Potassium ferric sulphide, K₂Fe₂S₄

Potassium ferric sulphide, K₂S.Fe₂S₃ or K₂Fe₂S₄, may be obtained by heating together iron and sulphur with potassium carbonate. The sulphide is extracted with water, and, upon concentration, purplish needle-shaped crystals are obtained, of density 2.86. These are combustible when heated in air, but are reduced to a black mass of K₂S.2FeS or K₂Fe₂S₃ upon ignition in hydrogen.