I believe I formerly told you that
their basis, or radical, was uniformly composed of hydrogen and carbon,
and that their difference consisted only in the various proportions of
oxygen which they contained.

The following are the names of the vegetable acids:

The _Mucous Acid_, obtained from gum or mucilage;
_Suberic_ - - - from cork;
_Camphoric_ - - - from camphor;
_Benzoic_ - - - from balsams;
_Gallic_ - - - from galls, bark, &c.
_Malic_ - - - from ripe fruits;
_Citric_ - - - from lemon juice;
_Oxalic_ - - - from sorrel;
_Succinic_ - - - from amber;
_Tartarous_ - - - from tartrit of potash:
_Acetic_ - - - from vinegar.

They are all decomposable by heat, soluble in water, and turn vegetable
blue colours red. The _succinic_, the _tartarous_, and the _acetous
acids_, are the products of the decomposition of vegetables; we shall,
therefore, reserve their examination for a future period.

The _oxalic acid_, distilled from sorrel, is the highest term of
vegetable acidification; for, if more oxygen be added to it, it loses
its vegetable nature, and is resolved into carbonic acid and water;
therefore, though all the other acids may be converted into the oxalic
by an addition of oxygen, the oxalic itself is not susceptible of a
further degree of oxygenation; nor can it be made, by any chemical
processes, to return to a state of lower acidification.

To conclude this subject, I have only to add a few words on the _gallic
acid_. . . . .

CAROLINE.

Is not this the same acid before mentioned, which forms ink, by
precipitating sulphat of iron from its solution?

MRS. B.

Yes. Though it is usually extracted from galls, on account of its being
most abundant in that vegetable substance, it may also be obtained from
a great variety of plants. It constitutes what is called the _astringent
principle_ of vegetables; it is generally combined with tannin, and you
will find that an infusion of tea, coffee, bark, red-wine, or any
vegetable substance that contains the astringent principle, will make a
black precipitate with a solution of sulphat of iron.

CAROLINE.

But pray what are galls?

MRS. B.

They are excrescences which grow on the bark of young oaks, and are
occasioned by an insect which wounds the bark of trees, and lays its
eggs in the aperture. The lacerated vessels of the tree then discharge
their contents, and form an ex