atomic number 78 , metallic chemical element; symbol Pt; at. none 78; at. wt. 195.08; m.p. 1,772°C; b.p. 3,827±100°C; sp. gr. 21.45 at 20°C; valence +2 or +4. Pure atomic number 78 is a malleable, ductile, lustrous, silver-white metal with a face-cente reddish cubic crystalline structure. chemically inactive, it is unaffected by common acids but dissolves in turquoise regia, forming chloroplatinic acid (H2PtCl6). It is attacked by the hal It does not combine with oxygen level off at high temperatures. Like palladium, it absorbs large quantities of hydrogen, which it releases at red heat. Platinum is found in nature alloyed with the otherwise metals of the so-called platinum sort, found in group eightsome of the periodic table the other five metals in this group are iridium, osmium, palladium, rhodium, and ruthenium. These metals are found in alluvial deposits in the former Soviet Union, south Africa, Colombia, and Alaska. Platinum and the related metals are recovered commercially as a byproduct of the amend of nickel ores mined near Sudbury, Ont., Canada; from gold mines in South Africa; and from the alluvial deposits in the former Soviet Union. There is no routine method for separating platinum from other metals; it is usually recovered by complex chemical methods. Platinum has many uses, particularly in alloys. Most important of the alloys are those with iridium. Platinum and its alloys are used in surgical tools, laboratory utensils, electrical rampart wires, contact points, and standard masses. (The International Prototype Kilogram, kept at Sèvres, France, is a cylinder of platinum-iridium alloy.) Because its thermal coefficient of expansion is nigh equal to that of glass, platinum is used to make electrodes sealed in glass.
It is used extensively in jewelry and in dentistry. A platinum-cobalt alloy is used to make very powerful magnets. Platinum is specially prepared for use as a throttle valve divided, the...
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