PLATINUM

So called from the Spanish word plat a,.mi aiii unit of its colour.) A metal of a white colour, exceedingly ductile, malleable, and difficult of fusion. It is the heaviest substance known, its specific gravity being 21 '5. It undergoes no change from air or moisture, and is not attacked by any of the pure acids; it is di olved by chlorine and nitro muriatic acid, and is oxidized at high temperatures by pure pota a and litliia. It is only found in South America and in the Uralian Mountains: it is usually in small grains of a metallic lustre, a ociated or combined with palladium, rhodium, iridium, and osmium; and with copper, iron, lead, titanium, chromium, gold and silver; it is also usually mixed with alluvial sand. The particles are seldom so large as a small pea, but sometimes lumps have been found of the size of a hazel nut to that of a pigeon's egg. In 1^-20. it was first discovered in a vein a ociated with gold by Bou ingault, in the province of Antioquia, in South America. When a perfectly clean surface of platinum is presented to a mixture of hydrogen and oxygen gas, it has the extraordinary property of causing them to combine so as to form water, ana often with such rapidity as to render the metal red hot: spongy platinum, as it is usually called, obtained by heating the ammonio-muriate of platinum, is most effective in producing this extraordinary result; and a jet of hydrogen directed upon it may be inflamed by the metal thus ignited, a property which has been applied to the construction of convenient instruments for procuring a light. The equivalent of platinum Is about 98. It is precipitated from its nitro muriatic solution by sal ammoniac, which throws It down in the form of a yellow powder, composed of bichloride of platinum and sal ammoniac. [s. 957]