupric oxide. The carbon of the substance is converted into carbon dioxide ; the hydrogen is converted into water ; the nitrogen is disen- gaged. The gases, nitrogen and carbon dioxide, are received in a graduated jar standing on the mercury-trough and con- taining potassium hydrate. The carbon dioxide is absorbed, the nitrogen remains. At the close of the operation, the last traces of nitrogen are expelled by a current of carbon dioxide. The volume of nitrogen is then measured, and its weight de- duced from its volume (Dumas). The second process (Fig. 121) consists in decomposing the nitrogenized organic matter with an alkali at a high tempera- ELEMENTARY ANALYSIS. 429 ture. By this means all of the nitrogen is converted into ammonia. The substance is intimately mixed with soda lime, that is, lime impregnated with caustic soda. The mixture is heated to redness in a tube of hard glass, and the ammonia is received in a tube with three bulbs containing dilute hydro- chloric acid. Ammonium chloride is formed ; when the opera- tion is terminated, the liquid containing the salt is mixed with a solution of platinic chloride. It is then evaporated and exhausted with alcohol, which leaves the platinum and ammo- nium double chloride, 2(XH 4 C1) + PtCl 4 . The latter is col- lected upon a tared filter, then washed and dried. From its weight is calculated that of the nitrogen contained in the organic substance (Will and Varrentrapp). The ammonia disengaged may also be received in 10 cubic centimetres of a normal solution of sulphuric acid, that is, an acid liquor containing a known quantity of sulphuric acid in a determined volume. The strength of this acid is determined by neutralizing 10 c.c. of it with a dilute alkaline solution of known strength and noting the volume of the latter required. The same operation is repeated with the 10 c.c. of which the acid has been par- tially neutralized by the ammonia. The quantity of ammonia corresponds to the difference between the volumes of the alka- line liquid employed in these two operations, and can easily be calculated by simple proportion (Peligot). Determination of the Molecular Weight of Organic Sub- stances. — Elementary analysis permits the determination of the centesimal composition of organic substances. This is indispensable, but it is insufficient for the establishment of their atomic composition, that is, the number of atoms of car- bon, hydrogen, oxygen, and nitrogen which are contained in a single molecule of a given organic compound. But if the weight of the molecule be known (hydrogen being taken as unity), it is easy to deduce the atomic composition from the figures given by elementary analysis, as will be seen by the following example. By elementary analysis it is found that 100 parts of acetic acid contain Carbon 40. Hydrogen 6.67 Oxygen 53.33 100.00 On the other hand, methods which will be described have 430 ELEMENTS OF MODERN CHEMISTRY. shown that the molecular weight of acetic acid is 60 ; that is to say, the total weight of the atoms of carbon, hydrogen, and oxygen contained in a molecule of acetic acid, is 60. Hence by the following proportions : If 100 parts acetic acid contain 40 of carbon, 60 parts contain x. « " « 6.67 of hydrogen, " " y. « « " 53.33 of oxygen " « z. From which, x = 24; y = 4 ; z = 32. Hence 24 represents the weight of the atoms of C contained in a molecule of acetic acid. 4 represents the weight of the atoms of H contained in a molecule of acetic acid. 32 represents the weight of the atoms of O contained in a molecule of acetic acid. By dividing these numbers by the weights of the respective atoms, the number of atoms of C, H, and O contained in a molecule of acetic acid is readily determined. 24 4- 12 = 2 atoms of carbon. 4^- 1 = 4 " hydrogen. 32 + 16 = 2 " oxygen. Hence the formula of acetic acid is C 2 H 4 2 . After the analysis of an organic substance has been made, it is only necessary to determine its molecular weight in order to establish its atomic composition. Several processes are em- ployed for this determination, of which the most sure is the determination of the vapor density. We know that if one atom of hydrogen occupy one volume, the molecules of organic substances occupy two volumes. To find the weights of these molecules it is then sufficient to deter- mine their vapor densities compared to hydrogen; that is, to find the weight of one volume of their vapors, that of one volume of H being taken as unity. The number found mul- tiplied by 2 gives the weight of two volumes, that is, the weight of the molecule. Hence a simple determination of the vapor density is suf- ficient for the establishment of the molecular weight. Ordi- narily these vapor densities are given as compared with air taken as unity. To bring them to the hydrogen scale it is then only necessary to multiply them by 14.44, which is the exact relation of the density of air to that of hydrogen. Thus the vapor density of acetic acid, determined at 295°, has been found equal to 2.083 (Cahours). This number multiplied by 14.44 gives for the density compared to hydrogen 30.08. The ISOMERISM, METAMERISM, POLYMERISM. 431 latter number expresses the weight of one volume of acetic acid vapor, the weight of one volume of hydrogen being con- sidered as 1. The weight of two volumes of this vapor, that is, the weight of the molecule, will then be 2 X 30.08 = 60.16, a number very nearly approaching 60, the theoretical molecular weight. The method just described can only be applied to substances which can be volatilized without decomposition. For other bodies another method must be adopted. The latter consists in forming with the organic body definite combinations, the atomic composition of which may be known. We will again consider acetic acid. Salts may be formed with this acid, and we know that these salts contain one atom of metal. We may then analyze silver acetate. 100 parts of that salt contain 64.67 parts of silver. This fact being known, it is easy to deter- mine the molecular weight of silver acetate. Since the latter contains one atom of silver, we can conclude, if 64.67 parts of silver are contained in 100 parts of silver acetate, 108 parts of silver, that is, one atom, are contained in x parts of silver acetate ; whence x = 167. This number represents the molec- ular weight of silver acetate. That of acetic acid may be de- duced by substituting the atomic weight of hydrogen for that of silver, which gives for the molecular weight of acetic acid 60. Analogous operations and reasoning permit the determina- tion of the molecular weights of bodies playing the part of bases. They are combined with an acid, the molecular weight of which is known, and the composition of the combination furnishes the data for the calculation of the molecular weight of the base. This method can be applied in a large number of analogous cases, and presents a great generality. ISOMERISM, METAMERISM, POLYMERISM. Elementary analysis demonstrates that many bodies which differ in their physical and chemical properties, possess exactly the same centesimal composition. Such bodies are said to be isomeric. Two kinds of isomerism exist. Sometimes the isomeric bodies contain the same number of similar atoms in molecules of the same size, and differ only by the arrange- ment of these atoms ; sometimes they contain similar atoms united in the same proportion, but not in the same number, in molecules of unequal magnitude. 432 ELEMENTS OF MODERN CHEMISTRY. In both cases the centesimal composition is the same, for it depends only on the relative number of the atoms. The first kind of isomerism constitutes metamerism; the second, polymerism. Acetic acid and methyl formate are an example of two metameric bodies. Each contains 2 atoms of carbon, 4 of hydrogen, and 2 of oxygen ; their molecules are equal in size, but different in atomic structure. The latter fact may be expressed by the following formulae : C 2 H 3 O.OH acetic acid CH 3 O.OCH methyl formate The first expresses that acetic acid contains a group of atoms, C 2 H 3 0, acetyl, which is united with hydroxyl, OH ; the second, that methyl formate contains a group, CHO, formyl, which is united with oxymethyl, CH 3 0. The difference in the atomic arrangement becomes evident, if the preceding formulae be developed in the graphic manner. (KH O-CH 3 C=0 G=0 i i CH 3 H Acetic acid. Methyl formate. By adopting the theory of atomicity, chemists have been enabled to discover the atomic structure of a great number of combinations, as we have seen in the case of acetic acid and methyl formate. Such considerations are of great importance for the interpretation of isomerism, and we will have frequent occasion to refer to the subject in the course of this work. Acetic acid and glucose or grape-sugar present an example of polymerism. Both contain the atoms of carbon, hydrogen, and oxygen, united together in the same proportions, but the molecule of the second contains three times as many of each as that of the first. C 2 H 4 2 acetic acid. 3 X C 2 H 4 2 = C 6 H 12 06 glucose. Among the more important and better known cases of po- lymerism, may be mentioned the numerous hydrocarbons which present, the centesimal composition of ethylene or olefiant gas, and which differ from it by the regularly increasing number of their atoms of carbon and hydrogen. These bodies form the following homologous series : FUNCTIONS OF ORGANIC COMPOUNDS. 433 C 2 H± ethylene. C 3 H6 propylene. C 4 H8 butylene. C5Hio auiylene. C6H12 hexylene. C 7 H 14 heptylene. C 8 H 16 octylene, etc. It will be seen that butylene contains twice as many carbon and hydrogen atoms as ethylene, hexylene contains three times as many, etc. FUNCTIONS OF ORGANIC COMPOUNDS. In the study of mineral chemistry it has been seen that bodies present great differences in properties, according to their composition. Some are simple and apt to enter into combina- tion ; others are compound and indifferent ; the first are more or less energetic in their affinities, the others saturated and satisfied. In one case, we have examined either more or less powerful acids or bases, some of which are hydrated, as potassa and soda, others anhydrous, as the oxides of lead and silver. In the other case, we have studied the salts resulting from the union of the former bodies. In organic chemistry we again encounter various kinds of bodies which have different functions, according to their com- position. It may be said, in a general manner, that the properties of compound bodies depend upon the nature of the atoms and their arrangement in the molecule. In treating of isomerism, the influence of the latter condition has been indicated ; that of the former is still more powerful. Water and potassium hydrate are both constituted, and in an analogous manner, of three elementary atoms. Each con- tains one atom of oxygen united to two monatomic atoms. HOH KOH Water. Potassium hydrate. But what a difference in their properties ! But may not this be expected when it is considered that one contains the energetic metal potassium, in the place occupied in the other by the light gas h} T drogen ? Is the difference between potassa and water greater than that between potassium and hydrogen ? t 37 434 ELEMENTS OF MODERN CHEMISTRY. And if for the two atoms of hydrogen we substitute two atoms of chlorine, is it not to be. expected that hypochlorous oxide Cl-O-Cl the molecule of which is similar in structure to that of water, shall differ from the latter in its properties as much as chlo- rine differs from hydrogen ? It is thus that the nature of the elements contained in compound bodies is the dominant condi- tion in the manifestation of their properties. The following considerations are of a nature to demonstrate the truth of this proposition inasmuch as concerns organic compounds : MONATOMIC COMPOUNDS. Saturated Hydrocarbons. — The hydrocarbons belonging to the series of marsh gas are all saturated. Consider, for example, C 2 H 6 ; all of the atomicities of two atoms of carbon are satisfied by the union of the latter together and with six atoms of hydrogen. HH i i H-C-C-H i i HH Ethane, or ethyl hydride. It is the same with all of its homologues ; the hydrides of propyl, butyl, amyl, etc., are all saturated hydrocarbons, as will be seen by developing the formula of any one of them, pentane, for example : HHHHH i I i i i H-C-C-C-C-C-H i i i i i HHHHH Pentane, or amyl hydride. All of these bodies are incapable of fixing other elements by direct addition, but they may be modified by substitution, that is, one or several of their atoms of hydrogen may be replaced by other elements. Monatomic Chlorides, Bromides, and Iodides. — By the reaction of bromine upon any of the hydrocarbons, we may MONATOMIC COMPOUNDS. 435 obtain compounds containing an atom of bromine in the place of an atom of hydrogen. C 2 H 6 + Br 2 = C 2 H 5 Br + HBr Ethane. Ethyl bromide. A saturated and indifferent hydrocarbon is thus converted into a bromide. The corresponding chloride and iodide exist, possessing the same constitution as the primitive hydrocarbon, and forming with it the following series : C 2 H 6 ethane. C 2 H5C1 ethyl chloride. C 2 H 5 Br ethyl bromide. C 2 H5I ethyl iodide. To the other hydrocarbons correspond chlorides, bromides, and iodides analogous to the preceding. Thus, the following groups are known : CH 4 methane. C 5 H 12 pentane. CH^Cl methyl chloride. C^IinCl amyl chloride. CH 3 Br methyl bromide. C 5 H n Br amyl bromide. CH 3 I methyl iodide. C 5 H n I amyl iodide. All of these bodies may be made to undergo the most varied transformations. They may be attacked by a number of re- agents, to which they present a hold, as it were, since the chlo- rine, bromine, and iodine which they contain are gifted with powerful affinities. The residues resulting from the subtraction of the chlorine, bromine, or iodine then enter into other combinations. It will be remarked that these residues represent the saturated hydro- carbons from which one atom of hydrogen has been removed. CH 8 = CH 3 Br — Br, orCH* - -H C 2 JP = C 2 H 6 Br — Br, or 2 H 6 - -H C 5 H U = C 6 H n Br — Br, or C 6 H 12 - -H The atoms of carbon contained in these residues, CH 3 , C 2 H 5 . and C 5 H n , are no longer entirely saturated, since CI, Br, I, or H has been removed, elements which saturated one atomicity. Therefore, these residues are capable of entering other com- binations, but as they possess only one free atomicity, they can only saturate one when they combine. This is expressed by saying that they play the part of monatomic radicals. The chlorides, bromides, and iodides from which they are derived are themselves monatomic. 436 ELEMENTS OP MODERN CHEMISTRY. Alcohols. — The neutral organic hydrates corresponding to the preceding chlorides, bromides, and iodides, are called alcohols. If ethyl iodide be heated for a sufficiently long time with potassium hydrate, potassium iodide will be formed, and the alkaline liquid will contain alcohol which may be separated. This body is ethyl hydrate and is formed according to the following reaction : C 2 H 5 I + KOH = KI + C 2 H 5 .OH Ethyl iodide. Ethyl hydrate. It is formed, as is seen, by double decomposition. The potassium having removed the iodine from the ethyl iodide, the monatomic residue C 2 H 5 combines with the monatomic residue OH. Alcohol is then the hydrate which corresponds to the iodide, C 2 H 5 I, and to the hydrocarbon, C 2 H 6 . Analo- gous hydrates correspond to the other hydrocarbons of the same series ; they constitute the series of monatomic alcohols, and may be denned as derived from the saturated hydrocarbons by the substitution of the group hydroxyl for one atom of hydrogen. The alcohols now known are numerous ; the follow- ing are some of them : CH 3 .OH methyl hydrate, or methylic alcohol. C 2 H 5 .OH ethyl hydrate, or ethylic alcohol. C 3 H 7 .OH propyl hydrate, or propylic alcohol. C 4 H 9 .OH butyi hydrate, or butylic alcohol. C 5 H n .OH amyl hydrate, or amylic alcohol. C 6 H 13 .OH hexyl hydrate, or hexylic alcohol. C 7 H 15 .OH heptyl hydrate, or heptylic alcohol. C 8 H 17 .OH octyl hydrate, or octylic alcohol. Each member of this series differs from that which follows by — CH 2 . All are allied by analogous properties. These two conditions characterize homologous bodies. The alcohols of which the general formula is C n H 2n+1 OH, form one of the most important series of homologues. If one of these alcohols be heated with hydrochloric, hydro- bromic, or hydriodic acid, water will be formed and the alcohol will be converted into a monatomic chloride, bromide, or iodide. In this reaction the hydroxyl, OH, is replaced by chlorine, bromine, or iodine. C 2 H 5 .OH -f HC1 = H 2 + C 2 H 5 C1 Ethyl hydrate. Ethyl chloride. The bodies thus formed are the monatomic chlorides, bro- MONATOMIC COMPOUNDS. 437 niides, or iodides before considered. These experiments expose the relations which exist between the latter compounds and the corresponding hydrates, which are the alcohols. Monobasic Acids. — Acetic acid, which exists in vinegar, is a derivative of alcohol, of which it is one of the products of oxidation. It is formed under many conditions, one of which is the oxidation of alcohol vapor on contact with platinum black and the air. C 2 H 5 .OH -f- O 2 = C 2 H 3 O.OH + H 2 Alcohol. Acetic acid. In this reaction an atom of oxygen removes two atoms of hydrogen to form water, and the place of these two atoms of hydrogen is filled by another atom of oxygen. The group ethyl, C 2 H 5 , thus becomes the group acetyl, C 2 H 3 0. and if alcohol be the hydrate of ethyl, acetic acid is the hydrate of acetyl. We can account for this reaction by developing the formulae of alcohol and acetic acid according to the principles before explained. H H HO H-C-C-OH + O 2 = H-C-C-OH + H 2 i i i HH H Alcohol. Acetic acid. In alcohol, the second carbon atom is combined with two atoms of hydrogen and with one group hydroxyl, while in acetic acid it is combined with an atom of oxygen and a group hydroxyl. Acetic acid contains two atoms of carbon united together, and combined, the one with H 3 . the second with and OH. It is thus formed of a group CH 3 united to a group CO-OH = C0 2 H. There exist many other acids analogous to acetic acid, and derived, like it, by oxidation of the monatomic alco- hols of the series C n H 2n+1 OH. All of these acids contain a hydrocarbon group analogous to methyl, combined with the group C0 2 H = CO-OH. "The hydrogen of the latter group can be readily replaced by an equivalent quantity of metal. This hydrogen is said to be strongly basic, and all of the organic acids which contain a single group, C0 2 H, united to a hydro- carbon group, are monobasic like acetic acid. The homologues of the latter form the following series : 37* 438 ELEMENTS OF MODERN CHEMISTRY. C H2 02 = H -C02H formic acid. m C2 H 4 2 = CH3 -C02H acetic acid. C3 H6 O 2 = C2H« -C02H propionic acid. C± m 02 = C3H7 -C0 2 H butyric acid. C5 H^O 2 = C±H 9 -C0 2 H valeric acid. C6 H^O 2 = C 5 HH-C02H caproic acid. C7 B.U02 = C6H 1 3-C0 2 H oenanthic acid. C 8 H1602 = C^H 1 5-C02H caprylic acid. C 9 H^O 2 = C8H"_C02H pelargonic acid. CiOH20()2 = C 9 Hi9-C02H capric acid, etc. The first series of formulae indicates simply the nature and number of atoms contained in the acids of the series C n H 2n 2 . They are empirical formulae. The second series gives certain indications upon the relations existing between these- atoms. They are rational formulae, and when developed so as to ex- press the relations between all of the atoms, they become constitutional formulae. Compound Ethers. — The compound ethers are combina- tions which represent acids of which the hydrogen has been replaced by an alcoholic group. If one of the alcohols of the preceding series, ordinary alco- hol, for example, be heated for a long time with acetic acid, water will be formed, and a volatile, neutral liquid possessing an agreeable odor may be separated from the product ; this sub- stance is ethyl acetate, or acetic ether. It is formed according to the following reaction : C 2 H 5 .OH + C 2 H 3 O.OH = C 2 H 5 0(C 2 H 3 0) + H 2 Alcohol. Acetic acid. Ethyl acetate. On comparing this compound with alcohol, we find that it is formed by substitution of the group C 2 H 3 0, the existence of which is admitted in acetic acid, and which is called acetyl, for one atom of hydrogen in alcohol ; and this atom of hydro- gen which is replaceable by acetyl is that which is united to the oxygen in alcohol, — that which forms a part of the hydroxy 1 group. The other atoms of hydrogen, those which constitute part of the group C 2 H 5 , cannot be replaced by acetyl. All of the acids can form with alcohol, and indeed with all of the alcohols, compounds analogous to ethyl acetate, and these combinations are called compound ethers. The property possessed by the alcohols of etherifying acids is general and characteristic of this class of compounds. Alcohols which require for etherification but a single molecule of an acid anal- MONATOMIC COMPOUNDS. 439 ogous to acetic acid are called monatoraic. Many exist which are not included in the preceding series. Aldehydes. — Acetic acid is not the only product of the oxidation of alcohol. There is another compound interme- diate between these two ; it results from the action of a single atom of oxygen upon the molecule of alcohol, which thus loses two atoms of hydrogen without other change. The new com- pound is aldehyde. C 2 H 6 + Q = H 2 + C 2 H 4 Alcohol. Aldehyde. It is a very volatile liquid having a great tendency to become oxidized and converted into acetic acid. It forms crystalline combinations with the alkaline acid-sulphites. To the other alcohols of the series C n H 2n+2 0, and other acids of the series C n H 2n 2 , correspond compounds analogous to aldehyde by their composition and by their properties. They form the following series : C 2 H 4 aldehyde or acetaldehyde. C 3 H 6 propionic aldehyde. OH 8 butyric aldehyde. C 5 H 10 O valeric aldehyde, etc. Acetones. — When calcium acetate is submitted to dry distil- lation a neutral, volatile liquid is obtained, having a peculiar aromatic odor, and known by the name acetone. Ca "{cw = CSH6 ° + CaC ° 3 Calcium acetate. Acetone. Calcium carhonate. To the other acids of the acetic acid series correspond bodies analogous to acetone, and forming with it a homologous series. These acetones are related by properties and composition to the aldehydes. Like the latter, they form crystalline combinations with the alkaline acid-sulphites. It may be considered that while aldehyde is the hydride of acetyl, acetone is the me thy 1- ide of acetyl, and that in general the acetones are derived by the substitution of an alcoholic group, analogous to methyl, for an atom of hydrogen in the aldehydes considered as hydrides. CH 3 -CO-H CH 3 -CO-CH 3 Aldehyde (acetyl hydride). Acetone (acetyl methylide). Hence, acetone contains two methyl groups united to a group, CO (carbonyl). Its mode of formation justifies this conclusion, 440 ELEMENTS OF MODERN CHEMISTRY. as shown in the following equation, in which the constitutional formula of acetic acid is employed : CHM300 >Ca = Ca " C ° 3 + CH3 - C °- CH3 Calcium acetate. Calcium carbonate. Acetone. Chlorides of Acid Radicals. — In the preceding compounds we have admitted the existence of a group, C 2 H 3 = CH 3 -CO, existing in combination with OH in acetic acid, C 2 H 3 O.OH, with hydrogen in aldehyde, C 2 H 3 O.H, and with methyl in ace- tone, C 2 H 3 O.CH 3 . A compound is known in which this same group is united with chlorine. Acetyl chloride, C 2 H 3 0.C1, is a monatomic chloride, like ethyl chloride, C 2 H 5 C1, from which it is distinguished by the strongly electro-negative nature of its radical. If acetyl chloride be poured into water, it disappears in a short time with development of heat and the formation of acetic and hydrochloric acids. C 2 H 3 0.C1 + H 2 = C 2 H 3 O.OH + HC1 Acetyl chloride. Acetic acid. To acetyl chloride correspond other chlorides which contain radicals of acids analogous to acetic acid. When they are treated with water they yield hydrochloric acid and the acids corresponding to their radicals. C 3 H 5 0.C1 C 3 H 5 O.OH Propionyl chloride. Propionic acid. C 4 H 7 0.C1 OH'O.OH Butyryl chloride. Butyric acid. C 7 H 6 0.C1 C 7 H 5 O.OH Benzoyl chloride. Benzoic acid. Amides. — If acetyl chloride be treated with ammonia, am- monium chloride will be formed, together with a solid, neutral, nitrogenized body called acetamide. C 2 H 5 0.C1 + 2NH 3 = NH 4 C1 + C 2 H 3 O.NH 2 Acetyl chloride. Acetamide. There are many other compounds similar to acetamide, and known by the name amides. They are formed by the action of ammonia upon organic chlorides analogous to acetyl chloride. They are also formed by the action of heat upon the ammo- niacal salts of the monobasic acids. The latter compounds then lose one molecule of water, and are converted into amides. C 5 H 9 O.ONH* = C 5 H 9 O.NH 2 + H 2 Ammonium valerate. Valeramide. MONATOMIC COMPOUNDS. 441 Aeetamide may be regarded as ammonia in which an atom of hydrogen has been replaced by the radical acetyl. ( H ( C 2 H 3 C C 5 H 9 n-Jh n]h n^h (h (h (h Ammonia. Aeetamide. Valeramide. Compound Ammonias, or Amines. — If ethyl iodide be heated with ammonia, one of the products of the reaction will be the hydriodide of a base derived from ammonia by the sub- stitution of an ethyl group for an atom of hydrogen. C 2 H 5 I + NH 8 = (C 2 H 5 )NH 2 .HI Ethyl iodide. Ethylaraine hydriodide. In this reaction, other ethylated bases are formed, independ- ently of ethylamine, among which must be mentioned diethyl- amine and triethylamine. All present the most striking anal- ogy to ammonia. They may be regarded as ammonia in which one, two, or three atoms of hydrogen have been replaced by one, two, or three ethyl groups. H) C 2 H 5 ) C 2 H 5 ) C 2 H 5 ) H V- N HiN C 2 H 5 y N C 2 H 5 y N H) H ) H ) C 2 H 5 ) Ammonia. Ethylamine. Diethylamine. Triethylamine. The other alcoholic groups, C n H 2n+1 , can in the same man- ner replace one or more atoms of hydrogen in ammonia. The results are bases having constitutions analogous to those of the ethyl bases. They are called amines, or compound ammonias. It is necessary that the signification of the formulas above given and those that are to follow shall be clearly understood. They are examples of typical notation, and indicate the rela- tions of the compounds with the type ammonia. N'" \ H u The brace joining the three hydrogen atoms signifies that the whole three are united to a single atom of triatomic nitro- gen, with which each exchanges one atomicity; this may be expressed by writing the formula for ammonia thus : / H F'fH 442 ELEMENTS OF MODERN CHEMISTRY. What, then, takes place when one or more atoms of hydro- gen are replaced by a group like ethyl ? The latter exchanges one atomicity with the nitrogen atom, precisely as the hydro- gen atom did, and combines with the nitrogen by one of the atoms of carbon of the group ethyl, CH 3 -CH 2 , which requires the satisfaction of one atomicity. This is clearly expressed in the following graphic formulae : H- H N-CH 2 -CH 3 i H Ethylamine. N-CH 2 -CH S ch 2 -ch 3 Diethylamine. However, such formulae would be too cumbrous for ordinary use, and our formulae must be more condensed. C 2 H 5 H X H Ethylamine. N: C 2 H 5 C 2 H 5 X H Diethylamine. m N(C 2 H 5 ) 3 Triethylamine. Phosphines. — Arsines. — Stibines. — There exist several se- ries of combinations belonging to the same type as the com- pound .ammonias, but in which the nitrogen is replaced by phosphorus, arsenic, or antimony. These compounds are de- rived from the hydrogen compounds of phosphorus, arsenic, and antimony by the substitution of one or more alcoholic groups for one or more atoms of hydrogen. in C 2 H 5 ~) C 2 Hn H [ P HfP C 2 H 5 [ P Hj H ) H ) Hydrogen phosphide. Ethylphosphine. Diethylphosphine. C 2 H 5 ) C 2 H S [■ P H As Hydrogen arsenide. H^Sb Hydrogen antimonide. Dimethylarsine chloride. C 2 H 5 ) Tr i ethyl phosphine. CH 3 ") CH 3 J- As CH 3 ) Trimethylarsine. C 2 H 5 ") era 5 £■ sb C 2 H 5 ) Triethylstibine. Organo-metallic Compounds. — Ethyl and its congeneric compounds, methyl, amyl, etc., can enter into combination not only with nitrogen, phosphorus, arsenic, etc., of which they saturate one or more atomicities, but with a large number of MONATOMIC COMPOUNDS. 443 metals. Thus, zinc, which is diatomic, can combine with two ethyl groups to form zinc ethyl. rj f C 2 H 5 Zn { C 2 H 5 Mercury, also diatomic, can unite with one or two ethyl or methyl groups, etc. In the second case, the new combination is saturated; in the first, it is monatomic, (Hg"C 2 H 5 )', and re- quires for saturation an atom of a monatomic element, or a monatomic group, iodine, for example. „,, | C 2 rP „ ,, f C 2 H 5 Hg j C2H5 Hg | j Mercur-ethyl. Mercur-monethyl iodide. Bismuth, which is triatomic, can fix three ethyl groups. f C 2 H 5 Bi'" \ C 2 H 5 ( C 2 H 5 Bismuth-ethyl. Stanno-tetrethyl is formed by the union of four ethyl groups with one atom of tetratomic tin. C 2 H 5 C 2 H 5 C 2 H 5 : c 2 h 5 If the four atomicities of tin be not all satisfied, non-satu- rated compounds may be formed. Sn" \ ~ 2 „ 5 - SniT 1 C2H5 or -Sn«^-CH 5 ( ^ ii ( C 2 H 5 X C 2 H 5 Stanno-diethyl. Stanuo-triethyl. Stanno-diethyl is known in the free state, but stanno-triethyl doubles its molecule as soon as it is set at liberty, combining with itself, as it can combine with iodine. ISn iv (C 2 H 5 ) 3 (C 2 H 5 ) 3 Sn iv -Sn iv (C 2 H 5 ) 3 = Sn 2 (C 2 H 5 ) 6 . Stanno-triethyl iodide. Sesquistannethyl. Non-saturated compounds are apt to combine with other elements or radicals. Stanno-tetrethyl, which is saturated, does not possess this faculty. The bodies just mentioned belong to the class of organo- metallic compounds. Their study is of great importance in the history of the atomicity of the metals, that is, their power of saturation. The theoretical considerations concerning them have been discussed by Frankland, Baeyer, and Cahours. Sn* 444 ELEMENTS OF MODERN CHEMISTRY. Monatomic Radicals. — From the preceding summary may be understood the position occupied in organic chemistry by certain groups containing carbon, groups that are distinguished as monatomic because they can manifest but a single atomicity. Only a single monatomic atom or group is wanting that all of the carbon atoms contained in these groups may be entirely saturated. These groups of atoms or radicals cannot exist in the state of liberty, but they can pass from one compound to another, replacing a single atom of hydrogen or other mon- atomic element, and consequently playing the part of that ele- ment in the new combination. This is expressed by saying that these groups act as monatomic radicals. To indicate the constitution of the combinations containing such groups, and especially the metamorphoses that they may undergo by exchanging these radicals by double decomposition, it is convenient to distinguish the latter by unique expressions, occupying a place in the formula distinct from that of the other elements. The composition of all of the bodies which have just been reviewed may be represented by very simple formulae, by comparing them to hydrogen compounds, such as free hydrogen, or hydrochloric acid, water, and ammonia. The notation then assumes a typical form, exceedingly clear for the interpretation of the majority of reactions. The following are the typical formulae for the combinations that have been considered : Type HH. (C 2 H 5 )C1 Ethyl chloride. (C 2 H 3 0)C1 Acetyl chloride. (C 2 H 3 0)H Aldehyde. (C 2 H 3 0)(CH 3 ) Acetone. Type l}»- Type (Cir>j (C 2 H 5 ) ") Ethyl hydrate. Ethylamine. (C 2 H 5 )-) (C 2 H 5 ) \ N (C 2 H 5 ) j u Ethyl oxide. J Diethylamine. :c 2 h 3 o) j (C 2 H 5 ) \ (C 2 H 5 ) \ N (C 2 H 5 ) ) Acetic acid. Triethylamine. (C 2 H 3 0) ) Q (C 2 H 5 ) } u (C 2 H 3 0) ^) HVN H) Ethyl acetate. Acetamide. 36* • t POLYATOMIC COMPOUNDS. 445 POLYATOMIC COMPOUNDS. If chlorine and olefiant gas. or ethylene, be mixed in equal volumes, both gases disappear and are converted into an oily substance, which was formerly called Dutch liquid. This body results from the combination of a molecule of ethylene with a molecule (two atoms) of chlorine. It is ethylene chloride. C 2 H* + . CP = CFEPCF Ethylene. Ethylene chloride. If the constitution of ethylene gas. C 2 H 4 , be compared with that of the saturated hydrocarbon ethane. C 2 H 6 . which like the former contains two atoms of carbon, it will be noticed that it contains two atoms of hydrogen less. C 2 H 6 — H 2 = C 2 IP In ethylene the six atomicities of the pair of carbon atoms are not saturated. Hence that gas can absorb directly two atoms of chlorine, bromine, or iodine to form a saturated com- pound. HH H H HH ii ii i i H-C-C-H -C-C- Cl-C-C-Cl ii ii ii HH HH HH Ethane. Ethylene. Ethylene chloride. It is a diatomic radical, and it can exist in the free state because until other atoms are presented to satisfy the atom- icities of the two atoms of carbon, those two atoms are bound together by a double affinity. Thus. H 2 C=CH 2 . One of these bonds is loosed when the ethylene manifests its affinities and enters directly into combination, because the affinity of carbon for chlorine or such an element is greater than its affinity for carbon Ethylene is the first of a numerous class. The following bodies form with it the homologous series C n H 2n •. C 2 H± ethylene. C 3 H 6 propylene. C±H 8 butylene. C 5 H 10 amvlene. C 6 H 12 hexylene. C 7 H U heptylene. C 8 H 16 octylene. C 9 H 18 nonylene. C10H20 decylene, etc. 38 446 ELEMENTS OF MODERN CHEMISTRY. All of these bodies are able to fix directly two atoms of chlorine or bromine. When they enter into combination, they take the place of two atoms of hydrogen. They can pass by double decomposition from one compound to another, and their combinations may undergo various metamorphoses analogous to those already indicated. Diatomic Alcohols or Glycols. — The glycols are compounds in which the two atomicities of the diatomic radicals are saturated by two hydroxyl groups. The two atoms of bromine in ethy- lene bromide, C 2 H 4 Br 2 , may be replaced by two hydroxyl groups (OH), and the resulting combination is ethylene dihydrate. The two atoms of hydrogen united to the oxygen in the hydroxyl groups in glycol may both be replaced by acid radi- cals analogous to acetyl, just as the single atom of hydrogen in the single hydroxyl group of a monatomic alcohol may be replaced by an acid radical. This is characteristic of a diatomic alcohol. To ethylene dihydrate, or ordinary glycol, correspond the hydrates of the other hydrocarbons homologous with ethylene. The following glycols are known : C»H*{°g glycol. C 3 H 6 j 0H propylglycol. C 4 H 8 | gg butylglycol. C 5 Hio | °g amylglycol. C 6 Hi2 | °g hexylglycol, etc. Around each of these bodies are grouped a great number of derivatives, among which we can only consider the ethers, acids, and compound ammonias. Ethers of the Glycols. — The ethers of the glycols result from the substitution of alcoholic or acid radicals for the hydro- gen of the groups OH. One or both of these hydrogens may be thus replaced, and the following examples will illustrate the constitution of the compounds so formed : C 2 H 4 I °- C2H5 n*H* I °' C2H5 C*H* I O.CPHSO r2H 4 f O.C*H30 U11 lOH U±1 10.C2H5 tH jOH GH {o.C 2 HSO Monethylic glycol. Diethylic glycol. Glycol monacetate. Glycol diacetate. POLYATOMIC COMPOUNDS. 447 Diatomic and Dibasic Acids. — Diatomic acids result from the oxidation of the glycols. Their formation and constitu- tion may be understood by developing the formula? of the hydrocarbons which constitute the radicals of these glycols. Ordinary glycol may yield two acids by oxidation, the first resulting from the substitution of an atom of oxygen for two atoms of hydrogen, the second from the substitution of two atoms of oxygen for four atoms of hydrogen. The following formulas express the constitution and derivation of these com- pounds : CH 2 CH 2 Br CH 2 .OH CH 2 .OH CO.OH CH 2 CH 2 Br CH 2 .OH CO.OH CO.OH Ethylene. Ethylene bromide. Glycol. Glycollic acid. Oxalic acid. Grlycollic and oxalic acids, which are produced by the oxida- tion of glycol, are both diatomic because they are both derived from a diatomic alcohol ; but the first is monobasic because it contains but a single atom of hydrogen that can be replaced by a metal. The second is dibasic, for it contains two atoms of hydrogen that are replaceable by an equivalent quantity of metal. This basic hydrogen is that which forms part of the group C0 2 H. Oxalic acid is composed simply of two groups -C0 2 H ; it is. dibasic. Grlycollic acid contains but one, and it is conse- quently monobasic. The hydrogen united to the oxygen in the group -CH 2 .OH is called alcoholic hydrogen ; it may be replaced by an acid radical, but it cannot be easily replaced by a metal. All bodies containing a group CH 2 .OH are alcohols, and all bodies containing a group CO.OH are acids. The alcohols and acids are thus defined by their constitution. Grly- collic acid is at the same time an alcohol and an acid, for it contains both a group CH 2 .OH and a group CO.OH. There exists a series of acids homologous with glycollic acid, and another series homologous with oxalic acid. Both series appertain to the superior diatomic alcohols. Diatomic Ammonias or Diamines. — Compounds exist which hold the same relation to the diatomic alcohols as ethyl- amine and its homologues to the monatomic alcohols. Such a compound is ethylene-diamine. Its relations with ethylene chloride and glycol are expressed by the following formulas : Ethylene chloride. Glycol. Ethylene-diamine. 448 ELEMENTS OF MODERN CHEMISTRY. Alcohols of Higher Atomicity. — There are alcohols of higher atomicity ; glycerin, for example, is a triatomic alco- hol. It contains a radical, C 3 H 5 , which is triatomic since it is derived from the saturated hydrocarbon C 3 H 8 , by the subtrac- tion of three atoms of hydrogen. Erythrite is a tetratomic alcohol ; it contains the tetratomic radical C 4 H 6 = C 4 H 10 — H 4 . Lastly, the sweet, sugar-like substance derived from manna and known as mannite is a hexatomic alcohol. There are numerous similar substances which are alcohols of higher atomicity. The following formulae express the composition and the functions of these polyatomic alcohols : OH roH C 3 H 5 '" \ OH C 4 H 6iv (OH Qg C 6 H 8vi (OH) 6 OH Glycerin. Erythrite. Mannite. Around these bodies are grouped the numerous correspond- ing derivatives, ethers, acids, etc. It will be seen by the preceding considerations that the neu- tral hydrates, called alcohols, are highly important in them- selves and on account of the derivatives which attach to them. Hence the elements of a natural classification of organic com- pounds are deduced. COMPOUNDS OP CYANOGEN. Gay-Lussac gave the name cyanogen to the radical of prussic or hydrocyanic acid, which was discovered by Scheele in 1782. This radical is composed of one atom of carbon and one atom of nitrogen. In hydrocyanic acid it is united with hydrogen ; in the cyanides it is combined with the metals. H(CN)' K(CN)' Hg"(CN) 2 Hydrocyanic acid. Potassium cyanide. Mercury cyanide. The preceding compounds may be compared with the corre- sponding chlorides : HC1 KC1 HgCP Hydrochloric acid. Potassium chloride. Mercuric chloride. It is somewhat remarkable that potassium cyanide is iso- morphous with potassium chloride. In the preceding compounds, cyanogen, which is composed of an atom of carbon and an atom of nitrogen, plays a part anal- ogous to that of chlorine. It is a monatomic radical ; nitrogen, CYANOGEN. 449 which is triatomic, can saturate only three of the four atomici- ties which reside in an atom of carbon. Hence there remains one free atomicity, and cyanogen can act as a monatomic radi- cal, -CEN. All of the compounds of cyanogen are prepared from potas- sium ferrocyanide, or yellow prussiate of potash, which is described on page 454. CYANOGEN. (CN) 2 = Cy 2 Formation. — Cyanogen occurs in small quantities in the gases from blast-furnaces. Nitrogen and carbon combine together with difficulty, but their direct union takes place in presence of potassium or potassium carbonate at a high tem- perature. When nitrogen gas is passed over an incandescent mixture of carbon and potassium carbonate, potassium cyanide is formed. A larger yield of cyanide is obtained if the nitrogen is replaced by ammonia gas. Also, if ammonia gas is passed over incandescent charcoal in a porcelain tube, ammonium cyanide is formed, and may be condensed in crystals in a cooled receiver (Kuhlmann). C + 2NH 3 = NH 4 .CN + H 2 Ammonium cyanide. Cyanogen is also formed by the dehydration of ammonium oxalate, when that salt is treated with phosphoric anhydride. This reaction allows cyanogen gas to be regarded as the nitrite of oxalic acid. A nitrile is a cyanide which may be converted into an acid by hydration, with elimination of ammonia, by the action of an alkaline hydrate. CO.ONH* = CN CO.ONH 4 CN ^ Ammonium oxalate. Cyanogen. Preparation. — Mercury cyanide is heated in a small retort fitted with a delivery-tube. The mercury volatilizes, and a gas is disengaged which may be collected over mercury. There remains in the retort a solid brown mass which possesses the same composition as cyanogen, and is known as paracyanogen. Hg(CN) 2 = (CN) 2 + Hg. Composition and Properties. — Cyanogen is a colorless gas, 38* 450 ELEMENTS OF MODERN CHEMISTRY. possessing a strong odor of bitter almonds. It may be easily liquefied by a pressure of 4 atmospheres or a temperature of — 25° Its density is 1.8064 compared to air, or 26 compared to hydrogen. This is free cyanogen. It has separated from the mercury, which is condensed in little drops in the dome of the retort. The atom of mercury was combined with two groups (CN), which unite together when they separate from the mercury, and remain combined together in the gas which is disengaged. The latter contains CN combined with CN. Its formula is : NC-CN = (CN) 2 = Cy 2 2 volumes of this gas contain two atoms of carbon and two atoms of nitrogen. This composition may be demonstrated by eudiometric analy- sis. 2 volumes of cyanogen and 4 volumes of oxygen are intro- duced into a mercury eudiometer. On the passage of an electric spark there is a flash of blue light, and the volume of the gas is not changed. If a solution of potassium hydrate be now passed into the eudiometer, the six volumes of gas will be reduced to two. 4 volumes of CO 2 are formed; 2 volumes of N remain. 2 volumes of cyanogen then contain the carbon contained in 2C0 2 , that is, C 2 , and N 2 . This is expressed by saying that the formula of cyanogen, C 2 N 2 = Cy 2 , corresponds to 2 volumes. On contact with flame, cyanogen takes fire and burns in the air with a purple flame, yielding carbon dioxide and nitrogen. Water dissolves four and one-half times its volume of cyan- ogen. When this solution is left to itself it deposits brown flakes. It then contains in solution urea, ammonium carbonate, ammonium cyanide, and ammonium oxalate. C 2 N 2 + 4H 2 = (NH 4 ) 2 C 2 4 Cyanogen. Ammonium oxalate. C 2 N 2 _|_ W Q _ HCN _j_ CO^ N Cyanogen. Hydrocyanic acid. Cyanic acid. C ^N + H 2 = CO 2 + NH 3 Cyanic acid. Ammonia. The ammonia formed by the latter reaction combines with HYDROCYANIC ACID. 451 the cyanic acid to form ammonium cyanate, which becomes converted into urea, as will be seen shortly. It is a curious fact that in the presence of a small quantity of aldehyde, the decomposition of an aqueous solution of cyanogen yields, almost entirely, but one product, — oxamide. C 2 N 2 + 2H 2 = C2 ° 2 NH It is, then, possible that there may be two isomeric modifica- tions of cyanuric acid. There are certainly two isomerides of its ethers : the trimethylic ether of the true cyanuric acid, C 3 N 3 (OCH 3 ) 3 , is formed by the action of cyanogen chloride on sodium methylate ; and, on the other hand, there are ethers of tricarbimide or isocyanuric acid, which will be described farther on. CARBAMIC ACID— UREA. 463 CARBAMIC ACID. OTT C0< NH2 This acid is not known in the free state. Its ammonium salt is commonly known as anhydrous ammonium carbonate ; its ether, urethane, or ethyl carbamate, is described on page 501. ro ONE* 0O^ 0C2H5 tU< NR2 UU Cyanic acid. Ethylaniine. Ethylurea. CON(C 2 H 5 ) + NPP = CO<^ 2 (C,2H5) Ethyl cyanate. Ethylurea. The following is the nomenclature and composition of some of the principal compound ureas : CH±N 2 urea. CH 3 (CH 3 )N 2 methvlurea. CH 3 (C 2 H5)N 2 ethylurea. CH 2 (C 2 H 5 ) 2 N 2 diethylurea. CH(C 2 H 5 ) 3 N 2 triethylurea. CH 3 (C5HH)N 2 amylurea. CH 3 (C 6 I15)N 2 phenylurea. CH 2 (C 6 H5)2]Sf20 diphenylurea. BIURET. C 2 H5N 3 Q 2 Biuret is the amide of allophanic acid, the ethyl compound of which is described on the preceding page, and is formed when allophanic ether is heated to 100° with aqueous ammonia. NH 2 CO<^; CaOC2H °+NH 3 = ^0 H >u [ethane, or methyl hydride. CH 3 C1 Methyl hydrate. CH >0 Methyl chloride. CHCP Methyl oxide. C 2 H 3 Ck n CH 3>U Chloroform. Methyl acetate. compounds will be but briefly described METHANE. (marsh gas.) CH 1 The inflammable gas which is disengaged from the mud of marshes is impure methane. The same gas is frequently evolved in the galleries of coal mines, and constitutes the fire-damp of miners. It is produced artificially by the action of an excess of alkali upon acetic acid (Persoz, Dumas). Preparation. — Methane is most conveniently prepared in the pure state by strongly heating in a glass flask or retort a mixture of 1 part of sodium acetate, 1 part of potassium hy- drate, and 1 J parts of lime ; the lime is added to prevent the action of the potassium hydrate upon the glass. The gas may be collected over water. NaC 2 H 3 2 + NaOH = _ CH 4 + Na 2 C0 3 Sodium acetate. Methane. Properties. — Methane is a colorless, odorless gas. Its den- sity is 0.559 ; it is but slightly soluble in water, somewhat more so in alcohol. It burns in the air with a yellow flame less lumi- nous than that of ethylene, or olefiant gas. A mixture of me- thane and oxygen explodes violently on the application of flame or the passage of an electric spark. If two volumes of methane and four volumes of oxygen be introduced into an eudiometer and the spark be passed, a bright flash is visible. After the combustion, the mercury rises in the tube, and it is found that the volume of gas is reduced to one- METHYL HYDRATE. 