The same quantity of Peruvian bark, and of lime water, without the
addition of any fresh lime, being rubbed in the same manner, afforded
a tincture tasting strongly of the bark, nearly of the same colour
as the simple tincture obtained by proof spirit, and retaining its
transparency when blown into. This tincture was much more strongly
impregnated than one made by triture with common rain water only. And
by this process, allowing a few hours for maceration, an infusion is
prepared, greatly superiour in strength to any decoction, infusion, or
tincture of bark I ever saw.
From the result of these experiments I suspect, that by using a
greater quantity of lime in the sixteenth and twentieth experiments
than the vegetable could saturate with fixed air, the water became so
impregnated with lime as to be more unfit to act on the vegetable.
From the purple colour of the residuum of number 2, it was evident
that the galls were decompounded, but the water was not capable of
dissolving and suspending the particles. Dr. Percival[u] mentions his
having unsuccessfully repeated Dr. Macbride's experiment with bark and
quick-lime. To what then can this difference be owing? Perhaps it may
be accounted for thus: It seems probable that the lime used by Dr.
Macbride, not being fresh calcined, had recovered part of its air; for
he says, "It will no doubt be reckoned superfluous, that lime water is
ordered to be added to these several substances, when they are also to
be rubbed along with quick-lime; but the reason is this. _If the lime
were so quick and fresh as to raise heat when common water is poured
on it, the solution might then be made without the aid of lime water;
but, as it will for the most part happen, that the lime kept in the
shops will not be perfectly fresh, it will be best that the prescriber
should direct lime water to be used._" On the contrary, Dr. Percival
used _lime fresh from the kiln_. These circumstances, if my theory be
just, would greatly vary the event of the experiment; and the trials I
have here recited seem to prove, that so great a quantity of lime, and
even a much smaller than is directed by Dr. Macbride, if fresh, instead
of increasing, diminishes the solvent power of water on astringent
vegetables.
[u] Percival's Essays Medical and Experimental, 2d Edit. p. 65.
But as different drugs yield their virtues with more ease, and in
greater quantity to some menstrua than to others, it seemed probable,
that even a very small quantity of lime might render water less solvent
of particular vegetables, than it is in its pure state, though with
others as large or perhaps a greater quantity than what I had used
might be necessary: and as the determination of this point might be
of some use in pharmacy, the following experiments were made; in
the relation of which I shall make use of numbers as before, viz.
the vegetable rubbed with four ounces of distilled water will be
distinguished by number 1, that with two scruples of lime and four
ounces of lime water, number 2, and that with lime water only, number
3.