Ferricyanides photography

Ferricyanide - [CHELATING AGENTS] (Vol 5) - [COBALT COMPOUNDS] (Vol 6) - [COLOR PHOTOGRAPHY] (Vol 6) -with osmium tetroxide catalyst [PLATINUM-GROUP METALS, COMPOUNDS] (Vol 19)... 

The iron salts of ferro and ferricyanic acid are the compounds to which the names cyanogen and cyanide are due. Two of these salts are of deep blue color and the Greek word from which cyanogen and cyanide are derived is cyanos which means blue. The ferric ferro-cyanide, Fe4 "(Fe"(CN6)3, is known as Prussian blue and the ferrous ferri-cyanide, Fe3"(Fe" (CN)6)2, is Turnbull s blue. These compounds are formed when ferric salts in solution are treated with potassium ferro-cyanide and when ferrous salts in solution are treated with potassium ferricyanide. They are common qualitative tests for the two forms of iron salts. The compounds are also used as laundry blueing and are formed in the blue print process of photography. 

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