MANGANESE, a metallic chemical element which is of a slightly brown appearance and has considerable hardness. Its diox ide (pyrolusite) has been known from very early times, and was at first mistaken for a magnetic oxide of iron. In 2740 J. H. Pott showed that pyrolusite did not contain iron and that it yielded a definite series of salts, whilst in 1774 C. Scheele proved that it was the oxide of a distinctive metal. Manganese (symbol Mn; atomic number 25, atomic weight 54.93) is found widely distributed in nature, being generally found to a greater or less extent associated with the carbonates and silicates of iron, calcium, and magnesium and also as the minerals braunite, hausmannite, psilomelane, man ganite, manganese spar and hauerite. It has also been recognized in the atmosphere of the sun, in sea water, and in many mineral waters.
The metal was isolated by J. G. Gahn in 1774, and in 2807 J. F. John obtained an impure metal by reducing the carbonate at a high temperature with charcoal mixed with a small quantity of oil. R. Bunsen prepared the metal by electrolysing manganese chloride in a porous cell surrounded by a carbon crucible contain ing hydrochloric acid. Various reduction methods have been em ployed for the isolation of the metal. C. Brunner reduced the fluoride by metallic sodium, and E. Glatzel the chloride by mag nesium; H. Moissan reduced the oxide with carbon in the electric furnace. Mostly, manganese is now prepared by the reduction of the oxide by aluminium as in H. Goldschmidt's "thermite" process. It is also prepared in large quantities as ferromanganese by re duction of the mixed ores of iron and manganese in the blast furnace. (See IRON AND STEEL.) Manganese has a specific gravity of 7.42, and the variety obtained by distilling pure manganese amalgam in vacuo is pyro phoric, and burns when heated in a current of sulphur dioxide. The pure metal readily evolves hydrogen when acted upon by sulphuric and hydrochloric acids, and is readily attacked by dilute nitric acid. It precipitates many metals from solutions of their salts. It melts at 2230° C.
a dark brown powder which readily loses water at above 'co° C; it dissolves in hot nitric acid, giving manganous nitrate and manga nese dioxide : 2Mn0 (OH) Mn Manganese dioxide, or pyrolusite (q.v.), which is the most important oxide, may be prepared by heating crystallized man ganous nitrate until red fumes are given off, decanting the clear liquid, and heating to I50° to 260° C for 4o to 6o hours, or by heating manganese carbonate to 26o° C in the presence of air and washing the residue with very dilute cold hydrochloric acid. It is a hard black solid which readily loses oxygen when strongly heated, leaving a residue of When heated with concentrated hydrochloric acid it yields chlorine, and with concentrated sul phuric acid it yields oxygen. It is reduced to the monoxide when heated in a current of hydrogen. It is a strong oxidizing agent. It dissolves in cold concentrated hydrochloric acid, forming a dark brown solution which probably contains manganic chloride, since salts of the type may be prepared from it. Salts cor responding to MnC14, e.g., have been obtained by boil ing potassium permanganate in glacial acetic acid and separating the solution with hydrogen chloride. It is almost impossible to prepare a pure hydrated manganese dioxide owing to the readiness with which it loses oxygen, leaving residues of the type Such mixtures are obtained by the action of alka line hypochlorites on manganous salts, or by suspending man ganous carbonate in water and passing chlorine through the mix ture. Manganese dioxide combines with other basic oxides to form manganites, and on this property is based the Weldon process for the recovery of manganese from the waste liquors of the chlorine stills. (See CHLORINE.) The manganites are amorphous brown solids, insoluble in water, and decomposed by hydrochloric acid with the evolution of chlorine. Manganese trioxide, is ob tained in small quantity as an unstable deliquescent red solid by dropping a solution of potassium permanganate in sulphuric acid on to dry sodium carbonate. Above 50° C it decomposes into the dioxide and oxygen. It dissolves in water, forming manganic acid, and permanganic acid. Manganese heptoxide, prepared by adding pure potassium permanganate to well cooled, concentrated sulphuric acid, when the oxide separates as a dark oil, is very unstable, continually giving off oxygen. It decomposes violently on heating, and explodes in contact with hydrogen, sul phur, phosphorus, etc. It dissolves in water to form a deep red solution which contains permanganic acid, This acid is also formed by decomposing barium or lead permanganate with dilute sulphuric acid. It is only known in aqueous solution. This solution is of a deep violet red colour, and is somewhat fluorescent ; it decomposes on exposure to light, or when heated. It is a mono basic acid, and a very powerful oxidizing agent.