If I let in air, it will not matter; but the moment I introduce water, the
red gas disappears; and I may go on in this way, putting in more and more
of the test-gas, until I come to something left behind which will not
redden any longer by the use of that particular body that rendered the air
and the oxygen red. Why is that? You see in a moment it is because there
is, besides oxygen, something else present which is left behind. I will
let a little more air into the jar, and if it turns red you will know that
some of that reddening gas is still present, and that consequently it was
not for the want of this producing body that that air was left behind.
Now, you will begin to understand what I am about to say. You saw that
when I burnt phosphorus in a jar, as the smoke produced by the phosphorus
and the oxygen of the air condensed, it left a good deal of gas unburnt,
just as this red gas left something untouched, there was, in fact, this
gas left behind, which the phosphorus cannot touch, which the reddening
gas cannot touch, and this something is not oxygen, and yet is part of the
atmosphere.
So that is one way of opening out air into the two things of which it is
composed oxygen, which burns our candles, our phosphorus, or anything
else; and this other substance nitrogen which will not burn them. This
other part of the air is by far the larger proportion, and it is a very
curious body, when we come to examine it; it is remarkably curious, and
yet you say, perhaps, that it is very uninteresting. It is uninteresting
in some respects because of this that it shews no brilliant effects of
combustion. If I test it with a taper as I do oxygen and hydrogen, it
does not burn like hydrogen, nor does it make the taper burn like oxygen.
Try it in any way I will, it does neither the one thing nor the other: it
will not take fire; it will not let the taper burn; it puts out the
combustion of everything. There is nothing that will burn in it in common
circumstances. It has no smell; it is not sour; it does not dissolve in
water; it is neither an acid nor an alkali; it is as indifferent to all
our organs as it is possible for a thing to be. And you might say, It is
nothing; it is not worth chemical attention; what does it do in the air?
Ah! then come our beautiful and fine results shewn us by an observant
philosophy. Suppose, in place of having nitrogen, or nitrogen and oxygen,
we had pure oxygen as our atmosphere; what would become of us? You know
very well that a piece of iron lit in a jar of oxygen goes on burning to
the end. When you see a fire in an iron grate, imagine where the grate
would go to if the whole of the atmosphere were oxygen. The grate would
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