On the various solvent powers of QUICK-LIME in different quantities.

THE difficulty of solution in the vegetable astringents has been complained of by various writers on the Materia Medica. Water and alcohol are the menstrua in use; but great quantities of each are necessary to procure even a slight impregnation, and much heat and long boiling are said actually to destroy the astringent quality, and vegetable texture.[t] As a menstruum capable of dissolving them with greater facility appeared to be a desideratum, not only in pharmacy, but in other arts, particularly in that of dying blacks, I resolved to try Dr. Macbride's method of increasing the solvent power of water, by means of quick-lime. But as I was aware that the quantity of lime he made use of in obtaining an aqueous tincture of Peruvian bark, would be too great for the dyer's use, I wished to use only such a quantity as would be sufficiently saturated with the air contained in the vegetable, to be itself precipitated; and to compare the tinctures thus made, with a standard prepared with simple water.

EXPERIMENT XV.

I rubbed three drachms of Aleppo galls reduced to powder, with four ounces of filtered rain water, for fifteen minutes, and then passed the solution through paper. It was very styptic to the taste, and was nearly of the same colour as Huxham's tincture of bark. The residuum in the filter was unchanged in colour. The bottle containing the liquor was marked number 1.

EXPERIMENT XVI.

Three drachms of the same galls, and two scruples of quick-lime, were triturated with four ounces of rain water, as in the last experiment. The filtered liquor had scarcely any astringency to the taste, and was of a very pale colour. The residuum was of a deep purple. Marked number 2.

EXPERIMENT XVII.

The same quantity of galls as in the two former experiments, after triture in the same degree with four ounces of lime-water, was separated by filtering through paper. The tincture thus obtained was highly astringent to the palate, of a deep chocolate colour, and the residuum was of a lighter brown than number 1. Marked number 3.

EXPERIMENT XVIII.

To each of the above tinctures were added forty drops of a strong solution of sal martis. Number 1 became very black. Number 2 changed colour but little, and on standing precipitated a brown sediment, which, the superiour part of the liquor being decanted off, became again transparent on the addition of a few drops of the vitriolic acid. Number 3 appeared to strike a deeper black than number 1; and these being tried as inks, number 3 seemed to have the superiority; but a slip of linen cloth being macerated in each for some hours, that in number 1 had taken a more perfect black than the slip number 3. No trial was made with cotton or woollen, which it is probable would have differed from the linen.

EXPERIMENT XIX.

Oak bark was used instead of galls, with similar success, except that the infusion made with lime-water was not so deep in colour as that with simple rain water, though much deeper than that prepared with quick-lime.

EXPERIMENT XX.

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.

Number 3, amber coloured, tastes of the root.

EXPERIMENT XXIII.

Two drachms of Columbo being triturated in the same manner,

Number 1, dark brown tincture; tastes much of the Columbo.

Number 2, yellow; faint taste of the Columbo, but that of the lime very disagreeably prevalent.

Number 3, colour as number 1; but tastes more highly of the Columbo.

EXPERIMENT XXIV.

Two drachms of contrayerva root with the same treatment yielded in the following proportions:

Number 1 gave a pale brown tincture, tasting of the contrayerva.

Number 2, bright amber colour; taste of the lime so strong as to admit of no other.

Number 3 exceeded number 1 both in colour and taste.

EXPERIMENT XXV.

Jalap being triturated in the same proportions,

Number 1 dark brown; taste of the jalap strong.

Number 2 pale yellow; taste of the lime predominant, though that of the jalap perceptible.

Number 3, colour not quite so high as number 1, but equal in taste.

EXPERIMENT XXVI.

The result of the same trial with ipecacuanha was, that number 1 was of a light brown colour, tasting highly of the ipecacuanha.

Number 2 was of a deep yellow, having the same disagreeable taste of the lime complained of in the other tinctures, but that of the ipecacuanha scarcely perceptible.

Number 3 produced a tincture of the colour of red port wine, strongly flavoured with the ipecacuanha, though it had not so much of the distinguishing sharpness of that root as number 1.

EXPERIMENT XXVII.

The different tinctures of rhubarb, prepared in the same manner as above, had the following appearances:

Number 1 brown, with a yellowish tinge, strongly impregnated with the taste of the rhubarb.

Number 2 deep yellow, taste of the lime as in the other tinctures prepared with it.

Number 3 crimson; taste of the rhubarb strong, but unequal to number 1.

None of the tinctures prepared with lime water grew turbid from a stream of fixed air being conveyed into them.

Hence it appears that the triture of quick-lime with all the above roots did not in the least degree promote, but rather impede their solution in water; that lime water extracts the soluble parts of many, and especially their colouring principles, more powerfully than distilled water; but that this is by no means always the case, as in three instances out of six, the tinctures prepared with distilled water exceeded those with lime water in taste, and in two instances were superiour, and in one equal in colour.