Ch. 2: Platinum in 1905

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	430	MINERAL RESOURCES.

	The latter will, with the exception of zircon, contain only comparatively light minerals, and will consist principally of quartz, which has entered into the concentrates through accident. This product will contain practically all of the gold and iridos-mium in the original concentrates and will present no difficulties in cleaning up in a hand pan, as the heavy minerals which would have prevented successful panning have been removed. Sodium amalgam.—The magnetic portion containing most of the platinum and small quantities of gold should then be treated with a very strong sodium amalgam. This picks up any gold almost immediately and, if the conditions are favorable, all of the platinum. The action of the sodium amalgam on the platinum is not one of amalgamation, but rather one of positive capillarity, by which the platinum grains are wet by the amalgam and retained within its mass. Pure quicksilver and weak sodium amalgam do not, unfortunately, possess this quality, and as sodium amalgam rapidly deteriorates in the presence of water, the material treated should be just sufficiently moist to allow its working, and the time of treatment should not be unnecessarily prolonged. This separation requires considerable experience and skill on the part of the operator. If a strong electro-magnet is not available the original concentrates from the table may be treated with sodium amalgam, but the results obtained in this way do not seem quite so satisfactory. PHYSICAL PROPERTIES. Crude platinum consists of an alloy of platinum with iridium, rhodium, palladium, osmium, iron, and often copper and gold. It is almost invariably associated with iridosmium, a natural alloy of iridium and osmium, with which the platinum seems to be combined mechanically. The following table gives analyses of four representative specimens: Analyses of crude platinum.^a



	a Ann. Chim. Phys.. 3d ser., vol. 56, 1859. p. 449. Sample No. 1 is from Oregon, No. 2 from California, No. 3 from Russia, and No. 4 from Colombia. The analyses are by Deville and Debray. Outside of its rare occurrence as sperrylite (PtAs₂) in copper ores from Sudbury, Ontario; from the Rambler mine, in Wyoming, and from North Carolina, platinum is found under the same conditions as placer gold, and generally in the form of small grains, scales, and nuggets in placer gravels. These scales have a metallic luster and vary in color from a bright silvery white to a dark steel gray. Their specific gravity varies a great deal, according to the percentage of iron they contain, and ranges from 14 to 19. The grains are malleable, sectile, have no cleavage, and possess a hackly fracture. Platinum crystallizes in the isometric system, and in extremely rare cases

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