PLATINUM ( Neo-Lat., from platina, from Sp. ptatina, platinum, from plata, silver, plate, from pinto. fiat, from Gk. platys, fiat, wide, broad ; connected with Lith. /thrills, broad, Skt. prthu, wide, from praflr, to spread nut). A metal lie element. the existence of which was first made km wn in Europe by Antonio de Ulloa in 1736. It was first described by Watson in 1750. It is found native, usually alloyed, however, with iron, palladium, rhodium. iridium, osmium, and other metals, generally in grains and scales in alluvial deposits in South America, the Urals. in Borneo. Santo Domingo, and New Zealand ; also in small quantities in the gold washings of the Pacific Slope. A few irregular lumps or nuggets have been found, one of which, now in the Demi doff cabinet in Saint Petersburg. weighs 7837 kilograms. For the of pure platinum the commercial metal may he melted with 6 parts of pure lead and the finely divided alloy treated with dilute nitric acid. The residual black pow der may then be dissolved in dilute aqua regia, the solution precipitated with dilute sulphuric acid. mud the filtrate further precipitated with an excess of ammonium chloride and some common salt. This precipitate is in turn heated with the acid sulphates of potassium and ammonium, and on cooling the resulting mass is treated with hot water, which leave, nothing hut pure platinum behind. The commercial metal is usually ob tained by a somewhat complicated wet process. although it is possible to obtain it more Or less pure also by a dry process.
Platinum (symbol I't.: atomic weight. 194.89) is a grayish-white metal with a specific gravity of 21.48 at about 17.6° ('. It fuses at about 2000' C. (3G30' F.). It is very malleable and ductile, becoming soft and workable at a tem perature far below its melting-point. Wires have teen drawn that are one twelve-hundredth of an inch in diameter. Molten platinum ab sorbs oxygen, which it gives off when rapidly cooled. Bed-hot platinum also occludes hydro gen. to the extent of about five times its own vol
ume, and retains it indefinitely after cooling. Spongy platinum is finely divided metallic plati num which possesses a very large surface com pared with its mass and is able to condense large quantities of oxygen. It is readily prepared by hmiting ammonium-platinum chloride- It forms a porous mass which may be polished with a bur nisher. Of similar nature is ptctinunr black, that is usually prepared by heating a solution of platinous chloride in potash and alcohol. It ab sorbs more than 800 times its volume of oxygen. Platinum forms alloys with most of the metals, some of which. such as the alloy with 10 per cent. iridium, have found use in the arts. especially for the purpose of making standard weights and measures. Metallic platinum is employed in making crucibles and similar utensils for labora tory use, and as it is not attacked by acids, ves sel, of it have been used in sulphuric acid works. It also finds extensive application in the manu facture of incandescent electric lamps, being the only metal that can be used to pass through the glass lamp bulbs making a tight joint. Methods have been proposed for its electrolytic deposi tion, but they have not been generally adopted. It has been used in 'Russia for the coinage of high values of money. During 1900 400 Troy ounces of metallic platinum. valued at $2500, were mined in the United States.
Platinum combines with oxygen to form a platinous oxide or monoxide (Pt0), which give, rise to a series of piaannons salts, a platino platinie oxide ( and a platinic oxide or dioxide which yields a series of platinic salts. The most important of the platinum salts is the platinic chloride or platinum tetrachloride, which is a brownish red deliquescent salt, a so lution of which is used in the laboratory as a reagent. Of considerable interest to the chemist are also the so-called platinum bases, which are compounds of platinum salts with ammonia.