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.
[566] Plin. xxxvi. 26, p. 759, and lib. xxxvii. cap. 6, p. 769; he says that artists could make glass vessels nearly similar to those of rock crystal; but he remarks that the latter had nevertheless risen in price.
[567] Lib. xxxvii. 24, § 66.
[568] Plin. xxxvi. 8, § 13, p. 735.
[569] Speculum Lapidum, Parisiis, 1610, 8vo, p. 71. It may not be superfluous here to remark, that this Alabandicus of Pliny must not, as is often the case, be confounded with the precious stone to which he gives the same name, lib. xxxvii. cap. 8. The name properly denotes only a stone from Alabanda in Caria. It occurs, but much corrupted, as the name of a costly stone, in writings of the middle ages. See in Du Cange Alamandinæ, Alavandinæ, Almandinæ; and even in our period so fertile in names, a stone which is sometimes classed with the ruby and sometimes with the garnet, and which is sometimes said to have an affinity to the topaz and hyacinth, is called Alamandine and Alabandiken. See Brückman on Precious Stones, who in the second continuation, p. 64, deduces the word from Allemands, without recollecting the proper derivation, which he gives himself, i. p. 89 according to Pliny.
[570] Canon Medicinæ, lib. ii. tract. 2, cap. 470, de Magnete; and cap. 472, de Magnesia.
[571] In his book De Mineralibus, lib. ii. tract. 2, cap. 11.
[572] Stirpium et Fossilium Silesiæ Catalogus, Lipsiæ, 1600, 4to, p. 381.