RUTHENIUM, the last of the six platinum metals to be identified, occurs in small amount only in ores from South Amer ica, and was hence overlooked by Wollaston and Tennant in 1803 04 (symbol Ru, atomic number 45, atomic weight, 101.7). The first indication of the existence of ruthenium was due to Osann (1828) who was working on platinum ore from the Ural moun tains. He first announced the discovery of three new platinum metals, one of which he called ruthenium after Ruthenia, a name for Russia, but subsequently withdrew his claim to discovery as regards one of them. The matter was not fully investigated till 1845 when Claus confirmed the existence of a new metal and re tained for it the name suggested by Osann. The metal is best obtained from osmiridium by the method of Deville and Debray.
Af ter a preliminary separation of osmium and iridium (see Osmium), a residue is left containing most of the ruthenium which is washed with aqueous ammonium chloride to remove the re mainder of the osmium. The final residue containing iridium and ruthenium is fused with caustic potash and nitre in a silver basin ; the melt is extracted with water yielding an orange solution of potassium ruthenate, which is decolorized by addition of nitric acid, when an oxide of ruthenium gradually separates. This oxide dried and fused in a graphite crucible gives a button of impure ruthenium. Alternately, the aqueous solution of potassium ruthenate is saturated with chlorine and the solution distilled on a water-bath in a stream of chlorine when pure ruthenium tetrox ide, distils over. This tetroxide is dissolved in caustic potash, reduced by alcohol to which on ignition with reducing agents gives pure ruthenium (Gutbier and Trenkner, 1905).
Ruthenium in the massive state is a greyish-white metal similar in appearance to platinum, but as no important use has been found for it or any of its compounds, its properties are at present of purely scientific interest. Its specific gravity is 12.063 and its melting point is about 1,950° C. It is not readily attacked by acids but is comparatively easily oxidized, as simply heating in air causes it to be covered with a film of oxide. If strongly heated in a cur rent of air, or preferably oxygen, it undergoes complete oxidation, the oxide RuO, being deposited some distance from the metal; this oxide, per se, is not volatile, however, but results from the decomposition of the volatile oxide, Ruthenium is practi cally insoluble in all acids, but is readily attacked by chlorine, and in a finely divided state it dissolves easily in solutions of alkaline hypochlorites.
Ruthenium has at various times been credited with forming at least 7 different oxides, but as the existence of some of these is doubtful and as others are known only in combination, those of undoubted authenticity will alone be mentioned here. Ruthenium sesquioxide, is produced when finely divided ruthenium is heated in air or, together with potassium ruthenate, when the oxide RuO, is fused with caustic potash ; it is a dark blue powder insoluble in acids. Ruthenium dioxide, RuO,, prepared either by igniting the sulphate in air or by burning the metal in a stream of air or oxygen, forms hard quadratic pyramids possessing a green metallic lustre. Ruthenium tetroxide, Ru0,, obtained by distilling a solution of in chlorine on the water-bath, forms golden-yellow crystals which melt at 40° and distil at about 100°. It possesses an odour resembling ozone and unless heated very carefully is liable to decompose with explosive violence. It blackens on exposure either to moisture or light, and is insoluble in water which slowly decomposes it with evolution of oxygen. The halogen salts of ruthenium are unimportant ; chlorides such as and RuCl, are known either in the free state or in the form of double chlorides, such as potassium ruthenochloride, LRuC15, and potassium ruthenichloride, an aqueous solution of the former gives a black precipitate of ruthenous iodide, Rul,, on addition of potassium iodide. Ruthenium sesqui sulphide, occurs in the mineral laurite, generally associated with other platinum ores and can be prepared by precipitating solutions of soluble ruthenium salts with sulphuretted hydrogen. This compound on treatment with nitric acid is converted into ruthenium sulphate, obtained on evaporation to dryness as a yellow, deliquescent, amorphous mass. A double cyanide, potassium ruthenocyanide, is interesting as being isomorphous with yellow prussiate of potash, the free acid is also known in the solid state (see PRUSSIC ACID). The curious basic ammoniacal compound, known as ruthenium red, is produced by the action of ammonia on a solution of at 40° C; it dyes silk in a beautiful permanent yellow shade, but its use as a dye has been abandoned on account of cost.