Palladium (Pa., at. wt. 1066), a rare metallic -element, which was first discovered in 1803. It occurs in nature in the free state, but not pure, being alloyed with platinum, gold, or iridium. In its general chemical properties it closely resembles platinum. It forms a series of salts, the palladious and palladio compounds. It has a specific gravity of about 118. Neither the metal nor its compounds are much used. An amalgam of mercury is employed in dentistry, and small quantities of the metal are said ,to improve the quality of steel for many purposes.