poses sulphuric acid when heated with it, the products being sulphurous and carbonic acids. Many metals also decompose sulphuric acid with the aid of heat, sulphurous acid being evolved, and sulphates of the metallic oxides produced. BIHYDRATED SULPHURIC ACID, 2HO.SO,, produced by the combination of one equivalent of sulphuric acid and two of water, is a liquid having the specific gravity 1.78; it solidifies to transparent colorless six-sided prisms, at about 39°.2 F. (4° C.); when it is heated to between 401° and 410° F. (205° and 210° C.), one equivalent of water is expelled together with some sulphuric acid, and oil of vitriol is obtained. TERHYDRATED SULPHURIC ACID, 3HO.SO,.-This hydrate of sulphuric acid has a spec. grav. of 1.632; it bofls at between 379°.4 and 390°.2 F. (193° and 199° C.), no acid being volatilized at that temperature. When dilute sulphuric acid is evaporated in vacuo over oil of vitriol, this hydrate is left. COMBINATIONS OF SULPHURIC ACID WITH METALLIC OXIDES.-Sulphuric acid may be considered as the most powerful acid, since, under ordinary circumstances, it expels all others from their combinations. There are two classes of sulphates; the neutral salts, represented by the general formula, MO.SO,, and the bisulphates, MO.SO,, HO.SO,, or MO.HO.2SO,. Many of the neutral sulphates are soluble with difficulty, or wholly insoluble in water. The acid sulphates of the alkalies, and some other oxides, are far more soluble than the corresponding neutral salts. Sulphates are decomposed by ignition with charcoal; in some cases the metallic sulphides are obtained, carbonic oxide and carbonic acid being disengaged; in others, the metals are reduced, and carbonic oxide, sulphurous and carbonic acids evolved. Many sulphates are decomposed by a current of hydrogen at a red heat, water, and the metallic sulphides being produced. Alkaline sulphates existing in somewhat dilute aqueous solutions (for example, in mineral waters) undergo gradual decomposition when allowed to remain in contact with organic matter; the sulphur parts with its oxygen, which oxidizes the organic matters, and metallic sulphides, or hydrosulphuric acid, are produced. A particle of cork allowed to fall accidentally into the water, is sufficient to induce this decomposition. Uses of Sulphuric Acid.-The great facility and cheapness with which sulphuric acid may be manufactured on a large scale, has rendered it by far the most valuable chemical agent in the manufactures and arts. The important functions which it exercises in the manufacture of soda need merely be adverted to. As a chemical agent, sulphuric acid is also one of the highest importance. In consequence of its powerful affinities for bases, it may be employed to separate most other acids from their combinations; its affinity for water is also turned to advantage by the chemist, as already mentioned. One of the most recent uses to which sulphuric acid has been applied as a reagent, is met with in the process of silver-refining, when auriferous silver is boiled with oil of vitriol, which dissolves the silver in the form of sulphate, without acting upon the gold. (The silver is precipitated from the solution by means of slips of copper.) The Nordhausen sulphuric acid possesses the property of dissolving indigo, yielding a solution much used by dyers. § 106. We have written the formula of hydrated sulphuric acid (HO.SO,), consistently with the older view, which regards it as a compound of water with the anhydrous acid, SO,. The circumstance, however, that SO, is not capable of entering into combination with bases, and does not appear to possess the properties of an acid, until it has been brought in contact with water, has led many It has been observed that well-water, containing much sulphate of lime, which had been shaken with an ethereal oil and allowed to stand in a close vessel for some weeks, became charged with hydrosulphuric acid, while the oil diminished in bulk, and carbonate of lime separated from the water. chemists to believe that the so-called hydrated acid is really the hydrogen-acid of a radical SO; for HO.SO, H.SO,, and sulphuric acid then becomes analogous to hydrochloric acid, containing the compound radical SO, in place of chlorine. Upon this hypothesis many of the reactions of sulphuric acid could be explained in a far simpler manner than upon the older view; compare, for example, its action upon zinc :— 3 Older view: Zn+HO.SO, ZnO.SO,+H. The latter equation is quite similar to that which represents the action of hydrochloric acid upon zinc: Zn+HCl=ZnCl + H. Upon this theory, the sulphates would no longer be regarded as compounds of sulphuric acid with the metallic oxides, but as haloid salts, composed of metals combined with the radical SO.. According to the older view of the constitution of sulphuric acid, sulphates are formed by the substitution of an equivalent of base for the equivalent of water in the hydrated acid, whereas the new theory regards them as produced by the replacement of the hydrogen by a metal, the oxygen of the oxide combining with the displaced hydrogen to produce water; the following equations exhibit the formation of sulphate of copper upon both views:Older view: CuO+HO.SO, CuO.SO,+HO. New view: Cu0+HSO,=CuSO,+HỔ. It will be seen that, in the latter case, the formation of a sulphate is analogous to that of a chloride, by the action of hydrochloric acid upon a metallic oxide : CuO+HCl=CuCl+HO. This binary theory, as it is generally termed, has been applied to other acids and salts, the formulæ of some of which are given in the subjoined list, in juxtaposition with those which they would have according to the new view : 6 3 One great objection to this theory is, that the new radicals are hypothetical; neither SO, NO, PO, PO,, nor PO,, has been obtained in the separate state. This, however, would not form an insuperable bar to its adoption, since the chemist does not refrain, in other cases, from assuming the existence of a radical when the behavior of a series of compounds appears to justify such an assump tion. LESS IMPORTANT Oxides of SULPHUR. § 107. TRITHIONIC ACID, S,O,. Eq. 88.