Potassium Vanadocyanide, K₄[(CN)₆].3H₂O

Potassium Vanadocyanide, K₄[(CN)₆].3H₂O, is obtained by reduction of a solution of vanadous oxide, V₂O₃, in acetic acid by means of potassium amalgam in the absence of air, the product being treated with potassium cyanide. Its aqueous solution is red, and addition of alcohol to it precipitates brownish-yellow, apparently tetragonal crystals which rapidly become dark blue in moist air. It reduces silver salts to metallic silver, mercuric chloride to mercurous chloride, and is analogous to the corresponding potassium ferro-, potassium mangano-, and potassium cobalto-double cyanides.