Arsenic subsulphide

In cold aqueous solution, sodium orthoarsenate reacts with sodium hydrosulphite to form sodium arsenohydrosulphite,6 NagAs(S204)3, a creamy white granular powder. In the presence of sodium sulphite this compound decomposes, forming sodium arsenothiosulphate, an unstable intermediate product, and finally arsenious sulphide.7 If the reduction by sodium hydrosulphite takes place in the presence of hydrochloric acid, some arsenic subsulphide, As3S, is also precipitated,8 and this product is also obtained when the orthoarsenate in aqueous solution is treated with phosphorus trichloride and the mixture saturated with sulphur dioxide.9... 

Arsenic subsulphide is a dark brown powder. It is insoluble in carbon disulphide, in aqueous ammonia and in colourless ammonium sulphide. It dissolves, however, in yellow ammonium sulphide, which is at the same time decolorised, and the addition of an excess of hydrochloric acid to the solution precipitates arsenious sulphide. It is decomposed by caustic alkali. When heated, arsenic subsulphide is resolved into realgar and arsenic. 

Arsenic Subsulphide—Tetrarsenic Trisulphide—Arsenic Disulphide—Arsenio Trisulphide Colloidal Arsenic Trisulphide—Arsenic Pentasulphide—Thio-arsenates—Oxythioarsenates—Sulphato-eompounds of Arsenic. 

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