HYDROSULPHWRIC ACID (HS), known also as sulphurefed hydrogen, sulphydric acid, and hydrothionic acid, is a natural gaseous constituent of many mineral waters, as, for example, those of Aix-la-Chapelle in Germany, Bareges in France, Abano in Judy, and Harrogate in England, and is evolved front fumaroles and volcanoes. It is formed spontaneously wherever sulphurous organic matters are undergoing putrefaction, as, for instance, in stagnant sewers and cesspools, and in waters charged with organic matter and sulphates, especially sulphate of lime.
There are several ways of preparing this gas, which is very extensively used in laboratory operations. The following is that which is most commonly employed. Sulphide (the old sulphuret) of iron, in small fragments, is placed in a bottle, and dilute sulphuric ceid is added. Water is decomposed, its hydrogen combining with the sul phur of the sulphide to form hydrosulphurie acid, which escapes as a gas, while its oxygen enters into combination with the iron, forming oxide of iron (AO), which unites with the sulphuric acid to form the ordinary protosulphatc of iron or green vitriol, which remains in solution. The reaction is expressed by the equation: Sulphide of Iron. Sulphuric Acid. Hydrosulphuric Acid. Sulvhate of Iron.
FeS HO,S0s = HS Hydrosulphuric acid is a colorless gas of a strong and very nauseous oar, resembling that of rotten eggs. It consists of two volumes of hydrogen and one volume of sul phur vapor condensed into two volumes, which form its combining measure. It is about'seventeen times heavier than hydrogen. By pressure it is liquefied, and by the additional application of cold, it may be Atainetlin the solid form (see GASES). Water dissolves, at 59°, 3.23 volumes of this gas, but the solution soon becomes milky when exposed to the air, in consequence of the oxygen of the air combining with the hydrogen of the gas. and sulphur being precipitated. It is highly combustible, and
burns with a pale blue flame, producing water and sulphurous acid, and. generally, a deposit of sulphur. It has a weak acid reaction, and forms one of the hydraeids. Although a feeble acid, it combines readily with bases.
Its use as a reagent is dependent on the fact, that many of the sulphides which it forms with metallic oxides are insoluble in water, and are thrown down from 'solutions as precipitates with characteristic colors. Thus the gas, or a watery solution of it. gives an orange precipitate with the compounds of antimony, whip with those of arsenic it gives a yellow—with those of lead and of silver, a black—and with those of zinc, a white precipitate.
The air of a room slightly impregnated with this gas may be breathed with im punity, but a small quantity of the undiluted gas inspired produces faintness. and its respiration, in a very moderate proportion, was found by Thenard to prove fatal—birils perishing in air which contained and a clog in air containing part of this gas. Its poisonous effects are best counteracted by the inhalation of very diluted chlorine gas, which may be readily obtained from a little chloride of lime placed in the folds of a napkin moistened with vinegar.
A. very minute trace of this gas may be detected by placing.a piece of paper, moist ened with a strong solution of sugar of lead, over the vessel or aperture—as, for in stance, over an opening iu a drain—from which we think it is escaping. If it be present, a more or less black—often only a brown—tint is developed after a few minutes, in consequence of the formation of sulphide of lead.