Bismuth Potassium Chromates

When potassium chromate, or dichromate, is added to a solution of a bismuth salt, the yellow precipitate formed, if allowed to remain in contact with the solution, gradually darkens in colour, yielding the double salt, K₂O.Bi₂O₃.4CrO₃. Boiling with water removes all the alkali and leaves the basic salt, Bi₂O₃.2CrO₃. On warming the double salt with a concentrated solution of chromic acid, dark red crystals of the compound, K₂O.Bi₂O₃.6CrO₃.H₂O, are formed, which likewise decompose on boiling with water.