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PLATINA. 100 PLAINER. and ilodrm Library of Theological Literature (2 vols., London, 1885). PLATING. See ELECTBo-CnEMisTBT, Indus- trial; anil KlecthoI'latixg. PLAT INIKID'IUM (XeoLat., from plati- num + irnlium I. A native alloy of iridium with platinum and allied metals that crystallizes in the isometric system, has a metallic lustre, and is silver-white in" color. It is found chiefly with platinum ores in the Urals and in Brazil ; also in the j.'ol(l alluvial deposits of the Pacific Coast. PLATINUM (Xeo-Lat., from platina, from Sp. plulina, platinum, from plain, silver, plate, from plato, tiat, fnmi Gk. ttXotm, pUilys, flat, wide, broad; connected with Lith. plains, broad, Skt. prihu. wide, from prnth, to spread out). A metallic element, the existence of which was first made known in Europe by . tonio 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 Xew 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 preparation of pure platinum the commercial metal may be melted with C parts of pure lead and the finely divided alloy treated with dilute nitric acid. The residual l>lack pow- der may then be dissolved in dilute aqua regia, the solution precipitated with dilute sulphuric acid, and the filtrate further precipitated with an .excess of aninioniuni chloride and some common salt. This precipitate is in turn heated with the aeid sulphates of potassium and ammonium, and on cooling the resulting mass is treated with hot water, which leaves nothing but pure platinum behind. The commercial metal is usually ob- tained by a somewhat complicated wet process, although it is possible to obtain it more 6t less pure also by a dry process. Platinum" (symbol Pt.; atomic weight, 194.80) is a gravish-white metal with a specific gravitv of 21.48 at about 17.6° C. It fuses at about 2000° C. (3630° F.). It is very malleable and ductile, becoming soft and workable at a tem- perature far below its nidting-point. Wires have been drawn that are one twelve-hundredth of an inch in diameter. Molten platinum ab- sorbs oxygen, which it gives ofT when rapidly cooled. Red-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 igniting ammonium-platinum chloride. It forms a porous mass which may be polished with a bur- nisher. Of similar nature is philinum hlncl:. 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 u.se, and as it is not attacked by acids, ves- sels 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 ])roposed 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 1000 400 Troy ounces of metallic platinum, valued at .$2,500, were mined in the United States. Platinum combines with oxygen to form a ])latinous oxide or monoxide (PtO), which gives rise to a series of platinous .salts, a platino- platinic oxide (PtjO,), and a platinic oxide or dioxide (PtOj), which yields a scries of platinic salts. Tlic 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 laboratorj' as a reagent. Of considerable interest to the chemist are also the so-called platinum bases, which are compounds of platinum salts with ammonia. Metallurgy. The extraction of platinum from the ore consists first in concentrating the ore by washing; the further treatment may be con- ducted either in the wet way or the dry way. The dry method does not produce pure platinum, but its alloys with iridium and rhodium, and the production of pure platinum requires the use of the wet method. Electrolysis is used to separate metallic platinum from its alloys with gold. Two methods of dry extraction have been used. One consists in melting the ore in a ves- sel made of lime and remelting the button thus obtained ; the second method is to melt the ore with galena and litharge in a reverberatory fur- nace and scorify the lead-platinum alloy ob- tained in order to remove the lead. Finally the platinum is fused into an ingot in the lime fur- nace. The wet method of extraction consists essentially in bringing platinum into solution with aqua regia, precipitating from this solution platinum-annuonium chloride by means of am- monium chloride and ammonia, and then decom- posing the compound and separating the plati- num at red heat. The wet method is the principal method of platinum refining now employed. Physi- cally metallic i)latinum has an almost silver white lustre, is ductible and malleable in a high de- gree, is about as hard as copper, and has a tenacity between that of gold and of copper. For a concise treatment of the metallurgy of plati- num, consult: Howe, Bibliography of the Metals of the Platinum Group, 17^8 to 1896 (Washing- ton, 1897) ; Schnabel, Band-book of Metallurgy (Xew York, 1898). PLATTIfER, -Jonx Wi.THROP (1865—). An American theologian and Church historian, born in Lee, Mass. He graduated at Yale Univer- sity in 1885, and at Union Theological Semi- nary in 1893, studied in Berlin, then was instruc- tor'in L'nion Seminars- (1895-96). in 1896 be- came assistant professor of ecclesiastical history at Harvard, and in 1901 accepted a similar chair at Andover Theological Seminary. He contrib- uted articles on historical theology to the New Intfnifttinnal Encyclopcedia. PLATNER, Sasiuel Bali, (1863—). An American classical scholar, born in LTnionville, Conn., and educated at Xewark Academy and