Sodium orthothioarsenate

The last two compounds are extremely unstable and decompose rapidly to form arsenic and sodium orthothioarsenate. 

Antimony Thioarsenate.—When sodium orthothioarsenate is added to a solution of an antimonious salt, a brownish-yellow precipitate is produced.3... 

Chromium Thioarsenate.—Sodium orthothioarsenate gives a yellow precipitate when added to an aqueous solution of a chromic salt.1... 

Cobalt Thioarsenate.—With solutions of cobalt salts, sodium orthothioarsenate gives a dark brown precipitate of cobalt pyrothio-arsenate, Co2As2S7, soluble in excess of the reagent.1... 

Copper Thioarsenates.—Cupric Orthothioarsenate, Cu3(AsS4)2, is formed as a dark brown precipitate when sodium orthothioarsenate is added to a solution of a cupric salt.2 The reaction, however, is complex, sulphides of copper and arsenic also being formed.3 A similar precipitate is formed when ammonium hydrosulphide or hydrogen sulphide is added to a solution of arsenic acid and a copper salt,4 and the proportion of sulphide and thio-salt in the precipitate varies with the concentration of the reactants. Copper hydroxide reacts with alkali thioarsenates to form copper sulphide and alkali arsenate, but some copper orthothioarsenate is formed and remains in solution in excess of alkali thioarsenate.5... 

Iron Thioarsenates.—Both ferrous and ferric salts, when treated with a solution of sodium orthothioarsenate, yield brown precipitates which are soluble in excess of the reagent. The ferric salt is stable in air and may be heated to fusion without decomposition at a higher temperature sulphur is expelled. The ferrous salt decomposes on drying in the air, ferric hydroxide and thioarsenate being formed.6 Ferrous sulphide dissolves in an aqueous solution of an alkah thioarsenate.7... 

Mercuric Orthothioarsenate, Hg3(AsS4)2, is formed as an orange-coloured precipitate by treating mercuric chloride solution with sodium orthothioarsenate.5 It may be dried at 100° C. and sublimed without decomposition. Mercuric pyrothioarsenate is obtained as a dark yellow precipitate when mercuric chloride solution is treated with sodium meta- or pyro-thioarsenate.8 The salt decomposes on heating with loss of arsenic and sulphur. 

Silver Thioarsenates.—Silver Ortkothioarsenate, Ag3AsS4, is formed as a dark brown precipitate when an aqueous solution of silver nitrate is treated with sodium orthothioarsenate.1 If, however, silver nitrate is added to a solution of sodium orthothioarsenate, silver orthothioarsenate is not formed but silver sulphide is precipitated and arsenious acid, nitric acid and sodium nitrate are formed in solution.8 The reactions involved probably take the following course 3... 

The double salt, Na3(NH4)3(AsS4)2, is obtained w hen alcohol is added to a mixture of the two thioarsenates in molecular proportions, or when a solution containing ammonium chloride and sodium orthothioarsenate is allowed to evaporate it crystallises as pale yellow hexagonal prisms. A corresponding sodium-potassium salt is obtained by evaporation of a solution of the mixed orthothioarsenates.1... 

Tin Thioarsenates.—By double decomposition with sodium orthothioarsenate, stannous and stannic salts yield, respectively, chestnut-brown and pale yellow precipitates.5... 

Cerium Thioarsenates.—The addition of sodium orthothio-arsenate to an aqueous solution of a cerous salt produces a pale yellow precipitate of cerous orthothioarsenate.1 With sodium hydrogen ortho-thioarsenate the precipitate approximates in composition to cerous pyro-thioarsenate. Ceric salts also give pale yellow precipitates, probably ceric orthothioarsenate. Thioarsenates of other rare earth metals have not been described. 

Gold Thioarsenates.—Auric Orthothioarsenate, AuAsS4, and auric pyrothioarsenate, Au4(As2S7)3, are obtained as brown precipitates when solutions of gold salts are precipitated respectively with sodium ortho-and pyro-thioarsenates.6 Both salts are soluble in water. 

Nickel Thioarsenates.—Nickel Orthothioarsenate, Nis(AsS4)2, and nickel pyrothioarsenate, NigAsgS, are formed as dark brown precipitates when aqueous solutions of a nickel salt are precipitated with sodium ortho- and pyro-thioarsenates, respectively.2... 

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