Potassium Thiomolybdate, K₂MoS₄

Potassium Thiomolybdate, K₂MoS₄, is prepared, according to Berzelius, by gradually heating to bright redness a mixture of molybdenum disulphide, potassium carbonate, sulphur, and a little powdered charcoal. The water solution of the cold black melt is dark red in colour, and on gentle evaporation yields crystals which may be further purified by precipitation of their aqueous solution with alcohol. The substance is not entirely stable.