"A gummy exudation from Acacia Senegal, Willdenow" (U. S. P.). The concrete juices of other species are also included under the commercial name Gum Acacia.
SYNONYMS: Gum arabic, Gum acacia, Gum mimosa, Gummi mimosae, Gummi arabicum.
ILLUSTRATION: Acacia Senegal, Bentley and Trimen, Med. Plants, 94; A. vera, Willdenow, Spec. Plant, iv., 1805.
Botanical Source.—The trees and shrubs yielding this gum are numerous, and all have leaves of the bipinnate variety and long spikes or globular heads of flowers, generally of a yellow color. They are more or less thorny, from the fact that the stipules are often transformed into spines. They all delight in dry, sandy situations, and will often be found where other shrubs and trees can not exist.
The Acacia Senegal of Willdenow (A. verek of Guillemin and Perottet and Mimosa Senegal of Linné) is a moderate-sized tree, usually about 20 feet high. It has a crooked stem with a grayish bark, and is much branched; the limbs being scattered over or covered with a purplish or yellowish-green bark. The leaves are smooth and bipinnate, the pinnae in two pairs, with a gland between them. The leaflets are oblong-linear and arranged in eight or ten pairs. The spines are sharp and in two pairs. The flowers, which are small and yellow, are densely crowded on axillary, stalked, globose heads, usually two together. The fruit is a smooth, compressed, moniliform legume, of a light-brown color, and usually about 5 inches long, containing about 6 flattish seeds.
The Acacia vera, Willdenow (A. arabica of Willdenow; A. nilotica, Desfontaines; Mimosa arabica, Roxburgh). A small, undersized tree or shrub, which occasionally, however, attains a height of about 40 feet, with a trunk from 3 to 4 feet in circumference. The thorns are stipulary, sometimes long, sometimes short, or almost wanting. The flowers are small, yellow, and in globose heads. Each flower has a five-cleft corolla and numerous, distinct stamens.
Botanical History.—The Acacia Senegal inhabits Africa from Senegal eastward to Egypt. It is called Hashab, and yields the most valuable gum, that coming from Dejara, in Kordofan, being the best product. It is known as Hashabi gum. The gums yielded by this species are known as the Kordofan and Senegal gums. It constitutes large forests north of the River Senegal.
Acacia vera (A. arabica). Near the Nile this tree is known as the Ssant or Sont, Egyptian thorn, or Egyptian gum arabic tree. It inhabits Egypt, Arabia, India, and is found abundantly as far south as Abyssinia, and westward to the regions of the Senegal. It produces an inferior brownish or reddish gum.
Jackson (Account of Morocco, 3d ed., p. 137) says:
"Of the trees from which gum arabic is obtained, and which inhabit the southern parts of Asia and the upper portions of Africa, the A. arabica is the most common. Several species are said to yield the gum, and probably contribute to supply that found in commerce, but that above-named furnishes the principal part or it. The gum flows naturally from the bark of the trees, in the form of a thick and rather frothy liquid, and speedily concretes in the sun into tears; sometimes the discharge is promoted by wounding the trunk and branches. The secretion is most abundant in dry, hot seasons, and among old stunted trees, especially after a rainy season has softened their bark, and rendered it apt to split during the succeeding hot weather. The more sickly the tree appears the more gum it yields; and the hotter the weather the more prolific it is."
Description and Tests.—The U. S. P. thus describes Acacia: "In roundish tears of various sizes, or broken into angular fragments, with a glass-like, sometimes iridescent fracture, opaque from numerous fissures, but transparent and nearly colorless in thin pieces; nearly inodorous; taste insipid, mucilaginous; insoluble in alcohol, but soluble in water, forming a thick, mucilaginous liquid. Acacia should be slowly but completely soluble in 2 parts of water. This solution shows an acid reaction with litmus paper, yields a gelatinous precipitate with basic lead acetate T.S., ferric chloride T.S., or concentrated solution of sodium borate,—and does not reduce alkaline cupric tartrate V.S. The powder is not colored blue (absence of starch) or red (absence of dextrin) by iodine T.S."—(U. S. P.).
The best quality of gum arabic—that known as Kordofan gum, Turkey gum, or White Sennaar gum—is perfectly colorless, of a shining, conchoidal, vitreous fracture, opaque in mass, but transparent in small fragments, hard but pulverable, inodorous, and of a faintly sweetish and viscous taste. It is generally in tears, round or angular, and seldom larger than a hazel nut. The very pale, yellowish-white, yellowish-red, or brownish tears belong to the second quality, and may be rendered colorless by the action of sunlight, or when treated with chlorine water. The specific gravity is from 1.33 to 1.52. It almost invariably forms a white powder.
