Ferrous thio-orthophosphate, Fe3(PS4)2, results on heating together ferrous sulphide and phosphorus pentasulphide, the latter being present in excess of that required by the equation
3FeS + P2S5 = Fe3(PS4)2.
The excess of pentasulphide distils away, leaving a black residue contaminated with ferrous sulphide, from which it is readily freed by treatment with dilute hydrochloric acid.
Ferrous thio-orthophosphate is a black crystalline substance which leaves a mark like graphite. When heated it does not fuse but burns, leaving a brown residue. It is insoluble in water and dilute acids. |