of a vitreous light ; its material is homogeneous, and resists acids, being harder than the Western agates.
Agates
of all sorts have the property of acquiring stains of every colour by
artificial means; black is given by boiling the stone in honey, in
olive oil, or in water and sugar, and afterwards in sulphuric acid,
which carbonizes the oil and sugar absorbed by the stone. To give a red
colour, protosulphate of iron is added to the sulphuric acid, by which
means the iron remains oxidized. The bluish colour is obtained by using
yellow prussiate of potassium, together with protoxide of iron.
The
Oriental as well as the Western agate, when much variegated, is used in
works of art. We have beautiful fragments of cups, both smooth and
carved, in this substance, which bear comparison with the most
classical remains of the art, wealth, and magnificence of antiquity.
IV.
ALABASTRITE AND ALABASTER.
A white chalk of very close substance is called alabastrite.
It is a species of sulphate of lime ; specific gravity from 2-7
to 2'8 ; and in scientific language is called chalky alabaster: it is
very different from true alabaster, for which it is often mistaken.
Much softer and more transparent than white marble, alabastrite excels
it in whiteness, and its substance is more homogeneous.
