xygen which it contains; the strongest, and that into
which the nitric is first converted, is of a yellow colour, as you see
in this bottle.

CAROLINE.

How it fumes when the stopper is taken out!

MRS. B.

The acid exists naturally in a gaseous state, and is here so strongly
concentrated in water, that it is constantly escaping.

Here is another bottle of nitrous acid, which, you see, is of an orange
red; this acid is weaker, the nitrogen being combined with a smaller
quantity of oxygen; and with a still less proportion of oxygen it is an
olive-green colour, as it appears in this third bottle. In short, the
weaker the acid, the deeper is its colour.

Nitrous acid acts still more powerfully on some inflammable substances
than the nitric.

EMILY.

I am surprised at that, as it contains less oxygen.

MRS. B.

But, on the other hand, it parts with its oxygen much more readily: you
may recollect that we once inflamed oil with this acid.

The next combinations of nitrogen and oxygen form only oxyds of
nitrogen, the first of which is commonly called _nitrous air_; or more
properly _nitric oxyd gas_. This may be obtained from nitric acid, by
exposing the latter to the action of metals, as in dissolving them it
does not yield the whole of its oxygen, but retains a portion of this
principle sufficient to convert it into this peculiar gas, a specimen of
which I have prepared, and preserved within this inverted glass bell.

EMILY.

It is a perfectly invisible elastic fluid.

MRS. B.

Yes; and it may be kept any length of time in this manner over water, as
it is not, like the nitric and nitrous acids, absorbable by it. It is
rather heavier than atmospherical air, and is incapable of supporting
either combustion or respiration. I am going to incline the glass gently
on one side, so as to let some of the gas escape--

EMILY.

How very curious! --It produces orange fumes like the nitrous acid! that
is the more extraordinary, as the gas within the glass is perfectly
invisible.

MRS. B.

It would give me much pleasure if you could make out the reason of this
curious change without requiring any further explanation.

CAROLINE.

It seems, by the colour and smell, as if it were converted into nitrous
acid gas: yet that cannot be, unless it combines with more oxygen; and
how can it obtain oxygen the very instant it escapes from the glass?

EMILY.

From the atmosphere, no doubt. Is it not so, Mrs. B.?

MRS.