Ferric carbonyl ferrocyanide, Fe[Fe(CN)₅CO]

Ferric carbonyl ferrocyanide, Fe[Fe(CN)₅CO], is prepared by double decomposition of an excess of ferric chloride solution and the potassium salt. It resembles indigo in appearance, and contains about 4 per cent, of combined water. Dried at a moderate temperature, it yields a friable resinous Inass with a brilliant conchoidal fracture.