Cadmium
. Cadmium, symbol Cd, silvery-white metallic element that can easily be shaped. The atomic number of cadmium is 48; the element is one of the transition elements in group 12 (or IIb) of the periodic table (see Periodic Law ). PROPERTIES AND OCCURRENCE Cadmium was discovered in 1817 by the German chemist Friedrich Stromeyer, who found it in incrustations in zinc furnaces. The element ranks about 65th in natural abundance among the elements in the earth's crust. Cadmium melts at 321° C (610° F), boils at 765° C (1409° F), and has a specific gravity of 8.64; the atomic weight of cadmium is 112.41. When heated, cadmium burns in air with a bright light, forming the oxide CdO. Cadmium occurs as the principal constituent of a mineral only in the rare greenockite. Almost the entire cadmium output of the United States is obtained as a by-product in the refining of zinc ores, chiefly from Missouri and Montana. It is also obtained from the zinc ores of Silesia. Fractional distillation or el...