tantly converted into vapour by the heat of the stomach, through the
intervention of which it acts on the nervous system. But the frequent
use of ether, like that of spirituous liquors, becomes prejudicial, and,
if taken to excess, it produces effects similar to those of
intoxication.

We may now take our leave of the vinous fermentation, of which, I hope,
you have acquired a clear idea; as well as of the several products that
are derived from it.

CAROLINE.

Though this process appears, at first sight, so much complicated, it
may, I think, be summed up in a few words, as it consists in the
conversion of sugar and fermentable bodies into alcohol and carbonic
acid, which give rise both to the formation of wine, and of all kinds of
spirituous liquors.

MRS. B.

We shall now proceed to the _acetous fermentation_, which is thus
called, because it converts wine into vinegar, by the formation of the
acetous acid, which is the basis or radical of vinegar.

CAROLINE.

But is not the acidifying principle of the acetous acid the same as that
of all other acids, oxygen?

MRS. B.

Certainly; and on that account the contact of air is essential to this
fermentation, as it affords the necessary supply of oxygen. Vinegar, in
order to obtain pure acetous acid from it, must be distilled and
rectified by certain processes.

EMILY.

But pray, Mrs. B., is not the acetous acid frequently formed without
this fermentation taking place? Is it not, for instance, contained in
acid fruits, and in every substance that becomes sour?

MRS. B.

No, not in fruits; you confound it with the citric, the malic, the
oxalic, and other vegetable acids, to which living vegetables owe their
acidity. But whenever a vegetable substance turns sour, after it has
ceased to live, the acetous acid is developed by means of the acetous
fermentation, in which the substance advances a step towards its final
decomposition.

Amongst the various instances of acetous fermentation, that of bread is
usually classed.

CAROLINE.

But the fermentation of bread is produced by yeast; how does that
effect it?

MRS. B.

It is found by experience that any substance that has already undergone
a fermentation, will readily excite it in one that is susceptible of
that process. If, for instance, you mix a little vinegar with wine, that
is intended to be acidified, it will absorb oxygen more rapidly, and the
process be completed much sooner, than if left to fermen