ferrocyanide
    n 1: salt of ferrocyanic acid usually obtained by a reaction of
         a cyanide with iron sulphate

Ferrocyanide \Fer`ro*cy"a*nide\ (? or ?; 104), n. [Ferro- +
   cyanide.] (Chem.)
   One of a series of complex double cyanides of ferrous iron
   and some other base.
   [1913 Webster]

   Potassium ferrocyanide (Chem.), yellow prussiate of potash;
      a tough, yellow, crystalline salt, K4(CN)6Fe, the
      starting point in the manufacture of almost all cyanogen
      compounds, and the basis of the ferric ferrocyanate,
      prussian blue. It is obtained by strongly heating together
      potash, scrap iron, and animal matter containing nitrogen,
      as horn, leather, blood, etc., in iron pots.
      [1913 Webster]