Nickel Chromate, NiCrO₄

Nickel Chromate, NiCrO₄, is obtained by maintaining a solution of nickel carbonate and chromic acid at 260° C. in a sealed tube for several hours. It yields black crystals, insoluble in hot dilute nitric acid, and only slowly attacked by concentrated nitric acid or aqua regia. On pouring alcohol into an ammoniacal solution of this salt, the hexammoniate, NiCrO₄.6NH₃, separates out in dichroic crystals.