Chlor-rhodites

The anhydrous sodium, potassium, and ammonium chlor-rhodites (vide infra) on being heated in a current of pure, dry chlorine are decomposed into insoluble rhodium trichloride and the alkali chloride. The resulting mass is cooled in chlorine, which gas is finally replaced by dry carbon dioxide. If ammonium chlor-rhodite was employed initially the product now consists of pure rhodium trichloride, the ammonium... 

Potassium chlor-rhodite is decomposed by water into potassium chloride and the double salt RhCl3.2KCl, which is anhydrous and crystallises readily from aqueous solution. Owing to this ready decomposition, potassium chlor-rhodite cannot be prepared by simply mixing potassium and rhodium chlorides in solution. 

The dihydrate of this salt, K2RhCls. 2H20, was stated by Claus1 to be formed on adding potassium chloride to a solution of sodium chlor-rhodite. It crystallises in small brown prisms which do not effloresce, and are rather difficultly soluble in water. 

Hydrogen sulphide slowly precipitates from solution rhodium sulphide. Mineral acids attack it, slowly in the cold, rapidly on warming. Warm hydrochloric acid converts it into sodium chlor-rhodite (vide supra), Na3RhClg.l8H.5O. When heated to incipient redness until evolution of gas ceases, the compound Na20.8Rh02 is obtained. 

Ammonium Rhodinitrite, (NH4)3Rh(N02)6, is best obtained by adding ammonium chloride to a solution of the sodium salt.1 With warm hydrochloric acid it yields ammonium chlor-rhodite, (NH4)3RhCl6.3H20. 

Ammonium rhodochlornitrate may be dried at 100-105° C. without decomposition. It is very soluble in water, being decomposed by the same. The solution on standing deposits crystals of ammonium chlor-rhodite, and this is a useful method of preparing the latter salt free from excess of ammonium chloride. The rhodochlornitrate is stable in solution or in the presence of aqua regia. It is but slightly soluble in nitric acid. 

Potassium Rhodicyanide, K3Rh(CN)6, may be obtained by heating ammonium chlor-rhodite with a slight excess of potassium cyanide to the fusion-point for ten to fifteen minutes,7 extraction of the melt with boiling water, and subsequent evaporation. 

When heated with sodium chloride in a current of chlorine, the double chloride, sodium chlor-rhodite,Na3RhCl6.Aq.,is formed, which dissolves in water, yielding a rose-red solution. 

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