Cold or hot water dissolves its own weight of gum arabic, forming a thick mucilaginous solution, and from which the gum may be obtained by evaporation, or by precipitation with, excess of alcohol; the concentrated solution may be kept much longer than the dilute, which latter, especially in warm weather, undergoes the acetous fermentation. The gum is also soluble in solutions of the pure alkalies, lime water, and dilute acids. Alcohol does not dissolve it, neither does ether or the oils. When boiled with sulphuric acid an unfermentable variety of sugar is formed; but with nitric acid it passes into mucic, malic, and finally into oxalic acid.—(Ed.) Treated with a solution of the neutral perchloride of iron, the mucilage of gum arabic becomes a light reddish jelly; with a solution of borax it forms a firm, colorless jelly, which is liquefied by powdered sugar; and, with a solution of sugar, it furnishes, by desiccation, a clear, hard, amorphous mass. Its decomposition is readily effected by the strong acids. The gums known as Gedda, Jiddah, and Turic gums were varieties of Kordofan gum.
Gum arabic does not deteriorate if kept dry, but its concentrated mucilage, after a long time, will become sour (acetic acid). Hot water is said to hasten this fermentation, if employed in making the mucilage. Dilute solutions of the gum become moldy. A few drops of sulphuric acid added to it-the solution being poured off from the resultant precipitate of calcium sulphate—is said to prevent this change—(Am. Jour. Pharm., 1872).
Varieties.—SENEGAL GUM.— This gum is one of the chief productions of the French colony of Senegal, being gathered by the Moors and negroes in the section north of the river of that name. It is gathered from November to July and shipped to Bordeaux, France, and some of it reaches America. It occurs in larger pieces than the Kordofan gum, and is often oblong or vermiform in shape. While some of it is colorless most of it is yellowish, reddish, or brownish in color. It is stated that it is sorted into several grades in America. Several species of Acacia, among them the A. Senegal, abounding in large forests, yield this gum. It breaks less easily, and seldom exhibits the fissures observed in the best variety, and while differing in appearance from the Egyptian gum, though being obtained, in part at least, from the same species, it does not exhibit different optical or chemical properties from those of the better variety. It was introduced by the Dutch, though its commerce is now controlled by the French.
MOROCCO GUM, Mogador or Barbary gum. —This gum is derived from the A. nilotica, Desfontaines (A. arabica, Willdenow), and derives its name from the port (Mogador) from which it is shipped from Morocco. It is gathered in July and August in the provinces bordering on Morocco, and in part from Timbuctoo. This gum comes in moderately large tears, occasionally worm-shaped, vitreous within, and crackles when exposed to a warm temperature. It has a nearly uniform, faintly brown, or dusky color, and is fissured externally. It dissolves completely in water.
CAPE GUM.—Exudes spontaneously, from the A. horrida, Willdenow, or very common Doornboom tree of South African forests. It is produced as tears or fragments, of a pale-amber color. It is shipped from Cape Colony by way of the Cape of Good Hope, and is regarded as an inferior gum.
AUSTRALIAN GUM, Wattle gum.—This gum occurs in large globular, transparent tears or masses, which are hard and of a pale yellow, amber, or brown color. It dissolves completely in water, producing a mucilage which is very adhesive, and less liable than other gums to crackle when dry. Tannin from the bark is apt to be present on this gum. It is the product of several species, among them A. pycnantha, Bentham; A . decurrens, Willdenow.A. mollisima, Willdenow), and A. homalophylla, A. Cunningham, the fragrance of the latter earning for its wood the name of "violet wood."
INDIA GUM, East India gum.—A gum has been introduced into commerce termed Gum of India, which is used for dressing cloths, etc. Being cheaper than gum arabic it is used to adulterate this gum, but it is unfit for pharmaceutical purposes. It reaches London in cases of about 535 pounds; the picking is done in France, where the whitest tears are mixed with gum arabic and gum Senegal. The method to detect this adulteration is to mix 30 grains of the suspected article with a pint of cold water, and allow the mixture to rest. In place of a homogeneous solution, a thick, transparent, tenacious magma is obtained, insoluble in a large amount of water. Though called India gum it all goes from Africa to Bombay, and from thence is shipped to other parts.
SUAKIN GUM, Savakin gum, Talca or Talha gum.—A very brittle gum, usually semi-pulverulent, obtained from the A. stenocarpa, Hochstetter, and the A. Seyal var. fistula, Schweinfurth. It is composed of colorless and brown gums, mixed, and is collected near the western shore of the Red Sea and delivered at the port of Suakin, from which it derives its name. It is sometimes partially insoluble, but gives a pasty magma with water.
SENNAAR GUM, Sennari gum.—A gum resembling Kordofan gum in beauty, but less valuable, is gathered on the Blue Nile and exported by the way of Sennaar. This gum is known by the native term Hashabi el Jesire. It is quite common in commerce.
MEZQUITE GUM.—Dr. G. G. Shumard introduced to the profession a species of gum discovered in Texas and New Mexico, and which answers the purpose of gum acacia, forming a beautiful mucilage with water. It exudes spontaneously from the Mezquite tree, in a semifluid state, and hardens in a few hours, forming lumps of various sizes and colors, which whiten by exposure to sunlight, all finally become translucent and often filled with minute fissures. It is called Gum mezquite, mezquit, muckeet, musquit, etc. The tree from which it is obtained is the Algarobia glandulosa, Torrey and Gray (Prosopis dulcis of Kunth, or P. juliflora of De Candolle.. It is from 25 to 40 feet high.
