Ferrous chromate

Ferrous chromate does not appear to be capable of existing. When solutions of ferrous sulphate and chromic acid, or its alkali salts, are mixed at low temperatures, the iron is oxidised, basic ferric sulphates resulting, the chromium being correspondingly reduced. If the ferrous sulphate is in excess, ferroso-ferric sulphate results.

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.