471 third of the primitive volume (to 2 volumes) ; if a solution of potassium hydrate be introduced, the whole of the remaining gas will be absorbed. 2 volumes of methane produce in burning 2 volumes of carbon dioxide, and require 4 volumes of oxygen. This experiment permits the determination of the composition of methane. 2 volumes of carbon dioxide contain 2 volumes of oxygen combined with 1 volume (1 atom) of carbon ; consequently two volumes of marsh gas contain one atom of carbon. The other two volumes of oxygen consumed have combined with four volumes of hydrogen, which are likewise contained in two volumes of methane. Consequently two volumes of methane contain 1 atom of carbon and 4 atoms of hydrogen. A mixture of chlorine and methane explodes when exposed to direct sunlight. In diffused daylight, the action is less violent, especially if an inert gas, such as carbon dioxide, be added. In this case, methyl chloride is formed, and in presence of an excess of chlorine, chloroform, and finally carbon tetrachloride. CH* + CP = HC1 + CH 3 C1 methyl chloride. CW + 3CP = 3HC1 + CHC1 3 chloroform. CH 4 + 4CP = 4HC1 + CCP carbon tetrachloride. It is seen that in these reactions the chlorine is substituted for hydrogen, atom for atom. Inversely, when chloroform or carbon tetrachloride is sub- mitted to the action of nascent hydrogen, an inverse substitu- tion may be effected, and these chlorine compounds may be converted into methane. This may be accomplished by putting them in contact with sodium amalgam and water. The latter is decomposed by the sodium, and constitutes a source of hy- drogen (Melsens). CHCP + 3H 2 = 3HC1 + CH* METHYL HYDRATE, OR METHYL ALCOHOL. (wood-spirit.) CHK) = CH3-OH The products of the dry distillation of wood contain about one per cent, of a spirituous liquid, which was discovered in 1812 by Taylor, and named wood-spirit. It is separated by 472 ELEMENTS OF MODERN CHEMISTRY. several distillations and rectifications over lime ; for, being more volatile than the other products, it passes over first. The methyl alcohol of commerce is always impure, and can- not be purified by fractional distillation, as it coutains a consid- erable proportion of acetone, of which the boiling-point (56°) is very near that of methyl alcohol. Bardy and Bordet have discovered a process by which it may be readily obtained per- fectly pure. The crude alcohol is purified as far as possible by rectification, and is then converted into methyl formate by treat- ment with sodium formate and hydrochloric acid. CH 3 .OH + NaCHO 2 + HC1 = CEF.CHO 2 + NaCl + H 2 Methyl hydrate. Sodium formate. Methyl formate. The methyl formate which distils over boils at 32°, and may thus be readily separated from the liquids of higher boiling- points. It is then introduced into a flask connected with a good condenser, and the required proportion of sodium hydrate is introduced. Methyl hydrate distils, and there remains sodium formate, which may be used for another operation. CH 3 .CH0 2 + NaOH s= CtP.OH + NaCHO 2 When pure, it is a mobile, colorless liquid, having an alco- holic odor. It boils at 66.5°. Its density at 0° is 0.8142 (Dumas and Peligot). It is inflammable and burns with an almost colorless flame. It is miscible with water, alcohol, and ether in all proportions. It dissolves caustic baryta and forms with it a definite combi- nation. It forms a crystalline compound with calcium chloride containing CaCl 2 -f 4CH 4 0. Potassium and sodium react energetically upon methyl hy- drate ; the metal dissolves with disengagement of hydrogen and formation of potassium or sodium methylate. CH 3 -OH CH 3 -OK Methyl hydrate. Potassium methylate. If methyl alcohol be placed under a bell-jar containing also some watch-glasses filled with platinum black, so that the vapor of the wood-spirit mixed with air may come in contact with the finely-divided metal, it is found that the liquid soon becomes strongly acid. By the slow oxidation of the wood-spirit under these conditions, formic acid is produced (Dumas and Peligot). CH 3 -OH + O 2 = CHO-OH + H 2 Methyl hydrate. Formic acid. CHLORIDE, BROMIDE, AND IODIDE OF METHYL. 473 When methyl alcohol is allowed to fall drop by drop on highly-heated zinc chloride, it is decomposed into a number of products, among which the most curious is hexaniethyl-benzol (p. 649). (Le Bel and Greene.) METHYL OXIDE. (CH3)20 When methyl alcohol is heated with twice its weight of concentrated sulphuric acid, a colorless gas is disengaged, which is methyl oxide. 2CH 3 .OH = (CH 3 ) 2 + H 2 Methyl hydrate. Methyl oxide. This gas is formed by the dehydration of methyl alcohol and the linking together of two methyl groups by an atom of oxygen. It is methylic ether. It holds the same relation to methyl hydrate that ordinary ether does to ethyl hydrate. It is colorless, very soluble in alcohol and* ether, and quite soluble in water. It liquefies at a very low temperature (—36°). CHLOKIDE, BROMIDE, AND IODIDE OF METHYL. These compounds may be regarded as marsh gas in which one atom of hydrogen is replaced by an atom of chlorine, bro- mine, or iodine. They are formed by the action of hydrochloric, hydrobromic, and hydriodic acids upon methyl alcohol. CH 3 .OH + HC1 = CH 3 C1 + H 2 They may be considered as derived from the hydracids by the substitution of the group methyl for the atom of hydrogen. HC1 (CH 3 )C1 Hydrochloric acid. Methyl chloride. Methyl chloride is a colorless gas, having an agreeable odor. When exposed to intense cold, it condenses to a liquid which boils at — 22°. When heated for a considerable time with a concentrated solution of potassium hydrate, it is converted into methyl alcohol. Methyl bromide, CH 3 Br, is a colorless liquid, boiling at 13°. Methyl iodide, CH 3 I, boils at 43° ; its density at 0° is 2.1992. 40* 474 ELEMENTS OF MODERN CHEMISTRY. It is made by gradually adding iodine to a mixture of methy alcohol and amorphous phosphorus, and distilling. The dis tilled liquid is mixed with water, which precipitates the iodide the dense liquid is separated, dried with calcium chloride, an< distilled. METHYLENE CHLORIDE. CH 2 C1 2 This compound may be prepared by the action of chlorine on methane, or on methyl chloride, or by the reduction of chloroform by nascent hydrogen. The latter method is the more convenient. An alcoholic solution of chloroform is treated with zinc in a flask connected with a condenser, and hydrochlo- ric acid is introduced in small portions. Methylene chloride and unaltered chloroform distil over, and towards the close of the operation the * distillation is continued by the aid of heat. The distillate is then washed, dried, and submitted to fractional distillation. Methylene chloride is a mobile liquid, having an odor resem- bling that of chloroform, and boiling at 40°. Its density at 0° is 1.36. METHYLENE IODIDE, CH 2 I 2 , is made by the action of hydriodic acid on chloroform or iodo- form in sealed tubes at a temperature of 150°. CHOP + 4HI = CH 2 I 2 + 3HC1 + I 2 It is also formed by the action of sodium e thy late on iodo- form. It is a yellow, highly refracting liquid, having a density of 3.342 at 5°, and solidifying at 2°. It boils at 182°, with partial decomposition. OCH 8 Methylal, or the dimethylic ether of methylene, CH 2 <^pTj 3 , is obtained by the action of sulphuric acid and manganese di- oxide on methyl alcohol. It is a limpid liquid, of an agreeable odor, boiling at 42° (Malaguti). OC 2 H 5 Methylene diethylate, CH 2 ° C2H X>° °S>0 Alcohol. Potassium ethylate. Sodium ethylate. Uses of Alcohol. — Alcohol is used as a combustible in spirit- lamps. In the arts, it is employed in the manufacture of ether, chloroform, eau de cologne, and many other products. It is largely used in the laboratory, and in pharmacy, as a solvent ; it serves for the preservation of anatomical specimens. In France and England, alcohol employed for certain industrial uses is exempted from part of the tax, when it has previously been mixed with about one-tenth of wood-spirit and a few per cent, of mineral oils and resin. Such a mixture is unfit for the manufacture of brandy and liquors, but its usefulness as a solvent is in many cases unimpaired. Alcohol exists in fermented liquors, such as wine, cider, and beer. It is contained in much larger quantities in brandies, whiskeys, and spirits. These are products of the distillation of various alcoholic liquids. They are more or less rich in alco- hol. Brandy is prepared by the distillation of wine, cider, or the products of fermentation of cherry-juice (cherry-brandy), sugar-cane (rum), beet-root molasses (beet-brandy). Whiskey is distilled from fermented starchy materials, such as corn, rye, potatoes, etc., the starch being first saccharified. The richness of these materials in alcohol is indicated by the degrees of an 488 ELEMENTS OF MODERN CHEMISTRY. alcoholometer. The following table gives the strength of some of these liquors. (For wine, beer, etc., see page 632). Percentage of Cartier's Areometer. Alcohol, by volume. Weak brandy 16° 37.9 Proof spirits 19° 50.1 Strong brandy 22° 59.2 Ordinary alcohol 33° 85.1 Rectified alcohol (strongest commercial) 40° 95. Absolute alcohol 41.2° 100. ETHYL OXIDE, OR ETHER. (C 2 H5)20 = CH3-CH 2 -0-CH 2 -CH 3 If ethyl iodide be added to an alcoholic solution of ethylate of sodium and a gentle heat be applied, a deposit of sodium iodide is formed and vapors are disengaged which may be con- densed in a cooled receiver into an ethereal liquid. It is oxide of ethyl. OTW * *£><> - *.! + gg>0 Ethyl iodide. Sodium ethylate. Ethyl oxide. If, in the preceding experiment, the ethyl iodide be replaced by methyl iodide, an extremely volatile liquid will be formed, which is the double oxide of methyl and ethyl. PTT3T J. C2H5 \H ATaT 4- Cm ^n CH * + Na>° ^ NaI + CH3>° Methyl iodide. Oxide of methyl and ethyl. These classic experiments, due to Williamson, show that the oxide of ethyl contains two ethyl groups. It may be regarded as alcohol in which the hydrogen atom of the group hydroxyl is replaced by ethyl. H-O-H C 2 H5-0-H C 2 H5-0-C 2 H5 Water. Alcohol. Ethyl oxide. Ether may also be obtained by the action of ethyl iodide on sodium oxide, or silver oxide. Preparation. — Ether is prepared in the arts by the action of sulphuric acid on alcohol. A mixture of 9 parts of con- centrated sulphuric acid and 5 parts of alcohol of 90 per cent. is heated in a flask, A (Fig. 122), and a small, continuous stream of alcohol is allowed to flow into this mixture through the funnel-tube a. The temperature of the liquid, indicated by the thermometer t, should not exceed 140 or 145°. The vapor disengaged is condensed in a Liebig's condenser, B, through ETHYL OXIDE. 489 which a stream of cold water flows continually. Under these conditions, a mixture of ether and water collects in the re- ceiver D, together with a little alcohol, and towards the close of the operation, a small quantity of sulphurous acid gas is disengaged. The product is purified by washing with milk of lime, and then with pure water, after which it is rectified over calcium chloride on a water-bath. Fig. 122 represents the apparatus used for public demonstration ; in the arts, the opera- tion is conducted on a large scale in apparatus of an analogous construction. Fig. 122. Theory of Etherification. —The transformation of alcohol into ether is a true dehydration, brought about by the sul- phuric acid. 2(C 2 H 5 .OH) = (C 2 H 5 ) 2 + H 2 Williamson clearly proved that it is effected in two distinct phases ; in the first, ethylsulphuric acid and water are formed. C2 h>° + n> soi - C2 h>so* + H*0 Alcohol. Sulphuric acid. Ethylsulphuric acid. V* 490 ELEMENTS OF MODERN CHEMISTRY. In the second, another molecule of alcohol reacts with the ethylsulphuric acid; ether is formed and sulphuric acid is regenerated. C2H H s >so* + *5>o - gg>d + *>so* Ethylsulphuric acid. Alcohol. Ether. Sulphuric acid. Hence the ether and water collected in the receiver are pro- ducts of two distinct phases of the reaction. Ethylsulphuric acid is continually formed and as continually decomposed, regenerating sulphuric acid ready to act upon new por- tions of alcohol. However, although the operation is con- tinuous, it cannot go on indefinitely, for the mixture blackens after a time and becomes unfit to etherify new quantities of alcohol. Properties of Ether.— Ether is a colorless, very mobile liquid ; its taste is at first burning, then cooling ; its odor is suave and agreeable, and is called ethereal. Density at 0°, 0.7366. Boiling-point under the normal pressure, 34.5°. It is but slightly miscible with water, on the surface of which it forms a separate layer. 9 parts of water dissolve 1 part of ether ; 36 parts of ether dissolve 1 part of water. Ether dis- solves in all proportions in alcohol and in methyl alcohol. It slightly dissolves sulphur and phosphorus, and notable quantities of bromine, iodine, ferric, mercuric, and auric chlo- rides, and many organic bodies, such as the oils, fats, resins, alkaloids, etc. Ether is largely used as an anaesthetic in surgical operations. It is very inflammable and burns with a quite luminous flame. Its vapor explodes violently when mixed with air or oxygen and ignited. If a heated spiral of platinum wire be suspended in a glass jar containing a little ether, in such a manner that the lower extremity of the wire is but a little distance from the surface of the liquid, the wire will soon become brightly incandescent and will ignite the ether. This effect is due to the ether vapor, which, coming in contact with the platinum, and being mixed with air, undergoes a slow combustion. Heat is thus developed, and the wire becomes incandescent. Chlorine acts on ether with extreme energy. If the action be moderated, various products of substitution are obtained, among which the following have been well studied : SULPHYDRATE AND SULPHIDE OF ETHYL. 491 * • Monochlorether C 2 H^° li( l uid foiling at 98-99°. Dichlorether C2 ^2H5>° li( l uid boiling at 140-147°. P 2 "FT 3 PI 2 Tetrachlorether c 2 H 3 Cl 2 ^ Kquid, density 1.5. C 2 C1 5 Perchlorether (^Cl 5 ^ colorless crystals, fusible at 69°. The last is a solid body, crystallizing in octahedra. By the action of heat it is decomposed into carbon sesquichloride and perchloraldehyde (Malaguti). J^15>° = C 2 C16 + C 2 C 140 Perchlorether. Carboii sesquichloride. Perchloraldehyde. When two parts of bromine are added to one part of ether, and the mixture is cooled, a garnet-colored liquid separates and soon crystallizes. It is a compound of bromine and ether, (C 2 H 5 ) 2 O.Br 2 , which crystallizes in thin, red plates, fusible at 22° ; it is easily decomposed (Schiitzenberger). SULPHYDRATE AND SULPHIDE OF ETHYL. Two bodies are known which are intimately related, as re- gards their constitutions, with alcohol and ether. They are the sulphydrate and the sulphide of ethyl. The first, formerly known as mercaptan, represents alcohol containing an atom of sulphur instead of an atom of oxygen ; the second represents ether in which the oxygen atom is replaced by sulphur. C 2 H 5 .OH (C 2 H 5 ) 2 Ethyl hydrate. Ethyl oxide. C 2 H 5 .SH (C 2 H 5 ) 2 S Ethyl sulphydrate. Ethyl sulphide. Ethyl sulphydrate is obtained by distilling a concentrated aqueous solution of potassium sulphydrate with a solution of potassium ethylsulphate. It may also be prepared by passing vapor of ethyl chloride into an alcoholic solution of potassium sulphydrate. The liquid is distilled as soon as it is saturated with ethyl chloride, and water is added to the distillate. Ethyl sulphydrate separates. KSH + C 2 H 5 C1 = KC1 + C 2 H 5 .SH Potassium sulphydrate. Ethyl chloride. Ethyl sulphydrate. 492 ELEMENTS OF MODERN CHEMISTRY. Ethyl sulphydrate is a transparent, colorless liquid, very mo- bile, and having a fetid odor. Density at 21°, 0.835. Boil- ing-point, 36.2° (Liebig). It reacts energetically with mercuric oxide, forming water and a white, crystalline body which represents ethyl sulphy- drate in which the hydrogen is replaced by mercury. Hence the name mercaptan (mercurium captans), given to the sulphy- drate of ethyl by Zeise. This mercuric compound is insoluble in water; it contains (C 2 H 5 S) 2 Hg". Ethyl sulphide is obtained, like the sulphydrate, by double decomposition. Vapor of ethyl chloride is passed into an alco- holic solution of potassium monosulphide. K 2 S + 2C 2 H 5 C1 = 2KC1 + (C 2 H 5 ) 2 S Potassium sulphide. Ethyl chloride. Ethyl sulphide. Ethyl sulphide is a colorless liquid, having a garlicky odor. It boils at 75°. It is insoluble in water. ETHYL CHLORIDE. C 2 H5C1 This body is prepared by saturating alcohol with hydrochloric acid gas and distilling on a water-bath. Ethyl chloride is dis- engaged, and should be passed first through a wash-bottle and then through a tube containing calcium chloride, after which it may be condensed in a receiver placed in a freezing mixture. Below 11° ethyl chloride is a mobile, colorless liquid, having a penetrating and agreeable odor. It boils at 11° ; it is inflam- mable, and burns with a flame tinged with green. If some solution of silver nitrate be agitated in a jar con- taining vapor of ethyl chloride, no precipitate will be formed ; but if the agitation be continued after the vapor has been ignited, an abundant precipitate of silver chloride will be formed, owing to decomposition of the silver nitrate by the hy- drochloric acid produced by combustion of the ethyl chloride. Ethyl chloride produces a precipitate of silver chloride when passed into an alcoholic solution of silver nitrate. Chlorinated Derivatives of Ethyl Chloride. — When ethyl chloride is submitted to the action of chlorine, various com- pounds are successively formed by the substitution of chlorine for hydrogen, atom for atom. The following is the nomencla- ETHYL BROMIDE. 493 ture and composition of these chlorinated compounds, which were discovered by V. Regnault. C 2 H 5 C1 ethyl chloride. C 2 H 4 C1 2 dichlorethane (ethylidine chloride) — boils at 57.5°. C 2 H 3 C1 3 trichlorethane— boils at 75°. C2H 2 C1* tetrachlorethane— boils at 127.5°. C 2 HC1 5 pentachlorethane— boils at 158°. C 2 C1 6 hexachlorethane (sesquichloride of carbon). It will be noticed that the second of these compounds is isomeric with ethylene chloride, or Dutch liquid, of which the description will be found farther on. It may be obtained by treating aldehyde with phosphorus pentachloride. CH 3 -CHO + PCI 5 = CH 3 -CHCP + POCP Aldehyde. Dichlorethane. Phosphorus oxychloride. This mode of formation indicates its constitution, which is expressed by the formula CH 3 CHCP To distinguish it from its isomeride ethylene chloride, CH 2 C1 CH 2 C1 it is named dichlorethane or ethylidene chloride. In the sesquichloride of carbon, C 2 CP, the hydrogen atoms are all replaced by chlorine. Carbon sesquichloride is a crys- stalline solid, melting at 162°, and boiling at 182° (Faraday). ETHYL BROMIDE. C 2 H5Br Ethyl bromide is prepared by distilling a mixture of alcohol, bromine, and amorphous phosphorus, or a mixture of potassium bromide, alcohol, and sulphuric acid diluted with its own volume of water. In either case the distillate is washed with water, and the oily ethyl bromide separated and dried with potassium carbonate. It is a colorless, refracting liquid, having an odor resembling that of chloroform, and a burning taste. It mixes in all pro- portions with alcohol and ether, but is insoluble in water. Its density at 15° is 1.4189, and it boils at 40.7°. It has been employed to a limited extent as an anaesthetic. 42 494 ei^Bments of modern chemistry. ETHYL IODIDE. C 2 H5I This important compound is prepared by the action of alco- hol on iodine in presence of amorphous phosphorus. Phos- phorus iodide is formed, and reacts upon the alcohol, yielding ethyl iodide and an acid of phosphorus. The former distils into the receiver, together with the alcohol which escapes the reaction. Water is added, and the lower layer of liquid is separated, dried with calcium chloride, and rectified on a water- bath. Ethyl iodide is a colorless liquid, but becomes brown when long kept, especially when exposed to light. Density at 0°, 1.9753. Boiling-point, 72.2°. It can exchange its iodine by double decomposition, as can potassium iodide. If ethyl iodide be added to an alcoholic solution of silver nitrate, a yellow precipitate of silver iodide is at once formed, while ethyl nitrate remains in solution. C 2 H 5 I + AgNO 3 = Agl + (C 2 H 5 )N0 3 Ethyl iodide. Silver nitrate. Ethyl nitrate. ETHYL CYANIDE. C3H&N = CH3-CH 2 -CN This compound is formed when ammonium propionate is distilled with phosphoric anhydride. (NH 4 )C 3 H 5 2 = C 3 H 5 N + 2H 2 Ammonium propionate. Ethyl cyanide. From this mode of formation, ethyl cyanide is sometimes called propionitrile. The same body exists in the product of the distillation of a mixture of potassium cyanide and potassium ethylsulphate. KCN+ C2]E ^>S0± = |>S0 4 + C 2 H5.CN Potassium Potassium Potassium Ethyl cyanide. cyanide. ethylsulphate. sulphate. But this product, which is liquid and has a variable boiling- point, contains, independently of the true cyanide of ethyl, an isomeride of that body, whose existence was foreseen by Meyer and discovered by Gautier in the product of the action of ethyl iodide on silver cyanide. NITRETHANE AND ITS DERIVATIVES. 495 Ethyl cyanide is a colorless liquid, having a penetrating and pleasant odor. It boils at 96.7°. When it is boiled with potassium hydrate, potassium propio- nate is formed and ammonia is disengaged (Dumas, Malaguti, and Le Blanc). C 3 H 5 N + KOH + H 2 = KC 3 H 5 2 + NH 3 Ethyl cyanide. Potassium propionate. When ethyl cyanide is brought into contact with dilute sul- phuric acid and zinc, it fixes 4 atoms of hydrogen and is converted into propylamine (Mendius). C 3 H 5 N + W = C 3 H 9 N Ethyl cyanide. Propylamine. Ethylcarbylamine. — This name was given by Gautier to the isomeride of ethyl cyanide already mentioned. It is a color- less liquid, having a very penetrating and intensely offensive odor. It boils at 79°. With potassium hydrate it yields po- tassium formate and ethylamine. 0" C2H5 \ P2W55 N + KOH + H 2 = H— N + ECHO 2 C 2 H^ H / Ethylcarbylamine. Ethylamine. Potassium formate. ETHYL NITRITE, OR NITROUS ETHER. C 2 EAO-NO This compound is obtained by the action of nitric acid on alcohol. The reaction is very violent, and abundant red vapors are evolved. After passing through a wash-bottle, they are conducted into a well- cooled receiver, where the ethyl nitrite condenses. It is a yellowish, very volatile liquid, Vhose odor recalls that of apples. It boils at 18°. It is but slightly soluble in water. Hot water immediately decomposes it into alcohol and nitrous acid, the latter being itself decomposed into nitric acid and nitrogen dioxide. NITRETHANE AND ITS DERIVATIVES. C 2 H5-N0 2 This isomeride of ethyl nitrite represents ethane, C 2 H 6 , in which one atom of hydrogen is replaced by the group (NO 2 )'. It is the superior homologue of nitromethane. 496 ELEMENTS OF MODERN CHEMISTRY. It is obtained, together with a certain quantity of ethyl nitrite, when ethyl iodide is treated with silver nitrite. C 2 H 5 I + AgNO 2 — C 2 H 5 (N0 2 ) + Agl Ethyl iodide. Silver nitrite. Nitrethane. It is a liquid having a peculiar, ethereal odor and boiling at 113-114°. Density at 13°, 1.0582 (V. Meyer). With nascent hydrogen, it furnishes pure ethylamine. C 2 H 5 (N0 2 ) + 3H 2 = C 2 H 5 (NH 2 ) + 2H 2 All of the homologues of nitrethane thus yield the corre- sponding amines. It is a general character of the nitro com- pounds, and one which is not possessed by their isomerides, the nitrous ethers. In constitution and properties, nitrethane approaches nitrobenzol, as will be seen by the following com- parison of their formulae: C 2 H 5 .H C 6 H 5 .H Ethane. Benzol. C 2 H 5 (N0 2 ) C 6 H 5 (N0 2 ) Nitrethane. Nitrobenzol. C 2 H 5 (NH 2 ) C 6 H 5 (NH 2 ) Ethylamine. Phenylamine (aniline). The presence of the group (NO 2 ) confers acid properties NO 2 upon nitrethane. Its sodium compound, C 2 H 4 <^ , is formed either by the action of an alcoholic solution of sodium hydrate on nitrethane, or by the direct action of sodium on the same body; in the latter case hydrogen is disengaged. Sodium- nitrethane is very explosive (V. Meyer and Stuber). When it is sought to prepare potassium-nitrethane by the action of alcoholic potassium hydrate on nitrethane, the latter body is decomposed, yielding, among other products, potassium nitrite. Now, the latter salt exerts a remarkable action on ni- trethane, giving rise to a new body of complex composition, potassium ethylnitrolate. Ethylnitrolic acid may be obtained by a process analogous to that which has been described for the preparation of methyl- nitrolic acid. Ethylnitrolic acid contains CH 3 G=N.OH NO 2 ETHYL NITRATE — ETHYL SULPHATE. 497 It crystallizes in light-yellow, transparent prisms, possessing a feeble bluish fluorescence and a very sweet taste. It decom- poses without violence at 81-82° into nitrogen, nitrous vapors, and acetic acid. When boiled with dilute sulphuric acid, it decomposes into acetic acid and nitrogen monoxide. C 2 H 4 N 2 3 = C 2 H 4 2 + ^0 Ethylnitrolic acid. Acetic acid. ETHYL NITRATE, OR NITRIC ETHER. (C 2 H5)N03 This is obtained by the action of nitric acid upon alcohol in presence of a small quantity of urea. The latter body prevents the reduction of the nitric acid to nitrous acid. Nitric ether condenses in the receiver. It is washed with water, dehydrated with calcium chloride, and rectified. It is a liquid, having an agreeable, ethereal odor. It boils at 86°. Density at 0°, 1.1322. Potassium hydrate decomposes it, like all compound ethers, forming potassium nitrate and alcohol. (C 2 H 5 )N0 3 + KOH = C 2 H 5 .OH + KNO 3 It dissolves in ammonia, especially if the latter be warm, yielding ammonium nitrate and ethylamine. The reaction is analogous to that of ammonia upon methyl nitrate. ETHYLSULPHATES. C 2 H 5 ) Ethylsulphuric or Sulphovinic Acid. — g > SO 4 .= ttq>S0 2 . This body is an example of an acid ether. It results from the substitution of a single ethyl group for one atom of hydrogen in sulphuric acid, which is dibasic. g J so* C2 ^ 5 >so* It is formed by the action of sulphuric acid upon alcohol. The mixture of the two bodies becomes hot, and if after cool- ing the liquid be diluted and saturated with barium carbonate, an abundant precipitate of barium sulphate will be formed, and a soluble salt of barium, the ethylsulphate, will remain in solu- tion. A solution of ethylsulphuric acid may be obtained by exactly decomposing this salt with dilute sulphuric acid. 42* 498 ELEMENTS OF MODERN CHEMISTRY. By boiling, ethylsulphuric acid is decomposed into sulphuric acid and alcohol. C 2 H 5 H }so» + g}o = c, S}o +g}flO The ethylsulphates are beautiful salts ; they are crystalliz- able and soluble in water. Ethyl Sulphate.— £ a g 6 J SO 4 = c 2 H 5 :o >S ° 2 * This body, which represents sulphuric acid in which the two atoms of hydrogen are replaced by two ethyl groups, is formed when vapor of sulphuric anhydride is passed into ether cooled in a freezing mixture (Wetherill). (C 2 H 5 ) 2 + SO 3 = (C 2 H 5 ) 2 S0 4 It is an oily liquid having an acrid taste. Its density is 1.120. It cannot be distilled under ordinary pressures. ETHYLSULPHUROUS ACID. C 2 H5.S03H When mercaptan, C 2 H 5 .SH, is oxidized by nitric acid, a thick, very acid liquid is obtained, which in a dry vacuum solidifies to a crystalline mass. It is ethylsulphurous acid, which con- centrated nitric acid oxidizes and converts into ethylsulphuric acid. Unlike the latter, ethylsulphurous acid is very stable. It is not decomposed by boiling with potassium hydrate : when fused with the latter, it yields potassium sulphite and alcohol. C 2 H 5 .S0 3 K + KOH = C 2 H 5 .OH + K 2 S0 3 Phosphorus pentachloride converts it into a-ethylsulphurous chloride, C 2 H 5 -S0 2 .C1, a liquid boiling at 173°. Ethylsulphurous acid is analogous in its properties and con- stitution to phenylsulphurous acid, and its analogues, which will be described ; they are known as sulphonic acids. Ethyl- sulphurous acid is the sulphonic derivative of ethane. C 2 H6 ethane. C 6 H 6 benzine. C 2 H 5 .S0 3 H ethylsulphurous acid. C 6 H 5 .S0 3 H phenylsulphurous acid. ETHYL SULPHITES. There are two sulphites of ethyl which present interesting relations of isomerism. ETHYL SULPHITES. 499 1. If silver sulphite and ethyl sulphite be heated together, a double decomposition takes place, yielding silver iodide and ethyl sulphite. AgS0 2 .OAg + 2C 2 H 5 T = 2AgI + C 2 H 5 .S0 2 .OC 2 H 5 Silver sulphite. Ethyl iodide. a-Ethyl sulphite. This sulphite is the ether of the ethylsulphurous acid which has been described. It may be obtained by the action of ethyl- sulphurous chloride on sodium ethylate. C 2 H 5 .S0 2 .C1 + C 2 H 5 .ONa = NaCl + C 2 H 5 .S0 2 .OC 2 H 5 It is a liquid, boiling at 208°, and having at 0° a density of 1.47. 2. By the action of thionyl (sulphuryl) chloride on abso- lute alcohol there is obtained an ethyl sulphite isomeric with the preceding. SO C0 + 2NH3 = C0 C0 Dumas obtained this ether by passing chlorocarbonic gas into alcohol. Water is added to the product of the reaction, and the insoluble liquid is separated, dried, and distilled. £J>CO + C2H&.0H = HC1 + C 2 H 5o> co Chlorocarbonic gas. Ethyl chlorocarbonate. It is a liquid having a pungent, ethereal odor. It boils at 94°. Hot water decomposes it. Ammonia converts it into ethyl carbamate, or urethane. C 2H5 C o> co + 2NH8 = NH4C1 + C2H?0> C0 ETHYL ISOCYANATE. C 2 H5-N=CO This compound is prepared by distilling on an oil-bath a mixture of 2 parts of potassium ethylsulphate and 1 part of recently-prepared and well-dried potassium isocyanate. The product which condenses in the receiver is rectified on a water- bath (Wurtz). Ethyl isocyanate is a colorless liquid, having a very irritating odor. It boils at 60°. Potassium hydrate de- composes it into carbonic acid gas and ethylamine. It com- bines with ammonia, developing heat and producing ethylurea (page 467). The bodies which were formerly known as cyanic acid and ethyl cyanate, are only isomerides of the oxygen compounds of cyanogen. They have been described as isocyanic acid and isocyanate of ethyl. The true cyanic ether, (C 2 H 5 .0)CN, or rather a polymeride of that body, has been obtained by Cloez. It is formed by the action of cyanogen chloride on ethyl ate of sodium. CNC1 + Na.OC 2 H 5 = CN.OC 2 H 5 + NaCl Cyanogen chloride. Sodium ethylate. Ethyl cyanate. Potassium hydrate decomposes the true ethyl cyanate, like SATURATED HYDROCARBONS. 503 all other compound ethers, into alcohol and the corresponding potassium salt (cyanate), or into the decomposition products of that body, — carbon dioxide and ammonia. CYANURIC ETHERS. When potassium isocyanate is distilled with ethyl sulphate, besides the ethyl isocyanate which has just been described, there is formed also the isocyanurate. C 3 3 N 3 ( C 2 H 5)3 _ (CO) 3 =(N.C 2 H 5 ) 3 The latter condenses in & solid white mass which may be purified by recrystallization from boiling alcohol. It crystallizes in brilliant prisms, fusible at 175° ; it boils at 296° (A. Wurtz). Boiling potassium hydrate decomposes it, like the isocyanate, with disengagement of carbon dioxide, a reaction which justi- fies the constitution indicated by the preceding formula. The cyanuric ether C 3 N 3 (OC 2 H 5 ) 3 , corresponding to the normal cyanuric acid (page 462), is not known. The mother liquor from which triethyl isocyanurate has deposited, contains diethyl isocyanurate, C 3 3 N 3 H(C 2 H 5 ) 2 , which crystallizes in six-sided prisms, fusible at 173°. Normal methyl cyanur ate is formed by the action of cyanogen chloride on sodium methylate. 3CNC1 + 3CH 3 .ONa = 3NaCl + C 3 N 3 (OCH 3 ) 3 . It crystallizes in needles fusible at 132°. It boils between 160 and 170°, and at this temperature is converted into its isomeride methyl isocyanurate, fusible at 175°, and boiling at 296°. By the action of boiling potassium hydrate, it is de- composed into potassium cyanurate and methyl alcohol. SERIES OF SATURATED HYDROCARBONS. C 2 H 2n + 2 To methane and ethane, which have already been described, are related numerous hydrocarbons belonging to the same series, C n H 2n+2 . They are called saturated because no hydro- carbons are known in which the number of hydrogen atoms exceeds that indicated by the preceding formula. Again, the hydrocarbons in question can fix directly no other atoms. For example, in order that chlorine can enter into one of their molecules, hydrogen must first be removed, and this displace- 504 ELEMENTS OF MODERN CHEMISTRY. inent is known to take place, atom for atom, according to the law of substitution. Thus, if chlorine be made to act upon the hydrocarbon C 6 H U (hexane), the compounds C 6 H 13 C1, C 6 H 12 C1 2 , C 6 H n Cl 3 , may be obtained successively. Let us con^ sider the first of these compounds, C 6 H 13 C1. The CI may be replaced by the group OH, and the chloride is thus converted into an alcohol. For this purpose the chloride is caused to react with a silver salt, the acetate, for example, and hexyl acetate is formed by double decomposition. C 6 H 13 C1 + AgC 2 H 3 2 = C 6 H. 13 .C 2 H 3 2 + AgCl Hexlyl chloride. Silver acetate. Hexyl acetate. Boiling potassium hydrate will transform this ether into hexyl hydrate. C 6 H i3 C 2 H 3 2 + K0H = KC 2 H 3 2 + C 6 H 13 .OH Hexyl acetate. Potassium acetate. Hexyl hydrate. This series of reactions permits of the successive transforma- tion of any hydrocarbon of the saturated series into a chloride, an acetate, and a hydrate, and the latter is the alcohol corre- sponding to the hydrocarbon. The following is the series of saturated hydrocarbons : CH 4 methane. C 2 H6 ethane. C 3 H 8 propane. OH™ butanes. C 5 H 12 pentanes. ' C 6 H 14 hexanes. C?H 16 heptanes. C 8 H 18 octanes. C 9 H 20 nonanes. C 10 H 22 decanes, etc. All of these hydrocarbons, after the fourth of the series, up to the term C 16 H 34 , have been obtained from petroleum and the products of distillation of bitumen and peat. Towards the close of the distillation, when the temperature passes above 300°, the products which distil condense to a solid mass on cooling. When properly purified, this solid forms a colorless, translucent mass, which has received the name paraffin. It is probably a mixture of several hydrocarbons of the series C n H 2n+2 . Its point of fusion varies between 45 and 65°. All of the compounds belonging to this series cannot be described here, but we may briefly consider their constitution. The third member of the series, propane, C 3 H 8 , has the con- stitution indicated by the formula CH 3 -CH 2 -CH 3 . It is a gas which liquefies at — 17°. PETROLEUM. 505 Its superior homologue, butane, C 4 H 10 , has the constitution CH 3 -CIf 2 -CH 2 -CH 3 , and can be obtained by the action of zinc or sodium on ethyl iodide. 2C 2 H 5 I + Na 2 = 2NaI + C 4 H 10 It is a colorless gas, condensable at +1°- But we have here a remarkable instance of isomerism. There is another butane, isomeric with the preceding, and having the consti- CH 3 tution expressed by the formula CH 3 -CHCH-CH 2 -CH 2 .OH, but contains also a variable quantity of active amyl alcohol. AMYL ALCOHOLS. 511 It may be obtained by fractional distillation of the fusel oil from beet-root and potatoes, as well as of that from the marc of grapes, whiskey, etc. These products are only the residues of the distillation of alcohol from various sources. The inactive amy! alcohol or isobutylcarbinol may be separated by the following process, indicated by Pasteur. By treatment with sulphuric acid the crude amyl alcohol is converted into amylsulphuric acid. The liquid is diluted with water, neutralized with barium carbonate, and filtered. Two barium amylsulphates are thus obtained, of which the one is less soluble than the other, and crystallizes first when the solu- tion is evaporated, while the other remains in the mother liquid. The former is derived from the inactive alcohol, the latter from the active alcohol ; these alcohols are obtained by decomposing the corresponding barium salts with sulphuric acid, filtering, and distilling with water the free amylsulphuric acids. s ° a CH-CH 2 -CHO + H 2 = ^3>CH-CH 2 -CH 2 .OH Valeric aldehyde. Isobutylcarbinol. Properties. — Pure isobutylcarbinol is a colorless, somewhat oily liquid, soluble in fifty parts of water at 13°. Its density at'0° is 0.823, and it boils at 131.4°. When oxidized it yields inactive valeric aldehyde and acid. C 5 H 12 + = H 2 + C 5 H 10 O Amyl alcohol. Valeric aldehyde (valeral). C 5 H 12 + O 2 = H 2 + C 5 H I0 O 2 Valeric acid. The crude alcohol of fermentation is an oily liquid, of a dis- agreeable odor. It boils at 129-132°. It turns the plane of 512 ELEMENTS OF MODERN CHEMISTRY. polarized light to the left, but its rotatory power is variable, for it contains variable proportions of active amyl alcohol. When distilled with zinc chloride, it yields ordiuary amylene, which is a mixture of several isomeric amylenes, trimethyl- ethylene being the most abundant. C 5 H 12 = C 5 H 10 + H 2 Amyl alcohol. Amylenes. Many amyl derivatives have been studied. They resemble the ethyl compounds, but contain, of course, the group C 5 H n instead of C 2 H 5 . C 5 H n Amyl oxide, p5rni>0, is formed, together with amylene, by the action of sulphuric acid on crude amyl alcohol (William- son). It is a colorless liquid, of an aromatic odor, boiling at 176°. Amyl chloride, C 5 H n Cl, is a colorless liquid, boiling at 101.4°. Amyl bromide, C 5 H n Br, boils at 120.4°. Amyl iodide, C 5 H n I, is prepared by a process similar to that which yields ethyl iodide. It is a colorless liquid, having at 0° a density of 1.4676, and boiling at 148°. It turns brown on exposure to the light. Amyl nitrite, C 6 H n N0 2 , is prepared by passing nitrous vapors, made by the action of nitric acid on starch, into amyl alcohol, and distilling the carefully washed product. It is a pale yellow liquid, boiling at 96°, and having a peculiar odor somewhat like that of apples. Its vapor when inhaled pro- duces dilatation of the capillary system, and violent but tran- sitory headache. Its inhalation has been recommended as a remedy for sea-sickness, in certain heart-affections, and as an antidote in cases of poisoning by chloroform vapor. Active Amyl Alcohol is contained to the extent of about thirteen per cent, in crude amyl alcohol. One method of separation has already been indicated, but Le Bel has proposed a better method when it is desired to prepare only the active alcohol. If hydrochloric acid gas be passed through the crude alcohol, the inactive alcohol is first attacked and converted into chloride ; the active alcohol then remains after the separation of the inactive chloride. It boils at 127°. It rotates the plane of polarized light to the left [a]D == —4.4°. Its chloride boils at 97-99° ; its iodide at 144-145°. Oxidation converts it into active valeric acid. HIGHER ALCOHOLS. 513 Tertiary Amyl Alcohol, or Hydrate of Amylene. This alcohol is prepared by treating with hydriodic acid triinethyl- ethylene, described on page 560, which forms the gre. ter part of crude amylene. £U'>C=CH-CH 3 + HI = ^[j!>CI-CH 2 -CH 3 Trimethylethylene. Trimethylethyl iodide. The iodide so formed, when acted on by water and silver oxide, yields the corresponding hydrate, which is tertiary amyl alcohol or dimethylethylcarbinol. It is a mobile, colorless liquid, having an odor somewhat like camphor. At — 12° it forms a crystalline mass; it boils at 102.5°, and at 200° is decomposed into amylene and water. By reason of the latter reaction, Wurtz, who discovered the alcohol, named it hydrate of amylene. Its chloride boils at 86°, its bromide at 108-109°, and its iodide at 127-128°. Oxidation converts it into acetic acid and acetone. HIGHER ALCOHOLS. Of the rapidly increasing members of this series which are becoming well known, we can consider but a few. Hexyl and Heptyl Alcohols. — Faget announced that the residues from the distillation of fusel-oil from fermented grape- juice contained a small quantity of hexyl (C H I1 14 ) and heptyl (C 7 H 16 0) alcohols, but such alcohols have not been refound in that product. Normal hexyl alcohol has been obtained from the volatile oil of the seeds of Heracleum giganteum. an oil which contains butvrate of hexyl, C 6 H 13 .C 4 H 7 2 . The normal alcohol boils at 157-158°. Normal heptyl alcohol, C 7 H 16 0. has been prepared by the action of nascent hydrogen # on cenanthic aldehyde C 7 H u O. It boils at 175-177°, and has an aromatic odor. Octyl Alcohols, C 8 H 18 0. — Normal oetyl alcohol may be ex- tracted from the seeds of Heracleum spondylium and Hera- cleum giganteum, in which octyl acetate. C 8 H 17 .C~H 3 2 . exists. This ether is separated and decomposed by boiling potassium hydrate. Its boiling-point is between 190 and 192°. Bouis discovered secondary octyl alcohol. By boiling one 514 ELEMENTS OP MODERN CHEMISTRY. of the acids produced by the saponification of castor-oil, rici- nolic acid, with potassium hydrate, Bouis decomposed it into sebacic acid and a new secondary alcohol. This is octyl alco- hol, C 8 H 18 0, a colorless liquid having a pleasant, aromatic odor, and boiling at 178°. The following equation explains its formation : C i8 H 34 3 + 2KOH == K 2 C 10 H 16 O 4 + C 8 H 18 + H 2 Ricinolic acid. Potassium sebate. Octyl hydrate. Cetyl Alcohol. — The concrete portion of an oil which fills the cranial sinuses of the sperm-whale is called spermaceti. When properly purified it occurs in beautiful pearly plates, fusible at 49°. It is a compound ether of which the nature was recognized by Chevreul in 1823. By submitting it to the action of potassium hydrate, that chemist decomposed it into palmitic acid and a new alcohol which he called ethal, to denote its relations with alcohol and ether. It is now called cetyl alcohol, or cetyl hydrate, C C^h2>° + K0H = cl6H33 - OH + KC16H310 2 Cetyl palmitate. Cetyl hydrate. Potassium palmitate. It belongs to the same homologous series as the preceding alcohols. Alcohols from Wax. — The most complex alcohols of the series under consideration were obtained from wax by Brodie. Ordinary beeswax is a mixture of a fatty acid, C 27 H 5 *0 2 , called cerotic acid (cerin), and a compound ether, the palmitate of myricyl (myricin). The two bodies are separated by alcohol, which readily dissolves the first, but in which the second is but slightly soluble. By boiling the palmitate of myricyl with potassium hydrate, it breaks up into palmitic acid and hydrate of myricyl^ or myricyl alcohol, C 30 H 62 O. Chinese wax is a compound ether ; it is cerotate of ceryl, and may be decomposed by caustic potassa into cerotic acid and ceryl hydrate, or ceryl alcohol, C 27 H 56 0. The hydrates of cetyl and ceryl are solid bodies. # ALLYL ALCOHOL. C 3 H5.0H = CH 2 ^CH-CH 2 .OH All of the alcohols thus far considered belong to the series C n H 2n+2 0. There are other monatomic alcohols which belong to different series, that is, in which there are different relations ALLYL ALCOHOL. 515 between the number of hydrogen atoms and the number of carbon atoms. Among these other alcoliols, the most impor- tant is allyl alcohol . or hydrate of allyl, so named because it is closely related to the essential oil of garlic, which is allyl sul- phide. Another natural oil, that of mustard, is sulphocyanate of allyl. C 3 H 5 .OH (C 3 H 5 ) 2 S C 3 H 5 .CXS Allyl hydrate. Allyl sulphide. Allyl sulphocyanate. Hofmann and Cahours prepared allyl hydrate and a great number of its derivatives artificially by the aid of allyl iodide. C 8 H 5 I, which is formed when glycerin is acted upon by iodide of phosphorus, P 2 I 4 (Berthelot and de Luca). This iodide, whose relations to allyl alcohol are the same as those of ethyl iodide to ordinary alcohol, is a colorless liquid, having a slightly pungent, garlicky odor, and boiling at 101°. When heated with mercury and concentrated hydrochloric acid, it yields pure propylene gas (Berthejot). 2C 3 H 5 I + 2HC1 + 4Hg = 2C 3 H 6 + Hg 2 ! 2 + Hg 2 Cl 2 Allyl iodide. Propylene. Tollens and Henninger discovered a very simple process for the preparation of allyl alcohol. It consists in heating formic acid, or oxalic acid, from which the former acid is produced, with glycerin to 220°. The allyl alcohol which distils is washed with a concentrated solution of potassium carbonate, and rectified over lime. In this reaction, a monoformine of glycerin is first produced, and this decomposes at 220° into carbon dioxide, water, and allyl alcohol. ro.CHO C3HM OH = CO 2 + H 2 + C 3 H5.0H (OH Monoformine of glycerin. Allyl alcohol. It will be seen that the reaction is really a reduction. Allyl alcohol is a colorless liquid, boiling at 97°, and having a pungent, alcoholic odor. It dissolves in all proportions of water. Density at 0°, 0.858. Allyl alcohol is an unsaturated compound ; it can fix directly two atoms of hydrogen, so form- ing normal propyl alcohol. It combines directly with bromine, forming dibromopropylalcohol. CH 2 Br-CHBr-CH 2 OH. Acrolein, a volatile liquid that is formed in the distillation of fatty bodies, is the aldehyde of allyl alcohol. Acrylic acid is the corresponding acid. 516 ELEMENTS OF MODERN CHEMISTRY. COMPOUND AMMONIAS, OR AMINES. Wurtz gave these names to the basic combinations resulting from the substitution of alcoholic radicals, such as methyl, ethyl, etc., for the hydrogen of ammonia. This substitution may be more or less complete ; 1, 2, or 3 atoms of hydrogen may be replaced by as many alcoholic groups. Hence there are various classes of amines ; they are designated by the names primary, secondary, and tertiary. PRIMARY AMINES. SECONDARY AMINES. TERTIARY AMINES. H ) CH3) CHn CH 3 ) H ^N h In CH 3 VN chs In Hj hJ Hj cm) Ammonia. Methylamine. Dimethylamine. Trimethylamine. C2H5) C 2 H5) C 2 H5) H ^N C 2 H5 [ N C 2 H5 I N h] HJ C 2 H5j Ethylamine. Diethylamine. Triethylamine. Lastly, bases are known which are the most energetic of all, and may be considered as derived from the hypothetical hydrate of ammonium by the substitution of alcoholic radicals for 4 atoms of hydrogen. ir H! H i hJ Ammonium hydrate. N.OH C 2 H5] C 2 H& ! >j ATT C2H5 N.OH C 2 H5J Hydrate of tetrethylammonium. The latter ammoniated bases, as well as the secondary and tertiary amines, were discovered by Hofmann. The compound ammonias, or amines, are formed in the fol- lowing reactions : 1. By the decomposition of an isocyanic or isocyanuric ether by potassium hydrate. In this case primary amines are obtained (A. Wurtz). CO=N-C 2 H5 + 2KOH = NH 2 (C 2 H5) + K 2 C0 3 Ethyl isocyanate. Ethylamine. 