TetraChromate, potassium

Zinc yellow is made by a variety of processes, all based on the reaction of 2inc compounds, chromates, and potassium salts in aqueous solution. If products free of chloride and especially sulfate are desired, they are excluded from the system. In one process, for example, 2inc oxide is swollen with potassium hydroxide and the chromates are added as a solution of potassium tetrachromate [12422-53-6] (194). 

Potassium Tetrachromate, KaCrjO, is prepared similarly to the trichromate (the nitric acid used haring density 1-41), and has similar properties. The crystals belong to the monoclinic system. ... 

Hexaethylenediamino-hexol-tetrachromic Sulphate, [Cr4(OH)6en6](SO4)3.10H2O, is prepared from partially dehydrated chromic alum. The bluish-grey powder obtained is heated with ethylene-diamine monohydrate on a water-bath till a red-coloured mass is produced, which consists of a mixture of potassium sulphate, luteo-chromic sulphate, and the sulphate of the hexol compound, and from the mixture the latter compound is obtained by dissolving out the more soluble salts with water. The crude, difficultly soluble sulphate is purified by dissolving in dilute sulphuric acid and reprecipitating with excess of ammonia. It crystallises in small needles which are almost insoluble in water and soluble in dilute acids. 

C. Schmidt used cone, nitric acid, but G. N. Wyroubofi said that if the nitric acid be too cone.—-over 1-41 sp. gr.—-some tetrachromate is formed. H. Eeinsch, and C. J. B. Karsten observed the tendency of potassium nitrate to crystallize out with the trichromate in nitric acid soln. -, and L. Darmstadter mistook the impure product for nitrochromate. M. Siewert separated the product from potassium nitrate by fractional crystallization. C. von Hauer, M. Siewert, and E. Jager and... 

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