Alloys of Irridium

With the exception of those obtained with allied metals, the alloys of iridium are unimportant. Osmiridium has already been described, and platinum alloys are dealt with in the sequel. On heating to redness with tin, the compound IrSn₂ is obtained in cubical crystals which may be isolated from the excess of tin by treatment with hydrochloric acid, in which the latter dissolves.

Iridium dissolves in lead, but without forming any definite compound. With copper, a pale red alloy is produced, which is fairly ductile and harder than copper. Nitric acid effects the solution of the lead and copper respectively, in the two foregoing alloys, leaving the iridium behind as an insoluble residue.

Iridium yields no definite compound with zinc, and perhaps not with iron.

Alloys of iridium with silver, gold, ruthenium, osmium, and platinum have been prepared.

Iridium renders platinum stiffer, and is for this reason frequently added to this metal when required for crucibles, etc. For high temperature work it has the disadvantage of rendering the alloy subject to proportionately greater losses in weight at temperatures above 900° C. in consequence of volatilisation. Below 900° C., however, and up to a content of 3 per cent, of iridium, the Joss in weight on heating is negligible.

Iridium Amalgam is not formed by direct union of ordinary iridium and mercury. It has been prepared, however, by triturating with mercury the dull grey, brittle metal saturated with hydrogen after being submitted to prolonged cathodic pulverisation in vacuo.