Uses In troduction

Platinum is a relative newcomer among the precious metals, having been known to the scientific world for only about 200 years, although used earlier than that by the natives in South America. In contrast, gold has been in use for at least 6,0{)0 years, while silver came into use some time later. Gold and silver were first used for appearance applications. The industrial use of silver is relatively recent, and that of gold is still minor. In contrast, platinum and, later, the other metals of this sextet were first used principally for scientific and industrial purposes. Jewelry uses developed only within the present century, the use of platinum for jewelry becoming important about 1906 and palladium within the past ten years. The chemical properties of the plati-num group metals are such that many difficult problems are encountered in effeeting clean-cut separations between these metals and also in eliminating impurities. Some of the salts exhibit unusual behaviors and, in some cases, their solutions yield practically zero concentrations of the platinum metal ion. At times this characteristic s use-ful, but at others it probably has re-sulted in running valuable solutions to waste because they were thought o be barren. Even after good separations were effeeted, the high melting tempera-ture of platinum challenged metallur-gists and chemists and led Knight, Wollaston, and others to develop the powder metallurgy process nearly 150 years ago. Wollaston described thi