Barium Thioarsenates

Barium Orthothioarsenate, Ba₃(AsS₄)₂.nH₂O, may be obtained by digesting barium sulphide with an aqueous solution of barium pyrothioarsenate and precipitating the resulting clear liquid with alcohol; or the pyro-salt may be heated to redness, when arsenious sulphide and sulphur are expelled. The salt does not decompose on heating. When barium hydrosulphide and arsenic pentasulphide are heated together in solution, double salts composed of thioarsenate and thioarsenite, such as 2Ba₃AsS₄.Ba₂As₂S₅, are formed.

Barium Pyrothioarsenate, Ba₂As₂S₇.wH₂O, is obtained as a lemon- yellow mass when sodium pyrothioarsenate is added to a solution of a barium salt and the liquid concentrated by evaporation. The metathioarsenate has not been isolated.