-This acid is prepared by boiling a saturated solution of bisulphite of potassa, for some days, with flowers of sulphur (until the yellow color at first observed disappears), and filtering while Trithionate of potassa crystallizes out, and is separated from excess of sul hot. IMO representing any basic protoxide. phur by solution in a small quantity of tepid water. The potassa-salt is afterwards decomposed by means of tartaric or perchloric acid; an aqueous solution of the acid is thus obtained, which may be concentrated by gentle evaporation. Properties. The aqueous solution of this acid is colorless, transparent, and inodorous; it is not a very powerful acid. It easily decomposes, even at ordinary temperatures, being resolved into sulphur, sulphurous, and sulphuric acids:S2O, SO2+SO,+S. 3 Heat accelerates the decomposition. It is also decomposed by nitric acid into sulphuric acid and sulphur. The trithionates have not been much studied; the potassa salt is the best known. It is easily decomposed by heat, or by more powerful acids, sulphur being precipitated, and sulphurous acid frequently evolved. TETRATHIONIC ACID, SO,. Eq. 104.-On dissolving iodine in hyposulphate of baryta, iodide of barium and tetrathionate of baryta are formed, as is shown by the following equation: 2(BaO.S ̧0,)+I=BaI+BaO.S ̧ ̧. The tetrathionate of baryta is insoluble in strong alcohol, and may therefore, by digestion in the latter, be separated from the admixture of iodine and iodide of barium. An aqueous solution of the acid may be obtained by carefully decomposing the baryta-salt with sulphuric acid. Properties.-The solution of tetrathionic acid is transparent and colorless; it is decomposed by heat into sulphur, sulphurous and sulphuric acids:— Nitric acid decomposes it, but hydrochloric and sulphuric acids do not. When in contact with a strong base, this acid sometimes decomposes into trithionic acid and sulphur. The salts of tetrathionic acid may be best obtained in the crystalline state by mixing their aqueous solutions with alcohol. They are decomposed by heat, like the trithionates. PENTATHIONIC ACID, S,O,. Eq. 120.-This acid is produced by the action of hydrosulphuric and sulphurous acids upon each other; water being simultaneously formed, and sulphur deposited : : 5HS+5SO, S,O,+5HO+S,. An aqueous solution is obtained by passing excess of hydrosulphuric acid into a saturated solution of sulphurous acid, digesting the filtered solution with slips. of copper until it is perfectly clear, separating the dissolved copper from the solution by hydrosulphuric acid, and expelling the excess of the latter by heat. Properties. The solution of pentathionic acid is colorless and inodorous; it does not decompose at ordinary temperatures, and a weak solution may be concentrated by the aid of heat, without decomposition, until it attains a specific gravity of 137, when it is decomposed, hyposulphurous, sulphurous, and sulphuric acids being formed, and sulphur deposited. Oxidizing agents convert it into sulphuric acid. But little is known respecting the pentathionates; they are very unstable, the fifth equivalent of sulphur existing, apparently, but very loosely combined in the acid; frequently, strong solutions of pentathionates resolve themselves into the more stable tetrathionates, with deposition of sulphur; it is, therefore, very difficult to obtain the pentathionates in a solid form, even by evaporation of their solutions in vacuo. SULPHUR AND HYDROGEN. PENTASULPHIDE OF HYDROGEN, OR HYDROSULPHUROUS ACID. §108. Preparation. When solutions of alkalies or alkaline earths are boiled with excess of sulphur, the metallic pentasulphides are obtained, together with the byposulphites. Upon gradually adding a clear solution of a pentasulphide thus prepared (which is of a deep orange color) to a great excess of moderately strong hydrochloric acid (one of concentrated acid to two of water), and rapidly stirring, a viscid, almost transparent, light yellow liquid separates, collecting at the bottom of the vessel. This liquid, which is the pentasulphide of hydrogen, generally contains an excess of sulphur, which is liberated by the decomposition of the hyposulphite by the acid. Properties.-Pentasulphide of hydrogen is a light yellow, transparent, oily liquid, possessing a peculiar acrid, somewhat sulphurous odor, and a taste both sweet and bitter. It dissolves sulphur to a considerable extent, becoming viscid; its true composition has therefore never been quite satisfactorily established. It undergoes spontaneous decomposition when kept, being resolved into hydrosulphuric acid and sulphur; hence it gradually becomes viscid, and finally solid, when preserved; and if the decomposition is allowed to take place in sealed tubes, the hydrosulphuric acid is liquefied by its own pressure. Elevation of temperature accelerates this decomposition; it is however prevented, or considerably retarded, by the presence of acids. Several metals and metallic oxides, some sulphides, powdered charcoal, and several other substances, promote the decomposition of pentasulphide of hydrogen, which, in this respect, is very similar to the binoxide of hydrogen. It is inflammable, burning with a blue flame, and yielding sulphurous acid and water. HYDROSULPHURIC ACID, SULPHURETTED HYDROGEN. HS. Eq. 17. Sp. Gr. 1.1912. Composition by Volume.