Detection of Ruthenium

Metallic Ruthenium is characterised by its ready solubility in a mixture of fused potassium hydroxide and nitrate, yielding a green mass of potassium ruthenate, K₂RuO₄. This dissolves in water to an orange-coloured solution which leaves a black stain upon the skin owing to the deposition of oxide or hydroxide. Nitric acid precipitates the hydroxide as a black mass from the solution.

Fused potassium hydrogen sulphate, which readily attacks rhodium, palladium and iridium, is without action upon ruthenium.

When heated with potassium chloride in a current of chlorine, ruthenium yields potassium chlor-ruthenate, K₂RuCl₆, which is soluble in water.

Metallic ruthenium is insoluble in the mineral acids, and is only slowly soluble in aqua regia.

A delicate and characteristic reaction of ruthenium chloride consists in formation of an azure-blue tint (possibly due to the formation of dichloride) when hydrogen sulphide is passed through its solution in water.

Ammonium sulphide, on the other hand, causes a dark brown precipitate to separate out in like circumstances, which is soluble in excess only with difficulty.

Alkalies precipitate the black hydrated oxide, Ru₂O₃.3H₂O, insoluble in excess, but which is readily soluble in hydrochloric acid, yielding an orange solution containing the trichloride, RuCl₃.

With concentrated solutions of ruthenium salts, alkali chlorides effect the deposition of violet crystalline precipitates of the double chlorides. These are soluble in water only with difficulty, but are decomposed with boiling water, yielding black insoluble residues of oxy-chloride.

Ruthenium trichloride solution is reduced by metallic zinc to the dichloride, the colour changing from orange to azure-blue. In the presence of excess of zinc the reduction proceeds even further, metallic ruthenium being deposited as a black powder.

Ruthenium may be detected in and separated from osmiridium by ignition in a current of oxygen at about 1080° C. Osmium tetroxide and ruthenium dioxide are volatilised, the latter being the first to condense.

In order to detect the presence of ruthenium in platinum alloys, a portion of the alloy is fused with lead. The melt is extracted with nitric acid and the residue ignited in contact with air in order to volatilise the osmium. The mass may now contain platinum, iridium, rhodium and ruthenium, and is fused with potassium nitrate and hydroxide. The whole is dissolved in water, treated with excess of nitric acid and allowed to stand in a flask covered with filter-paper. In a few hours (12-24) the filter-paper darkens if ruthenium is present, in consequence of the evolution of vapour of its tetroxide. To confirm the presence of ruthenium, the paper is ignited and the ash fused with potassium nitrate and hydroxide. On extraction with water the orange colour of potassium ruthenate is obtained.