Prussiate of Potash: Horn Char Calcined with Potash and Iron (Ure, 1839)

Yellow prussiate of potash, the salt behind Prussian blue, as Ure described its manufacture in 1839. Char horn, calcine the char with potash and a little iron in a closed iron pot until no more flame rises, leach the mass with water and filter it. Copperas turns the leftover cyanide into ferrocyanide, and evaporation gives lemon-yellow crystals. The melt and the first lye contain potassium cyanide. The picture: our diagram of the pot, the lye and the crystals.