Potassium carbonyl ferrocyanide

Copper carbonyl ferrocyanide, Cu3[Fe(CN)5.CO]2, is obtained1 by double decomposition in aqueous solution of copper sulphate and potassium carbonyl ferrocyanide. It forms as a yellowish green gelatinous precipitate, which is insoluble in dilute nitric or sulphuric acid, and which becomes an anhydrous dark brown powder at 110° C. 

Potassium carbonyl ferrocyanide, 2K3[Fe(CN)5C0].7H20.—The discovery and early preparation of this salt have already been described (see p. 232). It may be prepared in the laboratory by passing moist carbon monoxide over potassium ferrocyanide at 130° C. Thus —8... 

Silver carbonyl ferrocyanide, Ag3[Fe(CN)5CO], is obtained as a white curdy precipitate on addition of the potassium salt to silver nitrate solution in the presence of acetic acid.4 It rapidly darkens even when protected from the light. Insoluble in boiling acetic acid, it is slightly soluble in dilute mineral acids evolving hydrogen cyanide. Potassium hydroxide liberates silver oxide, potassium carbonyl ferrocyanide being simultaneously produced. 

Addition of ferric chloride to certain liquors produced in the manufacture of Prussian blue in a French factory by the methylamine method (see p. 213) resulted in the precipitation of a violet compound.1 Several hundred grams of this were isolated by Muller, warmed with potassium carbonate and hydroxide successively, and the filtered solution allowed to crystallise. The product thus isolated crystallised in thin scales and rectangular prisms, and proved to be the potassium salt of an entirely new acid, namely hydrogen carbonyl ferrocyanide, H3Fe(CN)5.CO. Following up this discovery, Muller succeeded in preparing a series of well-defined salts. 

Ferric carbonyl ferrocyanide, Fe[Fe(CN)5CO], is prepared by double decomposition of an excess of ferric chloride solution and the potassium salt.1 It resembles indigo in appearance, and contains about 4 per cent, of combined water.2 Dried at a moderate temperature, it yields a friable resinous mass with a brilliant conchoidal fracture.1... 

Sodium carbonyl ferrocyanide, Na3[Fe(CN)5C0].7H20, is obtained in a similar manner to the potassium salt. It crystallises m pale yellow monoclinic needles, which become anhydrous at 110° C. 

Uranyl carbonyl ferrocyanide, (U02)3[Fe(CN)5C0]25H20, is obtained2 as an orange-yellow gelatinous precipitate on adding the potassium salt to uranium nitrate. At 70° C. it becomes red, but acquires the yellow colour again on powdering. 

Potassium calcium carbonyl ferrocyanide, CaK.Fe(CN)5.C0.5H20, has been obtained as straw-coloured crystals.5... 

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