The Density of the Soda-Lime Glasses
T126-T128 (3 pages)
The density of a glass is by no means an unimportant property to the glass technologist, quite apart from its interest to the scientific worker. In the first place, the waves and cords seen in unsuccessfully founded glass correspond with portions of slightly different density, as also the striae in samples of unsatisfactory optical glass. Secondly, the density of glass in the fluid state is of importance since the strength of the containing vessel must be sufficient to bear the thrust of the glass in it. Lead glass, as is well known, is relatively heavier, that is, denser, than lime–soda glass, and at high temperatures when the pot softens will be more effective in bringing about bulging at the bottom and sides than the less dense lime–soda glass. Finally, of importance for optical purposes, the refractive index rises steadily with the density, not only in anyone series of similar glasses, but in those, also containing quite different constituents. Thus, the flint glasses, whether of lead or of barium, have both high density and high refractive index.
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