255. Acacia.—Gum Arabic.
A gummy exudation from Aca'cia sen'egal Willdenow and of other species of Acacia.
BOTANICAL CHARACTERISTICS.—A small tree about 20 feet high, with a gray bark. Leaves bi-pinnate. Flowers pale yellow, in dense spikes. Legumes broad, three to four inches long.
HABITAT.—The acacia tree forms dense scrubby forests in the sandy regions watered by the Senegal, and in Abyssinia and Kordofan.
DESCRIPTION OF DRUG.—In roundish, brittle tears or broken fragments about the size of a pea, or larger, with an opaque appearance, due to the numerous fissures. Inodorous; taste mucilaginous and insipid. Soluble in water, forming a thick mucilaginous liquid; insoluble in alcohol. The aqueous solution has an acid reaction and yields gelatinous precipitates with subacetate of lead, ferric chloride, and concentrated solution of borax. Oxalates precipitate the calcium base. There are two kinds of "powdered acacia" on the market, the "granulated" and the "finely dusted." The former is more soluble and less liable to form lumps, and is, therefore, preferable for pharmaceutical purposes.
VARIETIES AND GRADES.—The Kordofan and Senegal gums are the product of A. Senegal. The former has been described above. Gum Senegal, deriving its name from the river Senegal, comes in larger tears than the former, varying in color between yellow and yellowish-brown, being less fissured and more transparent. As to the grades of gum, it may be said that the quality entering the market varies exceedingly in its solubility, viscosity of its mucilage, and its color. In the market the grades are designated by numbers, No. 1 being the best carefully selected tears, No. 2 the next best, and so on until several selections have been made, the remaining colored pieces containing impurities being termed "sorts;" but this term is sometimes applied to unsorted gum arabic, often consisting of a mixture of the lower grades. The terms "strong" and "weak" have been applied, designating the quantity of moisture, the strong being the drier and probably the most soluble; the weak being that which possibly swells in water, does not completely dissolve, and hence yields a relatively small percentage of mucilage.
Mesquite gum is obtained from Prosopis juliflora, found in Southwestern America and South America. Quite abundant in some portions of Texas and New Mexico. It occurs in colorless or amber-brown tears; resembles gum arabic somewhat in fissures; specific gravity, solubility, its behavior to nitric acid, and the amount of ash yielded upon incineration (2.1 to 3 per cent.). Its aqueous solution is not precipitated by subacetate of lead, ferric salts, or borax. Acetate of lead, with ammonia added subsequently, yields a gelatinous precipitate. These reactions, however, differ to some extent in different samples.
CONSTITUENTS.—Arabic acid, C12H22O11, combined with calcium, magnesium, and potassium, to the presence of which its solubility is due; boiled with dilute acid it yields arabinose or arabin sugar. A solution of the gum is unaffected by neutral lead acetate. The gum contains about 14 per cent. of moisture and some sugar. Ash, not exceeding 4 per cent.
Preparation of Arabic Acid.—Obtained by adding alcohol to acidified (HCl) mucilage, and drying the precipitate. It yields arabiose in prismatic crystals when boiled with acids and possibly also galactose.
Powder.—Not more than 1 per cent. should be insoluble in water (limit of dirt, etc.), nor should the powder contain more than 15 per cent. moisture.
ACTION AND USES.—Demulcent. Used in pharmacy for suspending insoluble matters in water, as in emulsions, and as an excipient.
Powder—Elements of: See Part iv, Chap. I, B.
- Mucilago Acaciae (34 per cent.).
- Syrupus Acaciae (10 per cent. of acacia), Dose: 1 to 8 fl. dr. (4 to 30 mils).
- Pulvis Cretae Compositus (20 per cent.), used as an excipient.