arcoal; but the attraction of the alkali of lime for the phosphoric
acid, unites its power at the same time.

CAROLINE.

Cannot we make that experiment?

MRS. B.

Not easily; it requires being performed with extreme nicety, in order to
obtain any sensible quantity of carbon, and the experiment is much too
delicate for me to attempt it. But there can be no doubt of the accuracy
of Mr. Tennant's results; and all chemists now agree, that one hundred
parts of carbonic acid gas consists of about twenty-eight parts of
carbon to seventy-two of oxygen gas. But if you recollect, we decomposed
carbonic acid gas the other day by burning potassium in it.

CAROLINE.

True, so we did; and found the carbon precipitated on the regenerated
potash.

MRS. B.

Carbonic acid gas is found very abundantly in nature; it is supposed to
form about one thousandth part of the atmosphere, and is constantly
produced by the respiration of animals; it exists in a great variety of
combinations, and is exhaled from many natural decompositions. It is
contained in a state of great purity in certain caves, such as the
_Grotto del Cane_, near Naples.

EMILY.

I recollect having read an account of that grotto, and of the cruel
experiments made on the poor dogs, to gratify the curiosity of
strangers. But I understood that the vapour exhaled by this cave was
called _fixed air_.

MRS. B.

That is the name by which carbonic acid was known before its chemical
composition was discovered. --This gas is more destructive of life than
any other; and if the poor animals that are submitted to its effects are
not plunged into cold water as soon as they become senseless, they do
not recover. It extinguishes flame instantaneously. I have collected
some in this glass, which I will pour over the candle.

CAROLINE.

This is extremely singular--it seems to extinguish it as it were by
enchantment, as the gas is invisible. I never should have imagined that
gas could have been poured like a liquid.

MRS. B.

It can be done with carbonic acid only, as no other gas is sufficiently
heavy to be susceptible of being poured out in the atmospherical air
without mixing with it.

EMILY.

Pray by what means did you obtain this gas?

MRS. B.

I procured it from marble. Carbonic acid gas has so strong an attraction
for all the alkalies and alkaline earths, that these are always found in
nature in the state of carbonats. Combined with lime, this acid forms
chalk