pure oxygen
gas; and what will surprise you still more, it can be set on fire
without any considerable rise of temperature. You see this spiral iron
wire--I fasten it at one end to this cork, which is made to fit an
opening at the top of the glass-receiver. (PLATE VII. Fig. 4.)

EMILY.

I see the opening in the receiver; but it is carefully closed by a
ground glass-stopper.

MRS. B.

That is in order to prevent the gas from escaping; but I shall take out
the stopper, and put in the cork, to which the wire hangs. --Now I mean
to burn this wire in the oxygen gas, but I must fix a small piece of
lighted tinder to the extremity of it, in order to give the first
impulse to combustion; for, however powerful oxygen is in promoting
combustion, you must recollect that it cannot take place without some
elevation of temperature. I shall now introduce the wire into the
receiver, by quickly changing the stoppers.

CAROLINE.

Is there no danger of the gas escaping while you change the stoppers?

MRS. B.

Oxygen gas is a little heavier than atmospherical air, therefore it will
not mix with it very rapidly; and, if I do not leave the opening
uncovered, we shall not lose any----

CAROLINE.

Oh, what a brilliant and beautiful flame!

EMILY.

It is as white and dazzling as the sun! --Now a piece of the melted wire
drops to the bottom: I fear it is extinguished; but no, it burns again
as bright as ever.

MRS. B.

It will burn till the wire is entirely consumed, provided the oxygen is
not first expended: for you know it can burn only while there is oxygen
to combine with it.

CAROLINE.

I never saw a more beautiful light. My eyes can hardly bear it! How
astonishing to think that all this caloric was contained in the small
quantity of gas and iron that was enclosed in the receiver; and that,
without producing any sensible heat!

CAROLINE.

How wonderfully quick combustion goes on in pure oxygen gas! But pray,
are these drops of burnt iron as heavy as the wire was before?

MRS. B.

They are even heavier; for the iron, in burning, has acquired exactly
the weight of the oxygen which has disappeared, and is now combined with
it. It has become an oxyd of iron.

CAROLINE.

I do not know what you mean by saying that the oxygen has _disappeared_,
Mrs. B., for it was always invisible.

MRS. B.

True, my dear; the expression was incorrect. But though you could not
see the oxygen gas, I believe you had no doubt of