ver, which stands in a bason over
water, to prevent all communication with the external air.

[Illustration: Plate VII. Vol. I. p. 181.

Fig. 1. Combustion of a taper under a receiver.

Fig. 2. A Retort on a stand.

Fig. 3. Preparation of oxygen gas.
A Furnace.
B Earthen Retort in the furnace.
C Water bath.
D Receiver.
E.E Tube conveying the gas from the Retort through the water into
the Receiver.
F.F.F Shelf perforated on which the Receiver stands.

Fig. 4. Combustion of iron wire in oxygen gas.]

CAROLINE.

How dim the light burns already! --It is now extinguished.

MRS. B.

Can you tell us why it is extinguished?

CAROLINE.

Let me consider. --The receiver was full of atmospherical air; the
taper, in burning within it, must have combined with the oxygen
contained in that air, and the caloric that was disengaged produced the
light of the taper. But when the whole of the oxygen was absorbed, the
whole of its electricity was disengaged; consequently no more caloric
could be produced, the taper ceased to burn, and the flame was
extinguished.

MRS. B.

Your explanation is perfectly correct.

EMILY.

The two constituents of the oxygen gas being thus disposed of, what
remains under the receiver must be pure nitrogen gas?

MRS. B.

There are some circumstances which prevent the nitrogen gas, thus
obtained, from being perfectly pure; but we may easily try whether the
oxygen has disappeared, by putting another lighted taper under it. --You
see how instantaneously the flame is extinguished, for want of oxygen to
supply the negative electricity required for the formation of caloric;
and were you to put an animal under the receiver, it would immediately
be suffocated. But that is an experiment which I do not think your
curiosity will tempt you to try.

EMILY.

Certainly not. --But look, Mrs. B., the receiver is full of a thick
white smoke. Is that nitrogen gas?

MRS. B.

No, my dear; nitrogen gas is perfectly transparent and invisible, like
common air. This cloudiness proceeds from a variety of exhalations,
which arise from the burning taper, and the nature of which you cannot
yet understand.

CAROLINE.

The water within the receiver has now risen a little above its level in
the bason. What is the reason of this?

MRS. B.

With a moment's reflection, I dare say, you would have explained it
yourself. The water rises in consequence of the oxygen gas within it
havin