2. By the action of alcoholic bromides or iodides on ammo- nia (A. W. Hofmann). C 2 H&I + Ethyl iodide. 2C 2 IM + NH3 3C a H*I NH 3 = NH2(C2H5)HI Ethylamine hydriodide. = NH(C 2 fl5j 2 HI + HI Diethylamine hydriodide. NH 3 = NH(C 2 H5)3HI + 2HI Triethylamine hydriodide. COMPOUND AMMONIAS. 517 3. In the decomposition of carbylainines by dilute acids (A. Gautier). 4. By the reduction of nitromethane and its homologies by nascent hydrogen (V. Meyer, see p. 480). 5. By the action of nascent hydrogen on the alcoholic cya- nides, also called nitriles (Mendius). CH?.CN H* = CH 3 -CH 2 -XH2 Methyl cyanide, or acetonitrile. Ethylaniine. General Properties. — The amines are energetic bases, pre- senting great analogies with ammonia, having the same odor, the same solubility in water, and the same pronounced alkaline reaction. The more simple are combustible gases or volatile liquids. The basic energy increases with progressive substitu- tions : thus triethylamine is a stronger base than either ethyl- amine or ammonia, both of which it displaces from their com- binations. The hydrates of the quaternary bases, or compound ammoniums, are almost as caustic as potassium hydrate. All of the compound ammonias form with platinic chloride crystal- lizable double salts comparable to ammonio-platinic chloride. They can replace ammonia in ammonia alum. When the hydrochlorides of the- amines are subjected to de- structive distillation, they decompose into an alcoholic chloride and a lower amine, a reaction which allows the molecules to be simplified by a sort of inverse substitution. N(CH 3 )±C1 Tetramethylamnionium chloride. N(CH 3 ) 3 + Trimethylamine. CH 3 C1 N(CH 3 ) 3 .HC1 Trimethylamine hydrochloride. NH(CH 3 ) 2 + Diniethylamine. CH 3 C1 NH(CH3)2.HC1 = Diniethylaniine hydrochloride. XH2(CH 3 ) + Methylamine. CH 3 C1 Action of Nitrous Acid. — Nitrous acid converts the primary amines into alcohols, with formation of water and elimination of nitrogen. NH 2 (C 2 H 5 ) + HO.NO = C 2 H 5 .OH + H 2 + N 2 With the same acid the secondary amines undergo a remark- able reaction, giving rise to ?u7>*oso-bases, or nitroso-amines, formed by the substitution of the group nitrosyl, NO, for the single atom of hydrogen in the ammonia residue NH (imidogen). H /NO N V CH 3 + NO OH = N^CH 3 + H 2 X CH 3 X CH 3 Diniethylamine. Nitrosodimethylamine. 44 518 ELEMENTS OF MODERN CHEMISTRY. The nitrosamines are oleaginous liquids, insoluble in water ; they can be distilled without decomposition, and, generally, are unalterable by either acids or alkalies. On the addition of phenol and sulphuric acid they produce intense colors. When their alcoholic solutions are treated with zinc and acetic acid, the nascent hydrogen evolved converts them into disubstituted hydrazines (see below). In the amines, nitrogen acts as a triatomic element or tri- valent; but it may assume two other atomicities. In sal- ammoniac, it is pentatomic, and it may play precisely the same part in the amines. H 1 ft C 2 H& i CI H 1 H \!/ N (OH)' (C 2 H5)' (C 2 H5)' N H H Lmmonia. C 2H5 C 2 H5 Triethylamine. /\ H H Ammonium chloride. /\ (C 2 H*)' (C 2 H5)' Tetrethylammonium hydrate. Related to the amines are various organic combinations which have the same constitution, but in which the nitrogen is replaced by an analogous element, such as phosphorus, arsenic, or antimony. A great number of these bodies have been discovered, of which the more important are C 2 H5 ) C 2 H5 ) C 2 H& ) C 2 H 5 I p>" c 2 H5 [ As'" C 2 H5 V Sb C 2 H5J C 2 H5j C 2 H5J Triethylphosphine. Triethylarsine. Triethylstibine. Hydrazines. — The nitrogenized bases that have just been considered belong either to the type NX 3 or to the type NX 5 . A new class of compounds has recently been discovered, be- longing to the type N 2 X 4 . It is evident that the group NH 2 (amidogen) cannot exist in the free state. If it could be isolated, it would probably combine with itself, forming a double molecule NH 2 N 2 H* = i NH 2 Fischer has made known several substituted derivatives of this body, N 2 H 4 , which he names hydrazine. He has described ethylhydrazine, NH 2 -NH(C 2 H 5 ), and diethylhydrazine N(C 2 H 5 ) 2 -NH 2 Dimethyl- and diethylhydrazine are formed by the action of nascent hydrogen on the corresponding nitroso compounds (page 517). METHYL AMINE. 519 ^ 3 3 >N-NO + H* = H 2 + ^( CH3 ) 2 The hydrazines are closely related to the amines by their chemical and physical properties. They are very volatile liquids, having an ammoniacal odor, and soluble in water, alcohol, and ether. METHYLAMINE. H }» This body may be prepared by boiling together potassium hydrate and methyl cyanate or cyanurate, and passing the vapors which are disengaged into dilute hydrochloric acid; methylamine hydrochloride is thus formed. on CH3) C ^N + 2K0H = K2C0 3 + H^N Methyl cyanate. Methylamine. The solution is evaporated to dryness, and the residue fused and allowed to cool ; it is then mixed with double its weight of powdered quick-lime, and the mixture gently heated. The methylamine disengaged may be collected over mercury. It is a colorless gas, which condenses to a light liquid at a temperature a few degrees below 0°. It is inflammable, and burns with a pale flame. Its odor is strongly ammoniacal and, at the same time, recalls that of the sea. It is the most solu- ble of all gases. 1 volume of water at 12.5° absorbs 1153 volumes of methylamine. The aqueous solution possesses the odor of the gas, a caustic taste, and a strong, alkaline reaction. Like ammonia, it precipitates the oxides from solutions of the metallic salts. If a solution of methylamine be added to a solution of cupric sulphate, a light-blue precipitate is first formed, but disappears if an excess of methylamine be added, yielding a beautiful blue solution. Methylamine Hydrochloride, CH 5 N.HC1, differs from am- monium chloride by its solubility in boiling alcohol, from which it is deposited on cooling in large, colorless, deliquescent plates. With platinic chloride it forms a yellow precipitate, soluble in boiling water, from which it crystallizes in golden-yellow scales. It is a chlorojilatmate, (CH 5 N.HCl) 2 .PtCP. 520 ELEMENTS OF MODERN CHEMISTRY. DIMETHYLAMINE, TRIMETHYLAMINE, TETRA METHYLAMMONIUM HYDRATE. These compounds were discovered by Hofmann. Dimethylamine, (CH 3 ) 2 NH, is a combustible gas which lique- fies at 8°. Trimethylamine, (CH 3 ) 3 N, exists ready formed in the Cheno- podium vulvar ia, in the flowers of Cratsegus oxyacantha, in herring-brine, in cod-liver oil, and in coal-gas tar. Vincent extracts large quatities of it from the residues of the distilla- tion of fermented beet-juice. At ordinary temperatures it is a gas ; it liquefies at 9°. It is very soluble in water and in alcohol. It has a strong, ammoniacal odor, and an intense, alkaline reaction. It unites directly with methyl iodide, forming the iodide of tetramethylammonium. (CH 3 ) 3 N + CH 3 I = (CH 3 ) 4 NI This iodide possesses all the appearances of a salt. It is soluble in water, and the solution treated with silver oxide yields silver iodide and tetramethylammonium hydrate. 2(CH 3 ) 4 NI + Ag 2 + H 2 = 2AgI + 2(CH 3 ) 4 N.OH The latter body is very soluble in water, and the solution is caustic. When submitted to dry distillation, it decomposes into trimethylamine and methyl alcohol. (CH 3 ) 4 N.OH = CH 3 .OH + (CH 3 ) 3 N ETHYLAMINE. C 2 IPN === B.VN HJ Ethylamine is prepared by a process analogous to that which yields methylamine ; cyanate or cyanurate of ethyl is decom- posed with boiling potassium hydrate, and the vapors are con- densed in very dilute hydrochloric acid. The dry ethylamine hydrochloride is then treated with quick-lime (A. Wurtz). Another process has been indicated by Hofmann. It consists in causing ammonia to react upon the bromide or iodide of ethyl. in cm^ CW$Br + H [ N = H N.HBr Hj HJ Ethylamine hydrobromide. DIETHYLAMINE. 521 Ethylamine is a light, mobile, colorless liquid ; it boils ai 18.7°. Its odor is strong and exactly resembles that of am monia. Ethylamine is inflammable. It mixes with water, alcohol, and ether in all proportions. Its aqueous solution is caustic, and precipitates most of the metallic salts like solution of am- monia, and, like the latter, redissolves cupric hydrate, forming a blue liquid. Ethylamine Hydrochloride, C 2 H 7 N.HC1.— This salt crys- tallizes in large, deliquescent plates, soluble in absolute alcohol. Its aqueous solution yields with platinic chloride a precipitate composed of yellow scales, soluble in boiling water, and consti- tuting a chloro-platinate, (C 2 H 7 N.HCl) 2 .PtCl 4 . DIETHYLAMINE, TKIETHYLAMINE, TETRETHYL- AMMONIUM HYDRATE. C 2 H 5 ^ Diethylamine, C 2 H 5 I N, was obtained by Hofmann by heat- ing ethylamine with ethylbromide, and decomposing the die- thylamine hydrobromide formed by an alkali. CW°) c 2 H^ H [ N + C 2 H*Br = C 2 H5 [ KHBr Hj Hj Ethylamine. Diethylamine hydrobromide. The free base is a liquid having an ammoniacal odor and boiling at 57.5° Triethylamine may be formed by the action of ethyl bro- mide on diethylamine ; triethylamine hydrobromide is formed, C 2 H 5 ^ C 2 H 5 >■ N.HBr, from which alkalies cause the disengagement C 2 H 5 j of triethylamine, a colorless liquid, boiling at 91° ; its odor is ammoniacal and its reaction strongly alkaline. Tetrethylammonium Hydrate. — When a mixture of ethyl iodide and triethylamine is heated on a water-bath, the two bodies combine, forming the compound which Hofmann has named tetrethylammonium iodide. C 2 H 5 I + (C 2 H 5 ) 3 N == (C 2 H 5 ) 4 N.I Ethyl iodide. Triethylamine. Tetrethylammonium iodide. When this is treated with silver oxide and water, it yields silver iodide and tetrethylammonium hydrate, (C 2 H 5 ) 4 N.OH, a 44* 522 ELEMENTS OF MODERN CHEMISTRY. powerful base, which is crystallizable and soluble in water. Its energy is comparable to that of potassium hydrate. ETHYLPHOSPHINES. Primary, secondary, and tertiary ethylphosphines are known, as well as the compounds of tetrethylphosphonium. C 2 H5 I C 2 H5) C 2 H5 H ( P'" C 2 H 5 Lp'" C 2 H3 H J Hj C 2 H* C 2 H< p,„ C 2 J* r C 2 ff kl C 2 H*J Ethylphosphine. Diethylphosphine. Triethylphosphine. Tetrethylphosphonium. (Primary.) (Secondary.) (Tertiary.) The first two have been recently discovered by Hofmann. The third is due to an admirable research of Hofmann and Cahours, who obtained it by the action of phosphorus trichloride on zinc ethyl. 2PCP + 3[Zn(C 2 H 5 ) 2 ] = 2[P(C 2 H 5 )*] + 3ZnCl 2 Zinc ethyl. " Triethylphosphine. The operation must be conducted out of contact with the air, and the zinc ethyl must be diluted with anhydrous ether. Monethylphosphine and diethylphosphine are produced when ethyl iodide is made to react upon phosphonium iodide, PH 4 I, hydriodide of hydrogen phosphide (page 167), in presence of an excess of zinc oxide. 2C 2 H*I + 2PH±I + ZnO = 2[(C 2 H5)H 2 P.HI] + Znl 2 + H 2 2C 2 H 5 I + PH±I + ZnO = (C 2 H^) 2 HP.HI + Znl 2 + H 2 As both reactions are accomplished simultaneously, both phosphines are obtained at the same time. They are separated by the action of water upon the two hydriodides which are formed. That of monethylphosphine is decomposed by water, while that of diethylphosphine is only decomposed by the alka- lies. It is sufficient then to add water to the product of the reaction in order to set free the monethylphosphine ; when the latter has been completely expelled by heat, potassium hy- drate added to the residue will cause the disengagement of the diethylphosphine. These operations should be conducted in a current of hydrogen. Monethylphosphine, (C 2 H 5 )H 2 P. — This is a colorless liquid, lighter than water, in which it is insoluble, and boiling at 25°. It has a most disagreeable odor. It takes fire on contact with chlorine or nitric acid. Its hydriodide crystallizes in beautiful, white, quadrangular tables. Diethylphosphine, (C 2 H 5 ) 2 HP. — A colorless liquid, lighter PRODUCTS OF OXIDATION OF ETHYLPHOSPHIXES. 523 than water, and boiling at S5°. It is very avid of oxygen, and sometimes takes fire spontaneously on contact with the air. TriethylphospMne, (CPH 5 ) 3 P. — This is a colorless liquid. boiling at 127.5°. Density at 15°, 0812. It combines di- rectly with oxygen, forming triethylphosph ine oxidt. C~H : PO. The latter is a crystalline solid, very soluble in water and in alcohol. It distils at 240°. When treated with ethyl iodide, triethylphosphine yields tetrethyiphosphonium iodide, (C 2 H 5 )*PL a compound which may be obtained in beautiful crystals. When this iodide is acted upon by moist silver oxide, it furnishes the corresponding hydrate, which is an energetic base. 2[(C 2 H 5 )TI] + Ag~0 + H 2 = 2AgI + 2[(C 2 H 5 ) 4 P.OH] Tetrethylphosphonium Tetrethylphosphonium iodide. hydrate. PRODUCTS OF OXIDATION OF ETHYLPHOS- PHINES. When trie ethylphosphines are treated with fuming nitric acid under suitable conditions, they act in a characteristic man- ner. Monethylphosphine is transformed into a dibasic acid, monethylphosphinic ; diethylphosphine yields a monobasic acid. diethylphosphinic. Triethylphosphine yields an indifferent oxide, which- has already been mentioned. Now, if it be remem- bered that under the same circumstances hydrogen phosphide furnishes phosphoric acid, it will be seen that the preceding oxidation compounds may be regarded as phosphoric acid, in which 1. 2, or 3 groups OH are replaced by as many ethyl groups. f H (OH P^ H PO< OH u [OH Hydrogen phosphide. Phosphoric acid. ( C2H3 POs OH vi H u I oh Monethylphosphine. Monethylphosphinic acid. f C 2 H3 f C 2 H5 PO. C-H5 P I C 2 H 5 Ih [ OH Diethylphosphine. Diethylphosphinic acid. f C 2 H* P* C*H* 1 C-H5 PO- C»HS ( C»H* I CTBP Triethylphosphine. Triethylphosphine oxide. 524 ELEMENTS OF MODERN CHEMISTRY. The compounds of arsenic and ethyl are entirely analogous to the phosphines ; they have already been alluded to. Besides these, there are ethylic combinations corresponding to cacodyl and its derivatives. SILICON-ETHYL. Si(C 2 H5)4 This compound is obtained by treating silicon chloride with* zinc ethyl. SiCl 4 + 2Zn(C 2 H 5 ) 2 = 2ZnCP + Si(C 2 H 5 ) 4 Silicon- tetrethyl is a colorless, mobile liquid, not decomposed by water, combustible, burning with a brilliant white flame and production of white fumes of silicic acid. It is indifferent to the action of reagents, and acts in all points like a hydrocarbon, C(C 2 H 5 )* = C 9 H 20 , in which one atom of carbon is replaced by an atom of silicon. Its analogue, silicon-methyl, a liquid boil- ing at 30°, corresponds to tetramethylmethane, C 5 H 12 , a hydro- carbon boiling at 10°. Si(C 2 H 5 ) 4 Si(CH 3 ) 4 C(CH 3 ) 4 Silicon-ethyl. Silicon-methyl. Tetramethylmethane. The following facts, discovered by Friedel, show the analogy between these compounds of silicon and the corresponding hydro- carbons : When silicon-ethyl is submitted to the action of chlorine, an atom of hydrogen is exchanged for an atom of chlorine, and the chloride Si(C 2 H 4 Cl)(C 2 H 5 ) 3 is formed. The latter is a liquid boiling at 185°, and can have its chlorine atom replaced by other atoms or groups, like the alcoholic chlorides. When dis- tilled with potassium acetate, it yields the corresponding acetate, (C 2 H 5 ) 3 Si-C 2 H 4 .O.C 2 H 3 0, which may be saponified by potas- sium hydrate, like an alcoholic acetate, the oxyacetyl group, OC 2 H 3 0, being replaced by a hydroxyl group. The alcohol so formed, (C 2 H 5 ) 3 .Si-C 2 H 4 .OH, has been named by Friedel sili- cononyl hydrate, on account of its analogy with nonyl hydrate. SiC 8 H 19 .OH C 9 H 19 .OH Silicononyl hydrate. Nonyl hydrate. It is a colorless liquid, insoluble in water, and boiling at 190°. 0RGAN0-3IETALLIC COMPOUNDS. 525 ORGANO-METALLIC COMPOUNDS. ZINC-ETHYL. Zn // (C 2 H5)2 One of the more important of the compounds formed by the union of the metals with alcoholic radicals is zinc-ethyl, dis- covered by Frankland. It is prepared by heating ethyl iodide with zinc-turning* and a small quantity of sodium on a water-bath. Zinc iodide and zinc-ethyl are formed. When the reaction is terminated, the product is distilled and that portion collected which passes above 115°. Zinc-ethyl is a colorless, mobile, and highly-refractive liquid. It has a peculiar, penetrating, and very disagreeable odor. It boils at 118°. It takes fire spontaneously on contact with the air, burning with a green flame, and producing white fumes of zinc oxide. If water be added to a small quantity of zinc-ethyl contained in a tube, a brisk effervescence at once takes place, and a white deposit is formed. The gas is ethane, and the deposit is zinc hydrate. Zn(C 2 H 5 ) 2 + 2H 2 = Zn(OH) 2 + 2C 2 H 6 Zinc-ethyl will enter into double decompositions. By the action of phosphorus trichloride on this body, Hof- mann and Cahours obtained triethylphosphine and zinc chloride. There is a zinc-methyl, Zn(CH 3 ) 2 , corresponding to zinc- ethyl. MERCUR-METHYL AND MERCUR-ETHYL. These compounds were obtained by Frankland and Duppa. by the action of methyl and ethyl iodides on sodium amalgam (sodium 1, mercury 500), in presence of a small quantity of acetic ether. Mercur-ethyl is a colorless, inflammable liquid, insoluble in water. Density, 2.44. Boiling-point, 158-160°. It is one of the most dangerous poisons known. The inhalation of its vapor for any length of time, even in small quantity, will produce fatal poisoning. 526 ELEMENTS OF MODERN CHEMISTRY. Chlorine, bromine, and iodine instantly decompose mer cur- ethyl with formation of a compound of mercur-monethyl. Hg{gg; + I 2 - C'IPI + Hg|f H5 Mercur-ethyl. Ethyl iodide. Mercur-monethyl iodide. STANNETHYLS. The discovery of the numerous compounds of tin and ethyl is due to Lowig. Their history has been completed by Frank- land, Cahours, and EAche. As the nomenclature and constitution of the stannethyls have already been indicated (page 424), we need only consider a few of these interesting compounds. Stannodiethyl, Sn(C 2 H 5 ) 2 . — The iodide of this compound is obtained when ethyl iodide is heated with tin-filings to about 180°. This iodide, Sn(C 2 H 5 ) 2 I 2 , purified by crystallization in alcohol, furnishes free stannodiethyl when its solution is treated with zinc, which removes the iodine. Stannodiethyl is an oily, yellow liquid, which does not vola- tilize without decomposition. When heated to 150° it begins to boil, but the greater part of it is decomposed into stanno- tetrethyl and tin. 2[Sn(C 2 H 5 ) 2 ] = Sn(C 2 H 5 )* + Sn The iodide of stannodiethyl crystallizes in pale yellow needles. In its solution, the alkalies precipitate the oxide Sn(C 2 H 5 ) 2 0, which forms an amorphous, white precipitate, insoluble in water and alcohol, but soluble in the alkalies and acids with which it Stannotriethyl or Sesquistannethyl, Sn 2 (C 2 H 5 ) 6 = (C 2 H 5 ) 3 Sn-Sn(C 2 H 5 ) 3 . — This is formed, together with the preceding compound, by the reaction of ethyl iodide on an alloy of tin and sodium. It is separated by fractional distillation ; it boils between 265 and 270°. It plays the part of a radical and combines directly with oxygen. The oxide contains Sn 2 (C 2 H 5 ) 6 = [Sn(C 2 H 5 ) 3 ] 2 0. It combines with the elements of water, form- ing a hydrate, Sn(C 2 H 5 ) 3 .OH, crystallizable in prisms. These crystals are fusible at 44°. The oxide distils at 272°. It reacts with the acids to form crystallizable salts. [Sn(C 2 H 5 ) 3 ] 2 + 2HN0 3 = 2[Sn(C 2 H 5 ) 3 .N0 3 ] + H 2 Stannotriethyl oxide. Stannotriethyl nitrate. VOLATILE FATTY ACIDS. 527 The iodide. Sn(C 2 H 5 ) 3 I, is a liquid having a mustard-like odor, and distilling without decomposition towards 235-238°. Density at 15°, 1J333. Stannotetrethyl, Sn(C 2 H 5 ) 4 . — Colorless liquid, almost odor- less, and boiling at 181°. Density, 1.187. It is formed by the action of zinc ethyl on stannodiethyl iodide. Sn(C 2 H 5 ) 2 I 2 + Zn(C 2 H 5 ) 2 = Sn(C 2 H 5 ) 4 + Znl 2 Stannnodiethyl iodide. Zinc-ethyl. Stannotetrethyl. It is a saturated compound, and does not enter into combi- nation, but by the action of energetic reagents it yields com- pounds of stannodiethyl or stannotriethyl. Thus, with iodine, the following reaction takes place : Sn(C 2 H 5 ) 4 + I 2 = Sn(C 2 H 5 ) 3 I -f C 2 H 5 I VOLATILE FATTY ACIDS DERIVED FROM THE ALCOHOLS. Modes of Formation and Constitution. — These acids result from the oxidation of the alcohols of which the principal com- pounds have been described. They are formed in a great num- ber of reactions, and many of them exist already formed in nature, either in the free state or in combination in neutral fatty compounds, that is, the oils and fats. Their composition is expressed by the general formula C n H 2n O 2 ; they contain one more atom of oxygen and two atoms of hydrogen less than their corresponding alcohols. Their principal modes of formation are as follows : 1. By oxidation of an alcohol : CEPO + O 2 = CH 2 2 -4- H 2 Methyl alcohol. Formic acid. 2. By oxidation of an aldehyde : C 2 H 4 + = C 2 H 4 2 Aldehyde. Acetic acid. 3. By the decomposition of an organic cyanide with boiling- potassium hydrate: CH 3 CH S i + KOH + H 2 = i + NH S CN T CO.OK ■ Methyl cyanide. Potassium acetate. 528 ELEMENTS OF MODERN CHEMISTRY. The acetic acid is formed in this last reaction, by the union of the carbon of the cyanogen group with the oxygen of both the potassium hydrate and the water, the hydrogen of these two bodies combining with the nitrogen of the cyanogen to form ammonia. It may then be admitted that acetic acid con- tains a radical carbonyl, CO, united on the one hand with a methyl group (that of the methyl cyanide), and on the other with a hydroxyl group, OH. The other acids of the series possess an analogous constitu- tion. CH3 C 2 H5 C 3 H* C*H9 CO.OH CO.OH CO.OH CO.OH etc. Acetic acid. Propionic acid. Butyric acid. Valeric acid. 4. A method of synthesis, discovered by Wanklyn, furnishes a direct support to this theory of the constitution of the fatty acids. That chemist realized the synthesis of acetic and pro- pionic acids by passing a current of carbonic acid gas over sodium-methyl and sodium-ethyl, organo-metallic compounds which result from the action of sodium upon zinc-methyl and zinc-ethyl. NaCHS + CO.O = ? H CO.ONa Sodium-methyl. Sodium acetate. C 2 H 5 NaC2H& + CO.O = T CO.ONa Sodium- ethyl. Sodium propionate. General Properties. — 1. The volatile fatty acids of the series C n H 2n 2 are monobasic ; each contains one atom of hydrogen which may be replaced by an equivalent quantity of a metal. 2. When submitted to dry distillation, many of their salts yield an acetone and a carbonate. CH3 CH8-CaO> Ca " = CO + CaCO* CH3 Calcium acetate. Acetone. Calcium carbonate. 3. The same reaction may produce an aldehyde and a hydro carbon of the series C n H 2n (Chancel). C3H* (C 3 H?-CO.O) 2 Ca = i + C 3 H6 + CaCO* CHO Calcium butyrate. Butyral, or butyric Propylene, aldehyde. FORMIC ACID. 529 4. When a mixture of a salt of a fatty acid and a formate is subjected to dry distillation, the principal product of the reaction is an aldehyde (Piria). CH3 CH3-C0.0K + H-CO.OK = i + K 2 C0 3 CHO Potassium acetate. Potassium formate. Aldehyde. 5. The fatty acids are converted into chlorides by the action of phosphorus pentachloride,' or oxy chloride (Grerhardt). C 2 H 3 O.OK + PCI 5 = " C'WO.Cl + POC1 3 + KC1 Potassium acetate. Acetyl chloride. Phosphorus oxychloride. 6. By the action of these chlorides upon the salts of the fatty acids, the anhydrides of the acids are formed (Gerhardt). C2H k}° + C2H3 - 0C1 = KC1 + cSo} Potassium acetate. Acetyl chloride. Acetic anhydride. 7. When subjected to the action of phosphoric anhydride, the ammonium salts of these acids lose 2H 2 and are con- verted into nitriles or cyanogen ethers (Dumas, Malaguti and Le Blanc, Frankland and Kolbe). cm CH3 | =; 2H 2 4- 1 CO.O(iNTH*) + CN immonium acetate. Acetonitrile. (Methyl cyanide.) FORMIC ACID. CH 2 2 This acid, which was discovered by S. Fischer in 1760, in red ants, is formed in a great number of reactions, particularly in the oxidation of methyl alcohol, in the decomposition of hydrocyanic acid by acids or alkalies, in the distillation of oxalic acid, and in the oxidation of many organic matters, such as starch, sugar, etc. Berthelot achieved its direct synthesis by heating carbon monoxide for a long time to 100° in sealed flasks containing a concentrated solution of potassium hydrate. CO + KOH = HCO.OK Potassium formate. Preparation. — Starch, manganese dioxide, and dilute sul- phuric acid may be boiled together in a capacious retort, and the acid liquid which condenses in the receiver saturated with lead carbonate. Lead formate is thus obtained, and is purified x 45 530 ELEMENTS OF MODERN CHEMISTRY. by crystallization. To obtain formic acid, the salt is heated in a current of dry hydrogen sulphide. Formic acid distils (Dbbereiner). Another and better process consists in heating to 100° equal parts of oxalic acid and glycerin. Under these conditions, the oxalic acid breaks up into carbonic acid gas, and formic acid which distils. The liquid is saturated with lead carbonate, and the preparation concluded as before (Berthelot). Properties. — Formic acid is a colorless liquid, having a pungent odor and a very acid taste. It boils at 99°, and solid- ifies to a crystalline mass at 8.5°. It mixes with water in all proportions. If an excess of sulphuric acid be added to a small quantity of formic acid contained in a test-tube, and a gentle heat be applied, a regular disengagement of gas will take place ; it may be ignited at the mouth of the tube, and will burn with a blue flame. It is carbon monoxide, and is formed according to the fol- lowing equation : CH 2 2 = CO + H 2 If formic acid be added to a solution of silver nitrate, and the liquid be heated, it will soon become clouded ; silver will be precipitated as a gray powder, and carbon dioxide will be disengaged. The formic acid becomes oxidized in reducing the silver nitrate, CH 2 2 + = CO 2 + H 2 Chlorine determines an analogous decomposition. CH 2 2 + CI 2 = CO 2 + 2HC1 Formates. — Formic acid is an energetic acid, perfectly neu- tralizing the bases. It is monobasic; one of its hydrogen atoms can be replaced by an equivalent quantity of metal. The formates are soluble ; the most characteristic are cupric for- mate, Cu(CH0 2 ) 2 -f- 4H 2 0, which crystallizes in magnificent, oblique rhombic prisms, and lead formate, Pb(CH0 2 J 2 , which forms long, colorless needles, slightly soluble in cold water. Ammonium formate, which is obtained by saturating formic acid with ammonia, crystallizes in prisms which are very solu- ble in water. AYhen quickly heated to about 200°, it breaks up into hydrocyanic acid (formonitrile) and water (Pelouze). (NH*)CH0 2 = 2H 2 + CNH ACETIC COMBINATIONS. 5ol FORMIC ALDEHYDE. CH 2 = H-CHO Hofmann has recently obtained this body by the slow com- bustion of methyl alcohol, brought about by a spiral of platinum wire. CH*0 + = H 2 + CH 2 It is also formed in the distillation of barium and calcium formates. It is not known in the pure state. It has a great tendency to become polymerized, forming a solid compound, which Boutlerow has named trioxy methylene, and which prob- ably contains C 3 H 6 3 . ACETIC COMBINATIONS. It may be admitted that these compounds contain the mon- atomic radical acetyl (C 2 H 3 0) / = (CH 3 -CO)', which may be regarded as oxidized ethyl. CH 3 CH 3 (C 2 H5)'= i ( C 2H 3 0)'= i v ; -CH 2 -CO Ethyl. Acetyl. Aldehyde is the hydride of this radical ; acetic acid is its hydrate, and acetone its methylide. Besides these, there are known the oxide and chloride of acetyl, an acetyl ammonia, which is acetamide, etc. The following formulae indicate the relations between all of these bodies : C 2 H 3 O.H C 2 H 3 O.OH Acetyl hydride (aldehyde). Acetyl hydrate (acetic acid). C 2 H 3 0.C1 (C 2 H 3 0) 2 Acetyl chloride. Acetyl oxide (acetic anhydride). C 2 H 3 ) C 2 H 3 O.CH 3 H \ N H J ' Acetyl methylide (acetone). Acetamide. ACETIC ACID. C 2 HK) 2 Acetic acid is the acid of vinegar. It is the product of the oxidation of alcohol. It is formed in a number of other reac- tions, among which we may mention the oxidation of aldehyde, 532 ELEMENTS OF MODERN CHEMISTRY. the decomposition of methyl cyanide by potassium hydrate, the action of carbon dioxide on sodium-methyl, and the dry distil- lation of a great number of organic substances, such as wood, starch, gum, sugar, etc. Preparation. — The large quantities of acetic acid employed in the arts are obtained by the destructive distillation of wood. The operation is conducted in large iron cylinders, heated directly by a fire (Fig. 123). The products, of the distillation Fig. 123. consist of liquids and gases. The liquids are condensed in a large worm, tt, cooled by a continual circulation of cold water through surrounding pipes mm ; the gases are conducted back to the fire-grate by the pipe h. The condensed product consists of an aqueous portion and of tar. The greater part of the latter is separated by & new distillation; the first portions which pass contain wood-spirit, after which acetic acid distils. The acid liquid is neutralized by lime, and the calcium ace- tate formed is converted into sodium acetate by adding a solu- tion of sodium sulphate. The liquid, separated by filtration from the calcium sulphate, yields on evaporation sodium ace- tate, still colored brown by tarry matters. The latter are destroyed by frying the salt, that is, by heating it for some time to 250°, a temperature which carbonizes the tar but does not affect the sodium acetate. The mass is then exhausted with water, the solution filtered, concentrated, and crystallized. Crystals of pure sodium acetate are thus obtained, a salt which was formerly called pyrolignite of sbda. Acetic acid is pre- ACETIC ACID. 533 pared by drying this salt and distilling it with |- its weight of concentrated sulphuric acid. Or the dry salt may be decomposed by an exact quantity of sulphuric acid. The acetic acid which separates from the sodium sulphate may then be decanted, and cooled in a freez- ing mixture. The portion remaining liquid is separated and the solid mass constitutes pure acetic acid. Vinegar. — Vinegar is the product of the acid fermentation of wine and other alcoholic liquids. The following process is largely employed for the conversion of wine into vinegar. It is the Orleans process. A small quantity of warm vinegar is first introduced into large vats, which have already been used for the operation and are impregnated with the peculiar fer- ment formed ; quantities of wine are then added at intervals of several days, the vats being maintained at a temperature between 24 and 27°. In a fortnight, the acetification is com- plete, and a portion of the vinegar is withdrawn and replaced by a new- quantity of wine which also becomes converted into vinegar. The process is thus continuous. Under these cir- cumstances, the alcohol is converted into acetic acid by the influence of a peculiar ferment that is called mother of vinegar. It is a vegetable product, amycoclerm (Mycoderma aceti;. which appears on the surface of the liquid, where it absorbs oxygen from the air and subse- quently cedes it to the alcohol (Pasteur). Its action may be compared to that of platinum black. By another process, a mixture of weak alcohol, water, and albuminoid matter (the juice of pota- toes, beets, etc.), contain- ing the elements neces- sary for the production of the ferment, is allowed to trickle over beech-wood shavings. The latter, which have been previously steeped in strong'vinegar, are contained in a large cask, A (Fig. 124), 45* Fig. 124. 534 ELEMENTS OF MODERN CHEMISTRY. where they rest upon a double bottom perforated with holes. Tubes, tt, pass through the upper portion, maintaining a current of air which enters at the lower portion of the cask. Under these conditions, the liquid, which spreads over the shavings and exposes a considerable surface to the air, becomes oxidized with such energy that the temperature soon rises to 30° ; a second passage of the liquid through the casks completes the acetification. Properties of Acetic Acid. — Acetic acid is solid below 17°, and crystallizes in large plates. It boils at 118°. Its density at 0° is 1.0801. Its odor is pungent and acid. It is very corrosive. It mixes with water and alcohol in all proportions, and when it is added to water there is a contraction in volume. The maximum contraction, and consequently the maximum density of aqueous acetic acid, corresponds to a mixture con- taining C 2 H 4 2 + IPO. Vapor of acetic acid passed through an incandescent porce- lain tube yields gases and deposits carbon, at the same time forming small quantities of acetone, benzol, phenol, and naph- thaline (Berthelot). Phosphorus pentachloride converts acetic acid into acetyl chloride, with formation of hydrochloric acid and phosphorus oxychloride. C 2 H 3 O.OH -f PCI 5 = C 2 H 3 0.C1 + HC1 -f POCP Acetic acid. Acetyl chloride. If a mixture of small quantities of potassium acetate and arsenious oxide be heated in a test-tube, dense white vapors having an intense and disagreeable odor of garlic will be dis- engaged. This experiment permits the detection of minute traces of acetic acid ; if the latter exist in the free state in the liquid, its potassium compound must first be formed. The white vapor disengaged is due to a body formerly known as fuming liquor of Cadet (see page 453). ACETATES. The more important neutral acetates have the composition R/(C 2 H 3 2 ) or R"(C 2 H 3 2 ) 2 , according as the metal which replaces the basic hydrogen of the acetic acid is univalent or bivalent. There are many basic acetates. Potassium Acetate, KC 2 H 3 2 .— This is prepared by satu- ACETATES. 535 rating acetic acid with potassium carbonate and evaporating to dryness. It is thus obtained in crystalline, very deliquescent laminae. It melts at 292°, and is very soluble in water. Sodium Acetate, NaC 2 H 3 2 + 3H 2 0.— This salt is obtained on a large scale in the arts in the manufacture of acetic acid. It was formerly called pyrol Ignite of soda. It crystallizes in large, oblique rhombic prisms, which are very soluble in water, and effloresce in dry air. Acetates of Lead.— Neutral lead acetate, Pb(C 2 H 3 2 ) 2 + 3H 2 0, known also as sugar of lead, is made by neutralizing acetic acid with litharge. It crystallizes in transparent, efflor- escent, oblique rhombic prisms, having a sweet and astringent taste. It dissolves in half its weight of cold water, and in 8 parts of alcohol. It melts in its water of crystallization at 75.5°. The neutral solution of lead acetate dissolves oxide of lead, forming different basic salts, according to the proportion of oxide dissolved. The more important of these are a dibasic acetate, Pb(C 2 H 3 2 ) 2 + PbO + 4H 2 0, and a tribasic acetate, Pb(C 2 H 3 2 ) 2 -f 2PbO -f nH 2 0. These two salts are gener- ally formed simultaneously when a solution of lead acetate is boiled with litharge. The solution thus obtained is used in medicine as Goulard's solution. If a few drops of it be added to ordinary river or well water, a cloud is produced, owing to the formation of lead sulphate and carbonate. If carbonic acid gas be passed into a solution of the sub- acetate of lead, a deposit of lead carbonate is formed. In this reaction, which serves for the preparation of white lead by the Clichy method, the excess of lead is removed from the subace- tate by the carbonic acid, neutral acetate being formed and remaining in solution. Acetates of Copper.— The neutral acetate Cu(C 2 H 3 Q 2 ) 2 + H 2 0, is prepared by double decomposition by mixing hot solu- tions of sodium acetate and cupric sulphate. The cupric acetate is deposited on cooling in beautiful, oblique rhombic prisms of a deep bluish-green color. They dissolve in 5 times their weight of boiling water. The dilute aqueous solution is de- composed by boiling, a tribasic acetate being formed, while acetic acid is set free. When cupric acetate is heated, it first loses its water of crys- tallization, and decomposes when the temperature reaches 240 or 250°, disengaging acetic acid, acetone, and carbon dioxide 536 ELEMENTS OF MODERN CHEMISTRY. The residue is finely-divided copper. The product of the dis- tillation is a blue liquid, which, when rectified, yields colorless acetic acid mixed with a small quantity of acetone. It was formerly called radical vinegar. The name verdigris is applied to a basic acetate of copper consisting mostly of a dibasic acetate, Cu(C 2 H 3 2 ) 2 + CuO -\- 6H 2 0. Verdigris is prepared by exposing to the air copper sheets piled up in layers with the pulp of grapes. In a few weeks the metal becomes covered with bluish crusts of verdi- gris, which are scraped off and delivered to commerce in the form of light-blue balls. The alcohol, formed by the fermenta- tion of the sugar contained in the grape-pulp, becomes oxidized by the air and is converted into acetic acid, and under the in- fluence of the latter, the copper itself absorbs oxygen. Water and copper basic acetate are thus formed. Silver Acetate, AgC 2 H 3 2 .— This salt, which is but slightly soluble in water, is precipitated when concentrated solutions of sodium acetate and silver nitrate are mixed. It is deposited from boiling water in brilliant, pearly, flexible plates, which darken on exposure to light. Ammonium Acetate, (NH 4 )C 2 H 3 2 . — When acetic acid is saturated by a current of ammonia gas, this salt is obtained as a deliquescent, crystalline mass. It is very soluble in water and in alcohol. When heated, it first loses ammonia, then acetic acid, and acetamide finally distils. NH 4 .C 2 H 3 2 = H 2 + C 2 H 3 O.NH 2 Ammonium acetate. Acetamide. It is used in medicine under the name spirit of Mindererus. This is generally an impure solution of ammonium acetate, charged with empyreumatic matters. When distilled with phosphoric anhydride, ammonium ace- tate yields methyl cyanide, or acetonitrile. NH 4 .C 2 H 3 2 = C 2 H 3 N + 2H 2 ETHYL ACETATE. C 2 H5.C 2 H30 2 This acetate, ordinarily known as acetic ether, is prepared by distilling a mixture of alcohol, sulphuric acid, and potassium or sodium acetate. The ethyl acetate passes over, together with a certain quantity of alcohol which escapes the reaction. SUBSTITUTION PRODUCTS OF ACETIC ACID. 537 It is purified by agitation with a solution of calcium chloride, and the ether which floats is decanted, dried over calcium chloride, and rectified on the water-bath. It is a colorless liquid having a very agreeable, ethereal odor. It boils at 77°. Density at 0°, 0.9105. It is but slightly soluble in water, but dissolves in all proportions in alcohol and ether. Like all compound ethers, it is readily decomposed by potassium hydrate. C 2 H 5 .C 2 H 3 2 + KOH = KC 2 H 3 2 + C 2 H 5 .OH Ammonia converts it into acetamide and alcohol. C 2 H 3 O.OC 2 H 5 + NH 3 = C 2 H 5 .OH + C 2 H 3 O.NH 2 Ethyl acetate undergoes a remarkable reaction with sodium. The metal dissolves in the ether, forming sodium ethylate and the compound C 6 H 9 Xa0 3 . 2[C 2 H 3 O.OC 2 H 5 ] + Xa 2 = NaO.C 2 H 5 -f C 6 H 9 Xa0 3 + H 2 The body C 6 H 9 Na0 3 is the sodium compound of acetyl-acetic ether, C 6 H 10 O 3 = C 2 H 2 (C 2 H 3 0)0-OC 2 H 5 , which is derived from acetic ether, C 2 H 3 0-OC 2 H 5 , by the substitution of an acetyl group, C 2 H 3 0, for one atom of hydrogen in the radical acetyl. The free acetyl-acetic ether may be obtained by the action of hydrochloric acid upon the sodic compound C 6 H 9 Xa0 3 . It is a colorless liquid having an agreeable odor, and boiling at 182°. Density at 5°, 1.03. SUBSTITUTION PRODUCTS OF ACETIC ACID. Three chlorinated acids are known which are derived from acetic acid by substitution : Monochloracetic acid C 2 H 3 C10 2 Dichloracetic acid C 2 H 2 C1 2 2 Trichloracetic acid C 2 HC1 3 2 Monochloracetic acid is formed when a current of chlorine is passed into acetic acid heated to 100°, and containing a small quantity of iodine. As soon as chlorine begins to be disen- gaged at the extremity of the apparatus, the operation is arrested and the liquid distilled. That portion is collected which passes between 185 and 187°. Monochloracetic acid is solid, and crystallizes in deliquescent, rhomboidal tables or in prisms. It boils between 185 and 187.8°. 538 ELEMENTS OF MODERN CHEMISTRY. It is very corrosive. It is converted into glycollic" acid when heated with an excess of potassium hydrate. KC 2 H 2 C10 2 -f KOH = KC 2 H 2 (OH)0 2 + KC1 Potassium Potassium glycollate. monochloracetate. Ammonia converts it into acetamic or amidacetic acid C 2 H 2 (NH 2 )O.OH (glycocol) (Cahours). CH*C1 __ „ pi CH2.NH2 i + NH 3 = HC1 + i C0.0H C0.0H Monochloracetic acid. Glycocol. Trichloracetic acid, C 2 HC1 3 2 , a very important compound in the history of the science, was discovered by Dumas in 1840. It was then one of the most remarkable examples of a body formed by substitution, and a comparison of its properties with those of acetic acid led Dumas to announce the first idea of chemical types. It is obtained by exposing acetic acid to the action of a large excess of chlorine in direct sunlight. Trichloracetic acid is solid. It forms transparent and deli- quescent, rhombohedral crystals, fusible at 52.3°, and boiling between 195 and 200°. Its aqueous solution regenerates acetic acid by the action of sodium amalgam, an interesting reaction, since it furnished one of the first examples of inverse substitution (Melsens), as the replacement of chlorine by hydrogen is called. Water and sodium amalgam constitute a slow source of hydrogen. When boiled with potassium hydrate, trichloracetic acid fur- nishes potassium carbonate and chloroform. C 2 HCP0 2 = CHCP + CO 2 ACETIC ANHYDRIDE. (C 2 H 3 0) 2 This important body, discovered by Gerhardt in 1852, is prepared by the action of one part of phosphorus oxychloride on three parts of dry sodium acetate. In this operation, acetyl chloride is first formed, and this reacts upon an excess of so- dium acetate, producing sodium chloride and acetyl acetate, or acetic anhydride. C 2 H 3 0.C1 + ° 2H ^J0 = NaCl + gffo} Acetyl chloride. Sodium acetate. Acetic anhydride. ALDEHYDE. 539 Acetic anhydride is a colorless, mobile liquid, having a strong odor of acetic acid. It boils at 138°. When thrown into water, it first sinks to the bottom, and then, absorbing one mol- ecule of water, is converted into acetic acid, which dissolves. ALDEHYDE, OR HYDRIDE OF ACETYL. C 2 H 4 This body was discovered by Dbbereiner in 1821 ; its com- position and principal properties were studied by Liebig. Preparation. — Aldehyde is prepared by oxidizing alcohol by heating it with manganese dioxide and dilute sulphuric acid, or better, with potassium dichroniate and sulphuric acid. The vapors disengaged are condensed in a well-cooled receiver. The distilled liquid is rectified over calcium chloride, only the more volatile portion being collected. This is mixed with twice its volume of ether, and the ethereal solution saturated with ammonia gas. Crystals are deposited which constitute a com- bination of aldehyde with ammonia, and the aldehyde is ob- tained from them by adding a quantity of sulphuric acid exactly sufficient to form ammonium sulphate with the ammonia; a gentle heat is applied, and the aldehyde vapor is passed through a tube filled with calcium chloride, and finally condensed in a well-cooled receiver (Liebig). Properties. — Aldehyde is a colorless, very mobile liquid, having a penetrating and somewhat suffocating odor. It boils at 21°. It mixes in all proportions with water, alcohol, and ether. It combines with ammonia, forming aldehyde-ammonia, or acetylide of ammonium (Liebig). C 2 H 4 O.NH 3 = C 2 H 3 O.NH 4 It unites with the alkaline acid-sulphites, forming crystal- lizable combinations. It is very apt to become oxidized, being transformed into acetic acid. C 2 H*0 + = C 2 H 4 2 If some aldehyde and a few drops of ammonia be added to a solution of silver nitrate, and a gentle heat be applied, the liquid soon becomes clouded, and the sides of the vessel con- taining it are covered with a brilliant deposit of metallic silver. 540 ELEMENTS OF MODERN CHEMISTRY. By the action of sodium amalgam and water, aldehyde fixes two atoms of hydrogen, and is converted into alcohol (A. Wurtz). At the same time a small quantity of butyl glycol is formed (Kekule). C 2 H 4 + H 2 = C 2 H 6 When hydrochloric gas is passed into a mixture of aldehyde and absolute alcohol, monochlorether is formed. C 2 H±0 + C2H&.OH + HC1 = H20 + ^H^ Monochlorether. Chlorine converts aldehyde into acetyl chloride and then into butyl chloral. C 2 EFO.H + CI 2 = C 2 H 3 0.C1 + HC1 Acetyl chloride. When treated with phosphorus pentachloride, aldehyde ex- changes its atom of oxygen for two atoms of chlorine, and is transformed into monochlorethyl chloride, C 2 H 4 C1 2 (ethylidene chloride). CH^ CH3 i + PC15 = i + POCl 3 CHO CHCI 2 Aldehyde. Ethylidene chloride. Dry hydrochloric acid gas converts aldehyde into ethylidene oxychloride (an isomeride of dichlorether), eliminating water. 2C 2 H 4 + 2HC1 = C 4 H 8 C1 2 + H 2 Ethylidene oxychloride. By the action of hydrochloric acid diluted with twice its volume of water, aldehyde doubles its molecule and is converted into a thick, colorless, neutral body, boiling at 95° in a vacuum ; it is soluble in water and reduces ammoniacal silver nitrate. This body is aldol, C 4 H 8 2 (A. Wurtz). When heated with ordinary hydrochloric acid, aldehyde gives cro tonic aldehyde (Kekule). 