Most important of the alloys are those with iridium. Platinum and its alloys are used in surgical tools, laboratory utensils, electrical resistance wires, contact points, and standard masses. Because its thermal coefficient of expansion is nearly equal to that of glass, platinum is used to make electrodes sealed in glass. It is used extensively in jewelry and in dentistry. A platinum-cobalt alloy is used to make very powerful magnets.
Platinum is specially prepared for use as a catalyst .
Finely divided, the metal is platinum black, a powder. Platinum catalysts are used in the contact process for producing sulfuric acid, in the Ostwald process for the production of nitric acid, and in petroleum cracking, as well as in a variety of other reactions. Although natural platinum alloys may have been used several centuries before Christ, modern knowledge of the metal dates from about 1736, when its existence in South America was reported by A. de Ulloa. A process discovered about 1803 by W. H. Wollaston for making the metal malleable made possible its commercial use for laboratory apparatus and other purposes. Although platinum was used as an adulterant for gold over a century ago, it is now considered the more valuable of the two.