The ferric chloride and ferrocyanide react to form Prussian blue. The result is an insoluble, blue dye (ferric ferrocyanide) known as Prussian blue. Prussian blue is produced by oxidation of ferrous ferrocyanide salts. Prussian blue is a dark blue pigment produced by oxidation of ferrous ferrocyanide salts. Potassium ferricyanide is manufactured by passing chlorine through a solution of potassium ferrocyanide. Treatment of potassium ferrocyanide with nitric acid gives H[Fe(NO)(CN)]. Potassium ferrocyanide is used in the production of wine and citric acid. Potassium ferrocyanide is nontoxic, and is not decomposed to cyanide in the body. The yellow color is the color of ferrocyanide anion. It gives a violet color upon treatment with potassium ferrocyanide. Potassium ferrocyanide can be used as a fertilizer for plants. Cyanides as a chemical class were named because they were discovered in ferrocyanide. Metal oxides used include ferrocyanide and ferricyanide (yellow, red, green, blue). Sodium ferrocyanide is the sodium salt of the coordination compound of formula [Fe(CN)]. Potassium ferrocyanide finds many niche applications in industry.