Nickel Tetrasulphide, NiS₄

Nickel Tetrasulphide, NiS₄, is stated to result when sodium poly- sulphide saturated with sulphur is allowed to act on a solution of a nickel salt.

From the freezing-point curves of nickel sulphides the existence of two other sulphides has been inferred, namely, Ni₃S₂ and Ni₆S₅.

Double sulphides of iron and nickel are present in nickel matte, and are hence of commercial importance. Double sulphides with potassium, K₂S.3NiS, and barium, BaS.4NiS, may be obtained by fusing nickel, sulphur, and an alkali at a high temperature. They are crystalline compounds. Cobalt yields only the sesquisulphide, Co₂S₃, in like circumstances. Nickel thus resembles palladium and platinum, whilst cobalt resembles rhodium and iridium in these respects. The position of nickel after cobalt in the Periodic Table thus receives further justification.