RHODIUM

is a metal discovered by Dr. Wollaston in 1803, in the ore of platinum. It is contained to the amount of three per cent. in the platinum ore of Antioquia in Colombia, near Barbacoas; it occurs in the Ural ore, and, alloyed with gold, in Mexico. The palladium having been precipitated from the muriatic solution of the platinum ore previously saturated with soda, by the cyanide of mercury, muriatic acid is to be poured into the residuary liquid, and the mixture is to be evaporated to dryne , to expel the hydrocyanic acid, and convert the metallic salts into chlorides. The dry ma is to be reduced to a very fine powder, and washed with alcohol of specific gravity 0·837. This solvent takes po e ion of the double chlorides which the sodium forms with the platinum, iridium, copper, and mercury, and does not di olve the double chloride of rhodium and sodium, but leaves it in the form of a powder, of a fine dark-red colour. This salt being washed with alcohol, and then exposed to a very strong heat, affords the rhodium. But a better mode of reducing the metal upon the small scale, consists in heating the double chloride gently in a gla tube, while a stream of hydrogen pa es over it, and then to wash away the chloride of sodium with water. Rhodium resembles platinum in appearance. Any heat which can be produced in a chemical furnace is incapable of fusing it; and the only way of giving it cohesive solidity, is to calcine the sulphuret or arseniuret of rhodium in an open ve el at a white heat, till all the sulphur or arsenic be expelled. A button may thus be obtained, somewhat spongy, having the colour and lustre of silver. According to Wollaston, the specific gravity of rhodium is 11. It is insoluble by itself in any acid; but when an alloy of it with certain metals, as platinum, copper, bismuth, or lead, is treated with aqua regia, the rhodium di olves along with the other metals; but when alloyed with gold or silver, it will not di olve along with them. It may, however, be rendered very soluble by mixing it in the state of a fine powder with chloride of pota ium or sodium, and heating the mixture to a dull-red heat, in a stream of chlorine gas. It thus forms a triple salt, very soluble in water. The solutions of rhodium are of a beautiful rose colour, whence its name. In the dry way, it di olves by heat in bisulphate of pota a; and disengages sulphurous acid gas in the act of solution. There are two oxides of rhodium. Rhodium combines with almost all the metals; and, in small quantity, melted with steel, it has been supposed to improve the hardne , closene , and toughne of this metal. Its chief use at present is for making the inalterable nibs of the so-named rhodium pens.