Double Rhodium Sulphides, Rh₂S₃.3M₂S

When a neutral rhodium salt, such as an alkali chlor-rhodite, is mixed with excess of an alkali sulphide, a precipitate is obtained which, on analysis, is found to contain a good deal of alkali sulphide. This suggests that a double sulphide has been formed. The precipitate, however, is stable only in the presence of excess of alkali sulphide, water rapidly decomposing it, so that direct isolation of the pure compound is not possible. By indirect physical methods, however, for details of which the reader is advised to consult the original memoir, Leidie has obtained evidence of the existence of Rh₂S₃.3Na₂S, and apparently the corresponding potassium derivative is capable of existence.