its presence, as the
effect it produced on the wire was sufficiently evident.

CAROLINE.

Yes, indeed; yet you know it was the caloric, and not the oxygen gas
itself, that dazzled us so much.

MRS. B.

You are not quite correct in your turn, in saying the caloric dazzled
you; for caloric is invisible; it affects only the sense of feeling; it
was the light which dazzled you.

CAROLINE.

True; but light and caloric are such constant companions, that it is
difficult to separate them, even in idea.

MRS. B.

The easier it is to confound them, the more careful you should be in
making the distinction.

CAROLINE.

But why has the water now risen, and filled part of the receiver?

MRS. B.

Indeed, Caroline, I did not suppose you would have asked such a
question! I dare say, Emily, you can answer it.

EMILY.

Let me reflect . . . . . . The oxygen has combined with the wire; the
caloric has escaped; consequently nothing can remain in the receiver,
and the water will rise to fill the vacuum.

CAROLINE.

I wonder that I did not think of that. I wish that we had weighed the
wire and the oxygen gas before combustion; we might then have found
whether the weight of the oxyd was equal to that of both.

MRS. B.

You might try the experiment if you particularly wished it; but I can
assure you, that, if accurately performed, it never fails to show that
the additional weight of the oxyd is precisely equal to that of the
oxygen absorbed, whether the process has been a real combustion, or a
simple oxygenation.

CAROLINE.

But this cannot be the case with combustions in general; for when any
substance is burnt in the common air, so far from increasing in weight,
it is evidently diminished, and sometimes entirely consumed.

MRS. B.

But what do you mean by the expression _consumed_? You cannot suppose
that the smallest particle of any substance in nature can be actually
destroyed. A compound body is decomposed by combustion; some of its
constituent parts fly off in a gaseous form, while others remain in a
concrete state; the former are called the _volatile_, the latter the
_fixed products_ of combustion. But if we collect the whole of them, we
shall always find that they exceed the weight of the combustible body,
by that of the oxygen which has combined with them during combustion.

EMILY.

In the combustion of a coal fire, then, I suppose that the ashes are
what would be called the fixed product, and the smo