This acid has not been obtained free from water : the aqueous solution is sour, iuodorous, and reddens vegetable blues : if heated to 212°, it is decomposed into sulphurous and sulphuric acids; and when exposed to the air, it slowly absorbs oxygen ; and becomes sulphuric acid. Unlike sulphuric acid, it forms soluble compounds with lime, baryta, strontia, and oxide of lead ; but, like diluted sulphuric acid, it acts upon and dissolves zinc, with the evolution of hydrogen gas, and a solution of hyposulphate of zinc is formed ; its salts are decomposed at a high temperature, yielding sulphurous acid and sulphates remaining.
Trithionic add (HO, Sulphuretted hyposulphuric acid. As a potash salt this acid is formed when sulphur is digested in bisulphite of potash for several days, or until all yellow colour has disappeared. The resulting solution gives a black precipitate with subnitrate, and a white with pernitrate of mercury. From the trithionate of potash the acid may be liberated by tartaric acid, and obtained in unstable pris matic crystals by evaporation. By heat the trithionate split up into sulphur, sulphurous acid, and sulphate of the base.
Tetrathionic acid (HO, S,0,). llisulphurettcd hyposulphuric acid. Two equivalents of hyposulphite of baryta and one of iodine yield iodide of barium and tetrathionate of baryta. The latter may be purified by recrystallisation, and the acid liberated by the cautious addition of sulphuric acid. It is somewhat unstable.
Pentathionic acid (HO, SA). Trisulphuretted hyposulphuric acid. When sulphurous and hydrosulphuric acids come into contact, the following decomposition occurs :— Pentathionie acid is very unstable. Its baryta compound may be obtained in silky scales.
Chlorosulphuric acid or chloride of tulphuryl (SO, CI). A colourless liquid of pungent odour and powerful eye-irritating properties, formed on bringing together dry sulphurous acid and chlorine gases in bright sunlight. It is volatile without decomposition, but water instantly breaks it up. It does not appear to combine with bases.
Nitroaulpliuric acid (1iO, SO NO,). If nitric oxide (NO,) be primed through a cold solution of sulphite of ammonia containing large excess of ammonia, white crystals of nitrosulphate of ammonia (N11,0,SO,N0,) are deposited. Other nitrosulphates may be formed, but they are very unstable, and the acid cannot be liberated from them.
Sulpha:otised acids, discovered by Fremy, form with potash, but not with soda, a remarkable series of salts. They are derived from bask nitrite of potash, sulphurous acid and water, as indicated in the follow ing equations :— Nitrogen and Sulphur. [NITROGEN.] Hydrogen and Sulphur combine in two proportions, forming hydro sulphuric add (HS), frequently called sulphuretted hydrogen, and per aulphide of hydrogen (HS, I).
ilydrosulphuric add, formerly known by the name of hepatic gas, exists in sulphurous waters, such as those of Harrowgate. It may be formed, to a certain extent, by beating or subliming sulphur in hydro gen gas. It is usually produced by the action of hydrochloric acid on sulphide of antimony, or by acting upon protosulphide of iron with dilute sulphuric acid : In the former case the hydrogen of the hydro chloric acid unites with the sulphur of the sulphide, chloride of anti mony being also formed ; while in the latter, the decomposed water yields hydrogen to the sulphur and oxygen to the iron, which latter, being then dissolved by the acid, constitutes sulphate of iron. As it is difficult to combine the whole of any given quantity of iron with sulphur, the uneombined portion yields a little free hydrogen with the hydrosulphuric acid ; but this, in most cases, is of no con sequence. Although hydrosulphurie acid is soluble in one-fourth its bulk of water, yet the gas may for most purposes be received by dis placement in vessels filled with that liquid.
Hydrosulphuric acid is colourless, and gaseous at common tempera tures and pressures : it has a peculiarly nauseous and fetid odour, resembling that of putrid eggs ; its taste is also extremely disagreeable.
Its specific gravity is about 100 cubic inches weigh about 38 grains. It is composed of one equivalent of hydrogen and one equiva lent of sulphur, as indicated in the above formula. It reddens moist litmus-paper, but not strongly, and is soluble in about one-third of its bulk of water. At a temperature of 50°, and under a pressure of about 17 atmospheres, it is rendered a limpid liquid, of specific gravity about : this does not congeal till cooled down to 122' Fahr. It is ex tremely poisonous to animals : air containing 1-1500th of its bulk immediately killed a bird, and 1-1000th a middle-sized dog. When mixed and detonated with oxygen gas, the results are water and sul phurous acid.