MANGANESE

This name is generally given to a black mineral, originally described in the year 1774, by Scheele, as a peculiar earth; and which was afterwards shown by Gahn to be tlie oxide of a metallic substance which he called magnesium. This term, however, having been applied to the metallic base of magnesia, the word tnanganese has been adopted to designate the metal; and the ore above alluded to has been called black, or peroxide of, manganese. The metal itself has a specific gravity of about 8. It is grey, hard, brittle, and very difficult of fusion, and has not been applied to any use. The black oxide, on the contrary, is largely employed as a source of oxygen, and is especially important from the use which is made of it in the decomposition of common salt for the production of chlorine. Manganese may be represented by the equivalent 28; and the black oxide, being a compound of 1 atom of manganese and 2 of oxygen, has the equivalent 44 (28 + 16). There is also a protoxide of manganese, composed of 28 metal + 8 oxygen, which is the basis of the salts of this metal. When hydrate or carbonate of pota a, or nitre, are fused with peroxide of manganese in an open ve el, a dark-coloured compound is obtained, long known under the name of chameleon mineral, in consequence of its yielding in cold water a solution which is at first green, then blue, purple, red, brown, and ultimately deposits a brown powder, and becomes colourle . This substance has since been termed manganate of potash, and has been proved to contain a compound of 1 atom of manganese and 3 of oxygen, which has been called manganic acid, and is represented by the equivalent 52. In the pink solution, which is produced at once by the action of hot water, manganese exists in a still higher state of oxidizer a ent, forming the per-manganic acid; in which 2 atoms of manganese are combined with 7 of oxygen. Both these compounds are very easy of decomposition. Some of the proto-salts of manganese have lately been used in calico-printing as the source of brown colours, and occasionally as deoxidizing agents. [s. 722]