e nor snow.

MRS. B.

True: but we have other means of effecting this.* You recollect what an
intense cold can be produced by the evaporation of ether in an exhausted
receiver. We shall inclose the bulb in this little bag of fine flannel
(fig. 3.), then soke it in ether, and introduce it into the receiver of
the air-pump. (Fig. 5.) For this purpose we shall find it more
convenient to use a cryophorus of this shape (fig. 4.), as its elongated
bulb passes easily through a brass plate which closes the top of the
receiver. If we now exhaust the receiver quickly, you will see, in less
than a minute, the water freeze in the other bulb, out of the receiver.

[Footnote *: This mode of making the experiment was proposed, and
the particulars detailed, by Dr. Marcet, in the 34th vol. of
Nicholson's Journal, page 119.]

EMILY.

The bulb already looks quite dim, and small drops of water are
condensing on its surface.

CAROLINE.

And now crystals of ice shoot all over the water. This is, indeed,
a very curious experiment!

MRS. B.

You will see, some other day, that, by a similar method, even
quicksilver may be frozen. --But we cannot at present indulge in any
further digression.

Having advanced so far on the subject of heat, I may now give you an
account of the calorimeter, an instrument invented by Lavoisier, upon
the principles just explained, for the purpose of estimating the
specific heat of bodies. It consists of a vessel, the inner surface of
which is lined with ice, so as to form a sort of hollow globe of ice, in
the midst of which the body, whose specific heat is to be ascertained,
is placed. The ice absorbs caloric from this body, till it has brought
it down to the freezing point; this caloric converts into water a
certain portion of the ice which runs out through an aperture at the
bottom of the machine; and the quantity of ice changed to water is a
test of the quantity of caloric which the body has given out in
descending from a certain temperature to the freezing point.

CAROLINE.

In this apparatus, I suppose, the milk, chalk, and lead, would melt
different quantities of ice, in proportion to their different capacities
for caloric?

MRS. B.

Certainly: and thence we are able to ascertain, with precision, their
respective capacities for heat. But the calorimeter affords us no more
idea of the absolute quantity of heat contained in a body, than the
thermometer; for though by means of it w