2C 2 H 4 = H 2 + C 4 H 6 Aldehyde. Crotonic aldehyde. The same transformation takes place when aldehyde is heated to 100° with a small quantity of zinc chloride and a trace of water. Like all of its analogues, aldehyde can unite with hydro- cyanic acid, forming the compound CH 3 -CH(OH)(CN), a liquid soluble in water and alcohol, boiling at 183 9 , and con- ACETYL CHLORIDE. 541 verted by acids and alkalies into lactic acid, with disengage- ment of ammonia (see page 584). When aldehyde is heated to 100° with alcohol, acetal is formed ; this is also found in small quantities among the products of the oxidation of alcohol. CH 3 .CHO + C 2 H 5 .OH = H 2 + CH 3 CH<°^ Aldehyde. Alcohol. Acetal. Polymerides of Aldehyde. — Aldehyde has a great ten- dency to become converted into polymeric modifications. Among these are paraldehyde, which is liquid, and met alde- hyde, which is solid (Liebig). Paraldehyde, C 6 H 12 3 , is formed by the action of a trace of sulphuric acid or of zinc chloride on aldehyde. It is a color- less liquid, having a density of 0.998 at 15°, and boiling at 124°. At a low temperature it solidifies to a leaf-like, crys- talline mass, fusible at 10.5°. It dissolves in eight times its volume of water. When distilled with a small quantity of sulphuric acid, it is again converted into aldehyde. ACETYL CHLORIDE. CH 3 C2H30.C1 = 7 COC1 This body was obtained by Gerhard t in 1852, by treating sodium acetate with pentachloride, or oxychloride of phos- phorus. NaC 2 H 3 2 + PCI 5 = C 2 H 3 0C1 + XaCl + POC1 3 Sodium acetate. Acetyl chloride. Phosphorus oxychloride. It is also formed by the action of chlorine on aldehyde. It is a colorless, mobile liquid, having a pungent odor. It boils at 55°. If it be poured into water, it sinks to the bottom, but rapidly decomposes into hydrochloric and acetic acids. C 2 H 3 0.C1 + H 2 = HC1 + C 2 H 3 O.OH It undergoes a similar decomposition with alcohol, forming ethyl acetate and hydrochloric acid. C 2 H 3 0.C1 + C 2 H 5 .OH = HC1 + C 2 H 5 .C 2 H 3 2 With ammonia, it forms acet amide and ammonium chloride. C 2 H 3 0.C1 + 2NH 3 = NHH21 + C 2 H 3 O.XH 2 It reacts with acetates, forming acetic anhydride. 46 542 ELEMENTS OF MODERN CHEMISTRY. TRICHLORACETYL HYDRIDE, OR TRICHLORAL- DEHYDE. (chloral.) CC13 C 2 C1 3 H0 = CHO This important body was discovered by Liebig and Dumas. It is formed by the prolonged action of chlorine on alcohol. It -is a colorless, mobile liquid, having a peculiar, penetrating odor. It boils at 94.4° (Dumas). Grerhardt regarded it as aldehyde in which the three atoms of hydrogen of the radical are replaced by three atoms of chlorine. C 2 H 3 O.H C 2 CPO.H Aldehyde. Chloral. (Acetyl hydride.) (Trichloracetyl hydride.) Its reactions resemble those of aldehyde. It forms crystal- lizable compounds with the disulphites. Its ammoniacal solu- tion reduces silver nitrate. These facts seem to indicate that chloral contains the group CHO, which is characteristic of the aldehydes ; its constitution is then expressed by the formula CCP CHO It regenerates aldehyde by the action of nascent hydrogen (Personne). The alkaline hydrates decompose it into chloroform and a formate (Dumas). C 2 HCPO + KOH = KCHO 2 + CHCP. Chloral. Potassium formate. Nitric acid converts it into trichloracetic acid, in the same manner that aldehyde is converted into acetic acid. C 2 HCPO + = C 2 HCP0 2 Chloral forms a crystallizable compound with water, C 2 HCPO CCP 4- H 2 = I > called chloral hydrate. The latter ^ CH(OH) 2 J melts at 57°, and boils at 98° (Personne), being at the same time decomposed into anhydrous chloral and water. It is very soluble in water. ACETONE. 543 In contact with concentrated sulphuric acid, chloral is rapidly converted into a white, solid substance which is insol- uble in water ; it has the same composition as ordinary chloral, and is called insoluble chloral. Chloral also combines with alcohol, forming alcoholate of chloral (Personne). Chloral hydrate has for some time been successfully employed in medicine as an anodyne and hypnotic. ACETOXE. C 3 H60 Acetone is the methylide of acetyl. C 2 H 3 O.CH 3 , and since acetyl itself is carbonyl (carbon monoxide ) methylide, CH 3 -CO, acetone can be regarded as carbonyl dimethylide. CH 3 -CO-CH 3 . co „ J CI co „ {CH3 10 |C1 UJ < CH3 Carbonyl chloride. Carbonyl dimethylide (acetone). Indeed, the synthesis of acetone has been made both by treat- ing acetyl chloride with zinc methyl (Pebal and Freund), and by treating sodium methyl with chlorocarbonic gas (carbonyl chloride). Zn(CH 3 ) 2 + 2(C 2 H 3 0.C1) = 2(C 2 H 3 O.CH 3 ) + ZnCl 2 Zinc methyl. Acetyl chloride. Acetone. 2(CH 3 .Na) + CO j £j[ = 2NaCl + CO j £gl Sodium methyl. Carbonyl chloride. Acetone. Preparation. — Acetone is prepared by distilling dry calcium acetate in a clay retort. The vapors given off are condensed in a well-cooled receiver, and the liquid obtained is distilled on a water-bath with an excess of calcium chloride. Ca(C 2 H 3 2 ) 2 = C 3 H 6 + CaCO 3 Properties. — Acetone is a colorless liquid, having a slightly empyreumatic, ethereal odor. It boils at 56°. It dissolves in all proportions in water, alcohol, ether, and wood-spirit. Like aldehyde, it forms crystallizable combinations with the alkaline acid-sulphites. Acetone and its homologues are not susceptible of direct oxidation. If it be heated with a mixture of sulphuric acid and potassium dichromate, it breaks up into acetic acid and 544 ELEMENTS OF MODERN CHEMISTRY. formic acid, a portion of the latter being oxidized to carbon dioxide. CH 3 .CO.CH 3 + O 3 = CH 3 -CO.OH + HCO.OH In presence of nascent hydrogen, produced by sodium amal- gam and water, it fixes H 2 and is converted into isopropyl alcohol (Friedel). CH3 CH3 CO + H2 = CH.OH CH 3 CH3 Acetone. Isopropyl alcohol. It is seen by this method of formation that isopropyl alcohol contains a group CHOH, united to two methyl groups ; it is a secondary alcohol (page 508). Isopropyl alcohol is not the only product of the action of nascent hydrogen on acetone. The reaction gives rise to a product of condensation resulting from the addition of H 2 to two molecules of acetone. This has received the name pina- cone. 2C 3 H 6 + H 2 = C 6 H 14 2 Pinacone. It is a tertiary glycol (see page 563). It constitutes a color- less, crystallizable mass, fusible between 35 and 38°, and boil- ing at 171-172°. By the action of dilute and hot sulphuric or hydrochloric acid, it loses one molecule of water and is con- verted into a neutral liquid, boiling at 106°. This is pinaco- lin, C 6 H 12 0. When acetone is added in small portions to phosphorus pentachloride, a very energetic reaction takes place and two chlorides are formed. One of them, C 3 H 6 C1 2 (methylchlor- acetol), boils at 70°. The other, C 3 H 5 C1 (monochloropropy- lene), boils at 23° (Friedel). C»H 6 + PCI 5 = C 3 H 6 C1 2 + POC1 3 C 3 H 6 C1 2 = C 3 H 5 C1 + HC1 Hot, concentrated sulphuric acid removes the elements of water from acetone and converts it into a hydrocarbon, which has received the name mesitylene (Kane). 3C 3 H 6 — 3H 2 = C 9 H 12 Acetone. Mesitylene. Like aldehyde, acetone will unite with hydrocyanic acid, ACIDS OF THE SERIES C n H 2n 2 . 545 forming a cyanide (or cyanhydrin), which is decomposed by both acids and alkalies, with disengagement of ammonia and formation of an acid; the group CN is then converted in carboxyl CO.OH. g£>CO + HCN = ^:>CCH-CH 2 .OH, contains px™^ CH-CO.OH. The acid is derived from the alcohol by the substitution of for H 2 in the group (CH 2 .OH)'. 2. As we have already seen, the constitution of amyl alcohol of fermentation is expressed by the formula ^ 3 3 >CH-CH 2 -CH 2 .OH. The valeric acid produced by its oxidation is then CH 1 >CH-CH 2 -CO.OH ^ PROPIONIC ACID. 547 Normal valeric acid results from the oxidation of normal amyl alcohol, and contains CH 3 -CH 2 -CH 2 -CH 2 -CO.OH CH 3 Methylethylacetic acid, p 2 pr 5 >CH-CO.OH, or optically active valeric acid, is derived from active amyl alcohol. The trimethylacetic acid, which was discovered by Boutlerow, contains (CH 3 /C-CO.OH ; it is derived from the alcohol (CH 3 ) 3 C-CH 2 .OH, which, is not known. If we compare the three isomeric acids, C 5 H 10 O 2 , with acetic acid itself, we will find that their isomeric relations can be ex- pressed in a very simple manner, by saying that normal valeric acid is propylacetic acid, the acid derived from the alcohol of fermentation is isopropylacetic acid, and that the last two are methylethylacetic and trimethylacetic acids. CH 3 CH2(C 3 IP) CH2(CH<£g3) CO.OH CO.OH CO.OH Acetic acid. Propylacetic acid. Isopropylacetic acid. CHCH-CO.OH, isomeric with bu- tyric acid, was discovered by Morkownikof. It is formed by the oxidation of butyl alcohol of fermenta- 550 ELEMENTS OF MODERN CHEMISTRY. tion, and exists naturally in the fruit of the Ceratonia siliqua (carob locust, St. John's bread). It is also obtained by decom- posing isopropyl cyanide with potassium hydrate. (C 3 H 7 yON + 2H 2 = NH 3 + (CWy-CO 2 !! It is a liquid having a disagreeable odor, like that of the acid of fermentation. Density at 20°, 0.9503. It boils at 154°. ' VALERIC ACIDS. C 5 H 10 O 2 CH 3 Isovaleric Acid,p™>CH-CH 2 -CO.OH, was discovered by Chevreul, who first obtained it from dolphin oil (phocenic acid). It may be prepared by distillation of valerian root with water ; hence its name. It exists also in the root of angelica, in the Athamanta oreoselinum and in the fruit and bark of the Viburnum opulus. The same acid is formed when amyl alcolol is oxidized by a mixture of potassium dichromate and sulphuric acid. It is also formed when potassium hydrate is boiled with isobutyl cyanide, by a reaction similar to that which has already been indicated for the formation of isobutyric acid. ^3>CH-CH2-CN + 2H 2 - NH* + ^3>CH-CH2-CO.OH Isobutyl cyanide. Isovaleric acid. Valeric acid is a colorless liquid, having a pungent, disagree- able odor. Density at 0°, 0.947. It boils at 175°. It dissolves in 80 parts of water, from which it is precipitated by the addi- tion of neutral salts. Its ammonium salt is used in medicine. Normal Valeric Acid, which has already been mentioned (page 547), is a colorless liquid, smelling like butyric acid. It boils at 184-185°, and its density at 0° is 0.9577. PR 3 Methylethylacetic Acid, ^ 2 g 5 >CH-CO.OH, or optically active valeric acid, has been obtained by the oxidation of active amyl alcohol. It boils at 173°. Trimethylacetic Acid is formed when potassium hydrate is boiled with the cyanide derived from trimethylcarbinol. (CH 3 ) 3 C-CN + 2H 2 = (CH 3 ) 3 C-CO.OH + NH 3 It is a crystalline mass, fusible at 35°, and boiling at 163.8°. It dissolves in 40 parts of water at 20°. HIGHER FATTY ACIDS. 551 CAPROIC ACIDS. C 6 H 12 2 There are at present known several isomeric acids having the composition C 6 H 12 2 . One of them was discovered in butter by Chevreul. Normal caproic acid is formed by the oxidation of normal hexyl alcohol, and in the decomposition of normal amyl cyanide by boiling potassium hydrate. It is an oily liquid, having but a faint odor ; its density at 0° is 0.945, and it boils at 205°. Leucine, C 6 H 13 N0 2 . an important nitrogenized body which exists in the animal economy, is an amide. C 6 H n ( NH 2 )0 2 , of normal caproic acid. The caproic acid mentioned on page 546 is an isomeride of the preceding acid. It is obtained by decomposing, by potas- sium hydrate, amyl cyanide derived from the alcohol of fer- mentation. HIGHER FATTY ACIDS. Our limited space will not permit of a description of all of the acids of this series; we can only briefly consider the last members. Palmitic Acid, C 16 H 32 2 . — This exists in palm-oil in com- bination with glyceria. It is prepared on a large scale in England by distilling palm-oil by means of superheated steam, which decomposes the oil into fatty acid and glycerin. The fatty acids solidify on cooling. The mass is expressed to re- move the liquid oleic acid with which it is impregnated, and so obtained in dry. white cakes, which are used for the manufac- ture of candles. Margaric Acid, C 17 H 34 2 . — According to Chevreul, this acid exists in nearly all solid fats. To separate it from stearic acid, which always accompanies it, Chevreul recommends the following process : olive-oil is saponified with litharge and water, and the lead-plaster or soap thus obtained is allowed to cool; after separating it from the water which holds the glycerin in solu- tion, it is pulverized and exhausted with ether, which dissolves the lead oleate and leaves the margarate. The two salts being decomposed by hydrochloric acid, furnish respectively oleic and margaric acids. Margaric acid rflay be obtained synthetically by decomposing cetyl cyanide by potassium hydrate C 16 H 31 .CN + 2H 2 = C 16 H 31 CO.OH -f NH 3 552 ELEMENTS OF MODERN CHEMISTRY. Margaric acid crystallizes in white scales, fusible at 60°. Heintz considers that the margaric acid obtained from many fats is a mixture of palmitic and stearic acids. Stearic Acid, C 18 H 36 2 , was obtained from tallow by Chev- reul. It is a solid, melting at 69.2°. After cooling, the fused acid becomes a laminated, white mass. It is insoluble in water, but dissolves in alcohol and ether. The alcoholic solu- tion deposits it in small pearly scales, which are not greasy to the touch. Stearic acid is used for the manufacture of stearin candles. The alkaline stearates are soluble in water. If a large excess of water be added to the solution of a neutral stearate, a crystal- line precipitate is formed which, according to Chevreul, is an acid stearate. On this reaction he has founded a method for the preparation of stearic acid. The stearates of calcium, barium, and lead are insoluble in water, and can be obtained by double decomposition. Cerotic and Melissic Acids. — These acids have been ob- tained from wax by Brodie (page 514). OLEIC ACID AND ITS HOMOLOGIES. Oleic acid, which has just been mentioned and which Chev- reul obtained from olein, is the principal constituent of a great number of oils and fats ; it does not belong to the series of volatile fatty acids. Its formula, C 18 £P0 2 , shows that it differs from stearic acid by containing two atoms of hydrogen less than the latter acid. It belongs to the series C n H 2n ~ 2 2 . Acrylic Acid, CH 2 =CH-CO.OH.— This is the first term of the series C a H 2n2 2 . It receives its name from the fact that it results from the oxidation of acrolein, or acrylic alde- hyde, C 3 H 4 0, which is formed in the destructive distillation of neutral fatty substances and glycerin and its compounds ; it is a product of the dehydration of glycerin. C 3 H 8 3 _: C 3 H 4 + 2H 2 Glycerin. Acrolein. Acrolein reduces silver oxide, like the other aldehydes, being converted into acrylic acid. This acid is liquid, and boils above 100°. Nascent hydrogen converts it*nto propionic acid. Fusion with potassium hydrate decomposes it into formic and acetic acids. POLYATOMIC COMPOUNDS. 553 Crotonic Aldehyde and Acid. — These two bodies are homo- logies of acrylic aldehyde and acid. C 3 H 4 acrylic aldehyde. C 3 H±0 2 acrylic acid. OH 6 crotonic aldehyde. , OH 6 2 crotonic acid, Crotonic aldehyde is one of the numerous transformation products of ordinary aldehyde. When the latter body is sub- jected to the action of certain salts, it loses the elements of water and is converted into a body which Lieben called acral- dehyde, but which is no other than crotonic aldehyde. 2C 2 H 4 = C 4 H 6 + H 2 This aldehyde is a liquid having a very irritating odor and an acrid taste. It boils at 103°. When submitted to the action of oxidizing agents, such as silver oxide in presence of water, it is converted into crotonic acid. oh 6 o + o = cm 6 o 2 This acid crystallizes in large plates, fusible at 72°. It boils at 182°. Nascent hydrogen, produced by the action of sul- phuric acid and zinc, converts it into normal butyric acid, CH 3 -CH 2 -CH 2 -CO.OH. It combines directly with bromine, producing heat, and is changed into dibromobutyric acid, CH 3 -CHBr-CHBr-CO.OH. ^Fusion with potassium hydrate decomposes it into two molecules of acetic acid. There is an isocrotonic acid, CH 2 =CH-CH 2 -CO.OH, a liquid boiling at 172°. When heated to 170-180° in sealed tubes, it is converted into crotonic acid. Oleic Acid, C 18 H 34 2 . — This acid, of which the preparation has been indicated (page 551), is an oily liquid, which solidifies to a crystalline mass at 4°. Its concentrated alcoholic solution deposits it, when cooled, in small needles fusible at, 14°. When pure it is odorless, and does not redden litmus paper. On exposure to the air it absorbs oxygen, and becomes rancid and acid. Fusion with potassium hydrate converts it into acetic and palmitic acids. When boiled with nitric acid, it oxidizes, losing carbon dioxide, and there are formed volatile fatty acids from acetic to capric acid, and homologues of oxalic acid, including suberic (C 8 11 U 4 ) and succinic (C 4 H 6 4 ) acids; nitrogen peroxide con- verts oleic acid into an isomeride, elaidic acid, a solid body, crystallizing in brilliant plates, fusible at 44-45° (Boudet). y 47 554 ELEMENTS OP MODERN CHEMISTRY. POLYATOMIC COMPOUNDS. After the description of the comparatively simple compounds which are naturally grouped with the monatomic alcohols, we proceed to the more complex compounds constituting the poly- atomic alcohols and their derivatives. The latter alcohols are neutral hydrates, capable of reacting with the acids to form neu- tral combinations analogous to the compound ethers. Those better known are related to the saturated hydrocarbons, from which they are derived by the substitution of several hydroxyl groups for as many atoms of hydrogen. C 2 H6 Ethane. C 3 H8 Propane. Butane. Hexane. C 2 H4(OH)2 Ethylene dihydrate (glycol). C 3 H5(OH)3 Glyceryl tri- hydrate (glycerin). OH6(OH)± Erythrite. C 6 H8(OH)6 Mannite. By oxidation of these polyatomic alcohols, polyatomic acids are produced which bear the same relation to the former that acetic acid bears to ordinary alcohol. It will be noticed that the radicals of these alcohols are un- saturated hydrocarbons, that is, they contain less hydrogen than the saturated hydrocarbons, C n H 2n+2 . Of these radicals, only those can exist in a free state which contain an even number of atoms of hydrogen. We will briefly consider the more important of them. ETHYLENE. C 2 H* = CH 2 =CH 2 This gas, formerly known as olefiant gas or heavy carbu- retted hydrogen, is formed in a great number of reactions. It is produced, together with other hydrocarbons, when substances rich in carbon and hydrogen, such as fats and resins, are de- composed by dry distillation, that is, by the destructive action of heat. Preparation. — It is obtained in the laboratory by dehydrat- ing alcohol by a large excess of sulphuric acid. Ordinarily, a mixture of one part of alcohol and 4 parts of concentrated sul- phuric acid is heated in a flask containing almost enough sand to absorb the entire liquid. The gas disengaged is passed through a wash-bottle containing potassium hydrate, and may then be collected over water. ETHYLENE. 555 Towards the close of the operation the liquid blackens, and much sulphurous and carbonic acid gases are disengaged. These are absorbed by the potassa in the wash-bottle. The following equation expresses the reaction by which ethylene is formed : C 2 H 6 = C 2 H 4 + H 2 Composition and Properties. — Ethylene is a colorless gas, having a feeble, ethereal odor. Its density is 0.9784 compared to air, or 14 compared to hydrogen. Its composition may be deduced from the following experi- ment : 2 volumes of ethylene (2 cubic centimetres, for example) and 6 volumes of oxygen are introduced into an eudiometer over mercury. After the passage of the spark, the 8 volumes will be found to be reduced to 4 volumes, all of which will be entirely absorbed if a solution of potassium hydrate be passed into the tube. The 4 volumes are therefore carbon dioxide. 4 volumes of carbon dioxide represent 2C0 2 . 2 volumes of ethylene therefore contain C 2 . 4 volumes of carbon dioxide contain but 4 of the 6 volumes of oxygen employed ; the other two have therefore been used in the formation of water and have burned 4 volumes of hydrogen. 2 volumes of ethylene then contain 4 volumes of hydrogen. Eudiometric analysis therefore indicates the composition of ethylene to be C 2 W = 2 volumes. This gas is inflammable and burns in the air with a brill- iant flame. When mixed with three volumes of oxygen and ignited, it produces a violent explosion. It is slowly absorbed by concentrated sulphuric acid, ethyl- sulphuric acid being formed. When ethylene is heated with hydriodic acid, the two bodies combine directly to form ethyl iodide. If one volume of ethylene and two volumes of chlorine be rapidly mixed in a tall jar, and a lighted match be applied, the mixture takes fire ^nd burns with a red flame extending to the bottom of the jar, which becomes covered with a black deposit of carbon. C 2 H 4 + 2C1 2 = 4HC1 + C 2 If equal volumes of ethylene and chlorine be mixed and ex- posed to diffused light on the pneumatic trough, the water will 556 ELEMENTS OF MODERN CHEMISTRY. soon rise in the jar, and the two gases will disappear. At the same time, oily drops will appear on the sides of the jar and upon the surface of the liquid. The body so formed is a liquid insoluble in water, and results from the direct combination of ethylene and chlorine. It was formerly called Dutch liquid, or Dutch oil (hence the old name olefiant gas) ; it is now called ethylene chloride. Its composition is expressed by the formula C 2 H 4 CP. It boils at 82.5°. If a small quantity of bromine be poured into a large flask filled with ethylene, and manipulated so that the bromine may form a thin layer on the sides of the flask, an elevation of tem- perature will be observed, and the liquid will rapidly become colorless. The bromine has combined with the ethylene to form a colorless liquid, ethylene bromide, boiling at 131°. Ethylene iodide, C 2 H 4 I 2 , may be obtained by introducing iodine into large jars filled with ethylene, and exposing to dif- fused light during several days. The iodine is little by little converted into a solid, white body, which may be purified by crystallization in alcohol ; it is ethylene iodide. Chloro-Derivatives of Ethylene and Ethylene Chloride. — If ethylene chloride be heated with an alcoholic solution of potassium hydrate, a brisk reaction soon takes place. A gas is disengaged and may be collected over water ; on contact with a lighted taper, it burns with a flame tinged with green. This gas is chlor ethylene. It is formed according to the fol- lowing equation : C 2 H 4 CP + KOH = H 2 + KC1 + C 2 H 3 C1 Like ethylene itself, chlorethylene will combine directly with two atoms of chlorine, forming chlorethylene chloride, C 9 H 3 C1. CI 2 , which may also be obtained by the action of chlorine on ethylene chloride. Chlorethylene chloride is decomposed by alcoholic potassa, like ethylene chloride. Water, potassium chloride, and dichlor- ethylene are formed. C 2 H 3 CP + KOH = H 2 + KC1 + C 2 H 2 CP Chlorethylene chloride. Dichlorethylene. In its turn, dichlorethylene can fix two atoms of chlorine, forming dichlorethylene chloride. These reactions have permitted the preparation of two classes of chloro-compounds, — one derived from ethylene chlo- ride, the other from ethylene itself. DENSITIES. BOILING-POINTS. 1.256 at 12° 82.5° 1.422 at 17° 115° 1.576 at 19° 137° 158° 182° —18 to —15° 1.250 at 14° 35 to 40° 87 to 88° 2.619 at 20° 116.7° HOMOLOGOUS SERIES. C n H 22 . 557 C 2 H±C1 3 ethylene chloride. C 2 H 3 C1 3 chlorethylene chloride. C 2 H 2 C1 4 dichlorethylene chloride. C 2 HC1 5 trichlorethylene chloride. C 2 C1 6 carbon sesquichloride. C 2 H 4 ethylene. C 2 H 3 C1 chlorethylene. C 2 H 2 C1 2 dichlorethylene. C 2 HC1 3 trichlorethylene. C 2 C1 4 tetrachlorethylene. " Regnault, who carefully studied these bodies, has shown that the terms of the first series are isomeric with the chloro- derivatives of ethyl chloride, with the exception of the last two, which are the same in both series. That we may more thoroughly understand this isomerism, we will consider ethylene chloride. C 2 H 4 CP, and its isomeride dichlorethane. called also ethylidene chloride. In the first, two atoms of chlorine are united, each to a different atom of carbon ; in the second, both are united to the same carbon atom. CH 2 Cl CHCl 2 CH 2 C1 CH 3 Ethylene chloride. Ethylidene chloride. TetracJilor ethylene was discovered by Faraday in 1821. It is formed by the action of alcoholic potassium hydrate on tri- chlorethylene chloride. C 2 HC1 5 = C 2 CT + HC1 It is also formed by the action of a red heat on carbon sesquichloride. C 2 C1 6 = C 2 CP + CI 2 It is a very mobile liquid, which does not solidify at —18°. It absorbs chlorine under the influence of direct sunlight, being transformed into carbon sesquichloride, C 2 C1 6 . HOMOLOGOUS SERIES, C n H 2n Ethylene is the first member of a rich series of homologues. of which we will suniniarily describe a few of the others. It is, however, important to remark that since ethylene is (CH 2 ) 2 , it would seem that the constitution of the superior hydrocar- 47* 558 ELEMENTS OF MODERN CHEMISTRY. bous of the series should be expressed by the formula (CH 2 ) n . Thus far none of these normal hydrocarbons have been isolated. For example, normal propylene, CH 2 -CH 2 -CH 2 , is unknown. The compound C 3 H 6 , which will shortly be described, is an isomeride of normal propylene, and its constitution is expressed by the formula CH 3 -CHtCH 2 . It absorbs chlorine directly, forming the chloride CH 3 -CHC1-CH 2 C1 Above the fourth member of this series, butylene, the number of isomerides increases rapidly. Thus, the butylene derived by dehydration from butyl alcohol of fermentation is g£>OdOIP It is formed according to the following reaction : ^3>CH-CH 2 .OH — H 2 = ^3>C=CH 2 Independently of this butylene, there are two others, the formation and principal properties of which will be indicated farther on. Their constitutions are expressed by the formulae CH3-CH=CH-CH3 CH3-CH2-CH=CH 2 The isomeric relations of these three butylenes may be repre- sented in a very simple manner if we consider them to be derived from ethylene, H 2 C=CH 2 , the hydrogen of which is partly replaced by methyl or ethyl. The following compounds are thus obtained : Dimethylethylene a (CH 3 ) 2 C=CH 2 , boils at —6°. Dimethylethylene p (normal) (CH 3 )HC=CH(CH 3 ), boils at +3°. Ethylethylene (C 2 H5)HC=CH 2 , boils at —5°. The fifth member of the series, amylene or pentene, C 5 H 10 , presents still more numerous isomerides, but they can all be explained by the principles already exposed : they may be re- garded as derivatives of ethylene by the substitution of a pro- pylic or isopropylic group for one atom of hydrogen, or by the substitution of an ethyl group and a methyl group for two atoms of hydrogen, or lastly, by the substitution of three methyl groups for three atoms of hydrogen. PROPYLENES — BtJTYLENES. 559 PROPYLENES. C 3 H6 Ordinary Propylene, CH 3 -CH=CH 2 . — To prepare this gas in a pure state Berthelot and de Luca heat allyl iodide with mercury and concentrated hydrochloric acid. 2C 3 H 5 I -)- 4Hg + 2HC1 = Hg 2 Ci 2 + Hg 2 I 2 + 2C 3 H 6 It may also be made by allowing propyl alcohol to fall drop by drop on highly heated zinc chloride (Le Bel). Propylene is a colorless gas. having a feeble, alliaceous odor. It is rapidly absorbed by sulphuric acid, with formation of isopropylsulphuric acid (Berthelot)". C 3 H6 -r EPSO* = (C3H ^>S0 4 It unites directly with hydriodic acid, forming an iodide which is isomeric with propyl iodide. C 3 H 6 — HI = (C 3 !! 7 ) 1 ! Propylene unites directly with chlorine and bromine, forming propylene chloride. C 3 H 6 C1 2 . and propylene bromide. C 3 H 6 Br 2 . The latter is a colorless liquid, boiling at 145°. CH 2 Normal Propylene or Trimethylene, / \ — A, Freund CH 2 -CH 2 has recently isolated normal propylene by heating with sodium the bromide, CH 2 Br-CH 2 -CH 2 Br. It is a gas which is absorbed by bromine more slowly than ordinary propylene, the normal bromide, boiling at 164-165°, being regenerated. It combines with hydriodic acid forming the iodide of normal propyl, CH 3 -CH 2 -CH 2 I. Normal propylene bromide is obtained by heating allyl bromide, C 3 H 5 Br, with hydrobromic acid. CH 2 =CH-CH 2 Br + HBr = CH 2 Br-CH 2 -CH 2 Br Allyl bromide. Normal propylene bromide. It is a colorless liquid, boiling at 165°. BtJTYLENES, C A H 8 . ' 1. Dimethylethylene «. (CH 3 ) 2 CbCH 2 . — This body is formed when isobutyl alcohol is dehydrated by zinc chloride, or by the action of alcoholic potassium hydrate on butyl iodide, OH 9 I. It boils at — 6°. It unites directly with hydriodic acid, forming tertiary butyl iodide, (CH 3 ) 2 CI-CH 3 , and combines 560 ELEMENTS OF MODERN CHEMISTRY. with bromine, forming the bromide (CH 3 ) 2 CBr-CH 2 Br, which boils at 149°. 2. Dimethylethylene ft (normal or symetric) (CH 3 )HC= CH(CH 3 ). — Is formed by the action of alcoholic potassa on secondary butyl iodide, CH 3 -CH 2 -CHI-CH 3 . Boils at +3° and solidifies to a crystalline mass at 0°. Unites with HI, regenerating secondary butyl iodide, and with bromine, forming the bromide (CH 3 )HBrC-CHBr(CH 8 ), which boils at 159°. Le Bel and Greene have obtained normal dimethylethylene by dropping ordinary isobutyl alcohol on highly heated zinc chloride ; the disengaged gases are passed through bromine, and the bromides of ft dimethylethylene and ethylethylene — both gases are produced in the decomposition — separated by fractional distillation. De Luynes obtained secondary butyl iodide by reducing erythrite with a large excess of hydriodic acid (page 617). 3. Ethylethylene (ethyl-vinyl), (C 2 H 5 )HOCH 2 .— Is ob- tained by the action of sodium on a mixture of ethyl iodide and bromethylene. C 2 H5I + BrHC=CH 2 + Na 2 = Nal + NaBr + (C 2 H5)IIC=CH 2 Boiling-point, — 5°. It unites with HI, forming secondary butyl iodide, and with bromine, forming the bromide CH 3 - CH 2 -CHBr-CH 2 Br, boiling at 166°. AMYLENES, OR PENTENES, C 5 H 10 . Several isomeric hydrocarbons are known of the composition C 5 H 10 . They exist in unequal proportions in the product of the reaction of zinc chloride on amyl alcohol, a product gener- ally designated as amylene. It is prepared by heating amyl alcohol with zinc chloride, and passing the vapors given off into a well-cooled receiver. The product is rectified, that portion being retained which passes below 40°. It is a mixture of isomeric amylenes, whose boiling-points vary from 22 to 40°, and which result from the dehydration of amyl alcohol. Trimethylethylene or ordinary Amylene may be obtained in a pure state by dehydrating tertiary amyl alcohol (the hydrate of amylene of Wurtz), which may be accomplished by simply heating it. (CH 3 ) 2 =C(OH)-CH 2 -CH 3 — H 2 = (CH 3 ) 2 C=CH(CH 3 ) Tertiary amyl alcohol. Trimethylethylene. It boils at 36°, and unites directly with hydriodic acid, form- ing tertiary amyl iodide, (CH 3 ) 2 CI-CH 2 -CH 3 , boiling at 129°. HYDROCARBONS OF THE SERIES, C n H 2a 2 . 561 When bromine is poured into cooled amylene, the addition of each drop produces a hissing noise, indicating a violent reac- tion, and the product is a liquid amylene bromide, boiling be- tween 170 and 180°. If the operation be performed upon crude amylene, a mixture of several bromides will result, Trimethyl- ethylene yields a bromide containing (CH 3 ) 2 =CBr-CHBr-CH 3 . Isopropylethylene is formed by the action of alcoholic potassium hydrate on arnyl iodide (Flavitzky). • CH3> CH ~ CH2 " CH21 - — HI = ch3> ch - ch=CH2 Arayl iodide. Isopropylethylene. This body also exists in small quantity in the mixture of hydrocarbons formed by the action of zinc chloride on amyl alcohol. Boiling-point, 25°. It unites with hydriodic acid, forming a secondary iodide, (CH 3 ) 2 -CH-CHI-CH 3 , which boils at 137-139°. It combines with bromine, forming the bromide (CH 3 ) 2 =CH-CHBr-CH 2 Br, which boils between 180 and 190°. Propylethylene or Ethylallyl may be obtained by heating with sodium a mixture of allyl iodide and ethyl iodide. CH 3 -CH 2 I + CH 2 =CH-CH 2 I + Na 2 = 2NaI + CH3-CH 2 -CH 2 -CH=CH 2 Ethyl iodide. Allyl iodide. Ethylallyl. It is also formed by the action of zinc ethyl on ethyl iodide. It boils at 37°, and combines with hydriodic acid, forming the iodide C 3 H 7 -CHI-CH 3 , boiling at 144°. It combines ener- getically with bromine, forming a bromide C 3 H 7 -CHBr-CH 2 Br, boiling at 175°. Polymerides of Amylene. — By the action of zinc chloride on amyl alcohol, there are formed, independently of amylene, other hydrocarbons, among which are the polymeric modifica- tions known as diamylene, C 10 H 20 ; triamylene, C 15 H 30 ; tetra- mylene, C 20 H i0 (Balard, Bauer). These bodies are formed by the union of one, two, three, or four molecules of amylene. HYDROCARBONS OF THE SERIES C n H 2n " 2 . Among the more simple hydrocarbons is one which was dis- covered by E. Davy, and which Berthelot has recently suc- ceeded in preparing by various processes. It is acetylene, and is the first member of a series which includes, among others, the following hydrocarbons : Acetylene C 2 H 2 (E. Davy. Berthelot). Allylene C 3 H 4 (Sawitsch). Crotony'ene C 4 H 6 (E. Caventou). ^ Valerylene C 5 H 8 (Reboul). 562 ELEMENTS OF MODERN CHEMISTRY. Acetylene, C 2 H 2 = CH^CH. — This gas is produced by the incomplete combustion of many organic substances rich in car- bon (Berthelot). If a few drops of ether be poured upon the surface of an ammoniacal solution of cuprous chloride contained in a nar- row jar, and its vapor be ignited, a brownish-red deposit of acetylenide of copper will be formed and may be observed on flowing the liquid around on the sides of the jar. This reac- tion is characteristic of acetylene. This gas may be formed by the direct union of carbdh and hydrogen, as discovered by Berthelot, when the electric arc is passed between carbon points in a vessel containing pure hydro- gen. At the high temperature of the arc, the hydrogen com- bines directly with the carbon, forming acetylene. It is also formed when monobromethylene is heated with amylate of sodium (the sodium compound of amyl alcohol) (Sawitsch). C 2 H 3 Br + C 5 H u .ONa = C 2 H 2 + C 5 H n .OH + NaBr Monobrom- Amylate of sodium. Acetylene. Amyl alcohol, ethylene. Acetylene is a colorless gas, having a peculiar and disagree- able odor. It is quite soluble in water. It burns with a bright but smoky flame. It forms two compounds with bromine, a dibromide, C 2 H 2 Br 2 , and a tetrabromide, C 2 H 2 Br 4 . DIATOMIC ALCOHOLS, OR GLYCOLS. The name glycols was given by Wurtz to the dihydrates of the series of hydrocarbons, C n H 2n . If ordinary alcohol be ethyl hydrate, ordinary glycol is ethylene dihydrate. C 2 H 5 .OH C 2 H*(OH) 2 Ethyl hydrate. Ethylene dihydrate. While alcohol reacts with a single molecule of a monobasic acid to form a neutral ether, glycol can react with either one or two molecules of a monobasic acid, thus forming two ethers. In other words, while the mon atomic alcohols contain but one atom of hydrogen which is replaceable by a single radical of a monobasic acid, glycol contains in the two groups OH two such DENSITY AT 0°. BOILIXG-POIXTS. C 2 H 6 2 1.125 197.5° C 3 H*0 2 1.051 188-189° C±H 10 O 2 1.048 183-184° C 5 H 12 2 0.987 177° C6 H ii0 2 0.9667 207° DIATOMIC ALCOHOLS. 563 atoms of hydrogen, capable of being replaced by two radicals of a monobasic acid, or one radical of a dibasic acid. c <™ 5 >0 CH*>C*H«o. Ethyl acetate. Ethylene diacetate. Ethylene succinate. The glycols yield diatomic acids by oxidation. There are isomeric glycols, or isoglycols, corresponding to the isoalcohols which have already been defined (page 507). A number of glycols of the series C n H 2n+2 2 are now known. Ethylene glycol, or glycol . . Propylene glycol, or propylglycol Butyl ene glycol, or butylglycol Amylene glycol, or amylglycol . Hexylene glycol, or hexylglycol Octylene glycol, or octylglvcol (Ph de Clermont) C 8 H 16 2 It is to be remarked that all of the members of the above series are not. strictly speaking, homologous. The structure of the latter glycols is different from that of ethylene glycol ; they are isoglycoh. The propylglycol discovered by Wurtz is of this number. Xormal propylglycol has recently been discovered by Greromont. and obtained in a pure state by Reboul. The isomerism of the glycols, like that of the alcohols, is due to the constitutions of their molecules, which can contain, like the molecules of the alcohols, the following groups : The primary group -CH 2 .OH The secondary group =CH.OH The tertiary group =C.OH Thus, ethylene glycol is primary, since it contains two groups, CH 2 .OH. The amylglycol derived from trimethylethylene is at the same time secondary and tertiary. Pinacone, which has already been mentioned (page 504), is a tertiary glycol; it contains two groups =(C.OH). CH 2 .OH r5s> COH CH3> f.OH I ^^ I PTT3^ CH 2 .OH CH3-CH.OH CH3> COH Glycol. Amylglycol. Pinacone. (Secondary and tertiary.) (Tertiary.) Among the mixed glycols, that is, those containing at the 564 ELEMENTS OF MODERN CHEMISTRY. same time two different alcoholic groups, is ordinary propyl- glycol, which is primary and secondary. CH 2 .OH CH 3 CH 2 CH.OH CH2.0H CH 2 .OH Normal propyl glycol. Ordinary propylglycol. (Primary). (Primary and secondary). GLYCOL, OR ETHYLENE DIHYDRATE. C 2 H60 2 = C 2 H*(OH) a Wurtz first obtained glycol by cau-ing either iodide or bro- mide of ethylene to react with silver acetate P2TT4T2 I Ag.CWO 2 rr 2 H 4y'I C2H3 ° 2 + 2AffT C 2 H*I 2 -r A | >C 2 H 30 2 ' ° H } JC 2 H30 2 + iAgi Silver acetate. Ethylene diacetate. and saponifying the resulting ethylene diacetate by potassium hydrate. Sh'o'o 1 ( C2H4 )" + 2K0H — 2(C 2 H30.0K) + (C#)" | °g Ethylene diacetate. Potassium acetate. Glycol. Atkinson has shown that the silver acetate may be advan- tageously replaced by an alcoholic solution of potassium ace- tate. Bromide of ethylene reacts with the latter salt, forming potassium bromide, which is almost insoluble in alcohol, and ethylene acetate which is afterwards decomposed by caustic potassa or caustic baryta. Another process has been recently proposed by Hiifner and Zoller. 188 grammes of ethylene bromide, 138 grammes of potassium carbonate and 1 litre of water are introduced into a large flask connected with a reversed condenser, and the mix- ture is boiled until all of the ethylene bromide has disappeared. The aqueous liquid is then concentrated on a water-bath, and alcohol is added to precipitate the potassium bromide ; the alcoholic liquid is then distilled. Alcohol and water first pass, and when the temperature rises above 150°, the liquid which condenses is nearly pure glycol. Properties. — Glycol is a somewhat syrupy, colorless, and odorless liquid, having a sweet taste. It mixes with water and alcohol in all proportions, but is scarcely soluble in ether. It boils at 197.5°, and distils without alteration. GLYCOL. 565 Its analogy to alcohol, from which it differs by containing one more atom of oxygen, is demonstrated by the following exparinients : 1. If platinum black be moistened with glycol and then rapidly plunged into a jar of oxygen, a brilliant incandes- cence is manifested immediately, due to the energetic absorp- tion of oxygen. • With dilute glycol, the oxidation is slower, and gly collie acid is formed. CH 2 .OH " CH2.0H I _(_ f)2 I 4- TT20 CH2.0H + V — CO.OH ' M u Glycol. Gly collie acid. 2. If glycol be heated with ordinary nitric acid, torrents of red vapor are disengaged, and jJie liquid deposits crystals of oxalic acid on cooling. CH2.0H CO.OH CH 2 .OH + 2 ° 2 = CO.OH + 2H2 ° Glycol. Oxalic acid. 3. When glycol is heated with potassium hydrate to 250°, pure hydrogen is disengaged and potassium oxalate is formed. C 2 H 6 > _|_ 2KOH = C 2 OK 2 + 4H 2 Glycol. Potassium oxalate. These experiments establish between glycol and glycollic and oxalic acids, relations analogous to those which exist between alcohol and acetic acid. Ethylene Chlorhydrate, or Ethylenic Chlorhydrin. — When hydrochloric acid o*as is passed into glycol, a neutral compound is formed which constitutes the monoclilorhydrui of glycol, or ethylene chlorhydrate. ° 2H4 is formed by the action of ethylene bromide on an alcoholic solution of silver nitrate. It is a mobile, colorless liquid, insoluble in water. Density at 8°, 1.4837. It explodes by percussion (Henry). Ethylene Acetates. — When glycol is heated with acetic acid, it is converted into acetic ethers. C2H 4 <£g + C2H30.0H = C2H±<^ 2H3 ° + H 2 Acetic acid. Ethylene monacetate. C 2 H*<^ + 2(C2H30.0H) = C2H4 m Ethylene-diamine, ^ H2 _ NH2 =N2 i H 2 2 1S a M 111 ** Dase > boiling at 123°. By the prolonged action of an excess of ethylene bromide, it is converted successively into diethylene- diamine and trietliylene-diamiiie. 48* 570 ELEMENTS OF MODERN CHEMISTRY. f (C2H*)" f (C 2 H4)" f(C 2 H4)" W\ H2 N 2 J (C2H*)-'' Wt (C2H^)" (H 2 (H2 ((C 2 H±)" Ethylene-diamine. Diethylene-diamine. Triethylene-diamine. Diethylene-diamine boils at 170°, and triethylene-diamine at 210°. They are liquids. The ethlylene-diamines are diacid, that is, they combine with two molecules of a monatomic acid, such as hydrochloric or hydrobromic acid (Hofmann). ISETHIONIC ACID. C 2 H 6 S 0± = C 2 H 4 <^ 2>OH This acid, which has long been known, attaches to the ethy- lene derivatives. Oxide of ethylene unites directly with sodium acid-sulphite (bisulphite), forming sodium isethionate. C2H4.0 + N ^>S03 = C»H* C2 ° 2 + 2NH3 =" C2 ° 2 C2 ° 2 = C2 ° 2 C2 °" = C2 ° 2 = CH2 0 + PCI* = POCF +| CHMXT CH2-COC1 Succinic anhydride. Succinyl chloride. SUCCINIC ACID. 597 Kekule has obtained monobromo-succinic and dibromo-suc- cinic acids by heating moistened succinic acid with bromine in sealed tubes. Monobromo-succinic acid is converted into malic acid when treated with water and silver oxide. C2H3Br<^ + AgOH = C2H3(OH)<£^ + AgBr Monobromo-succinic acid. Malic acid. Under the same circumstances, dibromo-succinic acid is con- verted into tartaric acid. C2H2Br2<£^ + 2AgOH = C*H*(OH)2 = CO.OH-CH 2 -CH(OH)-CO.OH This acid, which exists in a number of vegetables, was ex- tracted by Scheele from apple-juice. It is generally prepared from the berries of the mountain-ash, gathered before their complete maturity ; they are strongly pressed, and the juice is boiled, filtered, and neutralized with milk of lime at the ordi- nary temperature. Calcium malate is deposited, and this is converted into the acid malate by dissolving it in boiling water acidulated with nitric acid. The calcium acid malate may be readily purified by crystallization, after which it is converted into malate of lead by double decomposition with lead acetate. The lead salt is suspended in pure water and decomposed by hydrogen sulphide ; the solution of malic acid is then filtered and evaporated (Liebig). Properties. — Malic acid crystallizes in little needles grouped in rounded grains. These deliquesce when exposed to the air. The aqueous solution of malic acid has a marked acid taste. When long kept, it becomes filled with vegetations. It de- viates the plane of polarization to the left. However, there is an inactive malic acid which has no effect on polarized light (Pasteur). Solution of malic acid does not produce a cloud in lime-water, neither in the cold, nor on boiling. When malic acid is heated, it begins to lose water at 130°, and between 150 and 200° is converted into two acids which are isomeric with each other, and are known as maleic and fumaric acids. C 4 H 6 5 Malic acid. C*H*0* + H 2 Maleic and fumaric acids. lumaric acid forms colorless prisms, not very soluble in cold water, and not fusible but volatilizing with partial decomposi- tion above 250°. Nascent hydrogen converts it into succinic acid. Maleic acid resembles fumaric acid, but is much more soluble in water. It melts at 130°, and at 160° decomposes into maleic anhydride and water. The constitutions of these two acids are probably expressed by the formulae CO.OH-CH=CH-CO.OH CH 2 =C(CO OH) 2 Maleic acid. Fumaric acid. ASPARAGIN. 599 By the action of potassium hydrate at about 150°, malic acid is decomposed into oxalic and acetic acids. C±H 6 5 + H 2 = C 2 H 2 0* + C 2 H*O a + H 2 Malic acid. Oxalic acid. Acetic acid. ASPARAGIN AND ASPARTIC ACID. Succinic and malic acids present simple and remarkable rela- tions with two nitrogenized bodies which have long been known ; they are asparagin and aspartic acids. The latter body is amidosuccinic acid, and bears the same relations to succinic acid that glycocol (amido-acetic acid) bears to acetic acid. On the other hand, its relations to malic acid are analogous to those of glycocol to glycollic acid. CH 3 CH^.OH CH*.NH 2 CO.OH CO.OH CO.OH Acetic acid. Glycollic acid. Glycocol. CH 2 -CO.OH CH 2 (OH)-CO.OH CH(NH2)-CO.OH CH 2 -CO.OH CH 2 -CO.OH CHMX).OH Succinic acid. sialic acid. Aspartic or amidosuccinic acid. Asparagin is the monamide of aspartic or amidosuccinic acid ; it is isomeric with the diamide of malic acid. CH(NH2)-CO.XH2 CH.OH-CO.XH2 CH2-CO.OH CH2-CO.NH 2 Asparagin. Malaniide. Asparagin, C 4 H 8 N 2 3 . — This body exists naturally in aspa- ragus, black salsify, the roots of marsh-mallow, licorice wood, and in the buds of cereals, peas, vetches, and beans before they flower. To extract it from these vegetables, they are expressed while fresh, and the juice is clarified and concentrated. The asparagin is deposited in colorless crystals. It is only slightly soluble in cold water and alcohol, but is more soluble in hot water. It forms combinations with both bases and acids. When boiled with these agents, it loses ammonia and is con- verted into aspartic acid. OH 8 N 2 3 + H 2 = NH 3 = CTBPNO 4 Asparagin. Aspartic acid. Aspartic Acid, C 4 H 7 NO, forms rhombic crystals, slightly soluble in cold, and more soluble in hot water. Like glycocol. aspartic acid can form compounds with both acids and bases. 