For the fiscal year ending 30 June 1918, the imports of umnanufactured platinum, and of bars and ingots, weighed 1,613.1 kilos, or 51,862 troy ounces, and were worth $4,572,614; the re torts, vases, etc., were valued at but $2,547, giv ing a total of $4,575,161 for all platinum im ports to the United States. Of this Colombia contributed $2,241,744 (27,030 troy ounces), just about half the total value and a little more than half the weight. A single, special ship ment of 21,000 ounces from Russia, acquired for $2,000,000, accounted for most of the re mainder.
The value of platinum, as measured by that of gold, has varied enormously in the course of years. About 1788 Colombian platinum was bought by the Spanish Royal Mint at a price equalling some 14 cents an ounce troy. At the time the Russian platinum coins were struck (from 1828 to 1845) the metal was reckoned to be worth but $7.15 an ounce troy. Fifty or 60 years later the price had increased greatly, rising from about $20 an ounce in 1906, to $45 $46 in 1911-13. With the advent of the great war, the interruption of Russian production and the increased demand for special uses caused the price to mount rapidly to $105 and even higher. When, in 1918, the United States government assumed control of the platinum market, it established the price of $105 per ounce for pure platinum.
The five allied platinum metals of the platinum group, making six in all, palladium, osmium, iridium, ruthenium and rhodiuM, as well as the combination osmiridium (iridos mine), each have their special characteristics and usefulness.
Palladium was found in 1803 by Wollaston as a constituent of crude platinum from Choc6, Colombia. Its name was suggested by the then recently sighted planetoid Pallas, discovered by the German astronomer Olbers in 1802. The melting point of palladium is between and 1,380° C. and its hardness is from four to five; the specific gravity is 11.4. It is more easily fusible than Ilatinum, indeed, it has the lowest melting point of any of the platinum metali. It has been much used for alloys in astronomical instruments and also in dentistry. In clock-making it has found employment for springs and movements. In 1919 it sold for $135 the ounce, troy.
Osmium is one of the heaviest of these metals, its specific gravity ranging from 21.3 to 22.48. It was discovered in 1804 by Smithson Tennant in the residuum of South American crude platinum, after it had been treated with aqua regia. 'the (from Greek osme, was bestowed because of the peculiar odor emitted by its volatile oxide.
Iridium was discovered by Tennant in 1804 and in the same way as osmium. Its hardness is between six and seven, that of platinum being. only about four, and its specific gravity of from 22.6 to 22.8 makes it the heaviest of the platinum group. Its melting point is about 2,200° C. The name (from Iris) was chosen because of the variegated hues of its oxide.
The combination of osmium and iridium, to which the name osmiridium or iridosmine has been given, was first observed by Wollaston in 1805. Some mineralogists have used the desig nations iridosmine and osmiridium as signifying a lighter-hued and a darker-hued form of the alloy, respectively.
Rhodium, discovered in 1804 by Wollaston, occurs in some platinum ores. The color is a grayish-white. Its fusion point is as high as 1,940° C. While very hard, the specific gravity is low, not exceeding 12.1. Rhodium has been less used than any other of the platinum metals.
Still another metallic element found in asso ciation with platinum bears the name ruthenium. It is obtainable from the residuum resulting from the separation of osmium from osmiri dium. The specific gravity is only 12.26. Ruthenium is practically unattackable by acids. It was discovered by Claus in 1845. The desig nation, derived from Ruthenia, an ancient name of Russia, had been applied in 1826 by Osann to one of three new metals he claimed to have found associated with platinum, another of which, his pluran, was probably the true rutht nium; his ruthenium and (pan* were sub senuentiv shown bv Claus to be errors.* Bibliography.— 'Relation historica del Viage a la America meridional' (Don Jorge Juan and Don Antonio de Ulloa, 2 vols., Madrid 1748) ; Philosophical Transactions, Vol. XLVI, 1751, pp, 584 sqq., letters of Brownrigg and Watson; 'La Platine, l'or blanc, ou le huitierne metal' (Paris 1758); Howe, J. L. and Holtz, H. C., 'Bibliography of the Plati num Group' (Smithsonian Institution, Miscel, Coll. No. 1084, Washington 1897; a new issue, considerably augmental, U. S. Geol. Surv., Bulletin 694); Annual Reports of United States Geological Survey, 'Mineral Resources,' with articles by David T. Day, F. W. Horton, Joseph Struthers, Waldemar Lindgren and J. W. Hill; Annual Reports in 'Mineral Industry' (Vol. I, 1892, to Vol. XXVII, 1918, with articles by Charles Bullman, Henry Louis, Joseph Struth ers, L Tovey, Frederick W. Horton, F. Lyn wood Garrison and George F. Kunz; Kunz, G. F., 'Platinum with Especial Reference to Latin-America' (in Bulletin of the Pan-Ameri can Union, November-December 1917 and 1919).