[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.