ed from the ashes of vegetables,
which are the residue that remains after all the other parts have been
volatilised by combustion.

CAROLINE.

But you once said, that after all the volatile parts of a vegetable were
evaporated, the substance that remained was charcoal?

MRS. B.

I am surprised that you should still confound the processes of
volatilisation and combustion. In order to procure charcoal, we
evaporate such parts as can be reduced to vapour by the operation of
heat alone; but when we _burn_ the vegetable, we burn the carbon also,
and convert it into carbonic acid gas.

CAROLINE.

That is true; I hope I shall make no more mistakes in my favourite
theory of combustion.

MRS. B.

Potash derives its name from the _pots_ in which the vegetables, from
which it was obtained, used formerly to be burnt; the alkali remained
mixed with the ashes at the bottom, and was thence called potash.

EMILY.

The ashes of a wood-fire, then, are potash, since they are vegetable
ashes?

MRS. B.

They always contain more or less potash, but are very far from
consisting of that substance alone, as they are a mixture of various
earths and salts which remain after the combustion of vegetables, and
from which it is not easy to separate the alkali in its pure form. The
process by which potash is obtained, even in the imperfect state in
which it is used in the arts, is much more complicated than simple
combustion. It was once deemed impossible to separate it entirely from
all foreign substances, and it is only in chemical laboratories that it
is to be met with in the state of purity in which you find it in this
phial. Wood-ashes are, however, valuable for the alkali which they
contain, and are used for some purposes without any further preparation.
Purified in a certain degree, they make what is commonly called
_pearlash_, which is of great efficacy in taking out grease, in washing
linen, &c.; for potash combines readily with oil or fat, with which it
forms a compound well known to you under the name of _soap_.

CAROLINE.

Really! Then I should think it would be better to wash all linen with
pearlash than with soap, as, in the latter case, the alkali being
already combined with oil, must be less efficacious in extracting
grease.

MRS. B.

Its effect would be too powerful on fine linen, and would injure its
texture; pearlash is therefore only used for that which is of a strong
coarse kind. For the same reason you ca