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A rare metallic element, of the same group as platinum, which it much resembles, being silver-white, but harder, and brittle, and indifferent to most corrosive agents. With the exception of osmium, it is the heaviest substance known, its specific gravity being 22.4. Symbol Ir. Atomic weight 192.5.

A natural alloy of platinum and iridium occurring in grayish metallic rounded or cubical grains with platinum.

Of or pertaining to iridium; -- said specifically of those compounds in which iridium has a relatively high valence.

Of or pertaining to iridium; -- applied specifically to compounds in which iridium has a low valence.

To point or tip with iridium, as a gold pen.

The native compound of iridium and osmium. It is found in flattened metallic grains of extreme hardness, and is often used for pointing gold pens.

adium, whose specific gravities are about 12; and the heavy platinum group, viz., osmium, iridium, and platinum, whose specific gravities are over 21. -- Platinum sponge (Chem.), metallic platinum in a gray, porous, spongy form, obtained by reducing the double chloride of platinum and ammonium. It absorbs oxygen, hydr…