RUTHENIUM [Symbol Ru atomic weight 101.7 (O=16)], in chemistry, a metallic element, found associated with platinum, in platinum ore and in osmiridium. The metal may be obtained from the residues obtained in the separation of osmium from osmiridium. These are washed with ammonium chloride until the filtrate is colourless, ignited, fused with caustic potash and nitre, the melt dissolved in water and nitric acid added to the solution until the colour of potassium rut hen ate disappears. A precipitate of ruthenium oxide gradually separates; this is collected and ignited in a graphite crucible and finally fused in the oxyhydrogen furnace (H. Sainte-Claire Deville and H. J. Debray, Ann. chim. phys., 1859, (3), 56, p. 406). For other methods see C. E. Claus, Pogg. Ann., 1845, 65, p. 200; E. Frémy, Comptes rendus, 1854, 38, p. 1008; T. Wilm, Ber., 1883, 16, p. 1524. A purer ruthenium is obtained by A. Gutbier and L. Trenkner (Zeit. anorg. Chem., 1905, 45, p. 166) by heating the crude metal (obtained by other processes) in a current of oxygen until all the osmium is volatilized as tetroxide. The residue is then fused with caustic potash and nitre, dissolved. in water, saturated with chlorine and distilled on the water-bath in a current of chlorine. Pure ruthenium tetroxide distils over. This is then dissolved in water, reduced by alcohol and ignited in oxygen. Ruthenium in bulk resembles platinum in its general appearance, and has been obtained crystalline by heating an alloy of ruthenium and tin in a current of hydrochloric acid gas. Its specific gravity (after fusion) is 12.063 (A. Joly, Comptes rendus, 1893, 116, p. 430). It fuses easily in the electric arc. It oxidizes superficially when heated, but fairly rapidly when ignited in an oxidizing blowpipe flame, forming a black smoke of the oxide. It is also oxidized when fused with caustic potash and nitre, forming a ruthenate. Acids have practically no action on the metal, but it is soluble in solutions of the alkaline hypochlorites. Like most of the other metals of the group, it absorbs gases. A colloidal form has been obtained by A. Gutbier and G. Hofmeier (Jour. prakt. Chem., 1905, (2), 71, p. 452) by reducing ruthenium salts with hydrazine hydrate in the presence of gum-arabic.
Several oxides of ruthenium, have been described, the definite existence of some of which appears to be doubtful. The dioxide, RuO2, is formed by heating sulphate, or by heating the metal in a current of oxygen. It crystallizes in octahedral isomorphous with stannic oxide. It is insoluble in acids and decomposes when heated to a sufficiently high temperature. Fusion with caustic potash converts it into a/mixture of potassium ruthenate and ruthenium sesquioxide, Ru2O3, which is a black, almost insoluble powder. An oxide of composition Ru4O9 is obtained as a black hydrated powder when the peroxide is heated with water for some time. It becomes anhydrous at about 360° C., and is unattached by acids and alkalis. The peroxide, RuO4, is formed when a solution of potassium ruthenate is decomposed by chlorine, or by oxidizing ruthenium compounds with potassium chlorate and hydrochloric acid, or with potassium permanganate and sulphuric acid. It forms a golden yellow crystalline mass, which sublimes slowly in vacuo, and melts at 25.5° C. It blackens on exposure to moisture, and decomposes when exposed to light. It is insoluble in water, but gradually decomposes, forming a hydrated oxide, Ru2O5·H2O. It is readily reduced. Its vapour possesses a characteristic smell, somewhat resembling that of ozone. Ruthenium dichloride, RuCl, is obtained (in solution) by reducing the sesquichloride by sulphuretted hydrogen or zinc. It is stable in the cold. The sesquichloride, Ru2Cl6, is formed when a mixture of chlorine and carbon monoxide is passed over finely divided ruthenium heated to 350° C. (Joly, Comptes rendus, 1892, 114, p. 291). It is a brown powder which is readily decomposed by boiling water. It absorbs ammonia readily, forming Ru2Cl4·7NH3. Numerous double chlorides are known, e.g. Ru2Cl6·4KCl; Ru2Cl6·4NH4Cl, &c. The pure tetrachloride, RuCl4, has not been isolated, but is chiefly known in the form of its double salts, such as potassium ruthenium chloride, K2RuCl6, which is obtained when finely divided ruthenium is fused with caustic potash and potassium chloride is gradually added to the fused mass (U. Antony and A. Luchesi, Gazz, 1899, 29, 11. p. 82). It is a red-brown crystalline powder, which is soluble in water. A similar ammonium salt has been obtained. Ruthenium sulphides are obtained when the metal is warmed with pyrites and some borax, and the fused mass treated with hydrochloric acid first in the cold and then hot. The insoluble residue contains a mixture of two sulphides, one of which is converted into the sulphate by nitric acid, whilst the other (a crystalline solid) is insoluble in acids. Ruthenium sulphate, Ru(SO4)2, as obtained by oxidizing the sulphide, is an orange-yellow mass which is deliquescent and dissolves in water, the solution possessing a strongly acid reaction. Rouge de Ruthene, Ru2(OH)2·Cl4·(NH4)7, is obtained from ammonia and ruthenium sesquichloride at 40° C., the product being purified by crystallization from ammonia.) It forms small brown lamellae which dissolve slowly in water to give a fuchsin-red solution possessing violet reflex. The solution possesses a considerable tinctorial power, dyeing silk in the cold. Potassium ruthenium cyanide, K4Ru(CN)6·3H2O, formed when potassium ruthenate is boiled with a solution of potassium cyanide, crystallizes in colourless plates which are soluble in water. A ruthenium silicide, RuSi, has been prepared by H. Moissan (Comptes rendus, 1903, 137, p. 229) by the direct combination of the two elements in the electric furnace. It forms very hard metallic-looking crystals, burns in oxygen and is not attacked by acids. Potassium ruthenate, K2RuO4·H2O, obtained by fusion of the metal with caustic potash and nitre, crystallizes in prisms which become covered wit a black deposit on exposure to moist air. It is soluble in water, giving an orange-red solution which becomes green on standing, and gradually deposits the hydrated pentoxitie, Ru2O5·H2O (H. Debray and A. Joly, Comptes rendus, 1888, 106, p. 1494). The per-ruthenate, KRuO4, formed by the action of chlorine on the rut enate, or of alkalis on the peroxide at 50° C., is a black crystalline solid which is stable in dry air but decomposes when heated strongly., On the nitroso, nitroso-ammonium and nitroso-diammonium compounds see C. E. Claus, Ann., 1856, 98, p. 317; A. Joly, Comptes rendus, 1888, 107, p. 994; 1889, 108, pp. 854, 1300; 1890, 111, p. 969; L. Brizard, ibid., 1896, 122, p. 730; 1896, 123, p. 182. The atomic weight of ruthenium was determined by A. Joly (Comptes rends,1889, 188, p. 946), who obtained the values 101.5 and 101.3.