Though by repeated boilings in water the bark may be so exhausted as to give out nothing to spirit, but after the repeated action of spirit still gives out something to water; yet spirit appears, to be the most active menstruum of its medicinal parts. For all, that spirit can dissolve, is extracted by a far less quantity of spirit than of water; and what spirit leaves undissolved is of little taste. Equal quantities of bark being digested for the same length of time with equal quantities of water and rectified spirit, with or without heat; the spirituous tinctures proved always stronger in taste than the watery, and left on evaporation a larger proportion of extract * ||.

|| This assertion seems contrary to the result of some experiments by Dr. Percival, related in his first vol. of Ess. Med. and Exper. p. 91, in which a dram of bark infused seven days in three ounces each of rectified spirit, proof spirit, and water, loft in the first, six grains; in the second, eight and a quarter; and in the third, eight. These accounts can be. reconciled only upon the fuppr.fition that watery liquors do, indeed, extract more of the inert gummy matter of bark; but spirituous, more of the active matter.

(a) I have endeavoured to compare the strength of the two preparations by characters that may be thought more satissactory than the taste. A cold infusion and decoction were made with equal quantities of bark and water, and both matter in vegetables, that the resinous parts become dissoluble in watery liquors; and it seems probable that, in boiling, part of the gummy principle of the bark is hastily dissolved and disunited from the resinous, whereas cold water, acting more gradually, extracts them both together. I have given the infusions in intermitting fevers as well as other disorders, with all the success that could have been expected from any preparation of this valuable medicine: the proportions commonly followed were, one ounce of the bark in fine powder, and eight or twelve of water, which were macerated without heat for twenty-four hours (a), and both liquors patted through a filter: the infusion ran through fast; the decoction exceeding slowly, and continued turbid and opake after filtration. The two liquors, examined hydroftatically, were found very nearly of the same specific gravity. Equal quantities of them being turned black with equal quantities of solution of vitriol, the quantity of water necessary for diluting the blackness of the mixtures to an imperceptible degree, was very nearly the same for both. These experiments were often repeated, and seemed to prove, that the infusion and decoction are not considerably different in the quantity of matter taken up from the bark, but that this matter is in the cold infusion transparently dissolved, whereas in the decoction great part of it is only diffused through the liquor in an undissolved state. - In the infusion itself, however, the solution does not appear to be very intimate. The transparent liquor becomes in a day or two turbid, and on {landing for some weeks (being now and then shaken to prevent its growing mouldy) deposites so much of the resinous part, that it is in taste simply bitter,, and produces no blackness with vitriol. The resinous sediment gives to spirit of wine a dark-coloured astringent tincture, which strikes a black with vitriol like the tincture of bark itself.

(a) Since the above- account was written, this preparation has been received in general practice, and found to answer the character here given of it. The time of maceration has been diminished to twelve hours, and some latexperiments and the clear liquor given in doses of two or three ounces.

* The London college seems now convinced that long coction of the bark is either unneces-sary, or hurtful by dissipating some of the more volatile parts, and precipitating the resinous ones; for they have given a formula for a decoction of bark, in which one ounce of the powder is boiled in a pint and three ounces of water for ten minutes only, in a close vessel., and then drained off while hot.

It is a common opinion, that bark in fub-ftance is more effectual than any preparation of it. Thus much is plain, that the infufions, as well as the decoctions, have not near so much effect as the quantity of bark they were made from, as the menstruum does not in either case completely extract its active matter: but their effects are evidently the same in kind, and the difference in degree may be compensated by an increase in the quantity.

The turbid decoctions, on the addition of any of the concentrated mineral acids, in the proportion of one drop to about a quarter of an ounce, become transparent, of a bright pale yellow colour, and of a rougher or more acerb experiments shew, that it may be still further reduced, without any injury to the medicine. A mixture of one part of bark and eight of water being filtered after Handing for one hour, the liquor appeared, from its taste, from its colour, from its specific gravity, and from the trial with solution of vitriol, to be very nearly, if not fully, as strong, as those which had flood 2, 4, 6, 8, 12, 24 hours. On doubling the quantity of bark, and making it with the water for only two or three minutes, the liquor proved rather stronger than any of the preceding; and being afterwards kept 24 hours on the same bark, it gained no sensible addition to its strength. So that a very strong infusion may be obtained in a very expeditious manner.

taste, but with the loss of their bitterness: the vegetable acids, added in proportionably larger quantity, render them likewise transparent and improve their roughness, without much dimi-nishing their bitterness: all these mixtures de-posite, on standing, a little powdery sediment. Alkalies, both fixt and volatile, occasion a more copious precipitation, and instead of making the turbid decoctions clear, make the clear turbid.

Decoct. cort. peruv. Pb. Lond.