, which may be considered as the basis of all kinds of marbles, and
calcareous stones. From these substances carbonic acid is easily
separated, as it adheres so slightly to its combinations, that the
carbonats are all decomposable by any of the other acids. I can easily
show you how I obtained this gas; I poured some diluted sulphuric acid
over pulverised marble in this bottle (the same which we used the other
day to prepare hydrogen gas), and the gas escaped through the tube
connected with it; the operation still continues, as you may easily
perceive--

EMILY.

Yes, it does; there is a great fermentation in the glass vessel. What
singular commotion is excited by the sulphuric acid taking possession of
the lime, and driving out the carbonic acid!

CAROLINE.

But did the carbonic acid exist in a gaseous state in the marble?

MRS. B.

Certainly not; the acid, when in a state of combination, is capable of
existing in a solid form.

CAROLINE.

Whence, then, does it obtain the caloric necessary to convert it into
gas?

MRS. B.

It may be supplied in this case from the mixture of sulphuric acid and
water, which produces an evolution of heat, even greater than is
required for the purpose; since, as you may perceive by touching the
glass vessel, a considerable quantity of the caloric disengaged becomes
sensible. But a supply of caloric may be obtained also from a diminution
of capacity for heat, occasioned by the new combination which takes
place; and, indeed, this must be the case when other acids are employed
for the disengagement of carbonic acid gas, which do not, like the
sulphuric, produce heat on being mixed with water. Carbonic acid may
likewise be disengaged from its combinations by heat alone, which
restores it to its gaseous state.

CAROLINE.

It appears to me very extraordinary that the same gas, which is produced
by the burning of wood and coals, should exist also in such bodies as
marble, and chalk, which are incombustible substances.

MRS. B.

I will not answer that objection, Caroline, because I think I can put
you in a way of doing it yourself. Is carbonic acid combustible?

CAROLINE.

Why, no--because it is a body that has been already burnt; it is carbon
only, and not the acid, that is combustible.

MRS. B.

Well, and what inference do you draw from this?

CAROLINE.

That carbonic acid cannot render the bodies with which it is united
combustible; but that simple carbon does, and