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Curiosities
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·Cover ·20 ·47 ·74 ·101 §128
·Title ·21 ·48 ·75 ·102 ·129
·iii ·22 ·49 ·76 ·103 ·130
·iv ·23 ·50 ·77 ·104 §Plate 1
·v ·24 ·51 ·78 ·105 ·131
·vi ·25 ·52 ·79 ·106 ·132
§Contents ·26 ·53 §80 ·107 ·Plate 2
·viii ·27 ·54 ·81 ·108 ·133
§1 ·28 ·55 ·82 ·109 ·134
·2 ·29 §56 ·83 ·110 ·135
·3 ·30 ·57 §84 ·111 ·Plate 3
·4 ·31 ·58 ·85 ·112 ·136
·5 ·32 ·59 ·86 ·113 ·137
·6 §33 ·60 ·87 ·114 ·138
·7 ·34 ·61 ·88 ·115 ·Plate 4
·8 ·35 §62 ·89 ·116 ·139
·9 ·36 ·63 ·90 ·117 ·Plate 5
·10 ·37 ·64 ·91 ·118 ·140
·11 ·38 ·65 ·92 ·119 ·Plate 6
·12 ·39 ·66 ·93 ·120 ·141
·13 ·40 ·67 ·94 ·121 ·142
·14 ·41 ·68 ·95 ·122 §Index
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·19 ·46 §73 ·100 ·127
 
COLOURED GLASS.
The chemistry of colours depends upon a very nice adjustment of relative quantities of carbon and oxygen, as well as of colouring oxide, and of alkali or lead. Uranium is specially affected by an excess of alkali, the colour varying from deep gold topaz to light amber-like opalescent green, as the alkali predominates. The proportion of lead is diminished in either case; and although an excess of alkali extracts most colour from the oxide, it renders the Glass liable to become unhomogeneous, by the exudation of its alkali. It is to be regretted that the specific gravities are not given by Klaproth in his analyses.
Notwithstanding the use of oxide of lead by the ancients in their coloured Glasses and artificial gems and enamels, the lightness of the fragments of their white cut Glass indicates the absence of lead from the constituents of much of the ancient artificial crystal. A fragment in the possession of Mr, Roach Smith, alluded to in another part of this work, and introduced into the coloured Plate (3, fig. 3) can have no lead in its constituents, as its specific gravity is but 2.049; Flint Glass of the ordinary gravity being 3.200, Plate Glass about 2.500, and real crystal about 2.500. No doubt, this relic possessed a large quantity of alkali, probably carbonate of soda or potash, part of which has exuded by lapse of time, leaving the entire atoms or particles of undecomposed silex; thus rendering the glass less compact, of diminished specific gravity, and less conservative. These fragments probably formed part of a Roman white drinking-glass, which, in the days of ancient Rome was scarce, and highly valuable. Had lead formed one of its constituents, the Glass would have been more permanent; the surface would not have been so much decomposed and "crazed," as it is technically termed, leaving more or less