This section is from the book "An Experimental History Of The Materia Medica", by William Lewis.
Gummi rubrum ajiringens gambienfe D. Fother gill in med. obf. Lond. vol. i. 1757. Kino, Pharm. Lond. & Edinb. Red astringent gum from Gambia; supposed to exude from incisions made in the trunks of certain trees, called pan desangue, growing in the inland parts of Africa.
It is very friable, so as to be crumbled in pieces by the hands; of an opake dark reddish or almost black colour in the mass, and when reduced to powder, of a deep brick red: small particles of it, viewed with a magnifying glass, appear of a femitranfparent red like bits of garnet. In chewing, it first crumbles, then sticks together a little, and in a short time seems wholly to dissolve, imprefling a very considerable astringency accompanied with a slight sweetifhnefs. It has no smell.
To oils it gives little or no tincture. On a red-hot iron, it glows for a long time like a bit of burning charcoal, without shewing any difpofition to melt: it yields, during a little while, a slight dull flame hovering about the sursace, and leaves at length a large proportion of greyish ashes.
Both rectified spirit and water dissolve, each, about two thirds of it, the spirit somewhat more than the water. Both solutions, when made with the same quantities of the two menstrua, as twenty or thirty times the weight of the powdered gum, appear of the same deep bright red colour, the spirituous rather deepest: with solution of chalybeate vitriol, they both produce inky mixtures, from which the black matter speedily concretes and settles to the bottom, leaving the liquors colourless (a). The watery solution suffers no apparent change from the addition of alkalies fixt or volatile; but acids render it turbid, and occasion a copious precipitation.
The part, which water leaves undissolved, seems as dark-coloured as the gum at first: it gives the same deep red tincture to spirit, and this tincture strikes the same black with solution of vitriol. The part which spirit leaves undis-solved is much paler than the original gum, gives. no tincture to water, and produces no change with the vitriolic solution.
It appears therefore that both the colouring and astringent matter are more completely taken up by spirit than by water; though water extracts readily enough a great (hare of both.
Only a little quantity of this drug has hitherto been brought over. Dr. Fothergill, the first person, as far as I can find, who gave notice of it to the public, and who favoured me with the specimens on which the above experiments were made, informs us, that he had the first intimation of it from a physician, who had met with good effects from it in obstinate chronical diarrhoeae; and that a parcel was afterwards shewn to him, which had been received from a Guinea ship, and taken for a fine kind of dragons blood, which it pretty much resembles in appearance, though in quality essentially different. He observes, that from the trials which have been made, and from its sensible qualities, it promises to be an article worth inquiring after, and to become in time a valuable addition to the materia medica. In disorders from laxity and acrimony, it may, doubtless, be of great advantage; nor do I recollect any other drug, that is so much of a gummy nature, and at the same time so astrin-gent. Terra japonica comes the nearese-to it, but is manieftly less aftringent. The terra japonica differs likewise, in its watery solutions buffering no considerable separation of their parts from the addition of acids; and in the black matter, which they produce with vitriol, being little difpofed to concrete and precipitate. Whether the cause, on which these kinds of diver-sities depend, be sufficient to influence also their medicinal powers, our knowledge, both in the chemical composition of bodies, and in the operation of medicines, is as yet too imperfect to permit us to judge. The London and Edinburgh colleges have now received this gum as an officinal, and the latter have directed a tincture, in which two ounces of it are dis-solved in a pound and a half of proof spirit.
(a) The black matter in these kinds of mixtures appears to consist of the iron of the vitriol, disengaged from its acid solvent, and combined with the vegetable astringent sub-stance; the acid serving only as a necessary intermedium for procuring this union. The above black precipitates, after repeated ablutions with water, retained their blackness; and the clear liquors from which they had settled, being examined with alkaline salt on the principles to be mentioned hereafter under the article sales alkalmi, seemed to contain as much acid as the quantity of vitriol employed in them.