Plat"i*num (?), n. [NL., fr. Sp. platina, from plata silver, LL. plata a thin plate of metal. See Plate, and cf. Platina.] Chem.
A metallic element, intermediate in value between silver and gold, occurring native or alloyed with other metals, also as the platinum arsenide (sperrylite). It is heavy tin-white metal which is ductile and malleable, but very infusible, and characterized by its resistance to strong chemical reagents. It is used for crucibles, for stills for sulphuric acid, rarely for coin, and in the form of foil and wire for many purposes. Specific gravity 21.5. Atomic weight 194.3. Symbol Pt. Formerly called platina.
Platinum black Chem., a soft, dull black powder, consisting of finely divided metallic platinum obtained by reduction and precipitation from its solutions. It absorbs oxygen to a high degree, and is employed as an oxidizer. -- Platinum lamp Elec., a kind of incandescent lamp of which the luminous medium is platinum. See under Incandescent. -- Platinum metals Chem., the group of metallic elements which in their chemical and physical properties resemble platinum. These consist of the light platinum group, viz., rhodium, ruthenium, and palladium, 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, hydrogen, and certain other gases, to a high degree, and is employed as an agent in oxidizing.
© Webster 1913.