600 ELEMENTS OF MODERN CHEMISTRY. TARTARIC ACID. OH60 6 = CO.OH-CH(OH)-CH(OH)-CO.OH This important acid was discovered by Scheele in the tartar, or argolj which is deposited in casks in which wine is kept. It is prepared from purified tartar, called cream of tartar, which is acid tartrate of potassium. Preparation. — The salt is dissolved in boiling water, and chalk is added until all effervescence, due to the disengage- ment of carbon dioxide, ceases. Insoluble calcium tartrate is deposited, and potassium neutral tartrate remains in solution. The calcium tartrate is collected on a filter, and the filtrate is precipitated by calcium chloride. A new portion of insoluble calcium tartrate is thus obtained, and is washed and united with the first portion. This salt is then suspended in water and exactly decomposed by dilute sulphuric acid ; calcium sulphate is precipitated, and separated by filtration, and the filtered liquid, when sufficiently concentrated and allowed to evaporate in a warm place, deposits crystals of tartaric acid. Properties. — Tartaric acid crystallizes in large, oblique rhom- bic prisms, which often present hemihedral facettes. They are unaltered by the air, and dissolve in about half their weight of cold water and still more abundantly in boiling water. They dissolve also in alcohol, but not in ether. The aqueous solution of tartaric acid turns the plane of polarization to the right. It forms white precipitates in lime- water and baryta-water, but an excess of the acid redissolves these precipitates. If an excess of tartaric acid be added to a solution of cupric sulphate, the liquid may be saturated with potassium hydrate, but no precipitation of cupric hydrate will take place. The liquid will remain transparent and will assume a beautiful dark-blue color ; it is called cupro-potassic solution. In the same manner, ferric chloride, to which tartaric acid has been added, is not precipitated by an excess of potassium hydrate. When tartaric acid is fused with potassium hydrate, it is decomposed into acetic and oxalic acids. C 4 H 6Q6 = C 2 H ±0 2 + C 2 H 2 4 Action of Heat on Tartaric Acid. — 1. Tartaric acid fuses between 170 and 180°, and when the action ot the heat is not TARTARIC ACID. 601 prolonged, it is converted into an isomeric acid, called meta- tartaric. 2. If the acid be maintained for some time in fusion, it loses water and is converted into ditartaric acid. 2C 4 H 6 6 = CTBPO 11 + H 2 Ditartaric acid. 3. When 15 or 20 grammes of tartaric acid are suddenly heated over a naked fire for four or five minutes, the mass swells up and a deliquescent, yellow, spongy mass is obtained, which constitutes what is called tartaric anhydride. C 4 H 6 e = C ±H 4 5 4- H 2 Tartaric anhydride. When heated for some time to 150° in a hot-air oven, tar- taric anhydride becomes insoluble. 4. When tartaric acid is distilled by heating it gradually in a retort to 300°, it is transformed into two pyrogenous acids, pyruvic and pyrotartaric acids. OH 6 6 = C 3 H*0 3 -r CO 2 + H 2 Pyruvic acid. 2C 4 H 6 6 = C 5 H s O + 3C0 2 + 2H 2 Pyrotartaric acid. It is seen that these acids, produced by the action of heat on a complex organic acid, differ from the latter only by the elements of water and carbon dioxide. Such is the law of pyrogenous acids established by Pelouze. When tartaric acid is heated to 170°. in sealed tubes, with water, it undergoes a remarkable modification : it is converted into paratartaric acid and inactive tartaric acid ; the latter is so named because it is without action .on polarized light, and cannot be broken up, as can paratartaric acid, into a dextrogy- rate and a levogyrate acid (Jungfleisch). Action -of Nitric Acid upon Tartaric Acid. — Very con- centrated nitric acid converts tartaric acid into nitrotartaric acid, OH 4 (X0 2 ) 2 6 (Dessaignes). This body may be obtained in crystals, but it is not stable. Its aqueous solution decom- poses between 40 and 50°, with a brisk effervescence of carbon dioxide, and formation* of oxalic acid. When the decompo- sition takes place below 36°, a peculiar, crystallizable acid is formed, which Dessaignes has named tartronic acid. Its com- position corresponds to the formula CPIPO 5 = C 3 EF0 3 (OH) 2 . aa 51 602 ELEMENTS OP MODERN CHEMISTRY. TARTRATES. Tartaric acid is dibasic ; it contains two hydrogen atoms which are replaceable by an equivalent quantity of metal. Neutral tartrates and acid tartrates are known. g } C±H 4 6 ^ | OHW M' | C±H*0 6 , or R"C*H*0« Tartaric acid. iicid tartrates. Neutral tartrates. Neutral tartrates are known in which one atom of metal is replaced by a monatomic oxidized group, such as (SbO)', (FeO)', (BoO)'. i} C4H4 ° 6 (SbOy} C4H4 ° 6 (FeO?} C4H4 ° 6 (BoOr} C4H4 ° 6 Potassium Tartar-emetic. Ferro-potassium tartrate. Boro-potassium acid tartrate. tartrate. Potassium Acid Tartrate, or Cream of Tartar, KHC 4 H 4 6 , is prepared from the crude tartar of wine-casks by subjecting that product to several crystallizations in boiling water. It crystallizes in right rhombic prisms, very slightly soluble in water. If a concentrated solution of tartaric acid be added to a saturated solution of potassium chloride, a precipitate of potassium acid-tartrate will be formed on agitating the liquid. Potassium Neutral Tartrate, K 2 OH 4 6 .— This salt is pre- pared by neutralizing a boiling solution of cream of tartar with potassium carbonate. The evaporated solution deposits on cooling oblique rhombic prisms, very soluble in water. Potassium and* Sodium Tartrate, N ^} c*h*o« + 4H20.-This salt, which is much used in medicine, was discovered in 1672 by Seignette, a pharmacist of Rochelle ; hence it is often called Rochelle salt/, or Seignette's salt. It is prepared by neutralizing a boiling solution of cream of tartar with sodium carbonate, and evaporating the solution. On cooling, the double tartrate is deposited in large, beautiful crystals, eight-sided right rhombic prisms. ANTIMONIO-POTASSIUM TARTRATE, OR TARTAR- EMETIC. < 8W £}o*H«6- This salt is prepared by boiling cream of tartar with water and oxide of antimony, which dissolves abundantly in the ANTIMONIO-POTASSIUM TARTRATE. 603 liquid. After nitration and cooling, the salt is deposited in crystals which are purified by a second crystallization. Tartar-emetic crystallizes in rhombic octahedra. and the crys- tals, which contain one molecule of water of crystallization for two molecules of salt, effloresce in dry air. Its taste is astringent and nauseating. It dissolves in 14.5 parts of cold water and in about two parts of boiling water. It is insoluble in alcohol. When heated to 200° it loses the elements of water and is converted into a double tartrate of antimony and potassium, in which the trivalent antimony replaces 3 atoms of hydrogen in the tartaric acid. C 4 H\SbO)'K0 6 = C*H 2 Sb"'HK0 6 + H 2 When heated to redness in a small, covered crucible, tartar- emetic leaves an alloy of potassium and antimony, disseminated in a mass of charcoal. When this mass is exposed to moist air. it suddenly takes fire and explodes, projecting brilliant sparks. The following are the characteristics of a solution of tartar- emetic : Hydrogen sulphide forms an orange precipitate of antimony sulphide. 9 A few drops of hydrochloric acid cause the appearance of a white precipitate of antimony oxychloride, which disappears in an excess of acid. Potassium hydrate produces a white precipitate of antimony oxide, which redissolves in an excess of alkali. A plate of tin immersed in a solution of emetic precipitates metallic antimony as a black deposit. Tartar-emetic is a much employed medicine. In large doses, or smaller ones frequently repeated, it is an energetic poison. Ferro-Potassium Tartrate. — This salt is prepared by dis- solving ferric hydrate in cream of tartar, and evaporating the solution. It forms brown, amorphous scales, very soluble in water. It is used in medicine. Boro-potassium Tartrate is formed when boric acid is dis- solved in a boiling solution of cream of tartar. It is an amor- phous salt, very soluble in water. 604 ELEMENTS OF MODERN CHEMISTRY. PARATARTARIC ACID. C 8 H 12 12 + 2H 2 This acid, which is isomeric with tartaric acid, exists in cer- tain tartars. It was discovered in 1822 by Kestner, and has been studied by Berzelius and by Pasteur. It crystallizes in transparent, dissymetric prisms, which efflo- resce in the air, losing their water of crystallization. It dis- solves in 5.7 parts of water at 15°. Its solution does not change the plane of polarized light, but Pasteur has succeeded in separating it into two other acids, both of which are optically active. One of them turns the plane of polarization to the right, and is ordinary tartaric acid; the other deflects it to the left, and is levo-tartaric acid. These two acids, which are iso- meric with each other, reproduce paratartaric acid when they are mixed in equivalent proportions. It is somewhat remark- able that the mixture of their solutions is attended by a development of heat (Pasteur). The solution of paratartaric acid precipitates solutions of sulphate, nitrate, and chloride of calcium, a character which tartaric acid does not possess. Independently of dextro-tartaric acid, levo-tartaric acid, and paratartaric acid, there is a fourth isotneride, which is inactive tartaric acid. It exerts no action on polarized light, and cannot be separated into two active acids (Pasteur). Jungfleisch has shown that these various modifications of tar- taric acid may be produced at will by the action of a tempera- ture of about 170° on a solution of ordinary tartaric acid. PYROGENOUS ACIDS DERIVED FROM TAR- TARIC ACID. Pyruvic Acid, C 3 H 4 3 = CH 3 -CO-CO.OH.— This acid, which is produced by the dry distillation of glycerin, tartaric and pyrotartaric acids, is formed synthetically by the action of concentrated hydrochloric acid on acetyl cyanide. 4- 2H 2 — CO<^^ 3 4- NH 3 CO.CN + Z11U ^ U< -CO.OH + 1>J1 Acetyl cyanide. Pyruvic acid. This reaction determines the constitution of pyruvic acid, and shows that it contains the group carbonyl, CO, like acetone, CH 3 -CO-CH 3 . All acids containing the group CO are called acetonic or ketonic acids. PYROGENOUS ACIDS DERIVED FROM TARTARIC ACID. 605 Pyruvic acid is a liquid, soluble in water, alcohol, and ether ; its odor is like that of acetic acid. It boils at 165-170°, being partially decomposed into carbon dioxide and pyrotartaric acid. 2C 3 H 4 3 = CO 2 + C 5 H 8 4 Pyruvic acid. Pyrotartaric acid. With sodium acid sulphite it forms a crystallizable compound, an evidence of its acetonic nature. Under the influence of nascent hydrogen it yields ordinary lactic acid. CH 3 -CO-CO.OH + H 2 = CH 3 -CH.OH-CO.OH Pyrotartaric Acid, C 5 H 8 4 - CH 3 -CH(CO.OH)-CH 2 - CO.OH. — This acid, of which the mode of formation has been already indicated, is one of the four acids of the formula C 5 H 8 4 , of which theory predicts the existence. It has been obtained synthetically by the action of boiling potassium hydrate on propylene cyanide. CH3 CEP CH.CN + 4H 2 = CH-CO.OH + 2NH 3 CH*CN CH*-CO.OH Propylene cyanide. Pyrotartaric acid. It is prepared by rapidly distilling a dry mixture of tartaric acid and pumice-stone. It crystallizes in small rhomboidal prisms, soluble in water, alcohol, and ether. It melts at 112°. When heated for a long time to about 210°, it decomposes into carbon dioxide and butyric acid. C 5 H 8 4 = CO 2 + C 4 H 8 2 CH 2 -CO OH Normal pyrotartaric acid, CH 2 <^pTT 2 _pfk OFP * s ^ orme( ^ when normal propylene cyanide, CH 2 .CN-CH 2 -CH 2 -CN, de- rived from normal propylene chloride, is boiled with potassium hydrate. It crystallizes in large clinorhombic tables, fusible at 97°, soluble in 1.2 parts of water at 14°. It distils almost unaltered towards 300° (Keboul). CITRIC ACID. C 6 H807 This acid, discovered by Scheele in 1784, is largely diffused throughout the vegetable kingdom. It exists in lemons, oranges, limes, currants, raspberries, cherries, etc. 61* 606 ELEMENTS OF MODERN CHEMISTRY. It may be advantageously prepared from lemon-juice, which is allowed to stand until it begins to ferment, and is then filtered, and saturated with chalk while boiling. The precipitate of calcium citrate is washed with boiling water, and decomposed by a slight excess of dilute sulphuric acid. The liquid sepa- rated from the calcium sulphate yields crystals of citric acid after concentration. Grrimaux and Adam have made the synthesis of citric acid from dichloracetone, CH 2 C1-C0-CH 2 C1, which is produced by the dehydration of a dichlorhydrin (page 574) by a mixture of potassium dichromate and sulphuric acid. Like all of its ana- logues, this acetone combines directly with hydrocyanic acid, yielding the cyanide • CH 2 C1 HO-6-CN (Wei, which by the action of alkalies or acids (hydrochloric acid answers best) yields the acid CH 2 C1 HO-C-CO.OH CH 2 CI An alcoholic solution of the sodium salt of the latter acid (dichloroxisobutyric) heated with potassium cyanide furnishes the cyanide CH 2 -CN HO-C-CO.OH 6h 2 -CN This is saturated with hydrochloric acid gas, and a solution containing citric acid is obtained, from which calcium citrate is precipitated when the liquid is neutralized with milk of lime. CH 2 -CN CH 2 -CO.OH HO-C-CO.OH + 4H 2 = HO-C-CO.OH + 2NH 3 CH 2 -CN CH 2 -CO.OH Properties. — This acid forms large, colorless crystals, derived from a right rhombic prism. It dissolves in three-fourths its weight of cold and half its weight of boiling water. PYROGENOUS ACIDS DERIVED FROM CITRIC ACID. 607 • Fused potassium hydrate converts citric acid into oxalic and acetic acids. C 6 H 8 7 + H 2 = C 2 H 2 0* + 2C 2 H*0 2 The solution of citric acid has an acid reaction and a very sour taste. It does not precipitate lime-water in the cold, but the solution becomes clouded after boiling. Citric acid is tribasic. Magnesium citrate, which is soluble, is employed in medi- cine ; it is a purgative, having a sweetish taste. Ferric citrate also is used in medicine. PYROGENOUS ACIDS DERIVED FROM CITRIC ACID. Aconitic Acid, C 6 H 6 6 . — When citric acid is heated, it melts; at 176° it disengages water and is converted into aconitic acid. CH2-CO.OH CH2-CO.OH HO-C-CO.OH = C-CO.OH + H20 Cp 2 -CO.OH CH-CO.OH Citric acid. Aconitic acid. Aconitic acid was first obtained from aconite (Aconitum Na- pellus). It also exists in shave-grass (Equisetum fliiviatile) and in sugar-cane. It crystallizes in little scales, soluble in water, alcohol and ether. It fuses at 140°, and when further heated it loses carbon dioxide, and is converted into itaconic acid and citraconic anhydride. C 6 H 6 6 = C Q2 _|_ C 5 H 6 4 Itaconic and citraconic acids. C 5 H 6 4 = C 5 H 4 3 + H 2 Citraconic anhydride. Aconitic acid, being unsaturated, is converted by tte action of sodium amalgam into tricarballylic acid by combining with two atoms of hydrogen. CH-CO.OH CH2-CO.OH C-CO.OH + H2 _ CH-CO.OH CH2-CO.OH CH2.CO.OH Aconitic acid. Tricarballylic acid. The latter acid is so named because it was first obtained by the hydration of allyl tricyanide, C 3 H 5 (CN) 3 , corresponding to allyl tribromide, or tribromhydrin (page 575). 608 ELEMENTS OF MODERN CHEMISTRY. Itaconic, Citraconic, and Mesaconic Acids, C 5 H 6 4 . — These three acids are isomeric. The first two are formed by the action of heat on citric and aconitic acids ; both of which are by dehydration converted into citraconic anhydride. Citra- conic acid is converted into mesaconic acid when it is boiled with dilute nitric acid, or when heated to 100° with concen- trated hydrochloric acid. The three acids are unsaturated, and can combine with nascent hydrogen, forming pyrotartaric acid. Q5JJ6Q4 + h 2 = C 5 H 8 4 Itaconic acid crystallizes in rhomboidal octahedra, fusible at 161°, soluble in seventeen parts of water at 10°. When strongly heated it yields citraconic anhydride, which distils. Citraconic acid crystallizes in quadratic tables, fusible at 80°. It is much more soluble in water than itaconic acid, and deli- quesces in moist air. Its anhydride, C 5 H 4 3 , is an oily liquid, boiling at 213-214°. On contact with water it regenerates citraconic acid. Mesaconic acid forms brilliant prisms, fusible at 202°, only slightly soluble in cold water. At 250° it decomposes into water and citraconic anhydride. URIC ACID. C5H*N*03 This body is related to the complex organic acids which have just been studied. Among the numerous products de- OH rived from its oxidation, we may mention oxalic acid, C 2 2 which has been called mesoxalic. Uric acid itself seems to be related, according to Baeyer, to tartronic acid, — one of the products of the transformation of tartaric acid (page 601). Uric acid was discovered by Scheele, and its numerous meta- morphoses were the subject of a classic research by Liebig and Wbhler, and have been more recently studied by Baeyer and other chemists. Preparation. — Uric acid may be extracted from the excre- ments of serpents, from guano, and from certain urinary cal- culi, which are almost entirely composed of it. These sub- stances are reduced to a fine powder, boiled with potassium URIC ACID. 609 carbonate and lime, and the solution filtered. The colored solution of potassium urate is mixed with a solution of ammo- nium chloride, which produces a white precipitate of ammonium urate. This salt is well washed, and treated with hydrochloric acid, which sets free uric acid. Uric acid may be obtained from guano by boiling that sub- stance with an aqueous solution of borax (borax 1, water 120). The boiling solution is filtered, and after cooling is precipitated by hydrochloric acid. J. Horbaczewski claims to have made the synthesis of uric acid by heating a mixture of urea and glycocol to 200-230°. 3CON 2 H 4 + C 2 H 5 N0 2 = C 5 H 4 N 4 3 + 3NH 3 + 2H 2 Urea. Glycocol. Uric acid. Properties. — Pure uric acid is a light, white powder, which has a crystalline aspect under the microscope. When slowly separated from dilute solutions, it sometimes forms larger crys- tals, containing 2 molecules of water of crystallization. It is often deposited from urine in small rhomboidal tables of a brownish-yellow color. Uric acid is insoluble in alcohol and in ether. It requires 15,000 parts of cold water, or 1800 parts of boiling water, for its solution. It dissolves in solutions of the alkalies, form- ing neutral urates containing two atoms of the alkaline metal. It is therefore a dibasic acid. When carbonic acid gas is passed into a solution of a neutral urate, an acid urate, which is almost insoluble, is precipitated. Hydrochloric acid forms a thick, white, gelatinous precip- itate of uric acid when added to the solution of a urate. When uric acid is heated to 160 or 170° with an excess of hydriodic acid, it absorbs water, and is decomposed into glyco- col, carbonic acid gas, and ammonia (Strecker). C 5 H 4 NH) 3 + 5H 2 = C 2 H 5 N0 2 + 3C0 2 + 3NH 3 Uric acid. Glycocol. If a small quantity of uric acid be gently heated with nitric acid in a porcelain capsule, it is dissolved with a disengagement of red vapors, and the solution, evaporated at a gentle heat, leaves a residue which assumes a purple color on the addition of a drop of ammonia. This test is characteristic of uric acid, and permits the de- tection of the least traces of that substance. The purple body formed is called murexide. AA* 610 ELEMENTS OF MODERN CHEMISTRY. DERIVATIVES OF URIC ACID. Among the numerous compounds which may be derived from uric acid, some are closely related to oxalic acid, or other acid containing two carbon atoms ; others are derived from mesoxalic acid (see farther on), which contains three carbon atoms. All of these derivatives are more or less closely related to urea ; they are substituted ureas, and are more specially designated by the name ureides. Those related to mesoxalic acid are the more direct derivatives. Alloxan, C 4 H 2 N 2 4 .— This body is one of the products of the oxidation of uric acid by nitric acid ; urea is formed at the same time. C 5 HW0 3 + H 2 + = C 4 H 2 N 2 4 -f CH 4 N 2 Uric acid. Alloxan. Urea. It may be prepared by introducing uric acid, in successive small quantities, into nitric acid of a density of 1.41-1.42, as long as it dissolves producing red vapors. The alloxan finally separates in a mass of delicate needles ; in about twenty-four hours they are drained and dissolved in water at 60 or 65°. On cooling, the alloxan separates in voluminous crystals con- taining 4 molecules of water of crystallization. They efflo- resce in dry air. When crystallized from a hot solution, alloxan forms rhombic octahedra, containing but a single molecule of water. It is very soluble in water, and the solution is acid. By the action of alkalies, baryta-water for example, alloxan is con- verted into alloxanic acid, which is formed by the direct com- bination of the elements of one molecule of water with alloxan. C 4 H 2 N 2 4 + H 2 = C 4 H 4 N 2 5 Alloxan. Alloxanic acid. The alloxanates are decomposed by boiling into mesoxalic acid and urea. Thus if a solution of alloxanic acid, or even alloxane, be added to a boiling solution of lead acetate, a precipi- tate of lead mesoxalate is formed. C 4 H 4 N 2 5 + H 2 = C 3 5 H 2 + CH 4 N 2 Alloxanic acid. Mesoxalic acid. Urea. Mesoxalic acid, C 3 3 (OH) 2 = CO.OH-CO-CO.OH, is a dibasic acid. According to Baeyer, its diatomic radical, mes- oxalyl, exists in alloxan itself, which is mesoxalylurea, that is, urea in which two atoms of hydrogen are replaced by the diatomic radical (C 3 3 )". DERIVATIVES OF URIC ACID. 611 C0<^ CO<^ >C 303 CO<™ 202 - CO - OH Urea. Hesoxalyl-urea Alloxatiic or (alloxan). m«soxaluric acid. Dialuric Acid, C 4 H 4 .N 2 4 , is the product of the prolonged action of hydrogen sulphide on a hot solution of alloxan or alloxan tin. C 4 H 2 N 2 4 + H 2 S = C 4 H 4 N 2 4 + S Alloxan. Dialuric acid. It is also formed by the action of sodium amalgam on the same solutions. It crystallizes in long needles, quite soluble in water ; these crystals assume a red color in the air, and are gradually trans- formed into alloxantin. When a solution of alloxan is added to a solution of dialuric acid, alloxantin is formed. C 4 H 4 N 2 4 + c 4 H 2 X 2 4 = C 8 H 4 N 4 7 + H 2 Dialuric acid. Alloxan. Alloxantin. Baeyer regards dialuric acid as tartronyl-urea, that is, urea in which two atoms of hydrogen are replaced by the diatomic radical of tartronic acid. CO.OH CH.OH Mm TVTT— CO TVTT— PO CO.OH C0 CO CO< NH _ co > CH.OH Tartronic acid. Urea. Alloxane. Dialuric acid (tartronyl-urea). Barbituric Acid, C 4 H 4 N 2 3 .— This acid, which is malonyl- urea, is formed by the action of nascent hydrogen on dibrom- alloxane. CO CBr2 + 2H2;=;=2HBr + CO CH2 Dibromalloxane. Barbituric acid. It crystallizes in large prisms, slightly soluble in cold and more soluble in boiling water. Ebullition with alkalies converts it into malonic acid and urea. CO CH2 + 2H20 = CH2< CaOH + C0< Nff Malonyl-urea. Malonic acid. Urea. Alloxan, dialuric and barbituric acids, which have been de- scribed, are ureides derived from a single molecule of urea by the substitution of the radical of a dibasic acid for two atoms of hydrogen. The groups C 2 2 , C 3 3 , C 2 2 -CH.OH, C 2 2 -CH 2 , 612 ELEMENTS OF MODERN CHEMISTRY. which in oxalic, mesoxalic, tartronic, and malonic acids are united to two hydroxyls, are diatomic. CO.OH ' CO.OH CO.OH CO CH(OH) CH2 CO.OH CO.OH CO.OH Mesoxalic acid. Tartronic acid. Malonic acid. co co co ch - oh co chj Mesoxalyl-urea Tartronyl-urea Malonyl-urea (alloxane). (dialuric acid). (barbituric acid). The following compounds are diureides ; they are derived from two molecules of urea in which four atoms of hydrogen are replaced by two dibasic acid radicals, each of which contains three atoms of carbon and is related to mesoxalyl : Alloxantin, C 8 H 4 N 4 7 . — This body is produced by the re- duction of alloxan. When a current of hydrogen sulphide is passed through a cold solution of alloxan, sulphur separates, and a crystalline precipitate of alloxantin soon forms. 2C 4 H 2 N 2 4 + H 2 S = C 8 H 4 N 4 7 + WO + S Alloxan. Alloxantin. Alloxantin is also formed directly, at the same time as alloxan, by the action of weak nitric acid on uric acid. It crystallizes in small, colorless prisms containing 3 molecules of water of crystallization. It is but slightly soluble in cold water. Nitric acid converts it into alloxan, and reducing agents transform it into dialuric acid. Purpuric Acid and Murexide. — Scheele had already ob- served murexide, which Prout studied and described as pur- purate of ammonia. It is, indeed, the ammonium salt of a nitrogenized acid, C 8 H 5 N 5 6 , for which it is convenient to pre- serve the name purpuric acid (Beilstein). Murexide is formed by the action of ammonia on dry allox- antin heated to 100°, or again, when ammonia or ammonium carbonate is added to a hot solution of alloxantin or alloxan. C 8 H 4 N 4 7 + 2NH 3 = C 8 H 4 (NH 4 )N 5 6 + H 2 Alloxantin. Murexide (ammonium purpurate). Murexide crystallizes in quadrangular prisms, or in tables which are green by reflected and red by transmitted light. These crystals, which contain one molecule of water, present the magnificent metallic reflections shown by the wings of can- tharides. They dissolve in water with a rich purple color. Allantoic C 4 H 6 N 4 8 .— This body was discovered in 1800, DERIVATIVES OF URIC ACID. 613 by Vauquelin and Buniva, in the allantoic liquid of the cow, that is, the urine of the fcetal calf. It occurs also in the urine of young calves. In 1836, Liebig and Wohler obtained it by oxidizing uric acid with lead dioxide. Gorup-Besanez has observed its formation in the action of ozone upon uric acid. Grimaux has recently made the synthesis of allantoin by heating one part of glyoxylic acid with two parts of urea, for eight or ten hours. C 2 H 2 3 + 2(CH 4 N 2 0) = OH 6 X 4 3 + 2H 2 Glyoxylic acid. Urea. Allantoin. From this remarkable synthesis, it appears that allantoin is derived from two molecules of urea ; it is the diureide of gly- oxylic acid. Allantoin may be prepared by boiling uric acid with water, and adding lead dioxide, in small quantities, as long as that oxide continues to be converted into a white powder, which is lead carbonate. The filtered liquid, freed from lead by hydro- gen sulphide, yields crystals of allantoin on evaporation. C 5 H 4 N 4 3 + h 2 + = eH 6 N 4 3 + CO 2 Uric acid. Allantoin. Allantoin crystallizes in brilliant, colorless prisms. It dis- solves in 30 parts of boiling water and in 160 parts of cold water ; it is also soluble in alcohol, but is insoluble in ether. It forms crystallizable compounds with certain metallic oxides. The following compounds are ureides of oxalic and glycolic acids : Parabanic Acid, C 3 H 2 N 2 3 .— This body is formed by the action of an excess of nitric acid on alloxan, which thus gives up the elements of carbon dioxide. C*H 2 N 2 jO + = CO 2 + C 3 H 2 N 2 3 Alloxan. Parabanic acid. Parabanic acid forms thin, transparent prisms, which are very soluble in water. By boiling with acids, it is transformed into oxalic acid and urea. Baeyer regards it as oxalylurea. ccx 1 " 1 - 1 ; NH-CO When parabanic acid is heated with ammonia, ammonium oxohirate is formed, and separates in fine needles. In this case the parabanic acid is converted into oxaluric acid by directly combining with the elements of water. 52 614 ELEMENTS OF MODERN CHEMISTRY. C 3 H 2 N 2 3 _|_ JJ2Q _ C 3 H 4 N 2 4 Parabanic acid. Oxaluric acid. It is seen that oxaluric acid is related to parabanic acid, as alloxanic acid is to alloxan. Hydantoin, or Glycolyl Urea. — The relations between this compound and parabanic acid are the same as those between glycolic and oxalic acids. It is glycolyl urea, C 3 H 4 N 2 2 , and is formed by the action of hydriodic acid on allantoin. NH-OH 2 C 4 H 6 N 4Q3 + 2H J _ C0< , CON 2 4 , p ^NH-CO Allantoin. Hydantoin. Urea. It crystallizes in needles, fusible at 206°, very soluble in hot water. Its solution is neutral. When hydantoin is heated with baryta-water, it is converted into hydantoic acid. C 3 H 4 N 2 2 _|_ H 2Q _ C 3 H 6 N 2 3 Hydantoin. Hydantoic acid. Hydantoic Acid, C 3 H 6 N 2 3 , may be obtained synthetically by heating urea with glycocol : ammonia is disengaged. C0< NH* NH* . C0< NH* . NH3 tU ^NH2 + CH2-COOH ~~ LU ^NH-CH 2 -CO.OH + ** Urea. Glycocol. Hydantoic acid. Indeed, hydantoic acid is formed by the replacement of one atom of hydrogen in urea by the group CH 2 -CO.OH, which is acetic acid less one atom of hydrogen. It crystallizes in large, rhomboidal prisms, soluble in water. It is monobasic. When heated with hydriodic acid it is con- verted into glycocol. CO <^S 2 nTi2 rnnu + H 2 - CO 2 + NH* + NH * ^NH-CH 2 -CO.OH T CH 2 -CO.OH Hydantoin and hydantoic acid present evident relations with parabanic and oxaluiic acids. CO< NH _^, CO< -NH-CO-CO.OH Parabanic acid. Oxaluric acid. ^ ^NH-CH 2 rn ^NH 2 co < NH _^ Q CU< -NH-CH 2 -CO.OH Hydantoin. Hydantoic acid. We cannot further continue the study of the numerous de- rivatives of uric acid. This study has already thrown great light upon the constitution of the acid, without definitely de- termining it. The synthesis indicated by Horbaczewski (page CREATINE— CREATININE. 615 609), if confirmed, will probably lead to the exact molecular structure of uric acid. DERIVATIVES OF GUANIDINE. There are interesting structural relations between urea and guanidine ; the latter is urea in which the oxygen is replaced by the imidogen group NH. CO<^ 2 2 C(NH)<^ 2 2 Urea. Guanidine. This analogy is borne out in the guanidine derivatives corre- sponding to the ureides just described. Hydantoin, or glycolyl-urea, corresponds to a glycolyl-guani- dine which has been named glycocyamidine. OC< NH -? H2 HX-C< NH - CH2 ^NH-CO ^NH-CO Hydantoin. Glycocyaniidine. Hydantoic or uracetic acid corresponds to a guanidine acetic acid called glycocyamine. u ^NH-CH2-CO.OH MJN " 0< ^NH-CH2-CO.OH Hydantoic or uracetic acid. Glycocyamine or guanidine- acetic acid. Glycocyamine is formed by the mixture of aqueous solutions of glycocol and cyanamide. ^NH CH2-NH2 tt ^ t „^NH* Cyanamide. Glycocol. Glycocyamine. Our space only permits the mention of these bodies, but we must describe their important homologues, creatine and creati- nine, which have long been known. CREATINE AND CREATININE. Creatine results from the direct combination of cyanamide and methylglycocol (sarcosine), a reaction discovered by Vol- hard, and entirely analogous to that which yields glycocyamine (see above). „^NH CH2-NH(CH 3 ) - „^/NH2 C< CnH + CO.OH = HN=C . When heated with a concentrated solution of hydliodic acid. it is converted into secondary butyl iodide I de Luynes). C*H 10 O 4 + 7 HI = OH 9 I + 4H-0 + 3I 2 Erythrite. Secondary butyl iodide. MANNITE. OtH"0*» C 6 IIM)H) 6 This body, discovered by Proul in 1806, exists in a -rent number of vegetables. It is the most abundant constituent of manna, a substance which flows from several species of ash, either naturally or from incisions. It is prepared by dis- solving manna in distilled water, in which the white of an has previously been beaten up. The solution is boiled several minutes and then filtered through a woollen cloth and allowed to cool. The liquid then solidifies to a mass of crystals which are purified by reerystallization after treatment with animal charcoal. Mannite forms large, right rhombic prisms. It- taste is sweet, and it is soluhlr in water and alcohol. When heated with a euneciit rated Solution of hydriodie acid, it is reduced to a secondary hezyl iodide. riro' 1 + inn = riri + i;ii 2 o + 5P Mannite. /3-secondary hexjl iodide. Berthelot has described a secondary hexastea/ric monm^e, containing C H H 8 (C 18 H 35 O 2 ) 6 . But, by the action of many acids upon mannite. compounds are obtained which are not ethers of mannite. strictly speak- ing, but of an anhydride of that bpdy, to which Berthelot has ♦rive the name mannitan. C 6 H 14 6 _ JJ2Q _ C 6 H 12 5 Mannite. Mannitan. Mannitan is isomeric with two sweet substances, quercite, or the sugar of the glands, which was discovered in the glands by Braconnot, andjpmtite, which has been extracted by Berthelot from the resin of the California pine. SUGARS AND STARCHES. 619 Didcite, C 6 H 14 6 , which has been obtained from Madagascar manna, exists in certain plants, such as the Melampyrum nemorosum, the Scrophularia nodosa, the Rhinanthus crista- gnllL and the Euonymus earopseus. It forms large, oblique rhombic prisms, and is less soluble in water than mannite ; it is but slightly soluble in alcohol. It melts at 188.5°. It dis- solves in the hydracids without producing heat. Like its isomeride, manna, it is reduced by hydriodic acid to a second- ary hexyl iodide (G. Bouchardat). Sorbite, C 6 H u 6 , recently obtained by J. Boussingault from the fermented juice of the mountain-ash, is another isomeride of mannite. SUGARS AND STARCHES. Among the more widely distributed products of the vege- table kingdom must be included the various kinds of sugar, starch, the gums, and the matter of young vegetable cells, or cellulose. These compounds contain carbon, hydrogen, and oxygen in such proportions that the oxygen is present in exactly sufficient quantity to form water with the hydrogen. Their composition is then expressed by the general formula C m (H 2 0) n . If all of the oxygen and hydrogen were removed in the form of water, only carbon would remain. Hence the name hydrates of car- bon, often applied to this class of bodies. Some of them contain 6, and the others 12 atoms of carbon, and they can be arranged in three different classes, of which the types are glucose, saccharose, and starch. 1. C 6 H 12 6 2. C 12 H 22 O n 3. C 6 H 10 O 5 GLUCOSE. SACCHAROSE. STARCH. LEVULOSE. LACTOSE. DEXTRIN. GALACTOSE. MALTOSE. INULIN. ARABINOSE. MELITOSE. GLYCOGEN. INOSITE. MELEZITOSE. GUMS. DAMBOSE. MYCOSE. CELLULOSE. All of these bodies have the power of rotating the plane of polarized light, either to the right or to the left. They react with several molecules of an acid, forming neu- tral compounds, a property which characterizes them as poly- atomic alcohols (Berthelot). 620 ELEMENTS OF MODERN CHEMISTRY. GLUCOSE. C 6 H 12 6 This important body, which forms the solid and crystalliza- ble part of honey, exists in a great number of dried fruits, on the surface of which it forms a well-known white efflorescence. It is also found in the urine in the disease known as diabetes. It may be made artificially by the action of dilute sulphuric acid on starch (KirchhofF), or on cellulose (Braconnot). Preparation. — Glucose is prepared in the arts by the fol- lowing process : 6000 litres of water and 42 kilogrammes of sulphuric acid are introduced into a large wooden trough, and the liquid is heated by jets of superheated steam. When it is in full ebul- lition, 2000 kilogrammes of starch suspended in 2000 litres of warm water are allowed to run in gradually, and in thirty or forty minutes the saccharification is complete. The sul- phuric acid is then saturated with pulverized chalk, the insol- uble calcium sulphate is separated, and the liquid concentrated in boilers heated by steam until it marks 40 or 41° Baunie. It is then allowed to crystallize, and solidifies to an opaque, yellowish, crystalline mass, which is glucose. The sulphuric acid has recently been replaced by hydrochlo- ric acid, which produces a whiter product. The small quantity of calcium chloride formed does not prevent the crystallization of the glucose. Properties. — This body crystallizes in small, white, rounded masses, agglomerated like cauliflowers. The crystals contain one molecule of water of crystallization (C 6 H 12 6 -f- H 2 0). They remain unchanged in the air. They melt when heated on a water-bath, and lose their water at 100°. Anhydrous glucose melts at 144°. Glucose dissolves in a little more than its own weight of water at 17°. It is three times less soluble than cane-sugar, and in solutions of equal concentration it is three times less sweet. It is much less soluble in alcohol than in water. The solution of glucose rotates the plane of polarization to the right. The deviation caused by a recently-prepared solution diminishes after a time as much as fifty per cent. ; it varies with the concentration. The specific rotatory power at 20° is for the yellow ray 4 X [«]d = -f 58.7° (Tollens). When glucose is heated to 170°, it loses the elements of GLUCOSE. 621 water and is converted into a colorless mass, not very sweet, which has received the name glucosan. C 6 H 12 6 = C 6 H 10()5 _|_ H 2 Glucose. Glucosan. Grlucose forms true compounds with the bases. There is a gluconate of calcium, C 6 H 10 Ca"O 6 + IPO. It is precipitated when alcohol is added to a solution of calcium hydrate in glu- cose. These compounds are not stable. If potassium hydrate be added to a solution of glucose and the liquid be heated, it first becomes yellow, and then rapidly assumes a deep-brown color. The same color is produced when glucose is heated with calcium or barium hydrate. According to Peligot, there are formed under these circum- stances two acids, which he named glucic and melassic acids. Ordinary or cane-sugar does not produce this reaction, and can thus be distinguished from glucose. In addition to these products, the action of lime on glucose gives rise to the formation of a substance which forms beautiful crystals of the orthorhombic type, and which Peligot called sac- charin. It is dextrogyrate ([«]d = +93.5°). According to Scheibler, it contains C 6 H 10 O 5 , and is the anhydride of a sac- charinic acid, C 6 H 12 6 . Grlucose reduces various metallic solutions. If a solution of cupric sulphate be poured into a solution of glucose, and potas- sium hydrate be added, no precipitate is formed, but the liquid acquires a dark-blue color. On heating it, a yellowish precip- itate of cuprous hydrate is formed. This reaction, which was discovered by Troemmer, is very sensitive, and can be used for the detection of the smallest quantities of glucose. In making the test, a cupro-alkaline solution is employed, made by dissolving cupric tartrate in potassium hydrate (Barreswill's solution), or by adding sodium and potassium tartrate and caustic soda to a solution of cupric sulphate (Fehling's solution). When a solution of glucose is heated with bismuth nitrate and an excess of potassium hydrate, a black precipitate of reduced metallic bismuth is formed. When a solution of common salt is added to a solution of glucose and the liquid is allowed to evaporate spontaneously, crystals are deposited which constitute a definite compound 622 ELEMENTS OF MODERN CHEMISTRY. of the two bodies. They contain 2(NaCl + 2C 6 H 12 6 ) + 3H 2 0. Glucose forms combinations with the acids, like mannite, and these combinations represent glucose in which a certain num- ber of hydrogen atoms are replaced by acid radicals. Ber- thelot had regarded glucose as a hexatomic alcohol, containing 6 hydroxyl groups, but Colley has shown that it is a penta- tomic alcohol. He has described a compound produced by the action of acetyl chloride on glucose, and which he names aceto- chlorhydrose. It contains C6ir0 { (C 2 H 3 2 ) 4 On account of the reducing properties of glucose, it may be considered that the oxygen atom of the group C 6 H 7 forms part of an aldehyde group CHO. Hence glucose is at the same time an aldehyde and a pentatomic alcohol, and its constitution would be represented by the formula CH 2 .OH- CH.OH-CH.OH-CH.OH-CH.OH-CHO. The following fact supports this view. When chlorine gas is passed into a solution of glucose, the latter is converted into an acid, gluconic acid, C 6 H 12 7 , which only differs from glucose by containing one more atom of oxygen. This acid corre- sponds to gluconic aldehyde, and the following formulae indi- cate the relations existing between the bodies just mentioned : CH2.0H CH 2 .C1 CH2.0H (CH.OH)* (CH.OC2H30)* (CH.OH)* CHO CHO CO.OH Glucose. Acetochlorhydrose. Gluconic acid. LEVULOSE, OR FRUIT-SUGAR. C 6 H 12 06 Independently of the glucose which effloresces on their sur- face after desiccation, many fruits contain another sugar, which strongly deviates the plane of polarization to the left. It is levulose. Levulose exists in inverted sugar (page 627). Many sweet fruits contain inverted sugar ; among them are grapes, cherries, figs, gooseberries, etc. It may be extracted from inverted sugar (a mixture of equal proportions of glucose and levulose). Dubrunfaut recommends LEVULOSE. 623 the following process : 10 grammes of inverted sugar, 6 grammes of slaked lime, and 100 grammes of water are intimately mixed. The mass, which is at first liquid, becomes pasty on agitation, and then contains a solution of calcium glucosate and solid cal- cium levulosate. It is strongly pressed in a cloth and the compound of levulose and lime is decomposed by oxalic acid. The levulose remains in solution, and after evaporation forms a syrup which is much sweeter than a solution of glucose. Levulose may be prepared more readily by treating inulin (page 637) with dilute acids. When pure it is crystallizable, whether it be obtained from inulin or from inverted sugar. Its rotatory power, at 14°, is [«]d == — 104°, but varies with the temperature, being at 90° only half as great. Levulose is directly fermentable. When heated to 170°, it loses the elements of water and is converted into levuhsan. C 6 H i2 6 = c 6 H 10 O 5 -f H 2 Levulosan. Other sugars are known which may be classed with glucose. Such are the following : 1. Sorbin, C 6 H 12 6 , a substance which crystallizes in large, transparent rhomboidal octahedra ; has been obtained from the berries of the mountain-ash by Pelouze. 2. Inosite, C 6 H 12 6 + H 2 0, a sugary matter extracted by Scherer in 1850 from the muscles, and which has since been found in the lungs, kidneys, spleen, and liver (Cloetta). In- osite is identical with a substance that Yohl extracted from green beans, and to which he gave the name phaseomannite. Inosite forms large, rhombic tables, or transparent, colorless prisms, having a sweet taste. The crystals effloresce in the air. They are soluble in water, but insoluble in absolute alcohol and in ether. The aqueous solution is optically inactive ; it is not converted into glucose by the action of dilute acids ; it does not reduce cupro-potassic solutions, nor will it ferment under the influence of yeast. 3. Dambose, C 6 H 12 6 . — This body exists as a dimethylether in dambonite, which H. Girard has extracted from an African caoutchouc by exhaustion with boiling alcohol. When dainbo- nite is heated with concentrated hydriodic acid, methyl iodide and dambose are formed. C 6 H 10 O\OCH. 3 ) 2 + 2HI = 2CH 3 I + C 6 H 12 6 Dambonite. Danibose. Dambose is crystallizable, and very soluble in water. It melts 624 ELEMENTS OF MODERN CHEMISTRY. at 190°, and sublimes at about 220°, a property which distin- guishes it from all other saccharine substances. GALACTOSE. C 6 H 12 6 This is one of the products of the action of dilute acids and of certain ferments on lactose (page 628). Galactose crystal- lizes in little masses, formed by the agglomeration of small needles. It is less soluble in water than glucose, and deviates the plane of polarization to the right. It is fermentable, and readily reduces cupro-potassic solutions. Nascent hydrogen con- verts it into dulcite. Nitric acid oxidizes it with formation of mucic acid. ARABINOSE. C 6 H 12 6 This is the sugar of gum. It is formed when arabin, or gum arabic, is boiled with dilute nitric acid. It crystallizes in bril- liant rhomboidal prisms, fusible at 160°. Its aqueous solution has a sweet taste and is dextrogyrate. It reduces cupro-potassic solutions, but is not fermentable. SACCHAROSE, OR CANE-SUGAR. C 12 H 22 O n Extraction. — Ordinary sugar, which is universally diffused in the vegetable kingdom, is extracted principally from sugar-cane, sugar-maple, and beet-root. Fresh sugar-cane contains about eighteen per cent, of sugar : beet-root contains only about ten per cent. (Peligot). Certain sweet fruits contain cane-sugar, independently of inverted sugar. According to Buignet, such are apricots, peaches, pine-apples, lemons, plums, and raspberries. We can only briefly indicate the processes which are em- ployed for the extraction of sugar from beet-root. The roots are washed, and reduced to pulp in a machine provided with a cylinder armed with teeth and having a rapid rotary motion. This pulp is then strongly pressed in woollen sacks by means of a hydraulic press, and the juice is imme- diately transferred to large boilers having double bottoms and heated by steam, and milk of lime is added. SACCHAROSE. 625 This operation, which is called defecation, is intended not only to separate certain substances which form insoluble com- pounds with the lime, but to prevent the juice from becoming altered by reason of its acidity. As the sugar itself dissolves a large quantity of lime, the latter must be got rid of. A cur- rent of carbon dioxide is consequently passed into the solution, and decomposes the saccharate of calcium. Another process of dechaulage, recently devised, depends on the employment of ammonium phosphate. Insoluble calcium phosphate is formed, and the ammonia is disengaged on account of the high temperature at which the operation is conducted. By this process the neutralization is more perfect. The liquid is then heated to about 95°, and filtered through a layer of animal charcoal in grains ; it is then concentrated in evaporating-pans heated by steam. When the syrup marks 25° Baume, it is again filtered through animal charcoal, and the concentration is finished in pans heated by steam, and in which a vacuum is maintained during the evaporation. The cooking of the syrup is thus carried on at a temperature not above 75 or 80°, and these conditions assure a fine quality of product and a good yield by preventing as much as possible the transformation of the sugar into uncrystallizable sugar. When the syrup marks 42 or 43°, it is run into cooling- pans, where it is continually stirred until the sugar is depos- ited in small crystals. These are distributed in moulds, which consist of terra-cotta cones having a hole in the summit, which for the time is closed. These cones are placed in an oven heated to 25°, where the crystallization takes place ; when the syrup has solidified, the holes in the cones are opened and the thick and colored mother-liquor is allowed to drain out ; it con- stitutes molasses. The loaves of sugar, drained and dried, are delivered to commerce as crude or brown sugar. For some years an apparatus has been used for draining and bleaching of crude sugars, which consists of a cylindrical cage having perforated metallic walls. It is put into rapid motion on its axis, and the molasses is expelled through the perforated walls by centrifugal force. The apparatus is called the centrifugal drier. Refining of Crude Sugar. — The crude sugar is crushed, sifted, and dissolved in about 30 per cent, its weight of water, the operation being conducted in a boiler heated by steam. 