nitrogen gas, for the taper is immediately extinguished.

MRS. B.

That is not a proof of its being pure, but only of the absence of
oxygen, as it is that principle alone which can produce combustion,
every other gas being absolutely incapable of it.

EMILY.

In the methods which you have shown us, for decomposing the atmosphere,
the oxygen always abandons the nitrogen; but is there no way of taking
the nitrogen from the oxygen, so as to obtain the latter pure from the
atmosphere?

MRS. B.

You must observe, that whenever oxygen is taken from the atmosphere, it
is by decomposing the oxygen gas; we cannot do the same with the
nitrogen gas, because nitrogen has a stronger affinity for caloric than
for any other known principle: it appears impossible therefore to
separate it from the atmosphere by the power of affinities. But if we
cannot obtain the oxygen gas, by this means, in its separate state, we
have no difficulty (as you have seen) to procure it in its gaseous form,
by taking it from those substances that have absorbed it from the
atmosphere, as we did with the oxyd of manganese.

EMILY.

Can atmospherical air be recomposed, by mixing due proportions of oxygen
and nitrogen gases?

MRS. B.

Yes: if about one part of oxygen gas be mixed with about four parts of
nitrogen gas, atmospherical air is produced.*

[Footnote *: The proportion of oxygen in the atmosphere varies
from 21 to 22 per cent.]

EMILY.

The air, then, must be an oxyd of nitrogen?

MRS. B.

No, my dear; for there must be a chemical combination between oxygen and
nitrogen in order to produce an oxyd; whilst in the atmosphere these two
substances are separately combined with caloric, forming two distinct
gases, which are simply mixed in the formation of the atmosphere.

I shall say nothing more of oxygen and nitrogen at present, as we shall
continually have occasion to refer to them in our future conversations.
They are both very abundant in nature; nitrogen is the most plentiful in
the atmosphere, and exists also in all animal substances; oxygen forms a
constituent part, both of the animal and vegetable kingdoms, from which
it may be obtained by a variety of chemical means. But it is now time to
conclude our lesson. I am afraid you have learnt more to-day than you
will be able to remember.

CAROLINE.

I assure you that I have been too much interested in it, ever to forget
it. In regard to nitrogen there seems to be but l