Manganese
. Manganese, symbol Mn, silvery white, brittle metallic element used principally in making alloys . Manganese is one of the transition elements of the periodic table (see Periodic Law ). The atomic number of manganese is 25. PROPERTIES AND OCCURRENCE Manganese was first distinguished as an element in 1774 by the Swedish chemist Johan Gottlieb Gahn. Manganese metal corrodes in moist air and dissolves in acid. Manganese melts at about 1245° C (about 2271° F), boils at about 1962° C (about 3564° F), and has a specific gravity of 7.2; the atomic weight of manganese is 54.938. Pure manganese is obtained by igniting pyrolusite (manganese dioxide) with aluminum powder or by electrolyzing manganese sulfate. The metal does not occur in the free state, except in meteors , but is widely distributed over the world in the form of ores, such as rhodochrosite, franklinite , psilomelane, and manganite. It ranks about 12th in abundance among elements in the earth's crust. The principal ore of manga...