5 per cent, of animal charcoal is then thrown into the hot solu- bb 53 626 ELEMENTS OF MODERN CHEMISTRY. tion, and, after stirring, } per cent, of beef's blood is added. The latter coagulates in the liquid and envelops all of the sus- pended particles, uniting them in a scum which is easily re- moved. When the liquid becomes clear, it is drawn off and filtered. It is then passed through grained animal charcoal, which completely decolorizes it. It is concentrated in vacuum- pans, from which it is drawn into a large copper vessel having a double bottom. It is continually stirred until crystallization commences, after which it is run into moulds, which are then placed in rooms heated to 20°. After the crystallization is completed, the syrup remaining liquid is allowed to drain out. At the termination of the draining, a creamy mixture of white clay and water is poured on the surface of the sugar in each mould, and the water of this broth slowly penetrates the mass of sugar, liquefies the syrup which remains between the crystals, and carries it to the lower part of the mass. The clay, having lost its water, contracts, dries up, and remains upon the decolorized sugar as a dry cake. It is removed, and a syrup of white sugar is run into the whitened and porous loaf and fills up all of the spaces when it solidifies in the oven. This operation, the object of which is the decolorizing of the sugar-loaves, is called claying. The clay broth may be replaced by syrup of white sugar, an operation which is called decoloring. The sugar solidified in the moulds is a compact, crystalline, white mass, composed of little grains. It may be obtained in voluminous crystals by concentrating the syrup until it marks 37° Baume, and then exposing it for some days to a tempera- ture of 30° in copper vessels, across which threads are stretched. The sugar is deposited on the threads in large crystals known as rock-candy. Properties of Sugar. — Sugar crystallizes in large, oblique rhombic prisms, having hemihedral facettes. The crystals are hard, anhydrous, and unalterable in the air. Density, 1.606. It dissolves in one-third its weight of cold water ; the solution is thick, and is known as simple syrup. Sugar is insoluble in ether and in cold absolute alcohol. Boiling absolute alcohol dissolves a little more than one per cent. ; ordinary alcohol will take up more. The aqueous solution of sugar deviates the plane of polarization to the right, ([a]D = +64.1°), at 20°. At 160°, sugar melts to a thick, transparent liquid, which solidifies to an amorphous, vitreous mass on cooling. SACCHAROSE. 627 AT hen maintained for a long time at a temperature of 160 or 161°, it breaks up into glucose and levulosan (Gelis). C i2 H 22 n _ c 6 H 12 6 + C 6 H 10 O 5 Saccharose. Glucose. Levulosan. * Between 190 and 200° it loses the elements of water and is converted into a bitter, brown, amorphous mass, which is desig- nated as caramel. Inverted Sugar. — By the action of dilute acids, sugar is converted, slowly in the cold and rapidly on boiling, into a mixture, in equal proportions, of two isomeric sugars which have opposite rotatory powers : they are glucose and levulose. The mixture is called inverted sugar. C 12 H 22 11 _|_ JJ2Q _ C 6 H 12 6 _|_ Q^UQ, Saccharose. Glucose. Levulose. The same transformation is effected by the soluble matter of yeast (Bert-helot), and also, according to Buignet, by the action of the peculiar ferments which exist in most fruits. Sugar only ferments after having first undergone this trans- formation into inverted sugar by the action of the ferment. Nitric acid converts sugar into saccharic acid, C 6 H 10 O 8 , and oxalic acid. Concentrated sulphuric acid carbonizes it. Saccharose resists the action of alkalies better than glucose. It forms with them and with the bases in general, definite com- binations known as saccharates. If a mixture of sugar and slaked lime be triturated with water and the whole be thrown upon a filter, the liquid which passes through will be colorless and strongly alkaline. When it is heated to ebullition, it changes into a solid mass which again becomes liquid on cooling. It is a solution of saccharate of calcium, (C 12 H 22 O n ) 2 .3CaO. Alcohol precipitates from it the compound C 12 H 22 O n .CaO. An analogous experiment may be made with a concentrated boiling solution of barium hydrate. When sugar is heated to 150 or 160° with barium hydrate, it yields lactic acid. When fused with potassium hydrate, it disengages hydrogen, and carbonate, oxalate, formate, acetate, and propionate of potassium are formed. When distilled with quick-lime, sugar is decomposed with formation of carbon dioxide, water, acetone, and metacetone, C 3 H 6 0, a liquid having a pleasant odor, insoluble in water, and boiling at 84°. 628 ELEMENTS OF MODERN CHEMISTRY. Sugar forms a combination with sodium chloride, consisting of deliquescent crystals which contain C 12 H 22 O n .NaCl. Ethers of Saccharose. — Like glucose, saccharose may be etherified. When it is heated to 160° with an excess of acetic anhydride, octacetic saccharose, C 12 H u 3 (C 2 H 3 2 ) 8 , a white mass, insoluble in water, is obtained (Schiitzenberger). Nitro- saccharose, or the tetranitric ether, C 12 H 18 7 (O.N0 2 ) 4 , is pre- pared by gradually adding powdered sugar to a cold mixture of concentrated nitric and sulphuric acids. Water then pre- cipitates from the mixture a white mass, which explodes vio- lently by percussion. LACTOSE, OR MILK-SUGAR This sugar exists in solution in the milk of mammals, and is extracted from the whey which remains after the manufacture of cheese. It is only necessary to evaporate this liquid to crystallization. Milk-sugar occurs in commerce in cylindrical masses, formed of an agglomeration of crystals around a little stick which serves as a nucleus. The crystals are colorless, hard, and creak when crushed by the teeth. They arc right rhombic prisms, terminated by octahedral points. They contain one molecule of water of crystallization which they lose at about 140°. They dissolve in (> parts of cold, and in - parts of boiling water. The solution turns the plane of polarization to the right. The rotatory power of old solutions is [a]D = -(-59.3°. When heated with nitric acid, lactose yields certain acids, among which is one which is but slightly soluble in water, and which is called mucic acid. It contains C G H 10 O 8 , and is Iso- meric with saccharic est adapted for the propagation of the cells. The latter increase with ex- treme energy in liquids which contain, besides the yeast, glu- cose, and a small quantity of Fig. 125. albuminoid matter ready formed. Lactic Fermentation. — This fermentation, of which the conditions have already been indicated (page 584), is accom- plished by the action of a peculiar ferment of vegetable char- acter. It is formed of small round or elongated cells, very short, and isolated, or in masses. They are much smaller than yeast cells, and constitute the lactic yeast of Pasteur. It only acts upon glucose or lactose in a neutral or alkaline liquid. Hence the necessity of adding sodium carbonate or chalk to the liquid. The reaction consists of a splitting of the glucose molecule. C 6 H i2 6 = 2C 3 H 6 3 Glucose. Lactic acid. Butyric Fermentation. — This consists in the transformation of calcium lactate into butyrate, — a transformation that is ac- companied by a disengagement of hydrogen. According to Pasteur, this fermentation is caused by infusoria, and the ani- malculae live and are developed in situations where they are deprived of free oxygen. Such is the energy of their respira- tory functions that free oxygen kills them (Pasteur). They 632 ELEMENTS OF MODERN CHEMISTRY. respire by decomposing oxidized bodies and assimilating the oxygen. We have already considered the acetic fermentation. We may add that by the action of a peculiar ferment, glucose is converted into mannite and a gummy matter, very soluble in water, and which gives a viscous consistence to the fermented liquid. This is called the viscous fermentation. Fermented Beverages. — The foregoing summary indi- cations regarding fermentation may be completed by some general notions upon the fermented beverages, particularly wine and beer. Wine. — It is universally known that wine is the product of the fermentation of grape-juice. This juice contains in solu- tion inverted sugar, a small trace of gummy matters, vegetable albumen, a trace of fatty matters, coloring matters, free tar- taric and malic acids, and various tartrates^principally potas- sium acid-tart rate, or cream of tartar. The clarified wine which results from the fermentation of this juice contains, independently of water, various products, some of which existed in the juice, and others which are the results of the transformation through which it has passed. Among the first are the mineral and vegetable salts of the juice (in smaller proportion, because they are partly deposited with the lees), the gummy matter, a small quantity of fatty and albuminoid substances, the coloring matters, free tartaric and malic acids, and the tannin derived from the grape-stems and from the skins and seeds. Among the substances which result from the fermentation are : 1. Alcohol, which is the principal product. 2. Carbonic acid gas ; it is well known that it exists abun- dantly in champagnes. 3. Small quantities of aldehyde and acetic acid produced by oxidation of the alcohol. The acetic acid reacts upon the alcohol contained in the wine, forming acetic ether. 4. Glycerin and succinic acid, in small quantities (Pasteur). 5 . Traces of compound ethers, which contribute to the bouquet of the wine. Besides acetic ether, traces of a compound ether called cenanthic ether have been found in wine ; it appears to be jpelargonic ether, C 9 H 17 2 (C 2 H 5 ). Berth elot states the exist- ence of but slightly volatile acid ethers (malic, tartaric) in wine. The following table indicates the quantities by volume of pure alcohol contained in 100 volumes of various wines : FERMENTATION. 633 Madeira 20.48 Port 20.22 Roussillon 16.67 Hermitage (white) 16.03 Malaga 15.87 Saint-Georges 15.00 Sauterne (white) 15.00 Cyprus 15.00 Lunel 14.27 Graves 12.30 Frontignan 11.76 Champagne 11.60 Rhine 11.11 Strongest Bordeaux 11.00 Lightest w 7.5 to 8 Red Bourgogne 7.66 Red Macon 7.66 Red Chablis 7. S3 Beer. — Beer is a fermented beverage, made from a icort of germinated barley, and ordinarily rendered aromatic by hops. Like all other cereals, barley contains a considerable proportion of starch. During the germination, this starch is partially con- verted into maltose by the action of a nitrogenized matter, which is formed in the sprouting grains, and which is called diastase. In order to saccharify the barley, it is then first necessary to cause it to germinate, and for this purpose it is moistened with water, and kept for some time at a temperature of 1 4 or 15° ; the object of this operation, called malting, is the development of the. diastase necessary for the saccharification of the starchy matter. "When the sprout has acquired about the same length as the grain (Fig. 126), the germination is arrested by ex- posing the malt to the action of a temperature of about 50°. The dry malt is then reduced to a coarse powder, placed in a large vat, and Fig. 126. brewed for about three hours with water heated to 50 or 60°. In this operation, the diastase of the malt con- verts the starch into dextrin and maltose, which dissolve, to- gether with the other soluble principles of the grain. The sweet wort thus obtained is heated with hops, which yield to it their essential aromatic oil. It is then properly cooled and allowed to ferment in deep vats, into which a cer- tain quantity of yeast produced in a previous operation is in- troduced at the same time. The alcoholic fermentation soon begins and goes on with great activity during a few days. As ; BB * 634 ELEMENTS OF MODERN CHEMISTRY. soon as it has ceased, the liquid can be delivered for consump- tion. The quality of beer is better when the fermentation takes place at a low temperature. Beer contains much water, free carbonic acid gas, alcohol (2 to 5 per cent.), variable quantities of saccharine matters, dex- trin, nitrogenized matters, extractive, bitter, and coloring mat- ters, essential oil, and various salts. STARCH. C 6 H 10 O 5 Starch is universally diffused throughout the vegetable king- dom. It is especially abundant in the seeds of leguminous plants and cereals, and in the potato. Extraction. — To extract starch from potatoes, they are re- duced to pulp by means of a rasp, and the pulp is placed in a sieve and washed by a stream of water. The water carries with it the fine granules of starch, while the torn cells of the potato remain in the sieve. The starch gradually deposits from the water, and collects in the bottom of the vessel, where it settles, forming a cake from which the supernatent water may be separated by decantation. Starch may be extracted from wheat by making a paste of flour and kneeding it in a sieve under a jet of water : the starch granules are carried with the water, and a soft, gray, elastic mass remains in the sieve, constituting the nitrogenized matter of the flour, or gluten. Another process, almost abandoned at present on account of its offensiveness, consists in allowing the coarsely-ground grain to putrefy. Putrefaction destroys the gluten, while the starch resists decomposition. Physical Properties. — Starch is a white powder, formed of granules which present an organic structure. Their size and shape are variable (Fig. 127), their diameter being from 2 to 185 thousandths of a millimetre. Those of potato starch are larger than those of starch from grain. These granules are made up of concentric layers, which are more dense as they are nearer the surface. It is easy to make this structure apparent by causing the granules to undergo a partial disintegration by the action of hot water. Thy swell up, burst open, and separate into thin layers, as shown in Fig. 128. STARCH. 635 Chemical Properties. — Starch is insoluble in water, alcohol, and ether. Contact with water heated to 60 or 70° causes it to swell up considerably, without dissolving. A semi-trans- parent, gelatinous mass results, which is known as starch paste. When starch is boiled with a large quantity of water and the whole is thrown on a filter, the liquid which passes is slightly turbid, and constitutes what is known as solution of starch. It contains in suspension flakes of amylaceous matter small enough to pass through the filter. It also contains a small quantity of soluble starch (see farther on). If a few drops of iodine be added to solution of starch, a deep-blue color is at once produced. This blue color disappears when the liquid is heated to 90°. and reappears on cooling. If a few drops of a neutral solution of calcium chloride be added to the liquid, dark-blue flakes are precipitated, constituting what is called iodide of starch. It is starch dyed by iodine. Fig.128. Metamorphoses of Starch — Dextrin. — When long heated to 100° starch is converted into soluble starch, which yields a blue color with iodine (Maschke). Between 160 and 200° it is converted into a body which is very soluble in water, and the solution of which is not colored by iodine. This solution strongly turns the plane of polariza- tion to the right ; hence the name dextrin given to this body. which is regarded as isomeric with starch. (C 6 H 10 O 5 ) n . A very concentrated solution of dextrin has the appearance of a solu- tion of gum. It is used as a mucilage for labels, and for the preparation of immovable surgical dressings. Alcohol added to a solution of dextrin precipitates the latter substance in the form of flakes. Subacetate of lead does not 636 ELEMENTS OF MODERN CHEMISTRY. precipitate dextrin, a character which permits the latter body to be distinguished from gum arabic. When starch is boiled with water containing a few per cent, of sulphuric acid, it is first converted into dextrin, then into glucose. It is generally considered that the dextrin is formed by a simple molecular transformation of the elements of the, starch, and that the glucose is then produced by the simple fixation of one molecule of water. C 6 H l0 O 5 _|_ JJ2Q _ C 6 H 12 6 Starch. Glucose. According to Musculus, this is not the case ; but soluble starch is the result of a metameric transformation of starch, and subsequently is converted into dextrin and glucose by a true decomposition. C i8 H 3o i5 _|_ H 2 _ c i2 H 20 O 10 C 6 H 12 6 Starch. Dextrin. Glucose. By the prolonged action of the acid, the dextrin itself is converted into glucose. The transformation of starch into dextrin and saccharine matter (maltose) takes place easily under the influence of a peculiar ferment which is developed in grain during germina- tion, and to which the name diastase has been given. It may be obtained by precipitating aqueous extract of malt by alcohol. If starch be triturated with one and a half times its weight of concentrated sulphuric acid, avoiding an elevation of tem- perature, and the mixture be left to itself for half an hour and alcohol then added, a substance is precipitated which is soluble in water and assumes a rich blue tint by the action of iodine. It is soluble starch (Bechamp). Starch dissolves abundantly in monohydrated nitric acid, and water precipitates from this solution a white substance, which, after washing and drying, constitutes xyloidin. It is mononitro- starch, and results from the substitution of a group NO 2 , for one atom of hydrogen in starch. C 6 H io 5 _|_HN0 3 = H 2 + C 6 H 9 (N0 2 )0 5 Starch. Xyloidin. Xyloidin burns with deflagration when heated to 180°. INULIN — GLYCOGEN — GUMS. 637 INULIN. C 6Hio05 This body also is largely diffused throughout the vegetable kingdom. It exists in the roots of the elecampane (Inula helenium), chicory, and Spanish chamomile, in the bulbs of eolchicuni, the tubers of the dahlia, in the Jerusalem arti- choke, etc. It may be extracted from the tubers of the dahlia by reducing them to a pulp and washing the latter in a sieve under a stream of water. The milky liquid which passes through deposits the inulin, which consists of granules analo- gous to those of starch. It swells in cold water, in which it is very slightly soluble. It is very soluble in boiling water, which again deposits it in a pulverulent form on cooling. The aqueous solution turns the plane of polarization to the left. It is not colored blue by iodine, which communicates to it a fugitive, yellow-brown tint. By long boiling with water, or by the action of dilute acids, inulin is converted into levulose. GLYCOGEN. Q6H10Q5 This body, isomeric with cellulose and starch, exists in the animal economy. Claude Bernard discovered it in the liver, and afterwards in the placenta. It exists also in many organs during the foetal life. Nearly pure glycogen may be obtained by adding a large quantity of crystallizable acetic acid to a cold and concentrated decoction of liver. It is also precipitated when alcohol is added to an aqueous decoction of liver. In a pure state, it is a white, amorphous powder. When dried in the air, it has the composition C 6 H 12 6 (E. Pelouze). At 100° it loses one molecule of water. AYith water it forms an opalescent liquid. Alcohol and ether do not dissolve it. Boiling with dilute acids converts it into glucose. Iodine communicates to it a violet or brown-red color. GUMS. By the names gums and mucilages are understood certain substances existing everywhere in the vegetable kingdom, and which dissolve or swell up in water, giving a mucilaginous 54 638 ELEMENTS OF MODERN CHEMISTRY. consistence to the liquid. The gums proper are distinguished from the mucilaginous substances, which are not really soluble. Both furnish mucic and oxalic acids when treated with nitric acid. Gum furnishes at the same time a small quantity of tartaric acid. Gum Arabic. — Gum arabic is identical with Senegal gum. It flows naturally from different species of acacia. It dissolves abundantly in cold water and is precipitated from its solution by alcohol. Fremy considers that it is composed essentially of the calcium and potassium salts of an acid which he designates as gummic acid (arabiri). When dried at 100°, the latter body has the composition indicated by the formula C 12 H 22 O n . It is very soluble in water, and its solution rotates the plane of polarization to the left, When heated to 120-150°, it becomes insoluble in water and is converted into metagummic acid. According to Fremy, the gum of cherry- and plum-trees is a mixture of gummates, which are soluble in cold water, and insoluble metagummates. The metagummates are insoluble in water, but when boiled with that liquid are transformed into soluble gummates. Subacetate of lead forms an abundant white precipitate in solutions of gum arabic. When gum arabic is boiled with dilute sulphuric acid, it is converted into a mixture of two saccharine substances ; one is uncrystallizable, the other crystallizes in large, colorless rhombic prisms, having a sweet taste, and fusible at 160°. It is called arabinose. It reduces the cupro-potassic solution and is not fermentable. It is isomeric with glucose (page 621). Gum Tragacanth. — This gum flows from the Astragalus of the Levant and of Persia. Bassora gum is derived from a spe- cies of cactus. Both contain a mucilaginous matter insoluble in water, but which swells up in that liquid, forming a transparent jelly. This matter is bassorin. With nitric acid, it yields much mucic acid. When boiled with dilute sulphuric acid, it is readily converted into crystallizable glucose. CELLULOSE. Q6H10O5 This name is given to the matter which forms the walls of young vegetable cells, and which is deposited, mixed with other CELLULOSE. 639 matters, in the older cells, particularly in ligneous fibre. The pith of the elder and of JEschynomene jpaludosa, cotton, old linen, and paper are almost pure cellulose. In ligneous fibres, in wood, the cellulose is permeated by various foreign substances, among which Payen has distin- guished the inc m sting matter which thickens the tissues and gives them rigidity. Among the others are nitrogenous mat- ters, resins, "various coloring matters, etc. With these organic- substances in the ligneous fibres, are united the mineral ele- ments which are found more or less modified in the ashes. Old linen and cotton serve for the preparation of pure cellulose. Such materials are boiled with a weak solution of potassium hydrate, washed, and successively exhausted with a solution of chlorine, acetic acid, alcohol, ether, and water, and dried at 100°. The insoluble product which remains after this treatment is considered as pure cellulose. Properties. — Cellulose is a diaphanous, white solid, of a density of 1.25 to 1.45. It is insoluble in water, alcohol, ether, and the dilute acids and alkalies. It dissolves in the cupro-ammoniacal liquid which is obtained by dissolving cupric hydrate or carbonate in a small quantity of concentrated am- monia, or better, by dissolving metallic copper in ammonia in contact with the air (Schweizer). When submitted to dry distillation, cellulose leaves a residue of carbon and yields numerous gaseous and liquid products. The gas obtained by the distillation of wood is used for illu- minating purposes in some localities. The liquid product ordinarily separates into two layers, one of which is aqueous and contains acetic acid, wood-spirit, acetone, etc. ; the other is insoluble in water and constitutes icood-tar. When cellulose, charpie for example, is sprinkled with con- centrated sulphuric acid and the mass is rapidly triturated, a viscous mass, having but little color, is obtained ; it contains, independently of a compound of sulphuric acid and cellulose (sulpho-ligneous acid), substances which result from the dis- integration of the cellulose. Accordingly, as the action of the acid is more or less prolonged, a substance is obtained which is insoluble in water and colored blue by iodine and consequently analogous to starch, or a soluble matter analogous to dextrin (Bechamp). When water is added to this viscous mass and the whole is submitted to a prolonged ebullition, fermentable glucose is formed (Braconnot). 640 ELEMENTS OP MODERN CHEMISTRY. C 6 H 10 O 5 _|_ H2Q __ C 6 H 12 6 Cellulose. Glucose. When paper is dipped into a cold mixture of sulphuric acid with half its volume of water, and is then carefully washed and dried, a semi-transparent matter is obtained which has a certain rigidity, and is similar to parchment in aspect (Figuier and Poumarede, Hofmann). It is called vegetable parchment. A cold solution of chloride of zinc converts cellulose into an amyloid matter which is colored blue by iodine ; if heat be applied, the whole is dissolved and glucose is formed. When charpie is heated with a concentrated solution of cal- cium hypochlorite (chloride of lime), a very violent reaction takes place, and torrents of carbon dioxide are evolved. If cellulose be heated to 180° with acetic anhydride it is converted into the triacetin, C 6 H 7 2 (C 2 H 3 2 ) 3 , an amorphous mass soluble in acetic acid. Gun-Cotton. — When carded cotton is immersed for half a minute in monohydrated nitric acid, and then rapidly washed in a large quantity of water and allowed to dry in the air, a substance is obtained which possesses all the exterior appear- ances of cotton, but is very inflammable and burns suddenly without residue. It is gun-cotton, or pyroxylin, which was discovered by Schonbein in 1847. In its preparation, the monohydrated nitric acid may be advantageously replaced by a mixture of one volume of fuming nitric acid and three volumes of sulphuric acid. Pyroxylin seems to be a mixture of dinitrocellulose and trinitrocellulose. C 6 H io 5 C 6 H 8 3 (0-N0 2 ) 2 C 6 H 7 2 (0-N0 2 ) 3 Cellulose. Dinitrocellulose. Trinitrocellulose. These bodies are true nitric ethers, analogous to nitro- glycerin. Alkalies decompose them into an alkaline nitrate and cellulose. Gun-cotton looks like cotton, but is more harsh to the touch and sometimes has a light yellowish tint. It burns with a sudden flash, leaving no residue, and produces a great volume of gaseons products consisting of carbon monoxide, carbon dioxide, nitrogen dioxide, etc., and vapor of water. Gun-cotton is insoluble in water, alcohol, ether, chloroform, and the cupro- ammoniacal solution. It is more or less soluble in a mixture of alcohol and ether, and the solution is employed in surgery and photography under the name collodion. Pure trinitrocellulose is, however, insoluble in alcoholic ether. When pyroxylin is GLUCOSIDES. 641 heated with a concentrated solution of ferrous chloride, ni- trogen dioxide is disengaged, and cellulose is regenerated (Bechamp). GLUCOSIDES. The glucosides are complex compounds, which break up under various conditions, fixing the elements of water and yielding glucose and other bodies, just as the compound ethers, in fixing the elements of water, are decomposed into alcohols and acids. This definition seems to relate the glucosides to the com- pound ethers, a relation with seems legitimate, since it has been shown by the experiments of Berthelot that glucose has the function of a polyatomic alcohol. Various immediate principles of vegetable origin can be classed as glucosides. We may mention particularly the fol- lowing : GLUCOSIDZS. FORMULAS. ORIGIN. Amygdalin .... C 20 H 27 NO n bitter almonds. Salicin C 13 H 18 7 willow and poplar bark. Populin C 20 H 22 O 8 bark and leaves of the aspen. Phloridzin .... C 21 H 24 10 bark and roots of fruit-trees. Arbutin C 12 H 16 7 leaves of the Arctostaphylos uva wsi Convolvulin. . . . C 31 H^0 16 ) . ian '.. Jalappin CS^HseO" J J ala P- root - Esculin C 21 H 2 K) 13 bark of India chestnut. Fraxin C 27 H 30 O 17 bark of the ash. Daphnin C 31 H 34 19 Daphne alpina, Daphne mezereum. Quinovin C 30 H 48 O 8 bark of China nova. Quereitrin .... C 36 H 38 20 bark of Quercus tinctoria (quercitron). Tannin C 27 H 22 17 oak-bark, nut-gall, etc. Among all of these bodies, we will only consider amygdalin, salicin, populin, phloridzin, and tannin, or tannic acid. Amygdalin, CfflEPNO 11 . — This body is extracted from the cake of bitter almonds, and it deposits from its alcoholic solu- tion in crystals containing two molecules of water. Its aqueous solution allows it to crystallize in quite large crystals contain- ing three molecules of water. Amygdalin is very soluble in water and in boiling alcohol. Its aqueous solution rotates the plane of polarization to the left. • By the action of dilute acids amygdalin is decomposed into hydrocyanic acid, benzoyl hydride, or benzoic aldehyde (oil of bitter almonds), and glucose. 54* 642 ELEMENTS OF MODERN CHEMISTRY. ] 20 H 2 'NO U -|- 2H 2 = = C'H 6 + CHN + 2C 6 H 12 6 Amygdalin. Benzoic Hydrocyanic Glucose. aldehyde. acid. The same decomposition takes place by the action of water and a peculiar ferment which is contained in both bitter and sweet almonds, and which is called emulsin, or synaptase. It is a nitrogenized matter, soluble in water, and only acts on amygdalin in presence of water. It is well known, indeed, that bitter almonds only develop the odor of prussic acid when moistened with water. Salicin, C 13 H 18 7 . — Salicin exists already formed in the bark of the willow and poplar. Wbhler discovered its existence in castor eum. It may be prepared by exhausting willow-bark with boiling water, concentrating the liquid and digesting it with litharge. The solution is then filtered and evaporated to a syrupy consistence ; the salicin deposits in a few days. It occurs in small scales, or brilliant needles, soluble in water and alcohol and insoluble in ether. Its aqueous solution turns the plane of polarization to the left. Salicin dissolves in sulphuric acid, forming a red liquid. By the action of a solution of emulsin (the nitrogenous mat- ter of almonds), it breaks up into a neutral body called salige- nin, and glucose. C 13 H 18 7 __|_ JJ2Q _ C 7 H 8 2 + C 6 H 12 6 Salicin. Saligenin. Glucose. Dilute sulphuric and hydrochloric acids decompose it by the aid of heat into saliretin and glucose. These bodies will be described farther on. When salicin is fused with potassium hydrate, hydrogen is disengaged, and salicylic and oxalic acids are formed. By the action of a mixture of potassium dichromate and sulphuric acid, salicin yields carbon dioxide, formic acid, and an oxidized oil, which is the hydride of salicyl or salicylic alde- hyde, C 7 H 6 2 (Piria). Populin, C 20 H 22 O 8 + 2H 2 0.— Braconnot discovered this sub- stance in the bark and leaves of the aspen (JPopulm trenmla). To extract it, those substances are exhausted with boiling water, the decoction is precipitated by subacetate of lead, filtered, and" the filtrate evaporated to a syrupy consistence. On cooling, the populin is deposited as a crystalline precipitate. When properly purified, it occurs in very fine, silky, colorless needles. GLUCOSIDES. 643 Its taste is sweet ; it is but slightly soluble in water, more soluble in alcohol. By the action of dilute acids, it is decom- posed into benzoic acid, saliretin. and glucose ; the latter two products result from the decomposition of salicin. so that popu- lin appears to be a combination of benzoic acid and salicin. C"H a O ! + IPO = C : H 6 2 + C 13 H 18 7 Populin. Benzoic acid. Salicin. Phloridzin, C 21 H 24 10 + 2H 2 0.— This substance exists in the bark of apple, pear, plum, and cherry trees, and principally in the roots of fruit-trees. It may be extracted by boiling the roots with water, decanting the boiling solution, concentrating it. and allowing it to stand in a cool place. The phloridzin deposits on cooling, and may be purified by recrystallization after decolorizing it with animal charcoal. When pure, it forms colorless, silky needles, having a bitter taste, and an after-taste which is sweet. It is scarcely soluble in cold water, but dissolves abundantly in boiling water and in alcohol. The alcoholic solution turns the plane of polariza- tion to the left. Dilute sulphuric and hydrochloric acids decompose it into phloretin and glucose. C 21 H 2i 10 + H 2 = C 15 H u 5 + C 6 H 12 6 Phloridzin. Phloretin. Glucose. Phloretin is a white substance which crystallizes in little scales, slightly soluble in water and very soluble in alcohol. When phloretin is heated with potassium hydrate, it breaks up into phhretic acid and pMoroglucin. C i5 H u o _j_ h 2 0= C 9 H 10 O 3 + C 6 H 6 3 Phloretin. Phloretic acid. Phloroglucin. Phloroglucin forms large crystals having a sweet taste. Tannin, or Tannic Acid, C 27 H 22 17 . — The names tannins and tannic acids are applied to certain slightly acid compounds which are largely diffused in the vegetable kingdom, and which have two important properties : they precipitate solutions of gelatin and albuminous matters, and produce a bluish or greenish-black color with the ferric salts. The most important of these compounds, the tannin of oak bark, or ijuereitannic acid, is a glucoside. By the action of dilute acids it is decom- posed into gallic acid and glucose (Strecker). Tannin exists in oak bark, in sumac, and in large quantities 644 ELEMENTS OF MODERN CHEMISTRY. in nut-galls, which are excrescences developed by the sting of an insect on the leaves and branches of the Quercus infectoria. It is prepared by introducing coarsely-powdered nut-galls into a percolator, and exhausting them with ordinary commercial ether. The ethereal solution which passes through is collected in a flask, and in the course of a day separates into two or sometimes three layers. The lower layer is a very concen- trated, aqueous solution of tannin. It is separated and dried in a hot-air oven. The tannin remains as a light, bulky mass, having a yellowish color. Tannin is a colorless, amorphous solid, having a very astrin- gent taste. It is very soluble in water, less soluble in alcohol, insoluble in pure ether. It melts when heated, and between 210 and 215° it dis- engages carbon dioxide and yields pyrogallol, C 6 H 6 3 , which volatilizes. A black residue remains (jnetagallic acid). On contact with the air, the aqueous solution of tannic acid absorbs oxygen, disengages carbon dioxide, and deposits gallic acid. This transformation takes place more rapidly when oak tannin is boiled with dilute sulphuric or hydrochloric acid. C 27 H 22Q17 _|_ 4JJ2Q _ 3C 7 H 6 5 + (^EPO 6 Tannin. Gallic acid. Glucose. The researches of H. Schiff seem to show that tannin, prop- erly speaking, is not a glucoside but is digallic acid, C u H 10 O 9 , that is, an acid derived from two molecules of gallic acid by the subtraction of one molecule of water. By fixing the elements of water, a molecule of tannin would form two molecules of gallic acid. C i4 H io 9 + H 2 _ 2C 7 H 6 5 Digallic acid. Gallic acid. A solution of tannic acid produces with ferric salts a bluish- black precipitate, which constitutes ink. Tannin does not color ferrous salts, but the mixture soon blackens on exposure to the air by absorbing oxygen. Tannin is employed in medicine as an astringent. Nut-galls, which are very rich in tannin, are used for the manufacture of ink. A good ink may be prepared by the following receipt: One kilogramme of powdered nut-galls is exhausted with 14 litres of water ; the solution is filtered, and a solution of 500 grammes of gum arabic is first added, then a solution of 500 grammes of ferrous sulphate (green vitriol). The mixture is well stirred up> and then exposed to the air until it has acquired a fine black color. ACIDS DERIVED FROM THE SACCHARINE BODIES. 645 ACIDS DERIVED FROM THE SACCHARINE BODIES. Two isomeric acids, gluconic and lactonic acids, result from the oxidation of glucose and lactose by silver oxide and chlorine water. C 6 H 12 6 + = C 6 H 12 7 gluconic, and lactonic acids. These acids are not crystallizable. and occur as thick syrups. They are monobasic. Two dibasic acids. C 6 H 10 O 8 , saccharic and mucic acids, are formed, the first by the oxidation of mannite, glucose, sac- charose, etc.. by nitric acid, the second by the oxidation of dulcite, lactose, and galactose by the same reagent. Saccharic acid is uncrystallizable, and constitutes a syrupy, very acid mass. The relations between glucose and these acids may be expressed by the following formula : CH 2 .OH CH^.OH CO. OH (CH.OH)* (CH.OH;4 (CH.OH)* CHO CO.OH CO.OH Glucose. Gluconic acid. Saccharic acid. MUCIC ACID. C 6 H 10 O 8 This acid, which was discovered by Scheele, is prepared by heating one part of lactose with two parts of nitric acid of density 1.4. As soon as red vapors appear, the mixture is allowed to cool, a/id afterwards re-heated until no more red vapors are disengaged. Mucic acid separates as a white, crystalline powder. It is almost insoluble in alcohol and cold water ; dissolves in 60 parts of boiling water. At 210° it fuses with partial de- composition. By long boiling with water, it is converted into an isomeride. paramucic acid. When boiled with nitric acid, it yields paratartaric and oxalic acids. Pyromucic acid, C 5 H 4 3 . — By dry distillation, mucic acid loses the elements of water and carbon dioxide, and is con- verted into the pyrogeuous pyromucic acid. C 6 H 10 O* = OTBPO 3 -f 3H 2 + CO 2 Pyromucic acid forms small needles or scales, soluble in alcohol and in hot water. It fuses at 134 . Its aqueous solution is colored green by ferric chloride. Pyromucic acid is monobasic. When treated by bromine 646 ELEMENTS OF MODERN CHEMISTRY. and water, it is oxidized into fumaric acid (page 598), carbon dioxide being disengaged. C 5 H 4 3 + Br 2 + H 2 _ c 4 H*0 4 + CO 2 + 2HBr Pyromucic Fumaric acid, acid. PECTIC MATTERS. These bodies, of which the constitution is still obscure, are largely diffused in the vegetable world, notably in fleshy fruits and in many roots. They all gelatinize with water. Among them we can only mention pectin, which exists in ripe fruit, in which it is formed by the action of a ferment on an insoluble body called pectose (Fremy). It may be obtained from ripe pears by precipitating the juice by oxalic acid, which removes the calcium. The filtered liquid is treated with tannin, which separates the albuminoid matters, and from the new filtrate alcohol will precipitate the pectin in long, gelatinous filaments. After drying, it forms an insipid, amorphous mass, soluble in water. It is precipitated from its solution by alcohol and by basic lead acetate. By alkalies, and by a peculiar ferment, called pectose, that may be separated from the juice of carrots by the addition of alcohol (Fremy), pectin is converted into gelatinous acids, pectosic acid, C 32 H 40 O 28 -f~ 3H 2 0, and pectic acid. AROMATIC COMPOUNDS. The compounds which we have studied thus far are rich in atoms of hydrogen. Most of them are saturated or derived from saturated compounds. The hydrocarbons of the series C n H 2n+2 , the alcohols C n H 2n+2 0, the fatty acids C n H 2n 2 , are of these classes of compounds the most rich in hydrogen that are known ; they belong to what is called the fatty series. But there are other compounds which possess, like the preceding, the characters of hydrocarbons, alcohols, and acids, in. which the relation between the atoms of carbon and of hydrogen is not the same. The atoms of the latter element decrease in num- ber in proportion to those of the former. These relations may be understood by a glance at the following formulae : CJIOH22 decane. C 10 H 22 O decyl hydrate. CIOH20 decylene. C 10 H 20 O mint camphor. C 10 H 18 menthene. C^H^O Borneo camphor. C 10 H 16 turpentine. C 10 H 16 O ordinary camphor. C 10 H U cymene. C 10 Hi 4 O thymol. C 10 H 8 naphthalene. C 10 H 12 O cuminic aldehyde. ■ AROMATIC COMPOUNDS. 647 A large number of these unsaturated compounds belong or are related to those aromatic substances which are called essences or essential oils. Hence the name aromatic com- pounds, which has been given to all of these bodies containing but little hydrogen. The most interesting of the hydrocarbons of the aromatic series is benzol, which is now obtained in large quantities from coal-tar. It is as important by reason of the applications which it has received in the arts as on account of the theoretical con- siderations which attach to it. Kekule has made it the centre of the aromatic series which would include, in a limited sense, only the derivatives of benzol. In a word, the latter body is the nucleus of all the aromatic compounds. While benzol is not a saturated hydrocarbon, it resembles the latter compounds in that, excepting a few cases, it forms other compounds only by substitution of other atoms or groups for its atoms of hydrogen. This curious property will be better understood when some of these substitution compounds shall have been explained, and we consider the constitution of benzol. Very numerous and very different aromatic compounds are derived by the substitution of different elements or groups for the hydrogen atoms in the molecule of benzol, that molecule forming, so to speak, the nucleus of all the aromatic com- pounds. 1. The hydrogen of benzol may be readily replaced by chlo- rine, bromine, etc., by which monochlorobenzol, monobromo- benzol, dichlorobenzol, etc., are obtained. C 6 H 6 C 6 H 5 C1 C 6 H 5 Br Benzol. Monochlorobenzol. Monobromobenzol. 6 H 4 C1 2 C 6 H 4 Br* Dichlorobenzol. Dibromobenzol. These chlorides and bromides are. analogous to the corre- sponding compounds of the fatty series, but the chlorine or bromine is much more strongly combined with the benzol nucleus, and cannot be exchanged by double decomposition, as is the case with ethyl bromide and ethylene bromide, etc. 2. By treatment with strong nitric acid, the hydrogen of benzol may be replaced by one or more groups (NO 2 ), forming the following compounds. C 6H6 C 6 H5-X02 c6H *;£ C 6 H 3 fOH OH x 0H Phenol. Oxyphenol Dioxyphenol (resorcine and isomerides). (phloroghicin and isomerides). 6. If one or more atoms of hydrogen in benzol be replaced by as many methyl groups, CH 3 , the superior homologues of benzol are obtained. AROMATIC COMPOUNDS. 649 C 6 H6 = C 6 H 6 benzol. C 7 H 8 = C 6 H 5 -CH 3 toluol (methylbenzol). C 8 H 10 = C 6 H*<^! xylol and isomerides (dimethylbenzols). S CH 3 C 9 H 12 = C 6 H 3 — CH 3 mesitvlene and isomerides (triinethylbenzols). ^CH 3 Oi2Hi8 = C(CH 3 ) 6 hexamethylbenzol. One ethyl group can replace one atom of hydrogen in ben- zol, and ethylbenzol, which is isomeric with dimethylbenzol, would result. C6H3-C 2 H*. C«H*<™3 Ethylbenzol. Dimethylbenzol. There are many instances of such isomerism, and they re- ceive the same interpretation. One atom of hydrogen in benzol may be replaced by a propyl group, C 3 H 7 , and propyl benzol, which is isomeric with trimethyl- benzol, is the result. One atom of hydrogen may be replaced by an ethyl group and another by a methyl group, and the new compound would be ethyl-methylbenzol, isomeric with propylbenzol and with tri- methylbenzol. C6H5-C 3 H? C«H* 0, menthol. Kekule* considers camphol and borneol as derivatives of cymene, an aromatic hydrocarbon which is methyl-propyl-benzol, CAMPHORIC ACID — BENZOL. 663 CH 3 C 6 H 4 < p 3 „ 7 . The following formula will explain this derivation : CH 3 CH 3 CH 3 CH 3 C C C . C HC CH HC CH HC CH.OH HC CO HC CH HC C.OH H 2 C CH2 H 2 C CH 2 C C HC HC C 3 H 7 C 3 H 7 C 3 H" C 3 H" Cyrnene. Thymol. Borneol. Caraphol. CAMPHORIC ACID. CWH 1 60*= C 8 H^<££ ^ This acid, which has long been known, is obtained by the prolonged boiling of camphor with dilute nitric acid. The camphor, which at first floats as an oily liquid, at last disappears, and camphoric acid deposits as the solution cools. It is puri- fied by dissolving it in a solution of an alkaline hydrate and precipitating with hydrochloric acid. Camphoric acid crystallizes by the cooling of its hot aqueous solution in colorless plates. It is only slightly soluble in cold water, but quite soluble in alcohol. It melts at 187°, and if heated above its fusing-point loses a molecule of water, and CO becomes converted into camphoric anhydride. C s H u <^p^>0, which sublimes in brilliant needles, fusible at 217°. Camphoric acid is dibasic ; its calcium salt yields by dry distilla- tion the compound camphorone, C 9 H u O, a liquid boiling at 208°. CaC 10 H u O 4 = CaCO 3 -f C 9 H u O Calcium campkorate. Camphorone. BENZOL AND ITS DERIVATIVES. BENZOL. C 6 H<5 This important body was discovered in 1825 by Faraday. Mitscherlich obtained it by heating benzoic acid with an excess of lime. C 7 H 6 2 = CO 2 + C 6 H 6 Benzoic acid. BeDzol. 664 ELEMENTS OF MODERN CHEMISTRY. It is now obtained in large quantities from coal-tar by dis- tilling the latter body. The more volatile products contain the benzol, which is purified by fractional distillation. That which passes below 85° is principally benzol, and the latter crystal- lizes out when the liquid which passes between 80 and 85° is cooled to — 5°. The crystals are collected and separated by expression from the product remaining liquid. They constitute pure benzol.* Berthelot has recently made the direct synthesis of benzol by exposing acetylene to a temperature near redness. 3C 2 H 2 = C 6 H 6 Acetylene. Benzol. Benzol is a colorless, strongly refracting liquid. At 0°, it solidifies to crystals which melt at 5.5°. It boils at 80.5°. It is insoluble in water, but dissolves in alcohol and ether. It is inflammable, and burns with a bright, smoky flame. When benzol vapor is passed through a red-hot tube, diphenyl, C 12 H 10 , is formed. 