seems to make an exception to the rule, it does not,
I believe, form any solid objection to the theory. The matter may be
explained thus: When water first comes in contact with the potash, it
produces an effect similar to the slaking of lime, that is, the water is
solidified in combining with the potash, and thus loses its latent heat;
this is the heat that you now feel, and which is, therefore, produced
not by the melting of the solid, but by the solidification of the fluid.
But when there is more water than the potash can absorb and solidify,
the latter then yields to the solvent power of the water; and if we do
not perceive the cold produced by its melting, it is because it is
counterbalanced by the heat previously disengaged.*

A very remarkable property of potash is the formation of glass by its
fusion with siliceous earth. You are not yet acquainted with this last
substance, further than its being in the list of simple bodies. It is
sufficient, for the present, that you should know that sand and flint
are chiefly composed of it; alone, it is infusible, but mixed with
potash, it melts when exposed to the heat of a furnace, combines with
the alkali, and runs into glass.

[Footnote *: This defence of the general theory, however
plausible, is liable to some obvious objections. The phenomenon
might perhaps be better accounted for by supposing that a solution
of alkali in water has less capacity for heat than either water or
alkali in their separate state.]

CAROLINE.

Who would ever have supposed that the same substance which converts
transparent oil into such an opake body as soap, should transform that
opake substance, sand, into transparent glass!

MRS. B.

The transparency, or opacity of bodies, does not, I conceive, depend so
much upon their intimate nature, as upon the arrangement of their
particles: we cannot have a more striking instance of this, than is
afforded by the different states of carbon, which, though it commonly
appears in the form of a black opake body, sometimes assumes the most
dazzling transparent form in nature, that of diamond, which, you
recollect, is carbon, and which, in all probability, derives its
beautiful transparency from the peculiar arrangement of its particles
during their crystallisation.

EMILY.

I never should have supposed that the formation of glass was so simple a
process as you describe it.

MRS. B.

It is by no means an easy operation to mak