isles, from the stem and roots of which it is extracted. Small
quantities have also been distilled from thyme, sage, and other aromatic
plants; and it is deposited in pretty large quantities by some volatile
oils after long standing. It is extremely volatile and inflammable. It
is insoluble in water, but is soluble in oils, in which state, as well
as in its solid form, it is frequently applied to medicinal purposes.
Amongst the particular properties of camphor, there is one too singular
to be passed over in silence. If you take a small piece of camphor, and
place it on the surface of a bason of pure water, it will immediately
begin to move round and round with great rapidity; but if you pour into
the bason a single drop of any odoriferous fluid, it will instantly put
a stop to this motion. You can at any time try this very simple
experiment; but you must not expect that I shall be able to account for
this phenomenon, as nothing satisfactory has yet been advanced for its
explanation.

CAROLINE.

It is very singular indeed; and I will certainly try the experiment.
Pray what are _resins_, which you just now mentioned?

MRS. B.

They are volatile oils, that have been acted on, and peculiarly
modified, by oxygen.

CAROLINE.

They are, therefore, oxygenated volatile oils?

MRS. B.

Not exactly; for the process does not appear to consist so much in the
oxygenation of the oil, as in the combustion of a portion of its
hydrogen, and a small portion of its carbon. For when resins are
artificially made by the combination of volatile oils with oxygen, the
vessel in which the process is performed is bedewed with water, and the
air included within is loaded with carbonic acid.

EMILY.

This process must be, in some respects, similar to that for preparing
drying oils?

MRS. B.

Yes; and it is by this operation that both of them acquire a greater
degree of consistence. Pitch, tar, and turpentine, are the most common
resins; they exude from the pine and fir trees. Copal, mastic, and
frankincense, are also of this class of vegetable substances.

EMILY.

Is it of these resins that the mastic and copal varnishes, so much used
in painting, are made?

MRS. B.

Yes. Dissolved either in oil, or in alcohol, resins form varnishes. From
these solutions they may be precipitated by water, in which they are
insoluble. This I can easily show you. --If you will pour some water
into this glass of mastic varnish, it will combine w