Potassium cuproferrocyanide, K₂Cu₂Fe(CN)₆

Potassium cuproferrocyanide, K₂Cu₂Fe(CN)₆, is prepared 1 by boiling cuprous cyanide with a solution of potassium ferrocyanide containing a little potassium sulphite; or by boiling cuprous chloride or potassium cuprous cyanide with potassium ferrocyanide solution. When rapidly cooled, the solution yields colourless cubes, but the crystals are liable to undergo partial oxidation, turning yellow or brown in colour.