Potassium Chlor-ruthenate, K₂RuCl₆

Ruthenium Tetrachloride, RuCl₄, probably exists in solution when the hydrated dioxide, obtained by the action of caustic alkali on the sulphate, is dissolved in hydrochloric acid. It yields a yellow solution from which the tetrachloride cannot be isolated in a pure condition, although double salts with the alkali metals have been obtained.

Potassium Chlor-ruthenate, K₂RuCl₆, may be prepared by adding hydrochloric acid to potassium ruthenate. The method adopted by Antony and Lucchesi consists in heating ruthenium with six times its weight of fused potassium hydroxide in a silver dish. Potassium chlorate is added little by little, and the whole stirred until all the ruthenium has dissolved. The heating is continued until evolution of gas ceases, indicating complete decomposition of the chlorate. On cooling, the orange-red-coloured melt is dissolved in cold water, and dilute hydrochloric acid added until the whole is slightly acid. Concentration is effected over quicklime until the salt crystallises out in reddish brown crystals. Potassium chlor-ruthenate may also be obtained by the action of chlorine on a concentrated, acidulated solution of potassium aquo-chlor-ruthenate, K₂Ru(OH₂)Cl₅. It then crystallises in minute black octahedra possessed of a greenish sheen, and which are easily soluble in and rapidly decomposed by water. In hydrochloric acid a pure yellow colour is obtained if the solution is dilute, the concentrated solution being deep yellowish red.