Iridium

Iridium (syn. Ir, atomic weight 192.5—sp. gr. 22.38) is one of the so-called noble metals. It is occasionally found native and nearly pure in considerable masses among the Uralian ores of platinum, but is usually combined with osmium as an alloy in flat scales. It is a very hard, white, brittle metal, which may be melted by the oxyhydrogen blowpipe, or by the heat of a voltaic current. It is malleable at a white heat. In its isolated form it is unacted upon by any acid, or by aqua regia, but as an alloy it dissolves in the latter fluid. It forms two oxides, $\backslash text\{Ir\}\_2\backslash text\{O\}\_3$ and $\backslash text\{IrO\}\_2$, and three series of salts distinguishable by their colours, usually much less soluble than the corresponding platinum compounds. Three sulphides and chlorides are obtainable. Iridium may be fused with phosphorus, becoming as hard as before, and is used for pen points, contact points in telegraphy, and wearing parts of scientific instruments. Iridium was discovered by Descotils and by Tennant in 1803.