s, and, like those substances, it is converted
into a peculiar acid, which flies off in a gaseous form. There is this
difference, however, that the acid is not, in this instance, as in the
two cases just mentioned, a mere condensable vapour, but a permanent
elastic fluid, which always remains in the state of gas, under any
pressure and at any temperature. The nature of this acid was first
ascertained by Dr. Black, of Edinburgh; and, before the introduction of
the new nomenclature, it was called _fixed air_. It is now distinguished
by the more appropriate name of _carbonic acid gas_.

EMILY.

Carbon, then, can be volatilized by burning, though, by heat alone, no
such effect is produced?

MRS. B.

Yes; but then it is no longer simple carbon, but an acid of which carbon
forms the basis. In this state, carbon retains no more appearance of
solidity or corporeal form, than the basis of any other gas. And you
may, I think, from this instance, derive a more clear idea of the basis
of the oxygen, hydrogen, and nitrogen gases, the existence of which, as
real bodies, you seemed to doubt, because they were not to be obtained
simply in a solid form.

EMILY.

That is true; we may conceive the basis of the oxygen, and of the other
gases, to be solid, heavy substances, like carbon; but so much expanded
by caloric as to become invisible.

CAROLINE.

But does not the carbonic acid gas partake of the blackness of charcoal?

MRS. B.

Not in the least. Blackness, you know, does not appear to be essential
to carbon, and it is pure carbon, and not charcoal, that we must
consider as the basis of carbonic acid. We shall make some carbonic
acid, and, in order to hasten the process, we shall burn the carbon in
oxygen gas.

EMILY.

But do you mean then to burn diamond?

MRS. B.

Charcoal will answer the purpose still better, being softer and more
easy to inflame; besides the experiments on diamond are rather
expensive.

CAROLINE.

But is it possible to burn diamond?

MRS. B.

Yes, it is; and in order to effect this combustion, nothing more is
required than to apply a sufficient degree of heat by means of the
blow-pipe, and of a stream of oxygen gas. Indeed it is by burning
diamond that its chemical nature has been ascertained. It has long been
known as a combustible substance, but it is within these few years only
that the product of its combustion has been proved to be pure carbonic
acid. This remarkable discovery is d