Note 22 — Chapter III
Reading edition
The potash and ferrous salt form potassium sulphate and ferrous hydroxide, the latter combines with cyanogen and more potash to form potassium ferro-cyanide, the ferric chloride with the potash produces ferric hydroxide and potassium chloride; when the hydrochloric acid is added, it dissolves up the excess of ferrous and ferric hydroxides, forming ferrous and ferric chlorides, and the ferric chloride unites with the potassium ferrocyanide to form ferric ferrocyanide or Prussian blue.