The tree yielding this gum is also found in California and Mexico, and south to Chili and the Argentine Republic. The uses of mezquite gum are identical with those of acacia.
HOGG GUM, Doctor gum.—(Not Gum Hogg, or the East Indian Kathira, from Cochlospermum Gossypium, De Candolle).—This gum occurs in irregular fragments or tears, sometimes transparent and reddish in color, at other times opaque. It is derived either from Rhus Metopium, Linné, or Moronobea coccinea, Aublet, possibly from both. Water only partially dissolves it.
CHAGUAL GUM.—From Puya lanuginosa, Molina (Pourretia lanuginosa, Ruiz et Pavon). Nat. Ord.—Bromeliaceae.—A Chilian product, of a thick, mucilaginous consistence and acidulous character, and but partially soluble in water. Borax does not precipitate it from solution, but precipitation may be effected with acetate of lead.
Admixtures.—Gum arabic is often adulterated with the inferior grades of gum, and in powdered form with starch or flour (which, however, will respond to the iodine test), besides fragments of dextrin. The latter may be detected by Trommer's test which gives a precipitate of cuprous oxide upon standing.
Chemical Composition.—Gum arabic is generally accepted to be a mixture of salts of calcium, magnesium, and potassium formed by the union of these elements with arabic acid. The gum is chiefly composed of the calcium arabate. Arabic acid, known also as gummic acid, forms salts containing an excess of acid. It is considered identical with the metapectic acid of Frémy, and is obtained from a solution of the gum, acidulated with chlorhydric acid, by precipitation with alcohol. Before drying arabic acid is soluble in water, but after drying it becomes metagummic acid, and refuses to dissolve in either hot or cold water unless they be alkalinized. Both gum arabic and arabic acid are known as arabin. Continued heating with dilute sulphuric acid changes arabin into sugar, while oxidation by means of nitric acid results in the production of mucic, oxalic, saccharic, and tartaric acids. Arabinose (C12H22O11) is produced by means of dilute sulphuric acid from those gums which yield none or but little of mucic acid.
Action, Medical Uses, and Dosage.—Gum arabic is nutritive and demulcent, and exerts a soothing influence upon irritated or inflamed mucous tissues, by shielding them from the influence of deleterious agents, atmospheric air, etc. On this account it has been used in diarrhoea and dysentery, to remove tenesmus and painful stools, in catarrh, cough, hoarseness, gonorrhoea, ardor urinae, etc.—(Coxe.) It may be given almost ad libitum in powder, lozenge, or solution, alone or combined with syrups, decoctions, etc. In acute diseases, where it becomes necessary to use the lightest and most readily digested food, there is no article, probably, equal to gum arabic. It maybe used for this purpose by dissolving half an ounce of the powdered gum in 5 ounces of water, and sweetening with loaf-sugar, of which a tablespoonful may be given every 2 or 3 hours; in low stages of fever, in typhoid fever, and wherever a mild stimulant is required, 1 ounce of a saturated solution of camphor in sulphuric ether may be added to the above, and administered in the same way; it is diuretic, promotes the action of the absorbents, and does not materially increase arterial action. Equal parts of pulverized alum and gum arabic form a good preparation to check hemorrhages from small cuts, wounds, etc. Externally, the application of its solution to burns and scalds has proved serviceable, repeating it until a complete coating is secured. It is likewise much used for compounding pills, lozenges, mixtures, and emulsions; also for administering insoluble substances in water, as oils, resins, balsams, camphor, musk, etc.
MUCILAGE OF GUM ARABIC.—To 4 ounces of finely pulverized gum arabic add, very gradually, a pint of boiling water, and rub the whole until perfectly blended. Dose, ad libitum. When gum arabic is adulterated with cherry gum, it is not easy to form a good mucilage; the cerasin of the cherry gum will cause it to be ropy. (For the official mucilage, see Mucilago Acaciae).
Related Products.—Flindersia maculosa, F. von Mueller (Elaeodendron maculosum, Lindley). Nat. Ord.—Meleaceae. Spotted tree, Leopard tree. This tree of New South Wales and Queensland is known by the above names on account of its spotted bark. The leaves are greedily devoured by sheep in times of drought. This tree exudes from the stems and branches during the summer months masses as large as pigeon eggs, of a clear amber-colored gum, having a pleasant taste, and which is eaten by the aborigines, and commonly employed by the bushmen for diarrhoea. It forms a good adhesive mucilage, and reminds one of a good quality of East India gum acacia. About 80 per cent of arabin, but no metarabin has been found in it—(J. H. Maiden, Useful Native Plants of Australia). The gum is known as Leopard tree gum.
CEDAR GUM.—A light-yellow gum derived from the Red cedar or Cedrella Australis of Queensland. The tears swell and subsequently dissolve in water. It contains no resin, but of arabin 68 per cent, and of metarabin 6 per cent—(P. J. Trans., 1890).