PALLADIUM, in chemistry, a metal discovered by Dr. Wollaston in the native platina : it is of a greyish colour, and,, when polished, of considerable lustre : it is very ductile and very malleable ; so that by the flatting mill it can be reduced into thin slips, which are flexible, but not very elastic. Its fracture is fibrous, and in diverging striae, sheaving a kind of crys taline arrangement. In hardness it is su perior to wrought iron. Its specific gravity varies according to its perfect fusion, and as it is more or less porous, from hammering or flatting, from 10.9 to 11.8. It is a less perfect conductor of caloric than the other metals, and is also less expansible. When exposed to a strong heat, its surface tarnishes a little, and becomes blue, but by increas ing the heat it again becomes bright. By a very great heat it is fused. It is not oxided by heat ; its oxides formed by the action of acids are reduced by means of a high temperature. It is acted
upon by a number of the acids ; and the solutions formed by them may be decomposed by the alkalies and earths ; precipitates being thrown down, which are generally of a beautiful orange colour. The alkalies act likewise on palladium even in the metallic state : the action is promoted by the contact of the atmospheric air. All the metals, except gold, silver, and platina, preci pitate palladium from its solution in the metallic state. Palladium combines rea dily with sulphur, but not with charcoal. It may be alloyed with a number of the metals. A full account of the discovery of palladium, with the controversy to which it gave rise, will be found in the Philosophical Transactions for the years 1802, 1803, 1804, 1805.