"Eating it up with that preparation of nitric
acid. Do you see it work?"
Lawrence did see, to his surprise, that the liquid
was beginning to bubble about it, like some brisk sort of wine, and that
the old hoop was gradually sinking down into it.
"It looks," he said, "as if the gold was on fire,
and sending up fine vaporous flames through the liquor. But is n't it a
poor use to put gold to? especially at the present premium."
"We use gold in coloring ruby glass; that is what
makes ruby glass so expensive. We use old bones, or the phosphate of lime,
as I told you, to make white glass, and the oxides of iron, copper, and
silver to make other colors. The yellowish tint, with shades of green and
opal, which you may have seen in Bohemian glass, is produced chiefly by
uranium."
"What is stained glass, such as we read of in
descriptions of old cathedral windows?"
"Staining is a kind of painting on glass. The
colors are a mineral composition; and they are melted into the glass,
so that nothing will ever fade them or wash them out. Fancy articles of
glass are often painted in the same way."
"How is silver glass made?" asked Lawrence,
taking up a door-knob from the bench. "It looks like silver, and it
always keeps bright. I have seen pitchers and sugar-bowls and
lamp-reflectors made of it."
"That is a new process, but quite simple. I'll
tell
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