Peruvian bark, quick-lime, and lime water, in the same proportion as directed by Dr. Macbride, were rubbed together. The filtered infusion had little colour, tasted very slightly of the bark, though strongly of the lime, and on my blowing in a stream of air from my lungs, the surface of it was immediately covered with a cremor calcis, the liquor grew turbid, and deposited a copious sediment.
EXPERIMENT XXI.
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.
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.
EXPERIMENT XXII.
Two drachms of snake root were rubbed for fifteen minutes with the above-mentioned different proportions of distilled water, quick-lime and lime water, and lime water alone.
Number 1 was a dark brown tincture, tasting strongly of the serpentaria.
Number 2, straw coloured, taste of the lime disagreeable, that of the root not distinguishable.