MANGANESE, in chemistry, a sub stance that has long been employed in the manufacture of glass, on account of its property of depriving that substance of its colour. From its appearance it was called black magnesia, or manganese. It was considered as an ore of iron, because it was found combined with the oxide of that metal. Bergman and Scheele gave an accurate description of its nature and properties. It is generally found in the state of an oxide either white, or black, or red. The white contains the smallest proportion of iron and of oxygen. This ore soon tarnishes in the air by absorbing oxy gen. The red contains more iron than the white, and is crystallized. The black or the brown ore is frequently crystalliz ed like the red. Manganese is procured in the metallic state, by reducing the ox ide to powder, and forming it into a paste with water. It is then exposed to a strong heat, not less than 160° of Wedgwodd, with charcoal, and the metal, after a time, is found at the bottom of the crucible, or in the midst of the scoriw in small glo bules, which amount to nearly one-third of the manganese employed. Manga nese, in the metallic state, is of a greyish white colour, with considerable brillian cy, and of a granular texture. The speci fic gravity is 6.85. It is hard as iron; is one of the most brittle and most infusible of the metals. When exposed to the air it is quickly tarnished, and at length falls into powder, which is found to have ac quired considerable addition to its weight. But when heated in the open air, it passes more rapidlythrough the different chang es of colour in proportion as it combines with oxygen, to the absorption of which these changes are owing : hence manga nese, like some other metals, combines with different portions of oxygen, forming with it different oxides. The different coloured oxides are combined of man ganese and oxygen in the following pro portions : White Brown or Black Oxide. Red Oxide. Oxide.
Manganese . . 80 74Oxygen . . . .20 26 40 100 100 100— — From the black, which is most abun dant in oxygen, the chemists usually ob tain what they use in their experiments. The black is evidently the metal at the maximum of oxydizement, the white is the one at the minimum. Manganese does not enter into combination with azote, hydrogen, or carbon. By means of charcoal the oxide is reduced, by being deprived of its oxygen. Phosphorus com bines very readily with manganese, form ing a phosphoret. It may likewise be made to combine with sulphur, forming a sulphuret. It enters into combination
with the acids, and forms salts with them. These salts may be decomposed by the alkalies, which throw down precipitates of a yellow or reddish colour. None of them are decomposed by aPy of the other metals, which shews the strong affinity of manganese to oxygen. The pure alkalies flivour the oxydation of manganese, and the decomposition of water, because they combine readily with this oxide. When the black oxide is ex posed to heat, with twice its weight of dry soda or potash, a compound is formed of a dark green colour, which is soluble in water. During the solution, this sub stance exhibits rapid changes of colour, and on that account has been denominat ed the " mineral camelion." There is no action between mangahese and any of the earths ; but its oxide combines with them, and forms vitreous matters, which are of different colours, according to the degree of oxydation of the manganese, and its mixture with iron. The native black oxide of manganese is applied to several purposes. It is the substance from which oxygen can be most econo mically obtained, large quantities of which are consumed in the formation of the oxy-muriatic acid employed in the art of bleaching. It is used in glass-mak ing, to remove from the substance the green colour which is derived from the oxide of iron. The theory of its action is thus explained: iron, in a low state of oxydizement, gives to glass a green tinge, while, if it be at a high degree of oxy dizement, it either does not enter into fusion with the ingredients of the glass, or at least does not communicate any co lour. Manganese, in the state of black oxide, gives a violet colour, but reduced to the white oxide the glass is colourless. In adding, therefore, the black oxide to glass, while it yields its oxygen to the iron, which it thus brings to a high state of oxydizement, it passes itself to the state of white oxide, and thus each metal is in that state in which it does not communi cate colour. The black oxide is also use ful, probably by consuming the carbona ceous matter and other substances pre sent in the materials which are suscepti ble of oxydizement. In large quantities it is used in the composition of ornament al glass, to give a purple colour. It is like wise employed to give a black colour to earthen ware, a quantity of it being mix ed with the composition before it is baked.