This member of the platinum group of metals occurs in osmiridium (1/2 to 6 1/2 per cent.) and platinum "ores," and as sulphide in laurite. It is best prepared by Deville et Debray's method from the osmiridium-ruthenium alloy. This latter is fused with zinc, and the regulus thus obtained is treated with hydrochloric acid; 1 part of the residue in a finely-comminuted state is mixed with 3 of barium binoxide and 1 of barium nitrate, and the mixture is heated for 2 hours to a temperature somewhat below the melting-point of silver; when cold, the solid mass is reduced to impalpable powder, and added to hydrochloric acid contained in a stoppered vessel, which is kept quite cold to prevent liberation of osmium tetroxide vapour, the operation being conducted where the ventilation is efficient, on account of the poisonous nature of this vapour; when all action has ceased, 1 part nitric and 2 parts sulphuric acid are added, the mixture is shaken, the barium sulphate deposit is allowed to settle, the clear liquid is poured off, and the residue is washed by decantation; the liquid is distilled till f have passed over, and the distillate is treated for recovery of osmium (see p. 400); the concentrated residue, mixed with 2 or 3 parts sal-ammoniac and a little nitric acid, is dried in a water-bath, and washed with water half saturated with sal-ammoniac till the filtrate is colourless, thus leaving behind an ammonium-iridichloride containing some ruthenium; on igniting this, it affords a spongy metallic mass, which is fused for 2 hours in a silver basin with 2 parts nitre and 1 of caustic potash, then dissolved in water (farming potassium ruthenate), and treated with nitric acid till the yellow colour disappears, when ruthenium oxide, contaminated with silicic acid, iridium, and osmium, separates out; this is ignited in a graphite crucible and fused in the oxyhydrogen furnace.

To obtain the metal chemically pure, it is heated in a current of oxygen till all the osmium tetroxide has been volatilized, then refused with nitre and caustic potash, dissolved in water, saturated with chlorine, and distilled in a stream of chlorine in a water-bath; the pure ruthenium tetroxide volatilizes; this is dissolved in caustic potash, and the sesquioxide is precipitated by alcohol, and again reduced to the metallic state by ignition in a stream of coal-gas or hydrogen. The fused metal oxidizes slowly in the air, taking on a brown film; the pure metal is almost unattacked even by aqua-regia, but combines with chlorine at a red heat; it is hard, brittle, almost as difficult to fuse as osmium, and has a sp. gr. of 12-261 at 32° F. (0° C).