it, that one grain of water will absorb
and condense ten grains of acid gas, and form the limpid fluid which you
see in this bottle.

CAROLINE.

What a strong offensive smell it has!

MRS. B.

This acid contains a greater abundance of oxygen than any other, but it
retains it with very little force.

EMILY.

Then it must be a powerful caustic, both from the facility with which it
parts with its oxygen, and the quantity which it affords?

MRS. B.

Very well, Emily; both cause and effect are exactly such as you
describe: nitric acid burns and destroys all kinds of organised matter.
It even sets fire to some of the most combustible substances. --We shall
pour a little of it over this piece of dry warm charcoal--you see it
inflames it immediately; it would do the same with oil of turpentine,
phosphorus, and several other very combustible bodies. This shows you
how easily this acid is decomposed by combustible bodies, since these
effects must depend upon the absorption of its oxygen.

Nitric acid has been used in the arts from time immemorial, but it is
only within these twenty-five years that its chemical nature has been
ascertained. The celebrated Mr. Cavendish discovered that it consisted
of about 10 parts of nitrogen and 25 of oxygen.* These principles, in
their gaseous state, combine at a high temperature; and this may be
effected by repeatedly passing the electrical spark through a mixture of
the two gases.

[Footnote *: The proportion stated by Sir H. Davy, in his Chemical
Researches, is as 1 to 2.389.]

EMILY.

The nitrogen and oxygen gases, of which the atmosphere is composed, do
not combine, I suppose, because their temperature is not sufficiently
elevated?

CAROLINE.

But in a thunder-storm, when the lightning repeatedly passes through
them, may it not produce nitric acid? We should be in a strange
situation, if a violent storm should at once convert the atmosphere into
nitric acid.

MRS. B.

There is no danger of it, my dear; the lightning can affect but a very
small portion of the atmosphere, and though it were occasionally to
produce a little nitric acid, yet this never could happen to such an
extent as to be perceivable.

EMILY.

But how could the nitric acid be known, and used, before the method of
combining its constituents was discovered?

MRS. B.

Before that period the nitric acid was obtained, and it is indeed still
extracted, for the common purposes of art, from the