[The distinctness of the metal contained in the manganese of commerce from iron was first proved by the experiments of Pott in 1740, by Kaim and Winterl in 1770, and by Scheele and Bergman in 1774. Soon after this the metal itself was obtained in an isolated state by Gahn, who gave to it the name of _magnesium_, which term however was subsequently applied to the metal contained in magnesia, and the word _manganese_ has been adopted to designate both the metal and the black ore. In addition to its application in the manufacture of glass, it is now very extensively used in the decomposition of common salt for the production of chlorine for bleaching. Some salts of the lower oxides of manganese have lately been used in calico-printing as a source of brown colours.] FOOTNOTES [561] [The word manganese, strictly speaking, designates the metal itself, the peroxide of which is understood by the author whenever the word manganese occurs in the text.] [562] Lib. xxxvi. 26, § 25.--See Hambergeri Vitri Historia, in Comment. Societ. Götting. tom. iv. anni 1754, p. 487. [563] Under this appellation, writers on the art of glass-making understand a mixture of sand or siliceous earth and alkaline salts, which at the German glass-houses, where the above word is seldom heard, is called _Einsatz_. It appears to have been brought to us, along with the art, from Italy, where it is written at present _fritta_, and to be derived from _fritto_, which signifies something broiled or roasted. It seems to be the same word as _freton_, which occurs in Thomas Norton’s Poem, Crede mihi, sive Ordinale, where it however signifies a particular kind of solid glass, fused together from small fragments. This Englishman lived about the year 1477. His treatise was several times printed. [564] [The action of peroxide of manganese (the only compound of the metal used in the manufacture of glass) is simple and clearly understood. The sand (silica) used in the manufacture of glass frequently contains iron, which by the heat necessary for the fusion of the glass becomes reduced to the state of protoxide, giving the glass a greenish or yellowish colour; also, if any organic substance be present in the materials (and where sulphate of soda is used, charcoal is added), the glass is not colourless. When peroxide of manganese is added, it parts with some of its oxygen, becoming reduced to the protoxide, which remains colourless in the glass, the protoxide of iron absorbing the oxygen, becomes at the same time converted into the peroxide, which also imparts no colour to the glass, which is thus rendered colourless. If more of the peroxide of manganese be added than the carbon or protoxide of iron can reduce, it will tinge the glass of an amethyst colour, as stated in the text.] [565] See the History of Ruby-glass in vol. i. p. 123.