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. |