ir being in a state of confinement, which prevents them from acting
upon our organs; and consequently, as soon as they are extricated from
the body in which they are imprisoned, they return to their state of
free caloric.

EMILY.

But I do not yet clearly see in what respect latent heat differs from
specific heat; for they are both of them imprisoned and concealed in
bodies.

MRS. B.

Specific heat is that which is employed in filling the capacity of a
body for caloric, in the state in which this body actually exists; while
latent heat is that which is employed only in effecting a change of
state, that is, in converting bodies from a solid to a liquid, or from a
liquid to an aeriform state. But I think that, in a general point of
view, both these modifications might be comprehended under the name of
_heat of capacity_, as in both cases the caloric is equally engaged in
filling the capacities of bodies.

I shall now show you an experiment, which I hope will give you a clear
idea of what is understood by latent heat.

The snow which you see in this phial has been cooled by certain chemical
means (which I cannot well explain to you at present), to 5 or 6 degrees
below the freezing point, as you will find indicated by the thermometer
which is placed in it. We shall expose it to the heat of a lamp, and you
will see the thermometer gradually rise, till it reaches the freezing
point----

EMILY.

But there it stops, Mrs. B., and yet the lamp burns just as well as
before. Why is not its heat communicated to the thermometer?

CAROLINE.

And the snow begins to melt, therefore it must be rising above the
freezing point?

MRS. B.

The heat no longer affects the thermometer, because it is wholly
employed in converting the ice into water. As the ice melts, the caloric
becomes _latent_ in the new-formed liquid, and therefore cannot raise
its temperature; and the thermometer will consequently remain
stationary, till the whole of the ice be melted.

CAROLINE.

Now it is all melted, and the thermometer begins to rise again.

MRS. B.

Because the conversion of the ice into water being completed, the
caloric no longer becomes latent; and therefore the heat which the water
now receives raises its temperature, as you find the thermometer
indicates.

EMILY.

But I do not think that the thermometer rises so quickly in the water as
it did in the ice, previous to its beginning to melt, though the lamp
burns equally wel