FERROCYAN'OGEN is a compound organic radical, generally regarded by chemists as existing in ferrocyanide of potassium, or the yellow prussiate of potash, but which has not yet been obtained in a separate state. The principal compound of F. is the ferrocyanide of potassium, which is prepared by heating to redness in a covered iron pot a mixture of 3 parts by weight of nitrogenized matter, such as dried blood, hoofs, parings of hides, scrapings of horn, or the flesh of old or diseased horses and other animals, 3 parts of carbonate of potash, and 1 part of iron filings. The carbon, nitro gen, and iron combine together, and form F. (FeCeN or Cfy), which, at the same time, unites with the potassium, and produces ferrocyanide of potassium, or yel low prussiate of potash (2K,Cfy). The compound which is obtained from the heated iron vessel is impure, but by repeated solutions in hot water, and recrystallization on cooling, the salt is obtained pure in fine large tabular crystals of a lemon-yellow color.
The ferrocyanide of potassium is largely used in dyeing and calico-printing (q.v.), in the production of many shades of Prussian blue; and when it is treated with sulphuric acid, and subjected to heat applied, hydrocyanic or prussic acid (HC,N = Hey) distills off from the mixture. The ferrocyanide of potassium is characterized by giving no indication of the presence of iron in its radical on the application of any of the tests for iron. It gives'' light-,bitio precipitate on the addition of a solution of pro tosulphate of iron; a dark-blue precipitate with perchloride of iron; a ruddy brown precipitate with sulphate of copper; and a white precipitate with acetate of lead.