it
is freely soluble in acetic acid ; in the second place, receives a mark
from steel ; and, finally, it is reduced to lime by fire while giving
out a great quantity of carbonic acid.
Marble
is partly composed of a sort of metal of ferruginous appearance,
combined with carbon and oxygen. The proportions of its component parts
vary according to the different qualities ; however, in general, it is
equal to three-tenths of metal, one-tenth of carbon, and the remainder
of fixed oxygen.
The specific gravity of this substance varies from 2-650 to 2-850.
The
purest marble is always white, and the various colourations which form
its different qualities are due to extraneous substances, either stony
or metallic, the different arrangements of which modify it by the
colour of its different tints.
Marble
of all kinds is amongst the productions which are most generally used
in art and manufactures. But to give their history and classification
would be beyond our proposed limits.
LXIII.
MICA.
For a
long time, this name has distinguished certain substances capable of
being divided into layers, which are elastic, very thin, translucent
and fusible, of which the surface always remains bright, whence its
name from