2C 6 H 6 = C 6 H 5 -C 6 H 5 + H 2 When long agitated with fuming, or even ordinary sulphuric acid, it dissolves, forming phenylsulphurous acid. C 6 H e + H 2 g0 * _ H 2 + c 6 H 5 .S0 3 H Phenylsulphurous acid. When heated to 275 or 280° for twenty-four hours with 80 to 100 parts of concentrated hydriodic acid, benzol is converted into hexane, C 6 H 14 , iodine being set free. CHLORINE AND BROMINE DERIVATIVES OF BENZOL. By the action of chlorine or bromine on benzol, two sorts of derivatives are obtained, — addition compounds and substitution compounds. Addition Compounds. — Two, four, or six atoms of chlorine may combine directly with benzol, forming the compounds Benzol dichloride, C 6 H 6 C1 2 ; Benzol tetrachloride, C 6 H 6 C1 4 ; Benzol hexachloride, C 6 H 6 C1 6 . The last is easily formed by the action of an excess of chlo- rine on benzol exposed to direct sunlight. It crystallizes in brilliant plates. There is a corresponding hexabromide, formed * Benzol must not be confounded with the benzine derived from petro- leum, which is a saturated hydrocarbon. CHLORINE AND BROMINE. 665 in the same manner. Boiling potassium hydrate removes the elements of three molecules of hydrochloric acid from benzol hexachloride, converting it into trichlorobenzol. C 6 H 6 C1 6 = 3HC1 + C 6 H 3 CP Substitution Compounds. — These compounds are numer- ous, and present interesting examples of isomerism. Only the monochloro-, pentachloro-, and hexachloro- derivatives have no - isomerides. Monochlorobenzol or phenyl chloride, C 6 H 5 C1, is prepared by passing chlorine through benzol in the presence of a small quantity of iodine. It is also formed by the action of phos- phorus pentachloride on phenol : hence the name phenyl chlo- ride. C 6 H 5 .OH + PCI 5 = HC1 + POC1 3 + C 6 H 5 C1 It is a colorless, strongly refracting liquid, having a pleasant odor, and boiling at 132°. Dichlorobenzols, C 6 H 4 C1 2 . — There are three isomerides :— Ortho-dichlorobenzol, C 6 H 4 4 <, is readily formed by the 56* 666 ELEMENTS OF MODERN CHEMISTRY. action of an excess of bromine on benzol. It crystallizes in beautiful prisms, fusible at 89°. It boils at 218°. NITRO-DERIVATIVES OF BENZOL. Nitrobenzol, C 6 H 5 (N0 2 ). — If benzol be poured in small portions into nionohydrated nitric acid, and water be added to the mixture, an oily, yellow liquid separates, constituting nitro- benzol. C 6 H 6 + HNO 3 = H 2 + C 6 H 5 (N0 2 ) It is benzol in which one hydrogen atom is replaced by the group (NO 2 )'. Nitrobenzol is a yellowish liquid, having a strong odor of bitter almonds. It boils at 205°, and solidifies at 3°. It is employed in perfumery under the name essence of Mirbane. By the action of reducing agents, such as hydrogen sulphide, ammonium sulphide, tin and hydrochloric acid, or iron-filings and acetic acid, nitrobenzol is converted into aniline or phenyl- amine. C 6 H 5 (N0 2 ) + 3H 2 = 2H 2 + C 6 H 5 (NH 2 ) Nitrobenzol. Aniline. Dinitrobenzols, C 6 H 4 (N0 2 ) 2 . — The three isomerides are formed when benzol is treated with a large excess of a mixture of nitric and sulphuric acids. The nitro-compounds separate on the addition of water, and are purified by crystallization in alcohol. Metadinitrobenzol separates first, crystallizing in long colorless needles, fusible at 89.9°. Reducing agents convert it successively into nitrophenylamine and phenylene-diamine. C«HV N ° 2 ( 1 ) CH^ N ° 2 ^ C 6 H^ NH2 « ^ n ^N0 2 ( 3 ) ^ n ^NH 2 ( 3 ) ° n ^NH 2 ( 3 ) Metadinitrobenzol. Metanitrophenylamine. Dipheuylene-diamine. AZO-DERIVATIVES OF BENZOL. Besides aniline, there are other products of the reduction of nitrobenzol, and they are of great importance, for they have become types of numerous analogous compounds. The first was described in 1834, by Mitsiherlich, under the name of azobenzide or azobenzol. Azobenzol, C 12 H 10 N 2 , is obtained by the action of sodium amalgam on an alcoholic solution of nitrobenzol. rt6TT5 M 2C 6 H 5 .N0 2 + 4H 2 = 4H 2 + C 6 H 5 .N AZO-DERIVATIVES OF BENZOL. 667 Azobenzol forms large red crystals, fusible at 66.5°. It boils at 293°. It is only slightly soluble in water, but dissolves readily in alcohol and ether. Azoxybenzol, C 12 H 10 NO. — This compound, which is a product of the incomplete reduction of nitrobenzol, was dis- covered by Zinin. It is formed by boiling an alcoholic solution of potassium hydrate with nitrobenzol. Under these conditions the alcohol is oxidized by the oxygen of the group NO 2 . 2C 6 H 5 .N0 2 + 3H 2 = 3H 2 + ™^>0 Azoxybenzol. Azoxybenzol crystallizes in long needles, soluble in alcohol and ether, insoluble in water. It melts at 36°, and is decom- posed when distilled. If heated with iron filings, it becomes converted into azobenzol. Hydrazobenzol, C 12 H 12 N 2 . — Alcoholic solutions of reducing agents, such as hydrogen sulphide, stannous chloride (tin and hydrochloric acid), convert azobenzol into hydrazobenzol. II + H2 = I C 6 H5-N C6H5-NH Azobenzol. Hydrazobenzol. The latter body crystallizes in tables, fusible at 131°, almost insoluble in water but soluble in alcohol and ether. When submitted to dry distillation, it breaks up into azobenzol and aniline. rC'H^.H OV.N (C'ffN.H C 6 H 5 .N ^ Hydrazobenzol. Azobenzol. Aniline. Acids convert hydrazobenzol into a basic isomeride, benzidine. C 6 H 5 N.H C 6 H*.NH 2 C 6 H s kH 6 6 H*.NH 2 Hydrazobenzol. Benzidine. Hydrazobenzol may be considered as derived from the group NH 2 i , which is called hydrazine, and which would be the radi- cal amidogen, NH 2 , united with another like group. Hydra- k t -j-i ;w • NH(C 6 H 5 ) zobenzol is a diplienyl-fiydrazine : i XTT ^ TT / r * * NH(C 6 H°). 668 ELEMENTS OF MODERN CHEMISTRY. PHENYLSULPHUROUS ACID. C 6 H&-S0 2 .OH Acids formed by the substitution of one or more groups (S0 2 .OH)' for one or more atoms of hydrogen in the aromatic nuclei are called sulphones or sulphonic acids. Indeed, the hydrogen of these nuclei exerts a reducing action on sulphuric acid, from which it removes a hydroxyl group, forming a mole- cule of water. The residue, SO 2 . OH, is then substituted for the hydrogen atom : thus, pheuylsulphurous or benzolsulphonic acid is formed by the following reaction : C 6 H 6 + S0 2 0. — Anisol was first obtained by distilling anisic acid (page 698) with barium oxide or lime. C6H4 <2S.OH = CH3 5 >° + C ° 2 Anisic acid. Anisol. It may be prepared more readily by synthesis in the reaction of methyl iodide on potassium phenate. C 6 H 5 .OK + CH 3 I = KI + C 6 H 5 .OCH 3 It is a colorless liquid, having an ethereal odor. Its density at 15° is 0.991 ; it is insoluble in water, and boils at 152°. C 6 H 5 Ethylphenyl Oxide, or Phenetol, n2jj 3 >0, may be ob- 672 ELEMENTS OF MODERN CHEMISTRY. tained by a process analogous to the last method indicated for preparing anisol. It is an aromatic liquid, boiling at 172°. Phenylsulphuric Acid is analogous to ethylsulphuric acid. S ° 2 2^NH.C 6 H 5 L ° ^NH^H 5 ) — ZMU + LU< NH.C 6 H 5 Aniline oxalate. Oxanilide. ANILIDES. By the action of heat, the aniline salts lose the elements of water, and form compounds which are analogous to the amides, and which Gerhardt named anilides. When aniline acetate is heated, it is converted into acetanilide, which is no other than acetamide in which an atom of hydrogen is replaced by a phenyl group, (C 6 H 5 ). C2Q2< /NH2 C202 .NH.C6H5 u ^NH 2 C ° NH This body is derived from ammonia by the substitution of two phenyl groups for two atoms of hydrogen. It is formed in various reactions, of which the most interesting was discov- ered by Grirard and de Laire. It consists in heating aniline hydrochloride to 256° with aniline. Ammonia is disengaged, and diphenylamine hydrochloride is formed. DIAZOBENZOL COMPOUNDS. 677 C6H5) C 6 ff) C 6 H5) H } X.HC1 + H X = C 6 H* i N.HC1 + NH* Hj HJ Hj Free diphenylaniine forms crystals fusible at 54°. It boils at 310°. It is insoluble in water, but dissolves in alcohol, ether, benzol, and petroleum. Its odor recalls that of oil of rose. When heated with a mixture of oxalic and sulphuric acids, it yields a splendid blue color, soluble in water, and known as diphenylainine blue (Girard and de Laire). DIAZOBENZOL COMPOUNDS. Nitrous acid exerts an energetic action upon aniline and the analogous bases ; it is indicated here because it presents a great generality and gives rise to remarkable bodies, which are called diazo-comp>ounds. When a current of nitrous gas is passed into a saturated so- lution of an aniline salt, such as the nitrate, crystals of diazo- benzol nitrate are deposited. C 6 H T N.HN0 3 + HNO 2 = 2H 2 + C 6 H 5 N 2 .N0 3 Aniline nitrate. Diazobenzol nitrate. This body is formed by the substitution of one atom of nitro- gen for three atoms of hydrogen in aniline nitrate. C 6 H5-NH 2 .HN0 3 aniline nitrate. C 6 H 5 -X=X-(X0 8 ) diazobenzol nitrate. It forms long, colorless prisms, very soluble in water, slightly soluble in alcohol, and insoluble in ether. It explodes violently by heat or by percussion. Besides this nitrate, there are other compounds of diazobenzol. They all contain the diatomic group N=N, combined on one hand with phenyl, and on the other with chlorine, bromine, or an oxidized group. The following formulae will explain their constitutions. C 6 H 5 -X=X.C1 diazobenzol chloride. C 6 H 5 -X=X.Br diazobenzol bromide. C 6 H 5 -X=X.X0 3 diazobenzol nitrate. CeHS-X^X.SO^H diazobenzol sulphate. These compounds present several interesting reactions. 1. When heated with water, they disengage nitrogen, and are converted into phenols. C 6 H 5 N 2 N0 3 + H 2 _ c 6 H 5 .OH + N 2 + HNO 8 57* 678 ELEMENTS OP MODERN CHEMISTRY. 2. When they are boiled with absolute alcohol, they are re- duced to hydrocarbons, nitrogen being disengaged and the alcohol being transformed into aldehyde. C 6 H 5 N 2 .HSO + C 2 H 6 = C 2 H*0 + C 6 H 6 + N 2 + H 2 S0 4 Diazobenzol sulphate. Aldehyde. Benzol. 3. With auric and platinic chlorides, diazobenzol chloride forms double salts. When the platino-chloride is submitted to dry distillation, it yields chlorobenzol. (C 6 H 5 .N 2 .Cl) 2 PtCl 4 = 2C 6 H 5 C1 + N 2 + 2C1 2 + Pt 4. Diazobenzol bromide can fix two atoms of bromine, and the bromide so formed yields, on dry distillation, nitrogen, bromine, and bromobenzol. C 6 H 5 .N 2 Br 3 = C 6 H 5 Br + Br 2 + N 2 These reactions are complete, and invariably accompanied by the disengagement of a molecule of nitrogen, N 2 , and the for- mation of a substituted benzol. They show that the diazo- derivatives are substitution compounds of benzol : thus diazo- benzol chloride results from the substitution of the group (N 2 C1) for an atom of hydrogen in benzol. C 6 H 6 C 6 H 5 .N 2 .C1 Benzol. Diazobenzol chloride. Diazoamidobenzol. — When aniline is added to an aqueous solution of diazobenzol nitrate or chloride, a diazo-compound is obtained which is more complex than the preceding and is called diazo amido ben zol. C 6 H 5 N 2 (N0 3 ) + NH 2 .C 6 H 5 = C 6 H 5 -N 2 -NH.C 6 H 5 -f HNO 8 ■Diazobenzol nitrate. Aniline. Diazoamidobenzol. The same body is formed when a current of nitrogen tri- oxide is passed into a cooled alcoholic solution of aniline. It forms brilliant, golden-yellow scales, fusible at 91°. It ex- plodes at a higher temperature. If an alcoholic solution of diazoamidobenzol be left to itself, it undergoes a curious transformation, first noticed by Kekule. The diazo-compound is converted into an azo-derivative, amida- zobenzol. C 6 H 5_ N 2_ NH C e H 5 C 6 H 5 -N 2 -C 6 H 4 .NH 2 Diazoamidobenzol. Amidazobenzol. This change shows the difference existing between the azo- derivatives described on page 666, and the diazo-compounds. Both contain the diatomic group N=N, but in the former com- pounds it is related to two aromatic groups, while in the latter ROSANILINE. 679 it links together an aromatic group, and a monatomic atom or group. This may be understood from the following formulae : Azo-derivatives. Diazo-derivatives. C 6 H 5 -N 2 -C 6 H 5 C 8 H 5 -N 2 .C1 Azobenzol. Diazobenzolchloride. C 6 H 5 -N 2 -C 6 H 4 (NH 2 ) C 6 H 5 -N 2 -NH(C 6 H 5 ) Amidazobenzol. Diazoamidobenzol. The salts of diazobenzol react not only with aniline and the other primary and secondary aromatic amines, yielding diazo- amidobenzol and its analogues; they undergo analogous re- actions with other aromatic compounds, such as the phenols, naptyols, tertiary aromatic amines, metaphenylene-diamine, etc. These reactions invariably form azo- compounds, of which a large number are manufactured and used as dye-stuffs. An example is the action of diazobenzol nitrate on phenol, and on its sulpho- derivative, metaphenolsulphurous acid (page 674). C6H5-N2-N0 3 + C6H5.0H = C6H5-N 2 -C 6 H4.0H + HNO 3 Diazobenzolnitrate. Phenol. Azobenzol-phenol. C6H5-N 2 -N0 3 + C 6 H*J . — This body is formed when QUINONE. 685 para-iodophenol, C 6 H*° Phthalic acid. Phthalic anhydride. Phthalic anhydride crystallizes in long, brilliant prisms, fusible at 127-128°. It boils at 277°. It possesses a remarka- ble property, which was discovered by A. Baeyer, and which is now applied practically in the arts. When heated with the phenols, it combines with them directly with elimination of the elements of water, and compounds are obtained which are designated as phthaleins. Thus, when phthalic anhydride is heated with ordinary phenol, two molecules of phenol combine with one molecule of phthalic anhydride, with elimination of one molecule of water, and the phthalein of phenol is obtained. r6m<^ co ^o + c6H5 -°h _ r6m /CO-cw.oh „ 2n ^ ° + C6H5.0H -*■ C H ° = H2 ° + 2C 6 H5-CH=CH-CO.OH Benzoic aldehyde. Acetic anhydride. Cinnamic acid. The latter reaction, discovered by Perdrin, can be applied to the synthesis of other aromatic acids. Cinnamic acid is colorless and odorless. It crystallizes from hot water in fine needles, and from alcohol in large prisms. It melts at 133°. When rapidly heated, it distils almost without alteration at 290°. When distilled with lime, or heated to INDIGO. 709 200° with water, it is decomposed, yielding styrolene and carbon dioxide. C9H 8 2 = CO 2 + C 8 H* By fusion with potassium hydrate it is converted into acetic and benzoic acids. C6H5-CH=CH-CO.OH + 2KOH = C 6 H5-CO.OK + CH^-CO.OK + H 2 Concentrated nitric acid converts it into two isomeric nitro- cinnamic acids, C 9 H 7 (N0 2 )0 2 ; orthonitrocinnamic acid, fusible at 232°, and paranitrocinnamic acid, fusible at 265°. Cinnamic acid can fix directly two atoms of chlorine, bromine, or hydrogen, so forming saturated compounds. Sodium amal- gam converts it into hydrocinnamic or phenylpropionic acid, C 6 H 5 -CH 2 -CH 2 -CO.OH, a compound crystallizing in fine, colorless needles, fusible at 47.5°, and boiling at 280°. The following formula will show the relations between acrylic and propionic acids, on one hand, and on the other those between cinnamic and hydrocinnamic acids. CH 2 =CH-CO.OH CH 3 -CH 2 -CO.OH Acrylic acid. Propionic acid. CH(C 6 H 5 )=CH-CO.OH CH 2 (C 6 H 5 )-CH 2 -CO.OH Cinnamic acid. Hydrocinnamic acid. (Phenyl acrylic.) (Phenylpropionic.) The cinnamates resemble the benzoates. Ferric chloride produces a yellow precipitate in their solutions. INDIGO. C 16 H 10 N 2 O 2 . Indigo is obtained from different species of the genus Indi- gofera. The pastel, or woad (Isatis tinctorial), also furnishes a coloring matter identical with indigo. In India, indigo is prepared by macerating the stems and leaves of the indigofera, collected at the time of flowering, with water, in vats where they are allowed to ferment. In 12 or 15 hours the liquid is drawn off into other vats, where it is agitated so as to bring it in contact with the air, an opera- tion which occasions the formation of a blue precipitate. The brown liquor is then drawn off, and the deposit is boiled in copper vessels ; it is then pressed between cloths and cut into cubical pieces and dried. In this form the indigo is delivered to commerce. Indigo is not contained ready formed in the plants which 60 710 ELEMENTS OF MODERN CHEMISTRY. serve for its manufacture. Schunck considers that these plants contain a substance analogous to the glucosides, indican, which is decomposed by fermentation into indigo and indoglucin, C 6 H 10 O 6 . The indigo of commerce contains from 50 to 90 per cent, of coloring matter. It generally occurs in irregular masses, some- times cubical, of which the shade varies from violet-blue to blackish-blue. The most esteemed varieties present a brilliant coppery reflection. Pure indigo is called indigotine. It may be obtained by heating the indigo of commerce in a current of hydrogen, or by subliming it in small quantities between two watch-glasses (Chevreul). It then forms right rhombic prisms having four or six faces. Indigotine is insoluble in water, in cold alcohol, and in ether. Boiling alcohol and oil of turpentine dissolve it to a slight extent. When carefully heated, and in small quan- tity, it volatilizes, and its vapor density corresponds to the formula C 16 H 10 N 2 O 2 . Concentrated, or better, fuming sulphuric acid dissolves in- digo at 50 or 60°, forming a beautiful blue solution, which contains two acids, sidphindigotic acid, C 8 IPNO.S0 3 H, and sulpliopurpurlc acid, C 16 H 9 N 2 2 .S0 3 H. The solution of indigo in sulphuric acid is used in dyeing; it is prepared by dissolving indigo in a hot mixture of fuming and ordinary sulphuric acids. The blue solution thus obtained is known as sulphate of indigo, Saxon blue, or composition blue. Boiling dilute nitric acid converts indigo into isatin. The concentrated acid converts it first into nitrosalicylic acid, C 7 H 5 (N0 2 )0 3 , and then into picric acid. When heated with potassium hydrate, indigo is converted into anthranilic acid, C 7 H 5 (NH 2 )0 2 , or into salicylic acid, which is formed at the expense of the anthranilic acid. C 7 H 5 (NH 2 )0 2 + KOH = KCTEPO 3 + NH 3 Anthranilic acid. Potassium salicylate. When indigo is distilled with potassium hydrate, aniline passes over, being formed at the expense of the anthranilic acid first formed. C 7 H 7 N0 2 = CO 2 + C 6 H 7 N Anthranilic acid. Aniline. Synthesis of indigo. — Various reactions have recently been discovered which are applicable to the synthesis of indigo. INDIGO. 711 Most of thein are due to the researches of Baeyer. We can consider them only summarily. 1. Isatin chloride, which will be described farther on, when dissolved in acetic acid and treated with zinc dust yields a colorless liquid, which, when exposed to the air, assumes a blue color, and deposits crystals of indigotine. Ammouium sulphydrate effects the reduction more rapidly than zinc and acetic acid (Baeyer and Emmerling). 2. There exists normally in human urine a compound which may also be prepared artificially, indoxyl sulphate of potassium. When it is heated in the air, or treated with feeble oxidizing agents, it is converted into indigo (Baumann and Tiemann). Potassium indoxylsulphate, C 8 H 6 NO.S0 3 K, is a derivative of indoxyl, C s H 6 (OH)N, and the conversion of the latter into indigo is represented in the equation, 2C 8 H 6 (OH)N + O 2 = C 16 H 10 N 2 O 2 + 2H 2 Indoxyl. Indigo. 3. By the action of ozone, indol (page 714) yields indigo (Nencki). 4. Baeyer has more recently made a new synthesis of indigo from orthonitrobenzoic aldehyde, C 6 H 4 <^Q 2 . 2 y . This com- pound reacts with acetone, in presence of sodium hydrate, form- ing a compound, C 10 H 9 NO 3 , which contains the elements of acetone and orthobenzoic aldehyde, less one molecule of water. C 7 H 5 (N0 2 )0 + C 3 H 6 = C 10 H 9 (NO 2 )O + H 2 Orthobenzoic aldehyde. Acetone. Acetonic derivative of ortho- benzoic aldehyde. An excess of sodium hydrate converts this last body into acetic acid and indigo. 2C 10 H 9 NO 3 = C 16 H 10 N 2 O 2 + 2C 2 H 4 2 Baeyer's researches indicate that the molecular structure of indigo is expressed by the following formula : C 6 H 4 -CO CO-C 6 H 4 i iii HN C=C— NH White Indigo, C 16 H 12 N 2 2 .— This body, which was discov- ered by Chevreul in 1812, results from the action of nascent hydrogen on indigo. It is produced when the latter substance is submitted to the action of alkaline solutions in presence of reducing matters, such as sulphurous or phosphorous acid, hydrogen sulphide, iron, zinc, or ferrous or stannous hydrate. C i6 H io N 2 2 _j_ h 2 = C 16 H 12 N 2 2 712 ELEMENTS OF MODERN CHEMISTRY. White indigo is ordinarily prepared by introducing a mix- ture of indigo, ferrous sulphate, slaked lime, and water into a vessel, which should be entirely filled with the mixture and then hermetically sealed and allowed to stand for two days. A clear, alkaline solution is thus obtained, which is decanted, and supersaturated with hydrochloric acid, out of contact with the air. A deposit of white indigo is formed, and must be collected on a filter, rapidly washed with boiled water, and dried in a vacuum. The body thus obtained has a dirty-white color, and is with- out either taste or smell. It is insoluble in water, but dissolves with a yellow color in alcohol, ether, and alkaline solutions. On contact with air it absorbs oxygen, and is converted into blue indigo. Nitric acid rapidly brings about this transformation. Uses. — Indigo is largely used in dyeing. The principle of its application depends on the conversion of the blue indigo into white indigo by reducing agents. The reduced white indigo is soluble in alkaline solutions and in this form is fixed on the fabrics, after which it is reconverted into blue indigo by ex- posure to the air. The mixture just indicated for the prepara- tion of white indigo (ferrous sulphate, indigo, lime, and water) is most frequently employed. It constitutes what is known as the vitriol vat. Schiitzenberger and de Lalande have recently described a process of dyeing with indigo, based on the employment of sodium hydrosulphite. ISATIN. C 8 H5^0 2 == C«H*<^°^COH This body was discovered by Erdmann and Laurent in 1841. It is a product of the oxidation of indigo by dilute nitric acid. C 8 H 5 NO + = C 8 H 5 N0 2 Pure isatin crystallizes sometimes in large, dark, gold- colored prisms, sometimes in small, reddish-yellow prisms having a brilliant lustre. It is only slightly soluble in cold water and in ether, but more soluble in boiling water, and very soluble in alcohol. Its solutions are brown-red. As it contains an acetonic group, CO, isatin forms, like other acetones, a crys- tallizable compound with sodium acid sulphite. When distilled with potassa, it yields aniline. ISATIN. 713 C 8 H 5 N0 2 -f- 4K0H = 2K 2 C0 3 + C 6 H 7 N + H 2 Isatin. ^ Aniline. It dissolves in solutions of the alkaline hydrates, forming violet solutions, which become yellow when boiled, the isatin being converted into isatic acid. C 8 H 5 iN0 2 + H 2 = C 8 H 7 N0 3 Isatin. Isatic acid. Synthesis. — Among various methods by which isatin may be prepared synthetically, the following, discovered by Baeyer, is most interesting : Orthonitrobenzoyl chloride is converted into a cyanide, which, by hydration, yields orthonitrobenzoyl-carbonic acid. By reduc- tion of the latter, the corresponding amide, isatic acid, is ob- tained, and this is converted into isatin by dehydration. C6 H ^^ C0 - 0H ( 1 ) c6m^ C0 - C1 r6TU^ C0 - CN r6 m^CO-CO.OH ^ U ^NO 2 ^) C H CC1 -f POCP + H C1 Isatin. Isatin chloride. Products of the Reduction of Isatin. — To isatin are re- lated certain products of its reduction, which are interesting and which have been studied by Knop and Baeyer. They are Dioxindol C 8 H 7 N0 2 ; Oxindol C8IFNO J Indol C^Bra. Isatic acid, which has been mentioned, may be considered as trioxindol, C 8 H 7 N0 3 . Dioxindol and oxindol are formed suc- cessively by the action of sodium amalgam on an aqueous solu- tion of isatin. C 8 H 5 N0 2 + H 2 = C 8 H 7 N0 2 Isatin. Dioxindol. C 8 H 7 N0 2 + H 2 = C 8 H'NO + H 2 Dioxindol. Oxindol. 60* 714 ELEMENTS OF MODERN CHEMISTRY. INDOL. By reducing oxindol by zinc powder with the aid of heat, Baeyer obtained indol. C 8 H 7 NO + Zn = C 8 H 7 N + ZnO Oxindol. Indol. He has also made the synthesis of indol by heating ortho- nitrocinnamic acid with potassium hydrate and iron filings. C 6 H 4 <^ 2 =CH " COOH = C 6 H*C 6 H* By treating anthraquinone with bromine, Grraebe and Lieber- mann converted it into dibromanthraquinone, C u H 6 Br 2 2 , a solid body, which crystallizes in yellow needles. Phenanthrene. — Besides anthracene, there is another hydro- carbon of the same composition, which exists in coal-tar, and may also be formed artificially. It is called phenanthrene, and forms colorless scales, having a bluish fluorescence. It melts at 100°, and boils at 3^0°. It is soluble in 50 parts of alco- hol at 13° ; very soluble in hot alcohol, and in ether and benzol. Its constitution is expressed by the formula C*H 4 — CH C 6 H 4 — CH ALIZARIN. C U H8CH = C u H6(OH) 2 02 Natural State and Synthesis. — Alizarin is the name applied to the coloring matter of madder which Robiquet was the first to extract in a pure state. Graebe and Liebermann have re- cently made its synthesis by heating dibromanthraquinone to 200° with potassium hydrate. 718 ELEMENTS OP MODERN CHEMISTRY. C"H 6 Br 2 2 + 2KOH == 2KBr + C u H 6 (OH) 2 2 Dibromanthraquinone. Alizarin. This reaction, slightly modified, has become within a few years the base of an important industry. Alizarin does not exist ready formed in the madder plant. The latter contains a glucoside to which Robiquet has given the name ruberythric acid, and which is decomposed by the action of acids into alizarin and glucose. C 26 H 28 i4 + 2 H 2 '= C u H 8 0* + 2C 6 H 12 6 Ruberythric acid. Alizarin. Glucose. Preparation. — Alizarin may be extracted from madder by boiling the latter with a solution of alum. The filtered liquid, left to itself for some days, deposits impure alizarin as a brown- red precipitate, and holds in solution another coloring matter which is called pwrpurin. The precipitated alizarin is purified by washing with dilute hydrochloric acid, and crystallization in alcohol. The product thus obtained is exhausted with a boiling solution of alum, which removes the purpurin, and is finally dissolved in ether, which deposits it in crystals. To prepare artificial alizarin from anthracene, that hydro- carbon is first transformed into anthraquinone, and the latter body is treated with sulphuric acid to convert it into disulpho- anthraquinonic acid, which is then heated with an excess of potassium hydrate. C u H 6 (S0 8 K) 2 2 + 2KOH = C u H 6 (OH) 2 2 + 2K 2 S0 3 Potassium Alizarin, disulphoanthraquinonate. The alkaline mass is dissolved in water, precipitated by hy- drochloric acid, and the precipitate purified by crystallization in alcohol and finally by sublimation. The artificial product is delivered to commerce in the form of a paste, but the reaction by which it is formed produces, at the same time, isomerides which remain mixed with the aliza- rin, properly so called. Eight isomeric compounds are known having the composition C u H 8 4 . One of them, purpuroxan- thin, is contained in small quantity in madder. Properties of Alizarin — Alizarin forms long, brilliant, orange-yellow prisms. It is scarcely soluble in cold water, but dissolves better in boiling water, and is soluble in alcohol, ether, and carbon-disulphide. It melts between 275 and 277°, and sublimes in long, orange-yellow needles. It dissolves in sul- PURPURIN — NATURAL ALKALOIDS. 719 phurie acid with a blood-red color, and water precipitates it without alteration from this solution. Boiling dilute nitric acid converts it into oxalic and phthalic acids. When alizarin is heated to redness with zinc powder, it is reduced to anthra- cene (Graebe and Liebermann). Alizarin forms combinations with the bases ; it dissolves in ammonia, with a purple color, and in the caustic alkalies, yield- ing purple solutions which have a blue reflection. Uses. — Alizarin produces a red color on fabrics that are mor- danted with alumina, and a violet on those which are mor- danted with ferric oxide. It is the coloring principle of madder and of the commercial product known as garancln. The latter product is obtained by heating powdered madder with sulphu- ric acid to 100°, and exhausting the mass with water. The residue is garancin. PURPURIN. * C u H&(OH)30 2 This name is given to another coloring matter which may be extracted from madder, and which has already been mentioned. It appears to exist in the plant as a glucoside. It dissolves readily in alcohol and ether, with a red color. It crystallizes from weak alcohol in orange-colored needles, which contain one molecule of water of crystallization. From concentrated alcohol, it deposits in red, anhydrous needles. When heated, it melts and sublimes in red needles. With aluminium mordants, it gives scarlet-red shades. Purpurin is an oxyalizarin, or a trioxyanthraquinone, C U H 5 (OH) 3 2 : indeed, it may be obtained by treating a solution of alizarin in concentrated sulphuric acid with an oxidizing agent, such as manganese dioxide (de Lalande). Inversely, the reduc- tion of purpurin reproduces alizarin (Rosenstiehl). It under- goes a complete reduction, and is converted into anthracene, when heated with zinc-dust. Independently of the purpurin just described, there are three other compounds isomeric with it. NATURAL ALKALOIDS. The alkaloids are nitrogenized substances capable of uniting with the acids, like ammonia, and forming with them definite combinations which constitute true salts. A large number 720 ELEMENTS OF MODERN CHEMISTRY. of these compounds can be formed artificially, and are derived directly from ammonia by the substitution of organic radicals for the hydrogen of that body. They are the compound, or substituted ammonias, and their constitutions are perfectly known. This is not, however, the case with the natural alka- loids, which have been discovered in many plants and vege- table products, and which often constitute the active principles to which these products owe their medicinal virtues. By anal- ogy, it may be inferred that these bodies also are derived from ammonia, like the compound ammonias. In 1806, the basic nature of one of the crystallizable princi- ples of opium was discovered by Sertiirner, but his discovery was unnoticed until 1817, when he published it in a treatise on morphine. Among the more important discoveries in this class of compounds must be mentioned those of strychine, brucine, and especially quinine, discoveries which are due to Pelletier and Caventou (1820). All of the alkaloids contain nitrogen. They are divided into two classes, the first of which includes the liquid and volatile bases, and the second the solids. The latter generally contain oxygen, the former do not. The alkaloids possess one charac- teristic property which indicates their analogy with ammonia. With platinic chloride their hydrochlorides form double salts, which are sometimes insoluble in water, sometimes soluble and crystallizable. If a solution of platinic chloride be poured into a solution of quinine hydrochloride, a yellow precipitate is at once formed ; it is a combination of platinic chloride and quinine hydrochlo- ride, and is sometimes called quinine chloroplatinate, or platino- chloride. PYRIDIC BASES. From the oil obtained by the dry distillation of animal mat- ters, and which was formerly known as the bone oil of Dip- pel, Anderson has extracted a series of bases isomeric with the aromatic amines. Among these bases are the following : Pyridine, C 5 H5N. Picolines, C 6 H 7 N, isomeric with aniline. Lutidines, C 7 H 9 N, isomeric with toluidine. Collidines, C 8 H n N, isomeric with xylidines. Some of these have been obtained synthetically by the action of ammonia on certain aldehydes. Thus, allylic and crotonic aldehydes form with ammonia oxidized bases. PYRIDIC BASES. 721 2C 3 H*0 + NH 3 = C 6 H 9 NO + H 2 Acrolein. 2C 4 H 6 + NH 3 = C 8 H 13 XO + H 2 By dehydration these condensation products yield pyridic D3.SGS C 6 H 9 NO = C 8 H 7 N + H 2 Picoliue. C 8 H 13 NO = C 8 H U N + H 2 Collidine. Baeyer and Ador have also obtained a collidine (aldehydrin) by heating aldehyde-ammonia in closed vessels. 4C 2 H 4 + NH 3 = C 8 H n N + 4H 2 Collidine. The first term of the series is pyridine. According to an ingenious hypothesis of Kbrner, this compound has a constitution analogous to that of benzol, the five carbon atoms and the nitro- gen atom forming a closed chain similar to the benzol nucleus. H H A A HC CH HC CH HC CH HC CH \\ / \N / C N H Benzol. Pyridine. The superior homologues of pyridine, such as picoline, luti- dine, and collidine, then result from the substitution of one or more methyl or other alcoholic groups for the hydrogen of pyri- dine. According to the position of these groups with relation to the nitrogen atom in the pyridic chain, isomerism will occur, precisely analogous to that which we have considered in the case of the aromatic amines. We cannot extend these theoretical considerations. How- ever, the pyridic bases and quinoline which is related to them, appear to take part in the constitution of the natural bases. Indeed, some of the latter, such as cinchonine and brucine, yield by distillation with potassium hydrate, a mixture of pyridic bases and quinoline. Pyridine, C 5 H 5 N. — This base has been obtained from the animal oil of Dippel by Anderson, and from coal-tar by Greville Williams. Chapman and Smith have made its synthesis by dehydrating amyl nitrate with phosphoric anhydride. C 5 H n .N0 3 = 3H 2 + C 5 H 5 N Amyl nitrate. Pyridine. FF 61 722 ELEMENTS OF MODERN CHEMISTRY. It is- a colorless liquid, having a characteristic odor, and at 0° a density 0.986. It boils at 117°, and is soluble in water and alcohol. It is an energetic base, forming deliquescent salts. Sodium converts it into a polymeride, dipyridine, C 10 H 10 N 2 . We cannot describe the other pyridic bases : they exist under several isomeric modifications. Thus, there are three picolines, or methyl-pyridines, C 5 H 4 (CH 3 )N: two lutidines, dimethyl- pyridine, or a-lutidine, C 5 H 3 (CH 3 ) 2 N, boiling towards 155°, and ethylpyridine or /?-lutidine, boiling at 165°. There are known at least two collidines ; a-collidine or trimethylpyridine (aldehydrine), C 5 H 2 (CH 3 )N, boils at 175-177°, and /5-collidine at 195° (Oechsner de Coninck). Under, the action of oxidizing agents, such as potassium permanganate in alkaline solution, the pyridic bases behave as aromatic hydrocarbons. The alcoholic lateral chains are oxidized and converted into carboxyl, CO. OH. Thus methylpyridine (/? picoline) and ethylpyridine (/3 lutidine) yield the same mono- carbopyridic acid. C5H4< CH 3 and C 5 H 4 < C 2 H 5 ^ ieM csh^CO.OH Methylpyridine. Ethylpyridine. Monocarbopyridic acid. When either of the several isomeric modifications of mono- carbopyridic acid is distilled with lime, it is reduced to pyridine. C 5 H 4 <^ OOH = CO 2 + C 5 H 5 N There are also several dicarbopyridic acids. /CO.OH C 5 H 3 ^CO.OH \ N QUINOLINE. Gerhardt obtained this base by distilling certain natural alkaloids, among which are quinine and cinchonine, with potas- sium hydrate. It appears identical with a base which Kunge had extracted, several years previous, from coal-tar, and whicli he named leucol or leucoline. At present, quinoline is manu- factured synthetically by heating a mixture of nitrobenzol, aniline, and glycerin. 3C3H803 + C6H5.N0 2 + 2C 6 H5.NH 2 = 11H 2 + SCOTN Glycerin. Nitrobenzol. Aniline. Quinoline. CONINE. 723 Quinoline is a mobile, colorless, strongly refracting liquid. Its density at 0° is 1.081, and it boils at 238°. It has a pene- trating odor and a very bitter taste. It is insoluble in water ; with acids it forms well-defined salts, and behaves as a tertiary amine. With ethyl-iodide it forms an ethyl-iodide. 0>H'N<£ 2H5 Quinoline is related to the true aromatic compounds, and at the same time to the pyridic bases. Its synthetical formation and its reactions have led to the following representation of its constitution, which is that of naphthaline in which a group CH is replaced by an atom of nitrogen. H H C C HC C CH HC C CH V V H CONINE. C 8 H!5]S" This is a liquid and volatile alkaloid which is extracted from the hemlock (Conium maculatum). The seeds of this tree are crushed and distilled with sodium hydrate. The alkaline liquid which collects in the receiver is neutralized by dilute sulphu- ric acid, evaporated to a syrupy consistence, and the residue exhausted with a mixture of alcohol and ether, which dissolves the conine sulphate, and leaves ammonium sulphate. The alco- hol and ether are driven out by evaporation ; a concentrated solution of sodium hydrate is added to the conine sulphate, and the liquid is distilled. The conine passes with a certain quan- tity of water, on which it floats. It is separated, dried over some fragments of calcium chloride, and rectified in a vacuum. Conine is a limpid, oleaginous liquid, having a penetrating and nauseating odor, recalling that of hemlock. It boils at 168°. It is slightly soluble in water, more so in cold than in hot water, so that a cold, saturated solution becomes clouded when heated. It is very soluble in alcohol and in ether. It has a strongly alkaline reaction, immediately restoring the blue color to reddened litmus-paper. It precipitates many metallic- oxides from solutions of their salts. On contact with the air 724 ELEMENTS OF MODERN CHEMISTRY. it becomes brown and resinified. The density of conine at 0° is 0.886 : it rotates the plane of polarized light towards the right. Conine is often mixed with methylconine, a compound de- rived from conine by the substitution of a methyl group for an atom of hydrogen (Planta and Kekule). This compound is formed artificially by the action of methyl iodide on conine, a reaction which shows that the latter body is a secondary base, C 8 H U =XH. Wertheim has obtained from the flowers and seeds of the hemlock a solid alkaloid, which he has named conhydrine, C 8 fl 17 NO, and which contains the elements of conine plus a molecule of water. Hugo Schiff has recently made the synthesis of an isomeride of conine, which he calls para con ine. Hofmann assigns to conine the formula C 8 H 17 N. NICOTINE. This alkaloid exists in tobacco. It may be obtained by ex- hausting tobacco with boiling water and evaporating the liquid to a syrupy consistence on a water-bath ; the still hot extract is then mixed with twice its volume of alcohol, allowed to settle, and the alcoholic liquid separated from the thick lower layer, which contains much calcium nialate. The alcohol is distilled off. and the residue exhausted with strong alcohol, of which the greater part is then driven off by evaporation. Potassium hydrate is added to the alcoholic extract, which is then agitated with ether, which dissolves the nicotine set free. A few grammes of oxalic acid added to the ethereal solution cause- the separa- tion of a syrupy deposit which contains oxalate of nicotine. This salt is decomposed by potassa. and the nicotine set free is dissolved out by ether. After the ether has been expelled on a water-bath, the nicotine is distilled in a current of hydrogen, that part being retained which passes above 180° (Schloesi _ Properties. — Nicotine is a colorless liquid, having an offen- sive, penetrating odor. It rotates the plane of polarization to the left. It boils between 240 and 250°, not. however, with- out undergoing partial decomposition. Above 146°, it begins to distil slowly, and at 100° it emits white vapors ; at ordinary temperatures it gives off so much vapor that a rod wet with ALKALOIDS OF OPIUM. 725 hydrochloric acid will be enveloped in white fumes if held a little distance above the nicotine. Nicotine dissolves in all proportions in water, alcohol, and ether. It has a strongly alkaline reaction, and perfectly neu- tralizes the acids, and precipitates the metallic oxides from solutions of their salts. It is one of the most violent poisons known. It is a diatomic base ; its platino-chloride, which crystallizes in red prisms, has the composition C 10 H u N.(HCl) 2 .PtCP ALKALOIDS OF OPIUM. Opium is the thickened juice of the capsules of the white poppy (Papaver somniferum). It is obtained by making in- cisions in these capsules from the base to the summit. A milky juice exudes, and in the course of a day thickens and solidifies in tears. These are removed, pressed together, and fashioned mto variously-formed masses. Opium contains a number of alkaloids combined with several acids. Among the latter are a syrupy acid, to which Ander- son gave the name thebolactic acid, but which has recently been recognized to be identical with lactic acid (Buchanan), and meconic acid, of which the composition is expressed by the formula C 7 H 4 7 . The latter is one of the more important constituents of opium ; it possesses the characteristic property of producing a blood-red color with ferric salts. Opium con- tains also a gummy matter, soluble in water, and a brown, in- soluble, resinous matter, which remains in the mass when opium is exhausted with water. The aqueous solution of opium has a brown color. The following alkaloids have been obtained from opium : Morphine C 17 H 19 X0 3 Codeine C^H-^XO 3 Thebaine C 19 H^X0 3 Papaverine C 21 H 21 X0± Narcotine 0*H*NC Narceine C 23 H 29 X0 9 Besides these. Merck has described another alkaloid of opium under the name porpliyroxine ; but, according to Hesse, this body is a mixture of several bases, to which he has given the names meconidinc. laudanine. codamine. and lauthopine. Opium sometimes contains an alkaloid which is designated as pseudamorphine, and which is oxymorphine, C 1T H 19 2sO\ 61* 726 ELEMENTS OF MODERN CHEMISTRY. Independently of these alkaloids, a neutral, crystallizable sub- stance has been extracted from opium, and called meconine, qiujjio04 Qf a ji these bodies, we will only consider morphine, codeine, and narcotine. MORPHINE. C 17 H 19 N0 3 + H 2 Preparation. — 1. Opium is cut into slices and exhausted with water. The solution is evaporated to a syrupy consistence and the still hot extract is mixed with an excess of pulverized sodium carbonate. After the lapse of twenty-four hours, the precipitate is collected and exhausted with dilute acetic acid, which dissolves the morphine and leaves the narcotine. The liquid is filtered, decolorized by animal charcoal, and super- saturated with ammonia. The morphine is precipitated, and is purified by crystallization in alcohol (Merck). 2. One kilogramme of opium is exhausted with cold water ; 100 grammes of pure lime are added to the liquid, which is then evaporated to a syrupy consistence at a temperature of 65 or 15°. After cooling, the mass is exhausted with 3 litres of water which leaves the meconate of calcium ; the latter is separated by filtration. The liquid is then evaporated to one- fourth its volume, and while it is still hot, 50 grammes of calcium chloride dissolved in 100 grammes of water and 8 grammes of hydrochloric acid are added. This mixture is left to itself for about two weeks, when it will be found to have set in a mass of crystals which are bathed in a colored mother-liquor. The deposit is pressed in a cloth, dissolved in boiling water, with addition of animal charcoal, and the solution filtered. On cooling, a mass of crystals is formed, consisting of a mixture of morphine hydrochloride and codeine hydrochloride. These are pressed, dissolved in water, and ammonia is added, which precipitates the greater portion of the morphine, while the codeine remains in solution. The deposit is collected on a filter and redissolved in boiling alcohol, from which the morphine crystallizes on cooling (Robertson and Gregory). Properties. — Morphine crystallizes in small, colorless, right rhombic prisms, having a bitter taste. It is insoluble in ether, in chloroform, and in benzol. The alcoholic solution rotates the plane of polarization to the left. The crystals contain one CODEINE. 727 molecule of water which they lose at 100°. Morphine dis- solves easily in a solution of potassium hydrate ; it is very slightly soluble in ammonia ; almost insoluble in water. Tests. — 1. If a few drops of a solution of iodic acid be added to an alcoholic solution of morphine, the liquid immediately assumes a brown or yellow color, due to the liberation of iodine. Iodic acid exerts an oxidizing action on morphine. 2. If a small quantity of morphine in powder be added to a solution of ferric chloride, a blue color is produced. This characteristic recalls an analogous reaction brought about by the phenols, and leads to the belief that morphine contains a phenolic hydroxyl group (Grimaux). 