der the water, a saucer, into which I slide the receiver, so
that it can be taken out of the bath and conveyed any where, the water
in the saucer being equally effectual in preventing its escape as that
in the bath. (PLATE VIII. fig. 4.)

EMILY.

I am quite surprised to see what a large quantity of hydrogen gas can be
produced by such a small quantity of water, especially as oxygen is the
principal constituent of water.

MRS. B.

In weight it is; but not in volume. For though the proportion, by
weight, is nearly six parts of oxygen to one of hydrogen, yet the
proportion of the volume of the gases, is about one part of oxygen to
two of hydrogen; so much heavier is the former than the latter.

CAROLINE.

But why is the vessel in which the water is decomposed so hot? As the
water changes from a liquid to a gaseous form, cold should be produced
instead of heat.

MRS. B.

No; for if one of the constituents of water is converted into a gas, the
other becomes solid in combining with the metal.

EMILY.

In this case, then, neither heat nor cold should be produced?

MRS. B.

True: but observe that the sensible heat which is disengaged in this
operation, is not owing to the decomposition of the water, but to an
extrication of heat produced by the mixture of water and sulphuric acid.
I will mix some water and sulphuric acid together in this glass, that
you may feel the surprising quantity of heat that is disengaged by their
union--now take hold of the glass----

CAROLINE.

Indeed I cannot; it feels as hot as boiling water. I should have
imagined there would have been heat enough disengaged to have rendered
the liquid solid.

MRS. B.

As, however, it does not produce that effect, we cannot refer this heat
to the modification called latent heat. We may, however, I think,
consider it as heat of capacity, as the liquid is condensed by its loss;
and if you were to repeat the experiment, in a graduated tube, you would
find that the two liquids, when mixed, occupy considerably less space
than they did separately. --But we will reserve this to another
opportunity, and attend at present to the hydrogen gas which we have
been producing.

If I now set the hydrogen gas, which is contained in this receiver, at
liberty all at once, and kindle it as soon as it comes in contact with
the atmosphere, by presenting it to a candle, it will so suddenly and
rapidly decompose the oxygen gas, by combining with its basis, that an