A metal of a whitish color, not malleable, found in the ore of platinum, and in a native allow with osmium. Its specific gravity is above 18. It takes its name from the variety of colors which it exhibits while dissolving in muriatic acid. The native allow with osmium, or native iridium is of a steel gray color and shining metallic luster. It usually occurs in small irregular flat grains, in alluvial soil, in S. America.
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Iridium
Encyclopedia Britannica
IRIDIUM, one of the metals of the platinum group (see vol. V. p. 536), has recently acquired increased importance from its employment in alloy with platinum in the construction of the international standards of length and weight. Its separation from the associated metals is a matter of very considerable difficulty, and involves a long series of operations. , These have been fully described by Deville and Debray {Comptes Pendus, Ixxxi. 839) and by Mr G. Matthey {Roy. Soc. Proc., 1879, xxviii. 463). In practice, even when prepared with the utmost care, it still contains a minute though almost inappreciable amount of oxygen, rhodium, ruthenium, and possibly iron (Matthey).
Seubert has redetermined the atomic weight of iridium by reducing ammonium iridichloride, (NH 4 ) 2 IrCl 6 and potassium iridichloride, K 2 IrCl 6 , by heating in a current of hydrogen, and finds as the mean of fifteen accordant experiments Ir=192 ’ 74 (Berichte d. deut. diem. Gesellsch. zu Berlin, 1878, 1767). This result justifies the placing of iridium before platinum in the table in vol. v. p. 543.
The alloy used in the construction of the international geodesic standard was prepared by fusing together platinum and iridium in a lime crucible by a powerful blast of oxygen and coal gas; it has the following composition: [table]...
It is almost indestructible, and has extreme rigidity, especially in the tube form; its coefficient of elasticity is very great; it has a high density, and a most beautifully polished surface can be obtained upon it (comp. Deville, Ann. Chim. Phys. 1879 [5] xvi. 506). An iridio-platinum alloy containing about 20 per cent, of iridium has also a very high coefficient of elasticity (22'20), whilst its malleability and ductility are almost without limit. A 25 per cent, alloy can only with great difficulty be worked into sheet and wire when heated at a low temperature, 30 and 40 per cent, with great difficulty only at a temperature little below melting; it is brittle when cold, but has a grain of great beauty and fineness (Matthey).
9th ed. Encyclopædia Britannica, vol. 13, p. 275
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[341 words — estimated reading time: 2 minutes]
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