Ferric Chromate

Ferric Chromate has not been obtained as the normal salt, but by digesting ferric hydroxide with chromic acid, a brown amorphous substance, soluble in water and alcohol, and of composition Fe₂O₃.4CrO₃, has been obtained. By the addition of potassium chromate to a solution of a ferric salt, a brown precipitate, of composition Fe₂O₃.CrO₃, is obtained. It is decomposed by water.

Numerous basic double ferric chromates have been prepared, namely:

3K₂O.6Fe₂O₃.2CrO₃ - obtained by the action of ferrous sulphate on potassium chromate at 0° C., at which temperature it is dried with alcohol and ether. It is black in appearance, but brown when moist. 4K₂O.3Fe₂O₃.4CrO₃ - a yellowish - brown micro-crystalline precipitate, obtained by addition of excess of potassium chromate to ferrous sulphate solution. 4Na₂O.7Fe₂O₃.10CrO₃ and 6(NH₄)₂O.5Fe₂O₃.6CrO₃ are obtained in a similar manner to the preceding salt, but replacing potassium chromate by sodium and ammonium chromates respectively.

Other complexes that have been prepared are:

7K₂O.6Fe₂O₃.10CrO₃; 4K₂O.3Fe₂O₃.11CrO₃.9H₂O; 6K₂O.2Fe₂O₃.9CrO₃.6H₂O; 6K₂O.3Fe₂O₃.10CrO₃.5H₂O; 2K₂O.2Fe₂O₃.7CrO₃.7H₂O; 3K₂O.2Fe₂O₃.6CrO₃; 5K₂O.4Fe₂O₃.16CrO₃.8H₂O.