xygen from the salt, and be converted into carbonic acid.--

EMILY.

But what occasions that crackling noise, and those vivid flashes that
accompany it?

MRS. B.

The rapidity with which the carbonic acid gas is formed occasions a
succession of small detonations, which, together with the emission of
flame, is called _deflagration_.

_Nitrat of ammonia_ we have already noticed, on account of the gaseous
oxyd of nitrogen which is obtained from it.

_Nitrat of silver_ is the lunar caustic, so remarkable for its property
of destroying animal fibre, for which purpose it is often used by
surgeons. --We have said so much on a former occasion, on the mode in
which caustics act on animal matter, that I shall not detain you any
longer on this subject.

We now come to the CARBONIC ACID, which we have already had many
opportunities of noticing. You recollect that this acid may be formed by
the combustion of carbon, whether in its imperfect state of charcoal, or
in its purest form of diamond. And it is not necessary, for this
purpose, to burn the carbon in oxygen gas, as we did in the preceding
lecture; for you need only light a piece of charcoal and suspend it
under a receiver on the water bath. The charcoal will soon be
extinguished, and the air in the receiver will be found mixed with
carbonic acid. The process, however, is much more expeditious if the
combustion be performed in pure oxygen gas.

CAROLINE.

But how can you separate the carbonic acid, obtained in this manner,
from the air with which it is mixed?

MRS. B.

The readiest mode is to introduce under the receiver a quantity of
caustic lime, or caustic alkali, which soon attracts the whole of the
carbonic acid to form a carbonat. --The alkali is found increased in
weight, and the volume of the air is diminished by a quantity equal to
that of the carbonic acid which was mixed with it.

EMILY.

Pray is there no method of obtaining pure carbon from carbonic acid?

MRS. B.

For a long time it was supposed that carbonic acid was not
decompoundable; but Mr. Tennant discovered, a few years ago, that this
acid may be decomposed by burning phosphorus in a closed vessel with
carbonat of soda or carbonat of lime: the phosphorus absorbs the oxygen
from the carbonat, whilst the carbon is separated in the form of a black
powder. This decomposition, however, is not effected simply by the
attraction of the phosphorus for oxygen, since it is weaker than that of
ch