-1 volume of sulphur-vapor and 6 volumes of hydrogen form 6 volumes of the gas. Sulphuretted hydrogen occurs in nature in a great number of mineral and sulphurous springs; also in marshy districts, as a product of vegetable decomposition. It is always formed in the putrefactive decomposition of organic matters containing sulphur. Preparation. This acid is prepared by introducing some fragments of sulphide of iron (of the size of a small nut) into the generating vessel of a hydrogenapparatus, provided with a washing-bottle (see § 27) containing a little water; the generating-bottle is half filled with water, and concentrated sulphuric acid gradually added, the bottle being slightly agitated after each fresh addition, so as to insure immediate mixture of the acid with the water. The production of the gas is as follows: FeS+HO.SO=FeO.SO2+HS. The gas must be collected over a strong solution of salt, or hot water, or even over mercury, although the latter is slightly acted upon. When obtained in this manner, it frequently contains a little free hydrogen, carburetted hydrogen, &c.; a purer gas may be obtained, although in much smaller quantity, by heating powdered tersulphide of antimony with concentrated hydrochloric acid: SbS,+3HCl=SbCl,+3HS. This gas must be dried, if necessary, by means of chloride of calcium, since it decomposes oil of vitriol. Properties.-Sulphuretted hydrogen is a colorless gas, possessing a peculiar odor (that of rotten eggs); it is highly poisonous, producing fainting and syncope when diluted with air, and acting as a narcotic poison when inhaled pure. It does not support combustion, but burns with a pale blue flame, the products being sulphurous acid and water:— HS+0,=HO+SO,. A little sulphuric acid is generally produced at the same time. It reddens litmus-paper, but this reddening disappears on exposing the paper to the air. Sulphuretted hydrogen may be converted by a pressure of 17 atmospheres, into a transparent colorless liquid, which is far more mobile than ether, has the specific gravity 0.9, and dissolves sulphur with the aid of heat, depositing it again on cooling. At a temperature of 122° F. (-85°.7 C.) sulphuretted hydrogen solidifies to a white crystalline translucent substance. If sulphuretted bydrogen be passed through a red hot tube, it is decomposed, hydrogen escaping, and sulphur being deposited. A mixture of sulphuretted hydrogen and oxygen explodes upon the approach of flame, the products being water and sulphur, or sulphurous acid, according to the proportion of oxygen employed.. Sulphuretted hydrogen is oxidized with great facility by some acids and by a few high metallic oxides, these becoming converted into lower oxides. Thus, chromic acid is converted into sesquioxide of chromium, and sesquioxide of iron into oxide, by treatment with sulphuretted hydrogen, water being formed, and sulphur precipitated, oxides of sulphur being also sometimes produced. When hydrosulphuric acid is passed into moderately strong nitric acid, its hydrogen is oxidized, and the greater portion of the sulphur separated in a peculiar viscid state. A little sulphate of ammonia is formed at the same time. When passed through concentrated sulphuric acid, this gas is also decomposed, water and sulphurous acid being formed, and sulphur deposited. Chlorine, bromine, and iodine decompose sulphuretted hydrogen, the results being hydrochloric, hydrobromic, and hydriodic acids respectively, and sulphur. A few metals also decompose this gas when heated in it, the sulphides being produced and hydrogen evolved. Sulphuretted hydrogen is soluble to a considerable extent in water, which absorbs about 2 times its own volume at ordinary temperatures; the solution possesses properties similar to those of the gas; it undergoes gradual decomposition on exposure to air and light, sulphur being deposited; it should, therefore, be kept in closely stoppered bottles, quite full. A hydrate of the acid may also be formed, existing only at low temperatures. Sulphuretted hydrogen acts upon metallic oxides in solution, converting them into sulphides with formation of water. These compounds will be presently re verted to. § 109. SULPHUR AND NITROGEN.-By the action of water upon a substance produced by the combination of chloride of sulphur (SCI) with ammonia, a light green solid is produced, which is a combination of sulphur with nitrogen, having the formula NS,,' and which is decomposed by water into byposulphurous acid and ammonia. NITROSULPHURIC ACID.-A compound of sulphurous acid and binoxide of nitrogen called sulphite of nitric oxide, or nitrosulphuric acid, having the formula NO, SO, exists in combination with the alkaline bases, but cannot be obtained in the separate state. The nitrosulphates are prepared by treating alkaline sulphites. with nitric oxide. They are crystalline and colorless, their composition is represented by the formula, MO.NO, SO,. 1 Or, according to Fordos and Gélis, NS, |