3. Nitric acid produces an orange-red color with morphine. The last two reactions are characteristic. When morphine is heated to 200° with potassium hydrate, it disengages methylamine. When heated with zinc dust, it yields phenanthrene, and various pyridic and quinolic bases studied by Gerichter and Schroetter. Morphine Hydrochloride. — This salt, of which the prepara- tion has already been indicated, crystallizes in silky needles, soluble in 1 part of boiling and 16 or 20 parts of cold water ; it is very soluble in alcohol. The crystals contain C 17 H 19 N0 3 . HC1 + 3H 2 0. Platinic chloride forms a yellow precipitate of a double chlo- ride in an aqueous solution of morphine hydrochloride. (C 17 H 19 N0 3 .HCl) 2 .PtCl* Hydrochloride of morphine is much used in medicine. When its solution is heated to 60° with silver nitrite, the base is oxidized and converted into oxymorphine, C 17 H 19 N0 4 . When morphine is heated to about 140° with concentrated hydrochloric acid, it is transformed into a new base, apomor- phine, C 17 H 17 N0 2 , derived from morphine by the removal of one molecule of water (Matthiessen). This base possesses special therapeutic properties. When administered by hypo- dermic injection or swallowed, it acts as an emetic. CODEINE. C 18 H 21 N0 3 + H 2 Codeine is methylmorphine. It is obtained from the am- moniacal mother-liquor from which the morphine is deposited, 728 ELEMENTS OF MODERN CHEMISTRY. in the preparation of the latter body by the process of Robert- son and Gregory. For this purpose, the mother-liquor is con- centrated and caustic potassa is added, which precipitates the codeine. It is collected, dissolved in hydrochloric acid, the solution decolorized with animal charcoal, and the codeine again precipitated by potassa. Lastly, the precipitate is dissolved in ordinary ether, which deposits the codeine in voluminous crys- tals by spontaneous evaporation. These crystals are right rhombic prisms, and contain one molecule of water. Anhydrous ether deposits codeine in anhy- drous rectangular octahedra, fusible at 150°. Codeine dissolves in 89 parts of water at 15°, and is more soluble in boiling water. Alcohol and ether dissolve it readily, and the alcoholic solution rotates the plane of polarization to the left. Starting with the idea that morphine contains a phenolic hydroxyl group, Grrimaux conceived that the solution of morphine in potassium hydrate should contain the compound C 17 H 18 N0 2 .OK : indeed, by treating this alkaline solution with methyl iodide, he obtained codeine. C i7 H i8 N0 2 0K + QJJ3J = KI _|_ c i7 H 18 N0 2 .OCH 3 This reaction certainly demonstrates that codeine is methyl- morphine. If bromine-water be poured upon codeine in fine powder, the latter dissolves, and is converted into hydrobromide of monobromo-codeine. By the continued addition of bromine- water, a yellow precipitate is formed, consisting of hydrobro- mide of tribromo-codeine, that is, codeine in which three atoms of hydrogen are replaced by three atoms of bromine. NARCOTINE. C 22 H 23 NO* Narcotine may be extracted from the residue of opium which has been exhausted by water. This is treated with hydrochloric acid, filtered, and the filtrate precipitated by sodium carbon- ate. The precipitate is dissolved in alcohol, and the alcoholic solution decolorized by animal charcoal. The narcotine crys- tallizes out on cooling. It forms brilliant, colorless prisms, belonging to the system of the right rhombic prism. It melts at 170°. It is insoluble in ALKALOIDS OF CINCHONA. 729 cold water, and requires for its solution about 60 parts of cold absolute alcohol, or 12 parts of boiling absolute alcohol. It is soluble in ether, a character which distinguishes it from mor- phine. Its alcoholic and ethereal solutions have a bitter taste, and turn the plane of polarization to the left. If a few crystals of narcotine in a watch-glass be moistened with sulphuric acid containing a trace of nitric acid, an intense blood-red color is produced. By the action of certain oxidizing agents, narcotine is de- composed into a new alkaloid, cotarnine, and an acid which is called opianic acid (Wbhler). C 22 H 23 N0 7 + = C 10 H 10 O 5 + C 12 H 13 N0 3 Narcotine. Opianic acid. Cotarnine. Cotarnine crystallizes in colorless, silky needles, grouped in stars. When heated with water, narcotine breaks up into cotarnine md meconine. C 22 H 23 N0 7 = c i0 H 10 O* + C 12 H 13 N0 3 Narcotine. Meconine. Cotarnine. When subjected to the action of hydrioclic acid, narcotine loses successively three methyl groups, and yields hydriodides of three new bases. One of them contains C 19 H 17 N0 7 , and has oeen designated as nornarcotine or normal narcotine. It is formed according to the equation C 22 H2 3 N0 7 _j_ 3HI = C 19 H 17 N0 7 + 3CH 3 I Narcotine. Nornarcotine. Methyl iodide. Hence narcotine itself represents trimethyl- nornarcotine, C 19 H U (CH 3 ) 3 N0 7 (Matthiessen and Foster). The intermediate terms between narcotine and nornarcotine are also known, ALKALOIDS OP CINCHONA. The different cinchona barks owe their febrifuge virtues to several alkaloids, of which the more important, quinine and cin- chonine, were discovered by Pelletier and Caventou in 1820. Since then, quinidine and cinchonidine have been isolated, the first isomeric with quinine, the second with cinchonine. All of these are crystallizable alkaloids. When their sulphates are heated with sulphuric acid, they are converted into two new isomerides, quinicine and cinchonicine. The latter are not crys- tallizable. 730 ELEMENTS OF MODERN CHEMISTRY. Hence the following six alkaloids are known : Cinchonine, cinchonidine, cinchonicine . . . C 20 H 24 N 2 O Quinine, quinidine, quinicine C 20 H 24 N 2 O 2 These alkaloids are by no means distributed in the same manner in the numerous species and varieties of cinchona bark, and these barks are not equally rich in alkaloids. The follow- ing summary gives some indications of this difference : CINCHONINE 1 KILOGRAMME OF BARK YIELDS : QUININE SULPHATE. SULPHATE Yellow bark (Cinchona Calisaya) . . 30-32 grammes. 6-8 grammes. Red bark ( Cinchona succirubra) . . . 20-25 " 8 " {Loxa (Cinchona condami- nea) 8 " 6 " Huanuco (Cinchona nitida) 6 " 12 " Quinic Acid. — In the cinchonas, the alkaloids are combined with a well-defined, crystallizable acid, whose composition is expressed by the formula C 7 H 12 6 . It is quinic acid. This acid is obtained from the calcium quinate which is de- posited in a few days, when the liquid separated from the quino- calcium precipitate is concentrated and allowed to stand (see farther on). This calcium quinate is purified by several crystallizations, and its solution decomposed by oxalic acid. The quinic acid remains in the solution, and separates in crystals when the liquid is properly concentrated. Quinic acid crystallizes in beautiful, transparent, oblique rhombic prisms. It is very soluble in water, and but slightly soluble in absolute alcohol. It melts at 161.5°, losing at the same time the elements of water. Its aqueous solution rotates the plane of polarization to the left. Its composition corresponds to the formula C 7 H 12 6 . When distilled with a mixture of sulphuric acid and manganese diox- ide, it yields quinone, C 6 H 4 2 . A substance is also found in cinchona bark which is called quinotannic acid. It belongs to the tannin group, and is a glucoside. Hlasiwetz states that it can be decomposed into glucose and cinchonine red, a substance noticed by Pelletier and Caventou as produced during the preparation of quinine. QUININE. 731 QUININE. C 20 H 2 ±X 2 O 2 When ammonia is added to a solution of sulphate of quinine, a white precipitate of quinine is obtained, which, when left to itself and moistened with water from time to time, becomes crystalline by combining with one molecule of water. Quinine is very bitter. It dissolves in 2266 parts of cold. and in 760 parts of boiling water; in 1.33 parts of cold alco- hol, and 22.6 parts of ether (J. Regnauld). It is also soluble in chloroform. Its alcoholic solution turns the plane of polar- ization to the left. When water at 32° is added to the hot alcoholic solution until a cloud begins to form, resinous quinine is deposited, and also colorless, prismatic crystals containing three molecules of water. From its ethereal or alcoholic solutiou, quinine crystallizes in delicate silky needles, fusible at 177°. Quinine is diacid, that is, each molecule of the base re- quires for the formation of saturated salts, two molecules of a monobasic or one of a dibasic acid. It is a ternary base, uniting directly with the alcoholic iodides to form quaternary iodides. Quinine Sulphate, 2(C 2 °H 2 ±N 2 2 ).S(>H 2 + 8H 2 0._ Prep- ration. — This salt, which is extensively used in medicine, is prepared by boiling yellow bark {Cinchona CaUsaya) or red bark (Cinchona $ucciruora~) with water acidulated with sul- phuric or hydrochloric acid. A slight excess of milk of lime is then added in small quantities to the decoction, and precip- itates not only the quinine and cinchonine, but all of the color- ing matter (cinchonine red), which forms an insoluble com- pound with the lime. The quinic acid remains in solution as calcium quinate. The quino-ealeium deposit contains also the excess of lime, and calcium sulphate, in case sulphuric acid has been employed. It is collected on a cloth, allowed to drain, pressed, and dried. It is then exhausted with boiling alcohol, which dissolves out the alkaloids. The alcoholic solution, concentrated by distillation, deposits the cinchonine in crystals, in case the bark employed be rich in that alkaloid. The mother-liquor retains the quinine. It is neutralized by sulphuric acid, and the alcohol distilled off. The quinine sulphate crystallizes in a mass on cooling, and is purified by redissolving it in boiling water and adding animal charcoal. It has been proposed to replace the alcohol, in the extrac- 732 ELEMENTS OF MODERN CHEMISTRY. tion of the quino-calcium deposit, by certain fixed or volatile oils, which dissolve quinine. For this purpose, petroleum and the heavy oils produced by the distillation of tar, and which are abundant in commerce, may be used with advantage. After having dissolved the alkaloids in these oils, the solutions are agitated with dilute sulphuric acid, which removes from them the quinine and cinchonine. Sulphates are thus obtained which may be crystallized. Properties. — Quinine sulphate occurs in long, thin, light needles, which are somewhat flexible. It requires for its solu- tion 740 parts of water at 13°, or about 30 parts of boiling water. The solution restores the blue color to reddened litmus- paper. It turns the plane of polarization to the left (Bouchar- dat). When crystallized in alcohol, quinine sulphate contains only two molecules of water. If some quinine sulphate be suspended in cold water, and a few drops of sulphuric acid be added, the sulphate dissolves and the liquid acquires a blue fluorescence. In this case, quinine sulphate, which is a basic salt, is con- verted into a salt, C^H^NW.SO'H 2 , which has an acid reac- tion, and is called quinine acid sulphate. This salt crystallizes in quadrilateral prisms containing 7 molecules of water : it is the normal sulphate. A still more acid sulphate is known, C 20 H 24 N 2 O 2 .(SO 4 H 2 ) 2 + 7H 2 0. If an excess of chlorine-water be added to a solution of quinine sulphate, and the liquid be supersaturated with ammo- nia, a beautiful green color will be produced. This reaction is characteristic of quinine. When tincture of iodine is added to a solution of quinine sulphate in hot acetic acid, in a few hours the liquid deposits large, thin plates. It is iodoquinine sulphate, C 20 H 24 N 2 OT. SOH 2 + 5H 2 (Herapath). These crystals appear green by reflected light, and are almost colorless by transmitted light. When two of them are crossed, the portions which are superposed almost entirely intercept the passage of light. In this respect, iodoquinine sulphate acts as a polarizer, like tourmaline. Uses. — Quinine sulphate is a valuable remedy. It is prin- cipally employed as a febrifuge, and generally in the treatment of diseases of an intermittent type. It is successfully admin- istered in other diseases, especially in acute articular rheuma- tism, gout, certain neuralgias, etc. STRYCHNINE AND BRUCINE. 733 CINCHONINE. C 20 H^N 2 O Cinclionine is obtained as an accessory product in the manu- facture of quinine. It deposits from its alcoholic solution in brilliant, colorless, quadrilateral prisms. It is insoluble in water, but soluble in alcohol and chloroform. It is almost insoluble in ether, a property which distinguishes it from qui- nine. Its alcoholic solution turns the plane of polarization to the right. Cinchonine has a bitter taste. It melts at 257°, and when cautiously heated in the bottom of a closed tube, it partly sub- limes in very light, delicate crystals. When treated with a dilute solution of potassium permanganate, it forms various substitution products, and a new base remains, less oxidizable than cinchonine. It is liydrocinchonine. Caventou and Willm consider that this base is contained, in the state of mixture, in commercial cinchonine. When distilled with potassium hydrate, cinchonine yields quinoline and a mixture of pyridic bases. Among the oxidation products obtained by the action of nitric acid, or, better, potassium permanganate, on cinchonine, we may mention two ; they are C 7 H 5 N0 4 = C 5 H 3 N(CO.OH) 2 Cinchomeronic or dicarbopyridic acid. C 10 H'NO* = C 9 H 6 N(CO.OH) Cincboninic or carboquinolic acid. Weidel, who has studied these acids, has also described another oxidation product of cinchonine, an acid, C 9 H 6 N 2 6 . From the nature of its decomposition products, it is probable that cinchonine contains a pyridic and a quinolic group. STRYCHNINE AND BRUCINE. Pelletier and Caventou discovered these two alkaloids in various vegetable products derived from plants belonging to the genus Strychnos, such as nux vomica (seeds of the Strychnos Nux vomica), false angustura bark, which comes from the same Strychnos, Saint Ignatius bean (seeds of the Strychnos Ignatii), etc. These alkaloids, to which igasurine has recently been added (Desnoix), appear to be combined in the Strychnos with an acid but little known, which Pelletier and Caventou called igasuric acid. f 734 ELEMENTS OP MODERN CHEMISTRY. Strychnine, C 21 H 22 N 2 2 . — Preparation. — Strychnine is ex- tracted from nux vomica by a process analogous to that which serves for the preparation of quinine. The crude strychnine which deposits in crystals from its alcoholic solution is always mixed with brucine. The two alkaloids are separated by con- verting them into nitrates, which are made to crystallize ; the strychnine nitrate, less soluble than that of brucine, deposits in needles, and the concentrated solution afterwards deposits voluminous crystals of brucine nitrate. To isolate the alka- loids, the corresponding nitrates are precipitated, by ammonia, and the alkaloid dissolved in boiling alcohol, which deposits it in crystals on cooling. Properties. — Strychnine crystallizes in rectangular octa- hedra, sometimes in quadrilateral prisms terminated by four- sided pyramids. It is colorless and odorless, but extremely bitter. It is insoluble in water and in ether, and scarcely soluble in absolute alcohol. It dissolves readily in ordinary alcohol, in chloroform, and in the volatile oils. Its alcoholic solution turns the plane of polarization to the left. When strychnine or one of its salts is moistened with strong sulphuric acid, and a little potassium dichromate added, a blue color is produced, which changes to violet and red, and at last disappears. Strychnine is one of the most active poisons known ; even in very small doses it produces violent tetanic spasms. Brucine, C 23 H 26 N 2 4 + 4H 2 0.— Brucine, separated from strychnine by the process above indicated, crystallizes by slow evaporation of its solution in weak alcohol in oblique rhombic prisms, which are often quite large. These crystals, which contain four molecules of water, rapidly effloresce in the air. Brucine is almost insoluble in water, but dissolves readily in alcohol and very slightly in ether. The alcoholic solution ro- tates the plane of polarization to the left. If brucine be moistened with nitric acid, it immediately assumes a blood-red color and, by the aid of a gentle heat, disengages carbon dioxide and vapors which contain methyl nitrite (Strecker). COCAINE. Cocaine was obtained by Niemann from coca leaves (Ery- throxylon Coca). It has been studied by Wohler and Lassen. ACONITINE — ATROPINE. 735 Preparation. — Coca leaves are exhausted several times with water at a temperature between 60 and 80°, and the solu- tion is precipitated by lead acetate, and filtered ; the filtered solution is freed from excess of lead acetate by addition of sodium sulphate and then, after a new filtration, the solution is evaporated. Sodium carbonate is then added until it pro- duces a faint alkaline reaction ; the liquid is lastly agitated with ether, which takes up the cocaine and leaves it on evapo- ration. Properties. — Cocaine crystallizes in oblique rhombic prisms of four or six sides, which are colorless and odorless, and fuse at 98°. It is but slightly soluble in cold water, more soluble in alcohol, very soluble in ether. Its taste is bitter, its reaction slightly alkaline. When heated with hydrochloric acid, it ab- sorbs two molecules of water and decomposes into methyl alco- hol, benzoic acid, and a crystallizable base, ecgonine. C 9 H 15 X0 8 + H 2 0. C 17 H 21 NO* + 2H 2 = C 9 H 15 N0 3 + CHM) + C 7 H 6 2 ACONITINE. C 27 B> XO 10 The Aconitum JYapellus contains, independently of aconitic acid, a base which was extracted by G-eiger and Hesse. It occurs as a white powder, or as colorless, tabular crystals, only slightly soluble in water, very soluble in alcohol. Its taste is acrid and bitter. It is a violent poison. Its nitrate crystal- tizes readily. ATROPINE. C 17 H 23 X0 3 This alkaloid, which is largely used in the treatment of dis- eases of the eyes, was discovered in 1833 by Geiger and Hesse, and by Mein, in the belladonna, or deadly nightshade (Atropa Belladonna). Planta has shown the identity of atropine and daturine, which has been obtained from the thorn-apple (Datura Stramonium). Preparation. — Belladonna-root is reduced to powder and digested several days with alcohol. The solution is filtered, slaked lime, in quantity equal to one-twentieth of the weight of root employed, is added, the solution again filtered, and rendered 736 ELEMENTS OF MODERN CHEMISTRY. slightly acid with sulphuric acid. It is again filtered, and f of the alcohol distilled off. The residue is concentrated at a gentle heat, and a concentrated solution of potassium carbonate is added until the liquid, now neutral, begins to be clouded. After a few hours, the precipitate is separated by filtration, and potassium carbonate is added to the filtrate as long as impure atropine is precipitated. The next day, the deposit is collected on a filter, pressed, dried, and exhausted with 96 per cent, alcohol. The solution is decolorized with animal charcoal, the liquid diluted with five or six times its volume of water and put in a cool, dark place. The atropine is deposited in 12 or 24 hours in crystalline needles. Properties. — Atropine crystallizes in delicate needles, fusi- ble at 90°. It dissolves in 300 parts of cold water, and in almost all proportions of alcohol. It is less soluble in ether. At 140° it volatilizes, but the greater part of it is decomposed. In burning, atropine diffuses the odor of benzoic acid. When it is treated with potassium dichromate and sulphuric acid, benzyl aldehyde distils and benzoic acid is formed (Pfeiffer). Atropine is a virulent poison. A solution of sulphate of atropine is used in medicine. A single drop, even of a very dilute solution of this salt, produces dilatation of the pupil. When heated with baryta water, or with hydrochloric acid, atropine breaks up into tropine and tropic acid (Lossen and Kraut). C 17 H 23 N0 3 _|_ H 2 Q _ C 9 H 10 O 3 + C 8 H 15 NO Atropine. Tropic acid. Tropine. Tropine is an energetic base, soluble in water, alcohol, and ether : from the latter solvent it separates in tables, fusible at 61°. Tropic acid is the phenyl derivative of hydracrylic or ethyl- enelactic acid. CH 2 .OH CH 2 .OH CIP.CO.OH ^ H UH The chloride of this ammoniated base is formed by synthesis by the action of ethylene chlorohydrate on trimethylamine (A. Wurtz). Wjgf + (CH3)3N= (C2I Jc^}NCl Trimethyl-hydroxethylene- ammonium chloride. Neurine is identical with a base which Strecker obtained from the bile and designated as choline. CHOLESTEMN. This body is largely diffused in the organism. It exists in the bile, and is the principal constituent of most biliary cal- culi. It is found also in small quantity in the serum of blood, in the brain, in yolk of egg, pus, the liquid of hydrocele, etc. Its solubility in alcohol and especially in ether, and the facility with which it crystallizes from its solutions, permits its easy isolation, and it may readily be prepared by extracting biliary calculi with ether, or with boiling alcohol, and allowing the solution to evaporate. Cholesterin ordinarily deposits in thin t and brilliant, rhombic plates. It melts at 145°, and can be sublimed, out of contact with air, at 360°. It forms neutral compounds with acids, analogous to the ethers ; it seems to be a monatomic alcohol. The principal organic constituents of the bile are two com- plex acids, both nitrogenized, and one of which contains sul- phur. These are glycocholic and taurocholic acids. They are not contained in the bile of all animals, and are generally ex- tracted from that of the ox. They enter into the composition of human bile, which contains in addition coloring matters of which the most important is bilirubin. We will briefly describe these bodies. GLYCOCHOLIC ACID — TAUROCHOLIC ACID. 753 GLYCOCHOLIC ACID. C*H«NO« This body exists in the bile in the form of sodium glycocho- late. which salt may be obtained in crystals from ox's bile. The latter is decolorized by animal charcoal, filtered, the liquid evaporated, and the residue perfectly dried and dissolved in absolute alcohol : the solution is introduced into a flask, and ether is cautiously added so that the two liquids may not mix. but form two layers. The latter gradually mingle and the sodium glycocholate deposits in crystals (Planner). When dilute sulphuric acid is added to a solution of this salt, a cloud is formed, and glycocholic acid is soon deposited in fine needles. This acid is only slightly soluble in water and ether, but dis- solves in alcohol. It is dextrogyrate (Hoppe-Seylerj. By the action of hydrochloric acid, it is decomposed into cholalic acid and glycocol (Strecker). CH^NC + H 2 = C 2i H w 5 + C 2 H 5 X0 2 Glycocholic acid. Cholalic acid. Glycocol. Cholalic Acid exists in the amorphous state and crystallized. It deposits from its ethereal solution in four-sided prisms, beveled at the ends, and containing two molecules of water of crystallization. By boiling with acids, it is convened into a resinous body which Berzelius called dydysin. C 24 H*°0 5 = C 24 H 36 3 + 2H 2 Dyslysin. TAUROCHOLIC ACID. The sodium salt of this acid remains dissolved in the ethe- real solution from which sodium glycocholate has deposited. It has not vet been obtained crystallized. It is dextrogyrate. When boiled with dilute acids, or with alkalies, it breaks up into cholalic acid and taurine (Strecker). C 26 H^XS0 7 + H 2 = C 2 *H*>0 5 + C 2 H 7 XS0 3 Taurocholic acid. Cholalic acid. Taurine. Taurine, which was discovered by Leopold Gnielin, has already been described (page 571). GO* 754 ELEMENTS OF MODERN CHEMISTRY. BILIRUBIN. C 16 H 18 N 2 3 This substance exists in human bile and in biliary calculi. It may be extracted from the latter, which contain it as calcu- lary pigment. They are crushed, and exhausted, first with ether, which removes the cholesterin, then with boiling water, and finally with chloroform. The coloring matter remains in the residue as a calcareous combination ; this is decomposed by adding hydrochloric acid, evaporating to dryness, and ex- hausting the dried residue with chloroform. After evaporation, the chloroform solution leaves a residue which contains, inde- pendently of bilirubin, three other biliary pigments which we will only mention : biliprasin, bilifuscin, and bilihumin. Alco- hol dissolves the bilifuscin from this residue, and the new residue is exhausted with chloroform, which takes up the bili- rubin, which alcohol precipitates in orange-colored flakes from the chloroform solution. Bilirubin is obtained in small, dark-red crystals by evapora- tion of its solution in chloroform. It is insoluble in water, and very slightly soluble in ether and alcohol, but dissolves in chlo- roform, benzol, and carbon disulphide. It is very soluble in the alkalies, forming an orange-red solution, which becomes pure yellow on addition of water, and from which hydrochloric acid precipitates bilirubin. The ammoniacal solution of bili- rubin gives precipitates with calcium chloride, barium chloride, and lead acetate. BILIVERDIN. C 16 H 18 N 2 0* When a solution of bilirubin in sodium hydrate is agitated with air, it absorbs oxygen and becomes green. Hydrochloric acid precipitates biliverdin from the solution. It is a bright green powder, insoluble in water, ether, and chloroform, but soluble in alcohol. It contains one more atom of oxygen than bilirubin. We may add that other coloring matters have also been derived from bile. They are bilifuscin, C 16 H 20 N 2 O, biliprpsin, C 16 H 22 N 2 6 , and bilihumin. PRODUCTS OF DISASSIMILATION. 755 Among the products of disassiniilation we may also mention : Leucine, C 6 H 13 N0 2 , which belongs to the homologous series of glycocol, and is found in many organs, especially in the pancreas, the salivary glands, the spleen, and the liver (page 590). Tyrosine, C 9 H n NQ 3 , a body crystallizing in fine needles, may be obtained from the pancreas and the spleen (page 701). It is known also that leucine and tyrosine may be obtained directly by the action of alkalies upon complex nitrogenized matters (page 742). Hippuric Acid, C 9 H 9 N0 3 , the origin of which has already been indicated (page 697). Uric Acid, C 5 H 4 N 4 3 , which exists in small quantity in human urine, and which constitutes a large proportion of the urine of birds and reptiles (page 608). Allantoin, C 4 H 6 N 4 3 , a product of the oxidation of uric acid, which Vauquelin and Buniva formerly extracted from the am- niotic liquor of the cow, and which has also been found in the urine of young calves (page 612). Various other products are related to uric acid. They are : •Xanthine, C 5 H 4 N 4 2 , a yellow matter, which Proust discov- ered in certain rare calculi (xanthic calculi), and which has also been found in small quantity in the muscles, pancreas, liver, and urine. Hypoxanthine or sarcine, C 5 H 4 N 4 0, a white, amorphous sub- stance which Scherer obtained from the spleen, and of which Strecker has noticed the existence in muscular tissue. Hypo- xanthine forms a crystallizable combination with hydrochloric acid. It presents interesting relations of composition with xan- thine and uric acid. Uric acid C5HW03 Xanthine C^NW Hypoxanthine C5H*N*0 When hypoxanthine is boiled with nitric acid, it is converted into a nitrogenized body. By the action of reducing agents, such as ferrous sulphate, this nitrogenized body is converted into guanine, C 5 H 5 N 5 0. The latter body was first obtained from guano. It has been found in the tissue of the pancreas. MEASURES OF WEIGHT. OUNCES TROY POUNDS GRAINS. = 480 GRAINS. AVOIRDUPOIS. 1 Milligramme = 0.01543 0.000032 0.0000022 1 Centigramme .= 0.15432 0.000321 0.0000220 1 Decigramme = 1.54323 0.003215 0.0002204 1 Gramme =3 15.43234 0.032150 0.0022046 1 Decagramme = 154.32349 0.321507 0.0220462 1 Hectogramme = 1543.23488 3.215072 0.2204621 1 Kilogramme = 15432.34880 32.150726 2.2046212 1 Grain = 0.064799 grammes. 1 Oz. Troy = 31.103496 " 1 Lb. Avoirdupois = 0.453495 kilogrammes. 1 Cubic Centimetre of water weighs 1 gramme. To convert Centigrade degrees into Fahrenheit degrees, multiply by 9 and divide by 5 ; add 32°. To convert Fahrenheit degrees into Centigrade degrees, subtract 32°, then multiply by 5 and divide by 9. • 1 Metre = 39.370708 inches. 1 Centimetre = 0.39370 " 1 Millimetre = 0.03937 llnch = 2.539954 centimetres. 756 INDEX. Acetal, 568. Acetamide, 549. Acetates, 534. Acetic anhydride, 538. Acetone, 543. Acetones, 439. Acetonitrile, 479. Acetyl chloride, 541. Acetylene, 562. Acid, 42, 437. acetic, 531. aconitic, 607. acrylic, 552. alloxanic, 610 amalic, 738. amidacetic, 588. amidopropionic, 590. anisic, 701. anthranilic, 710. antimonic, 189. arsenic, 182. arsenious, 179. aspartic, 599. atropic, 736. barbituric, 611. benzoic, 695. boric, 193. bromic, 130. butyric, 548. campholic, 661. camphoric, 663. caproic, 551. carbarn ic, 463. carbonic, 209. cerotic, 552. chlorethylsulphurous, 571. chloric, 125. chlorous, 123. cholalic, 753. chromic, 401. cinchomeronic, 753. cinchoninic, 733. cinnamic, 708. citraconic, 608. 64 Acid, citric, 605. crotonic, 553. cyanic, 460. cyanuric, 461. dialuric, 611. dibromosuccinic, 597. dicarbopyridic, 722, 733. dichloracetic, 537. digallic, 590. dilactic, 585. ditartaric, 601. dithionic, 97, 108. elaidic, 553. ethylnitrolic, 496. ethylphosphinic, 523. ethylsulphuric, 497. ethylsulphurous, 498. formic, 529. fumaric, 598. gallic, 702. glucic, 621. gluconic, 622, 645. glutamic, 740. glyceric, 572, 587. glycocholic, 753. glycollic, 581. glyoxylic, 582. hippuric, 697. hydantoic, 614. hydracrylic, 583, 587. bydriodic, 132. hydrobromic, 128. hydrochloric, 116. hydrocinnamic, 709. v hydrocyanic, 451. hydrofluoric, 136. hydrofluosilicic, 198. hydrosulphurous, 100. hypobromous, 129. hypochlorous, 122. hypophosphorous, 171. hyposulphuric, 109. hyposulphurous, 109. iodic, 134. 757 758 INDEX. Acid, iodopropionic, 547. isatic, 713. isethionic, 570. isobutyric, 549. isocrotonic, 553. isocyanic, 460. isophthalic, 705. isosuccinic, 597.' isovaleric, 550. itaconic, 608. lactic, 583., lactonic, 645. leucic, 591. maleic, 598. malic, 598. malonic, 595. manganic, 396, margaric, 551. meconic, 725. melassic, 621. melissic, 552. mellic, 649. mesaconic, 608. mesoxalic, 610. mesoxaluric, 611. metaboric, 194. metantimonic, 189. metaphosphoric, 175. metaphthalic, 705. metatartaric, 601. metavanadic, 361. inethylethylacetic, 550. methylnitrolic, 480. methylparoxybenzoic, 701. metoxybenzoic, 700. molybdic, 404. monobromsuccinic, 597. monocarbopyridic, 722. monochloroacetic, 537. mucic, 645. niobic, 362. nitric, 157. nitrocinnamic, 709. nitre-hydrochloric, 160. nitrosalicylic, 699. nitrotartaric, 601. nitrous, 154. oleic, 553. opianic, 729. ortharsenic, 182. orthophosphoric, 173. orthoxybenzoic, 698. oxalic, 592. oxamic, 595. oxybenzoic, 698, 700. Acid, oxymalonic, 595. palmitic, 552. parabanic, 613. paralactic, 583, 586. paratartaric, 604. paroxybenzoic, 700. pectic, 646. pectosic, 646. pentathionic, 97. perbromic, 130. perchloric, 125. perchromic, 87. periodic, 135. permanganic, 397. persulphuric, 96, 110. phenolsulphonic, 673. phenolsulphurous, 674. phenylacrylic, 708. phenylpropionic, 709. phenylsulphuric, 672. phenylsulphurous, 668. phosphoric, 173. phosphorous, 172. phthalic, 704. picramic, 673. picric, 673. propionic, 547. purpuric, 612. pyrantimonic, 189. pyrogallic, 702. pyromucic, 645. pyrophosphoric, 174. pyrotartaric, 601, 605. pyruvic, 601, 604. quinio, 730. quinnotannic, 730. quinolic, 653. rosolic, 682. ruberythric, 718. saccharic, 627, 645. saccharinic, 621. salicylic, 698. silicic, 199. stannic, 408. stearic, 552. succinic, 596. sulphydric, 92. sulphindigotic, 710. sulphocarbonic, 215. - sulphopurpuric, 710. sulphosulphuric, 97, 109. sulphuric, 102. constitution of, 105. fuming, 108. test for, 108. INDEX. 759 Acid, sulphurous, 97. tannic, 643. tantalic, 362. tartaric, 600. inactive, 604. tartronic, 595, 601. taurocholic, 753. terephthalic, 658, 704. tetraboric, 194. tetrathionic, 97. thiosulphuric, 109. tricar bally lie, 607. trichloracetic, 538. trim ethyl acetic, 550. trithionic, 97. tropic, 736. tungstic, 405. uric, 608, 755. valeric, 550. Acids, 42, 437. diatomic, 447. fatty, 527, 545. synthesis of, 528. metallic, 247. monatomic, 437. polyatomic, 580. AcoDitine, 735. Acraldehyde, 553. Acrolein, 552. Affinity, 11. Air, 63. analysis, 63, 68. dew-point, 75. Alabaster, 318. Alanine, 590. Albite, 375. Albumen, 740. Albuminoid matters, 738. Alcohol radicals, 444. Alcohol, allyl, 514. amyl, 510. active, 512. fermentation, 510. normal, 510. tertiary, 513. benzyl, 692. butyl, 508. fermentation, 508. normal, 509. secondary, 509. tertiary, 509. cetyl, 514. cinnamyl,. 708. ethyl, 484. heptyl, 513. Alcohol, hexyl, 513. isopropyl, 508. methyl, 471. octyl, 513. propyl, 508. Alcohols, diatomic, 446, 562. monatomic, 436, 469, 506. polyatomic, 448, 617. primary, secondary, tertiary, 507. Aldehyde, acetic, 539. polymerides of, 541. anisic, 701. benzoic, 624. butyric, 509. cinnamic, 707. crotonic, 540, 553. formic, 531. salicylic, 697. Aldehydes, 439. Aldehydrin, 721. Aldol, 540. ♦ Alizarin, 717. Alkaloids, 719. Allantoin, 612. Alloxan, 610. Alloxantin, 612. Alloys, 238. Allyl alcohol, 514. bromide, 559. iodide, 515. sulphide, 515. sulphocyanate, 515. tribromide, 575. Alum, 374. Aluminium, 371. chloride, 372. oxide, 372. silicates, 375. sulphate, 373. Amalgams, 238. Amelide, 458. Amides, 440. Amines, 441, 447, 516. -nitroso, 517 Ammonia, 13& action of CI and I, 143. action of potassium, 145. combustion of, 143. composition, 141. in air, 69. in gas liquor, 147. liquefaction, 140. -water, 141. Ammonias, compound, 441. 760 INDEX. Ammonium acetate, 536. amalgam, 145. carbamate, 149, 463. carbonate, 148. chloride, 146. formate, 530. isocyanate, 461. molybdate, 404. nitrate, 148. oxalate, 594. oxalurate, 613. sulphate, 149. sulphide, 147. sulphocyanate, 468. sulphydrate, 147. theory of, 146. Ampere's theory, 30. Amygdalin, 641. Amyl alcohols, 510. chloride, 512. iodide, 512. nitrite, 512. oxide, 512. Amylenes, 560. bromides, 561. polymerides of, 561. Anatase, 411. Anhydrite, 318. Aniline, 674. colors, 681. salts, 675. Anisic compounds, 701. Anisol, 671. Anthracene, 716. Anthracite, 202. Anthraquinone, 717. Antimonio-potassium tartrate, 602. Antimony, 185. antimonate, 188. oxide, 187. pentachloride, 187. pentasulphide, 190. pentoxide, 189. trichloride, 186. trioxide, 188. trisulphide, 189. Apomorphine, 727. Aquamarine, 323. Aqua-regia, 160. Arabinose, 624, 638. Aragonite, 317. Aromatic compounds, 646. isomerism of, 649, 650. Arsenic, 176. chloride, 179. Arsenic, disulphide, 183. pentasulphide, 184. pentoxide, 182. tests for, 180. trioxide, 179. trisulphide, 183. Arsine, 178. Ar sines, 442. Asparagin, 599. Assimilation, 750. Atomic heats, 34. theory, 27. weights, 39. determination of, 31-37. Atomicity, theory of, 222. Atoms, 13, 26. Atropine, 735. Aurin, 683. Australine, 657. Avogadro's law, 32. Azobenzol, 666. Azoxybenzol, 667. Azurite, 350. Barium, 321. carbonate, 323. chloride, 322. dioxide, 322. nitrate, 322. oxide, 321. sulphate, 323. sulphide, 322. tests, 323. Beer, 633. Benzamide, 696. Benzine, 506. Benzoin, 694. Benzol, 663. addition compounds, 664. azo-, 666. azoxy-, 667. constitution of, 651. dibromo-, 665. dichloro-, 665. dinitro-, 666. hexachloro-, 665. hydrazo-, 667. monobromo-, 665. monochloro-, 665. nitro-, 666. substitution compounds, 665. sulphone, 668. Benzophenone, 696. Benzoyl chloride, 694. hydride, 693. INDEX. 761 Benzyl alcohol, 692. aldehyde, 693. chloride, 693. Benzylamine, 693. Berthollet's laws, 267. Beryllium, 323. Bilirubin, 754. Biliverdin, 754, Bismuth, 368. chloride, 369. nitrate, 370. oxide, 369. tests, 370. Bituminous coal, 202. Biuret, 467. Bleaching, chlorine, 115. -liquids, 123. -powder, 318. sulphurous oxide, 100. Blende, 327. Bone-oil, 720. Borax, 303. Boron, 191. chloride, 192. crystallized, 192. fluoride, 193. oxide, 193. Boro-potassium tartrate, 603. Bromine, 127. oxides, 129. Bromoform, 467. Bromopicrin, 478. Brookite, 411. Brucine, 733. Bunsen burner, 221. Butane, 484. Butyl alcohols, 508. Butylenes, 559. Butyral, 549. Butyrone, 549. Cacodyl, 482. Cadmics, 332. Cadmium, 332. iodide, 332. oxide, 332. sulphate, 333. sulphide, 332. Caesium, 305. Caffeidine, 738. Caffeine, 737. Calamine, 327. Calcium, 314. carbonate, 81, 317. Calcium, chloride, 316. glucosate, 621. hydrate, 315. hypochlorite, 319. lactate, 585. nitrate, 317. oxide, 315. sulphate, 318. tests, 320. Calomel, 355. Camphenes, 659. Camphor, 660. artificial, 658. Borneo, 662. mint, 662. thyme, 706. Camphorone, 363. Caramel, 627. Carbamide, 460, 463. Carbimide, 461. Carbon, 200. dioxide, 209. in air, 67, 69. liquefaction, 212. disulphide, 215. estimation of, 425. monoxide, 207. compounds of, 459. oxysulphide, 216. sesquichloride, 557. tetrachloride, 478. Carbonates, 277. tests for, 279. Carbonyl chloride, 208. Carbylamines, 479, 495. Carvacrol, 706. Casein, 748. Cassiterite, 406, 408. Celestine, 321. Cellulose, 638. Cement, 316. Cerium, 376. Chalk, 317. Charcoal, 202. absorbent properties of, 204. animal, 204. reduction by, 205. wood, 202. Chemical energy, 230. Chloral, 542. Chloranile, 686. Chlorides, 248. monatomic, 434. of acid radicals, 440. Chlorine, 112. 64* 762 INDEX. Chlorine, analogies with Br and I, 136. bleaching by, 115. liquefaction, 114. oxides, 121. Chloroform, 475. Chloropicrin, 477. Chlorous anhydride, 123. Cholesterin, 752. Chondrin, 742. Chromates, 402. Chrome iron, 400. yellow, 343. Chromium, 400. chlorides, 403. oxides, 401. Cinchona bark, 729. Cinchonine, 733. Cinnabar, 351, 354. Cinnamic alcohol, 708. aldehyde, 707. Citrine, 660. Clay, 375. Coal, 202. Cobalt, 391. chloride, 392. oxides, 391. sulphate, 392. tests, 392. Cocaine, 734. Codeine, 727. Cohesion, 11, 15. Coke, 202. Collidines, 722. Collodion, 640. Combination, 9, 13. laws of, 23-27. Combustion, 58. Conhydrine, 724. Conine, 723. Copper, 344. acetates, 535. alloys, 347. atomicity of, 360. carbonates, 350. chlorides, 348. formate, 530. •oxides, 347. pyrites, 344. sulphates, 349. sulphides, 348. tests, 351. Corrosive sublimate, 356. Corundum, 372. Cotarnine, 729. Creatine, 616. Creatinine, 616. Cresols, 690. Cumene, 706. Oupellation, 308, 312. Cyamelide, 460. Cyanamide, 457. Cyanides, 453. Cyanobenzol, 668. Cyanogen, 449. bromide, 457. chlorides, 456. iodide, 457. Cymene, 706. Dalton's laws, 23, 26. Dambonite, 623. Dambose, 623. Decomposition, 13, 17, 20. Definite proportions, law of, 21. Descloizite, 360. Dew-point, 75. Dextrin, 635. Diamines, 447. Diamond, 201. combustion of, 210. Diastase, 633, 636. Diazoamidobenzol, 678. Diazobenzol compounds, 67bo. iodide, 357. Mercury, 351. atomicity of, 360. cyanide, 453. fulminate, 481. nitrates, 358. oxides, 354. sulphates, 359. sulphide, 354. tests, 359. Mesitylene, 705. Mesoxalyl-urea, 611. Metaldehyde, 541. Metallic carbonates, 277. chlorides, 24S. hydrates, 246. nitrates, 273. oxides, 240. sulphates, 275. sulphides, 247. Metals, classification of, 279, 2S6. diatomic, 2S0. general properties of, 233. monatomic, 280. tetratomic, 283. Metamerism, 431. Metastyrolene, 707. Metaxylol, 703. Methane, 470. Methylal, 474. Methylamines, 519. Methylaniline, 676. Methylbenzol, 687. Methyl bromide, 473. carbylamine, 479. chloride, 473. compounds, 469. cyanide, 478. 766 INDEX. Methyl cyanurate, 503. hydrate, 471. iodide, 473. nitrate, 479. nitrite, 479. oxide, 473. salicylate, 700. Methylene chloride, 474. diacetate, 475. diethylate, 474. iodide, 474. Methylglycocol, 589. Methylmorphine, 728. Mica, 375. Mineral waters, 82. Minium, 362. Molecular weights, determination of, 32, 429. Molecules, 11. Molybdenite, 404. Molybdenum, 404. Monochlorhydrin, 573. Morphine, 726. Mortar, 315. Murexide, 609, 612. Mycose, 629. Myosin, 744. Naphtha, 506. Naphthalene, 714. Naphthol, 715. Naphthylamine, 716. Narceine, 725. Narcotine, 728. Neurine, 568, 751. Nickel, 393. chloride, 394. oxides, 393. plating, 393. sulphate, 394. tests, 394. Nicotine, 724. Niobium, 361. chlorides, 362. oxides, 362. Nitrates, 273. tests for, 274. Nitrethane, 495. Nitric anhydride, 157. Nitrobenzol, 666. Nitroferrocyanides, 456. Nitroform, 477. Nitrogen, 138. chloride, 144. dioxyde, 153. Nitrogen, estimation of, 428. group of elements, 190. in air, 63. iodide, 145. monoxide, 151. oxides, 150. pentoxide, 157. peroxide, 155. trioxide, 154. Nitroglycerin, 575. Nitromethane, 479. Nitronaphthalene, 715. Nitrophenols, 672. Nitroso-amines, 517. bases, 517. Nitrosodimethylaniline, 676. Nitrosoinethjlaniline, 676. Nitrosyl-chloride, 161. Nitrotoluols, 690. Nitryl, chloride and bromide, 156 Nomenclature, 37. Nornarcotine, 729. Notation, 37-47. Oils, essential, 656. fatty and drying, 577. Olein, 577. Opium, 726. Orcin, 691. Organo-metallic compounds, - Orpiment, 183. Orthoxylol, 703. Osmium, 417. Oxalates, 593. Oxalyl-urea, 613. Oxamide, 451, 594. Oxides, 40, 241. acid, 241. antimonic, 189. antimonous, 188. arsenic, 182. arsenious, 179. basic, 241. boric, 194. chlorocarbonic, 208. chlorous, 123. cupric, 348. cuprous, 347. ferric, 387. ferroso-ferric, 387. ferrous, 386. hypochlorous, 122. manganic, 395. manganoso-manganic, 395. mercuric, 354. INDEX. 767 Oxides, mercurous, 354. metallic, 240. classification of, 241. molybdic, 404. niobic, 362. nitric, 153. nitrous, 151. persulpkuric, 110. phosphoric, 173. plumbic, 337. plumboso-plumbic, 338. saline, 241. silicic, 199. singular, 241. stannic, 408. stannous, 408. sulphuric, 101. sulphurous, 97. tantalic, 362. vanadic, 360. Oxindol, 713. Oxygen, 54. in air, 63. liquefaction, 66. preparation, 55. properties. 55-59. Oxy hydrogen blowpipe, 59. Oxyphenols, 683. Ozone, 59. composition, 62. in air, 70. liquefaction, 61. tests for, 59. Palladium, 417. Palmitin, 577. Papaverine, 725. Paraconine, 724. Paracyanogen, 449. Paraldehyde, 541. Paraxylol, 703. Pectic matters, 646. Pectose, 646. Pepsin, 744. Peptones, 744. Petroleum, 505. Phenanthrene, 717.' Phenetol, 671. Phenol, 669. ethers of, 671. Phenyl cyanide, 668. nitro-, 672. nitroso-, 672. oxide, 672. Phenylamine, 674. Phloretin, 643. Phloridzin, 643. Phloroglucin, 643, 687. Phosgene gas, 209. Phosphine, 165. Phosphines, 442. Phosphonium, 167. Phosphoric anhydride, 173. Phosphorus, 161. amorphous, 163. bromide, 169. iodide, 170. oxides, 170. oxychloride, 169. pentachloride, 168. pentoxide, 173. sulphides, 176. sulphochloride, 159. trichloride, 168. Phthaleins, 704. Phthalic anhydride, 704. Pinacolin, 544. Pinacone, 544. Pinite, 618. Piperidine, 737. Piperine, 737. Pitchblende, 399. Plaster of Paris, 318. Platinum, 413. black, 52, 415. chlorides, 415. sponge, 414. Plumbago, 201. Polymerism, 431. Populin, 642. Porcelain, 375. Potassamide, 145. Potassium, 287. acetate, 534. acid carbonate, 295. acid sulphate, 293. bromide, 291. carbonate, 294. chlorate, 293. chloride, 290. chromate, 402. cyanate, 461. cyanide, 453. dichromate, 402. ferricyanide, 455. ferrocyanide, 454. hydrate, 288. iodide, 290. " isocyanate, 460. manganate, 396. 768 INDEX. Potassium, methylate, 472. nitrate, 291. oxalates, 593. oxides, 288. perchlorate, 294. permanganate, 397. picrate, 673. sulphate, 293. sulphides, 289. sulphocyanate, 468. tartrates, 602. tests, 295. Pottery, 317. lead glazing, 339. Propionitrile, 465. Propyl alcohols, 508. glycols, 571. iodides, 474. Propylenes, 559. Propylethylene, 561. Prussian b]ne, 455. Pseudocumene, 705. Pseudomorphine, 725. Purple of Cassius, 366. Purpurin, 719. Pyridic bases, 720. Pyridine, 721. Pyrocatechin, 683. Pyrogallol, 702. Pyrolusite, 395. Pyroxylin, 640. Quercite, 618. Quinhydrone, 685. Quinine, 731. Quinoline, 722. Quinone, 685. Radicals, monatomic, 444. polyatomic, 445. Realgar, 183. Resorcin, 684. Respiration, 59, 750. Rhodium, 416. Richter's laws, 255. Rochelle salt, 602. Rosaniline, 679. colors, 681. Rubidium, 305. Ruby, 372. Ruthenium, 416. Rutile, 411. Saccharin, 621. Saccharose, 624. Saccharose, ethers of, 628. Safety-lamp, 219. Salicin, 642. Salicyl hydride, 697. Saligenin, 642, 698. Salts, 43, 252. action of acids, 267. bases, 269. electricity, 264. heat, 263. metals, 266. salts, 270, 272. water, 258. efflorescent, 260. neutral, acid and basic, 254. Samarium, 378. Saponification, 579. Sapphire, 372. Sarcine, 755. Sarcosine, 589. Scandium, 378. Scheelite, 404. Silica, 199. soluble, 200. Silicon, 194. chloride, 196. crystallized, 195. fluoride, 197. oxide, 199. Silicon-ethyl, 524. Silver, 307. acetate, 536. assay, 312. chloride, 310. cupellation, 308. fulminate, 481. fulminating, 310. iodide, 311. nitrate, 311. oxide, 310. sulphide, 310. tests, 312. Silvering, 312. Slow combustion, 58. Smalt, 391. Soap, 578. Sodio-potassium tartrate, 602. Sodium, 296. acetate, 535. acid carbonate, 303. acid sulphate, 300. borate, 303. carbonate, 300. chloride, 298. hydracrylate, 587. INDEX. 7G9 Sodium hydrate, 297. hydrosulphite, 100. hyposulphite, 109. nitroferrocyanide, 456. oxides, 297. phosphates, 303. sulphate, 299. sulphide, 297. sulphydrate, 297. tests, 304. thiosulphate, 109. tungstate, 405. uranate, 399. Solution, 79, 258. Sorbin, 623. Sorbite, 619. Specific heat, 34. Spectrum analysis, 305. Spermaceti, 514. Stannethyls, 526. Starch, 634. Stassfurth salt, 290. Stearin, 577. candles, 578. • Steel, 384. Stibines, 442. Strontianite, 321. Strontium, 320. Strychnine, 733. Styracin, 708. Styroline, 707. Succinic anhydride, 596. Succinyl chloride, 596. Sugar, cane, 624. grape, 620. inverted, 627. milk, 628. Sugars, 619. Sulphates, 275. tests for, 277. Sulphides, metallic, 247. * Sulphobenzide, 668. Sulphocarbamide, 469. Sulpho-urea, 469. Sulphur, 88. analogies with oxygen, 92. chlorides, 126. dimorphism of, 90. dioxide, 97. oxygen acids, 96. peroxide, 101. soft, 90. trioxide, 101. Sulphuric anhydride, .101. Sulphurous anhydride, 97. Sulphuryl chloride, 100, 106. Supersaturation, 261. Synanthrose, 629. Syntonin, 745. Tannin, 643. Tantalum, 361. chloride, 362. oxide, 362. Tartar-emetic, 602. Tartaric anhydride, 601. Tartrate, 602. . Tartronyl-urea, 611. Taurine, 571. Tellurium, 111. Terebene, 659. Terpilene, 659. Terpin, 658. hydrate, 658. Tetrachlorethylene, 557. Tetramethylammoniun\, 520. Tetrethylammonium, 521. Thallium, 367. Thebaine, 725. Theine, 737. Theobromine, 737. Thermo-chemistry, 230. Thorium, 413. Thymol, 706. Tin, 406. dichloride, 409. oxides, 408. sulphides, 409. tests, 411. tetrachloride, 410. Titanium, 411. dioxide, 411. Toluidines, 691. Toluol, 687. chloro-, 690. nitro-, 690. Topaz, 372. I Trehalose, 629. Tribenzylamine, 693. Tribromhydrin, 575. Trichloraldehyde, 542. Trichlorhydrin, 574. Triethylamine, 521. Trimethylamine, 520. Trimethylbenzols, 705. Trimethylcarbinol, 509. i Trimethylene, 559. | Trimethylethylene, 560. Trinitroacetonitrile, 479. ; Trinitrophenol, 673. <55 770 INDEX. Trioxy methylene, 531. Tungsten, 404. Turpentine, 656. Type metal, 186. Tyrosine, 701. Uranium, 399. chlorides, 400. oxides, 399. yellow, 399. Uranyl nitrate, 399. Urea, 463. Ureas, compound, 467. Ureides, 610. Urethane, 501. Vanadanite, 360. Vanadium, 360. bronze, 361. Verdigris, 536. Vermilion, 355. Vinegar, 531. Vitriol, blue, 349. green, 389. white, 330. Water, 70. analysis, 71. charcoal filter for, 205. hard, 80, 81. in air, 67. Water, maximum density, 75. mineral, 82. natural state of, 79. of crystallization, 260. reactions of, 77. soft, 80. solvent properties of, 79. Wax, 514. Wine, 632. Witherite, 323. Wolfram, 404. Wolframine, 405. Wood-spirit, 447. Yeast, 576. Yttrium, 378. Zeolites, 375. Zinc, 327. chloride, 330. hydracrylate, 587. lactate, 586. oxide, 329. sulphate, 330. sulphide, 330. tests, 331. Zinc-ethyl, 525. Zinc-methyl, 525. Zircon, 412. Zirconium, 412. 0{> 'J THE END. 9$5* '* < *W ^ V" s -a V Vl*oL " ^ A ' ^ °' C> \> , X ■>V\ ■ \ - % ^ .*>■ -'%■ ., 003 775 444 4 mtMmM mam 11 IBB ittlM H 1 I WW