mallest degree.

EMILY.

But, Mrs. B., the smoke that rises is white; if it was only pure caloric
which escaped, we might feel, but could not see it.

MRS. B.

This white vapour is formed by some of the particles of lime, in a state
of fine dust, which are carried off by the caloric.

EMILY.

In all changes of state, then, a body either absorbs or disengages
latent heat?

MRS. B.

You cannot exactly say _absorbs latent heat_, as the heat becomes latent
only on being confined in the body; but you may say, generally, that
bodies, in passing from a solid to a liquid form, or from the liquid
state to that of vapour, absorb heat; and that when the reverse takes
place, heat is disengaged.*

[Footnote *: This rule, if not universal, admits of very few
exceptions.]

EMILY.

We can now, I think, account for the ether boiling, and the water
freezing in vacuo, at the same temperature.**

[Footnote **: See page 102.]

MRS. B.

Let me hear how you explain it.

EMILY.

The latent heat, which the water gave out in freezing, was immediately
absorbed by the ether, during its conversion into vapour; and therefore,
from a latent state in one liquid, it passed into a latent state in the
other.

MRS. B.

But this only partly accounts for the result of the experiment; it
remains to be explained why the temperature of the ether, while in a
state of ebullition, is brought down to the freezing temperature of the
water. --It is because the ether, during its evaporation, reduces its
own temperature, in the same proportion as that of the water, by
converting its free caloric into latent heat: so that, though one liquid
boils, and the other freezes, their temperatures remain in a state of
equilibrium.

EMILY.

But why does not water, as well as ether, reduce its own temperature by
evaporating?

MRS. B.

The fact is that it does, though much less rapidly than ether. Thus, for
instance, you may often have observed, in the heat of summer, how much
any particular spot may be cooled by watering, though the water used for
that purpose be as warm as the air itself. Indeed so much cold may be
produced by the mere evaporation of water, that the inhabitants of
India, by availing themselves of the most favourable circumstances for
this process which their warm climate can afford, namely, the cool of
the night, and situations most exposed to the night breeze, succeed in
causing water to freeze, though the temperat