Cobalt Monosulphide, CoS

Cobalt Monosulphide, Cobaltous Sulphide, CoS, occurs in nature as the mineral syepoorite or jaipurite. The mineral has been prepared artificially by fusing cobalt sulphate with barium sulphide and sodium chloride. The monosulphide is also obtained by heating a solution of cobalt sulphite to 200° C., or a mixture of solutions of cobalt salts with ammonium thiocyanate to 180° C., in either case in sealed tubes, and by heating cobalt sulphate and carbon to the temperature of the electric arc.

By the first of these methods cobalt monosulphide is obtained as steel-grey, elongated prisms of density 5.45. The remaining processes yield the amorphous substance. Prolonged contact with air and water effects its oxidation to the sulphate. Acids dissolve it, yielding cobaltous salts.

Cobalt monosulphide is also obtained as a black hydrated precipitate on addition of ammonium sulphide to a neutral solution of a cobalt salt. Although the precipitate is soluble only with difficulty in hydrochloric acid it is not obtained when hydrogen sulphide is passed into a solution of a cobalt salt acidified with a mineral acid. The explanation is probably similar to that given for the nickel analogue (q.v.). An Oxysulphide, CoO.CoS, is stated to result on heating cobalt monoxide in a current of hydrogen sulphide.