Manganese Thioarsenates

Manganese salts do not yield precipitates with alkali orthothioarsenates. The pyrothioar senate, Mn₂As₂S₇, and some orthoarsenate, are formed when manganese carbonate and arsenic pentasulphide are digested with water; and when freshly precipitated manganese sulphide and arsenic pentasulphide are suspended in water, some pyrothioarsenate is precipitated but redissolved when more water is added. Evaporation of the solution causes decomposition. A brick-red basic salt is formed when the pyrothioarsenate is boiled with concentrated aqueous ammonia.