s, for
instance, if you mix together a pound of mercury, heated at 50 degrees,
and a pound of water heated at 100 degrees, the temperature of the
mixture, instead of being 75 degrees, will be 80 degrees; so that the
water will have lost only 12 degrees, whilst the mercury will have
gained 38 degrees; from which you will conclude that the capacity of
mercury for heat is less than that of water.

CAROLINE.

I wonder that mercury should have so little specific heat. Did we not
see it was a much better conductor of heat than water?

MRS. B.

And it is precisely on that account that its specific heat is less. For
since the conductive power of bodies depends, as we have observed
before, on their readiness to receive heat and part with it, it is
natural to expect that those bodies which are the worst conductors
should absorb the most caloric before they are disposed to part with it
to other bodies. But let us now proceed to LATENT HEAT.

CAROLINE.

And pray what kind of heat is that?

MRS. B.

It is another modification of combined caloric, which is so analogous to
specific heat, that most chemists make no distinction between them; but
Mr. Pictet, in his Essay on Fire, has so clearly discriminated them,
that I am induced to adopt his view of the subject. We therefore call
_latent heat_ that portion of insensible caloric which is employed in
changing the state of bodies; that is to say, in converting solids into
liquids, or liquids; into vapour. When a body changes its state from
solid to liquid, or from liquid to vapour, its expansion occasions a
sudden and considerable increase of capacity for heat, in consequence of
which it immediately absorbs a quantity of caloric, which becomes fixed
in the body which it has transformed; and, as it is perfectly concealed
from our senses, it has obtained the name of _latent_ heat.

CAROLINE.

I think it would be much more correct to call this modification latent
caloric instead of latent heat, since it does not excite the sensation
of heat.

MRS. B.

This modification of heat was discovered and named by Dr. Black long
before the French chemists introduced the term caloric, and we must not
presume to alter it, as it is still used by much better chemists than
ourselves. And, besides, you are not to suppose that the nature of heat
is altered by being variously modified: for if latent heat and specific
heat do not excite the same sensations as free caloric, it is owing to
the