Ferrocyanide anion has a complicated looking structure but it is easy to synthesize. The input materials are hydrogen cyanide (cheaply produced from methane an

Ferrocyanide anion has a complicated looking structure but it is easy to synthesize. The input materials are hydrogen cyanide (cheaply produced from methane and ammonia via the Andrussow process), calcium hydroxide, and iron(II) chloride. Combined, they form ferrocyanide. Despite the toxic hydrogen cyanide used in production, ferrocyanides are nontoxic because the cyanide is so tightly bound to iron. Potassium ferrocyanide is used as an anticaking agent in table salt. I have made Prussian blue before by roasting dried blood (organic fertilizer) with sodium hydroxide, extracting with water, and letting it partially oxidize in air. Blood provides both iron and nitrogen. This was an industrial process, historically, before artificial nitrogen fixation.