Hydrosulphurous acid

Oharaeter,—Like hydrosulphuric acid, it produces precipi tates in solutions of most of the heavy metals. 

Potassic seleniate is prepared by fbsing seleniam or metallio selenides with nitre. The acid is obtained by transforming the potassic salt into a plumbic salt, and subsequently deoompo-ring the latter with hydrosulphuric acid. 

By passing carbonic disulphide and hydrosulphuric acid, or carbonic disulphide and steam, over ignited copper —... 

The eSect of an excess of hydrogen sulphide has very little influence on the solubility of potassium hydrosulphide because, as V. Rothmund has indicated, this salt is too little ionized for the slightly dissociated hydrosulphuric acid to have an appreciable influence on the solubility. 

Test an aqueous hydrogen sulphide solution with litmus. What do you observe Find the dissociation constants of hydrosulphuric acid in a textbook. 

Hydrogen Sulphide, Sulphuretted Hydrogen or Hydrosulphuric Acid, HaS. 

Hydrogen Sulphide as an Acid. — In the anhydrous condition, whether as gas or liquid, hydrogen sulphide has no acidic properties. When moist or in aqueous solution, however, it behaves as a feeble acid, whence the occasional name hydrosulphuric acid. For the characteristic test with lead acetate paper or for the reddening of litmus paper, the presence of at least a little moisture is essential.3... 

Electrolysis of sulphurous acid causes anodic oxidation to sulphuric acid, whilst hydrosulphurous acid, H2S204, is produced by the reducing action of the current at the cathode 3 the former change may be rendered quantitative by the addition of a manganese salt 4 the hydrosulphurous acid may be accompanied by various of its decomposition products.5... 

Hydrosulphurous acid is also formed by the action of many metals on sulphurous acid 7 the crust of ferrous sulphite and hydrosulphite formed on the surface of metallic iron is of great protective value in the iron cylinders used for storing liquid sulphur dioxide, which generally contains traces of water.8... 

The composition of the oxide suggests that it may be an acid anhydride, but all attempts to convert it into hydrosulphurous acid, H2S204, or its derivatives, have been unsuccessful.7... 

Hydrosulphurous acid is also formed as an intermediate product in the reduction of sulphurous acid by hypophosphorous acid.8... 

The hydrosulphites are very liable to atmospheric oxidation, especially in the hydrated or moist condition in their preparation and preservation it is therefore desirable to exclude air. When exposed to the atmosphere a solution of a hydrosulphite first becomes yellow, probably due to the transient presence of free hydrosulphurous acid, but soon becomes colourless, the final product being sulphite.2 Much heat is evolved during this oxidation, as may readily be observed with the exposed moistened salt ... 

J. Tafel believed that the soln. of hydroxylamine sulphate in 50 per cent, sulphuric acid contained a salt NH2OH.H2S04, hydroxylamine hydrosulphate. A, Lidaff obtained this salt by the action of hydrosulphurous acid on potassium nitrite and E. Divers, by digesting the normal chloride with the calculated quantity of sulphuric acid, and evaporating in cold air. The prismatic crystals are very deliquescent. 

In solution the acidic properties of hydrogen sulphide appear and under the name of hydrosulphuric acid the compound may be compared with hydrochloric acid. 

The protochloride of antimony is easily prepared by boiling in hydrochloric acid the powdered native sulphide of antimony. When the disengagement of hydrosulphuric acid begins to be slow, the whole is boiled for a few minutes. After cooling, the clear liquid Is decanted. 

Sys. Hydrosulphuric Acid.—This compound is formed when hydrogen and sulphur come in contact in the nascent state. It is best prepared by causing diluted hydrochloric or sulphuric acid to act on sulphuret of iron in the apparatus, p. 46, when sulphuretted hydrogen is disengaged as a gas, which may be collected over warm water, or solution of sSt. The action is as follows Fe S -f H Cl = Fe Cl -b HS. 

It is formed by the action of hydrosulphuric acid (sulphuretted hydrogen) on peroxide of iron, at a heat not above 212°, as a yellowish grey powder or by adding perchloiide of iron to an excess of hydrosulphuret of ammonia, as a black powder, rapidly oxidised by exposure to the air. 

Characters and Tests.—Colourless, heavy, oily, intensely acid liquid. Sp. gr. 1 843. Mixed with water, much heat is evolved. Diluted with five or six times its volume of water, it gives, with barium chloride, a white precipitate (barium sulphate), which is insoluble in nitric acid it should yield no precipitate or darkening of colour with hydrosulphuric acid, indicating the absence of lead. When a solution of ferrous sulphate is carefully poured upon the sur ce of the acid, there should be no brown colour developed where the two liquids unite, showing the absence of nitric acid and oxides of nitrogen. The acid should leave no residue on evaporation. 

Blue Fe Fdcy ) with potassium ferridcyanide, and a nearly white or light blue precipitate (ferrous ferro cyanide, Fe2Fcyt) with potassium fernK anide. It should give no precipitate with hydrosulphuric acid, showing its free Iom from lead and other metals precipitable by this reagent. 

In an investigation of the action of hydrogen sulphide on sulphur dioxide in presence of water, he suspected the presence in the precipitate of sulphur of a new oxyacid of sulphur which he called hydrosulphurous acid. This was afterwards recognised as pentathionic acid by Wackenroder in 1845, who was unaware of Thomson s work, which, if he had followed it up, would have given him the credit of the discovery. In Thomson s paper On some Compounds of Chromium , he describes the discovery ( about a year and a half ago ) of chromyl chloride ( chlorochromic acid , which he thought was a compound of i atom chromic acid and i atom chlorine ), of chromium chromate, some new chromates and dichromates, and some double and complex compounds of chromium. Some compounds he described were mixtures, and carbonate of chromium and disulphuretted oxide of chromium are non-existent. 

The hydrosulphites (dithionites), studied by Schiitzenberger from 1869, were closely connected with the application of commercial dyes. Following the isolation of hydrosulphurous acid , an unstable chemical, Schiitzenberger began to understand, and to explain, phenomena observed by colourists. These studies led to the control of certain industrial operations in which it was necessary to use a reducing agent. At the same time he developed a method for the determination of the quantity of dissolved oxygen in various liquids with sodium hydrosulphite (sodium dithionite). ... 

---