Platinum Composition, Crystallization, Structure and Occurrence

Composition. Platinum, usually alloyed with several per cent of iron and with smaller amounts of iridium, osmium, etc. The amount of metallic platinum present seldom exceeds 80 per cent. 

Crystallization. Isometric. Crystals very rare. Sometimes in irregular masses and nuggets of larger size.

Physical Properties. H. = 4-4.5 (unusually high for a metal). G. = 14-19 native; 21-22 when chemically pure. Malleable and ductile. Color steel-gray, with bright luster.

Test. B. B. infusible. Unattached by ordinary reagents; soluble in a mixture of hydrochloric and nitric acids. Determined by its high specific gravity, infusibility and insolubility.

Occurrence. Platinum is a rare metal which occurs almost exclusively native (only one rare compound, sperrylite, PtAs₂, being known). It is found in quantity in only in the stream sands, as placer deposits, where it has been preserved on account of its great weight and hardness. Occurs in the alluvial deposits associated with the rarer metals of the Platinum Group, gold, iron-nickel alloys, chromite, etc. Its original source is probably usually in peridotite rocks or the serpentine rocks resulting room their metamorphism. It occurs so sparingly disseminated through such rocks, however, that it is only after their disintegration and the subsequent concentration of the platinum in the resulting sands that workable deposits of the metal are formed. Placer deposits of platinum are therefore to be looked for in the vicinity of masses of such perioditite rocks.

Practically the entire world’s supply of platinum at present comes from the Ural Mountains in Russia. The central and northern end of this range has large masses of altered perioditite rocks, and in the sands of the streams descending form it, chiefly on the eastern slope in Siberia, platinum is found in considerable quantity. The chief districts are near Nizhne Tagilsk, and farther to the north, Bogoslovsk.

Platinum was first discovered in the United States of Colombia, South America, where, it received its name platina form plata (Silver). It is to be found there in two districts near the Pacific coast. The chief district covers the greater part of the intendencia of Chocó, department of Cauca. The platinum occurs here with gold in placer deposits, and, while the fields are not largely productive a t present they may become so.

The only platinum found in the United States comes from the gold placer deposits of Oregon and California, but the yearly yield amounts ton only a few thousand dollars in value.

Use. the uses of the metal depend chiefly upon its insolubility, infusibility and superior hardness. It is used for various scientific instruments such as crucibles, dishes, etc., in the chemical laboratory; to line the distilling apparatus in the manufacture of sulfuric acid; in the electrical industry for contacts, etc.; in jewelry, chiefly as the setting for diamonds; as anodes in the electrolytic chemical industry; for diamonds; as anodes in the electrolytic chemical industry; for electric heating apparatus; for the measurement of high temperatures by the use of thermoelectricity; for sparking plugs in explosive motors; in incandescent electric light; in the manufacture of false teeth and in fillings for teeth; and in various chemical reactions which are facilitated by the use of finely divided platinum.