Gum acacia (Acacia, U.S.P.) is a variety of gum arabic obtained from certain species of Acacia (N.O. Leguminosae), the chief being Acacia Senegal, Willd., a small tree indigenous to East and West Africa. The gum exudes from the stem and branches spontaneously, but the flow is usually stimulated by incisions in the bark. The method of tapping consists in cutting the bark with a small axe, and tearing off a thin strip, about 2 or 3 feet in length and 1 to 3 inches wide, according to the size of the branch. The exuded gum hardens on exposure to the air, and is then collected, dried and exported. Much is sent to Trieste, where it is sorted for the European and other markets. Many varieties of gum arabic occur in commerce, but the most esteemed is that collected in Kordofan, the best qualities of which are almost colourless, and opaque because of the numerous fissures. Mogadore gum closely approaches it, but is of less fine appearance. The best qualities of Senegal gum are also suitable for pharmaceutical use; they are less opaque than the Kordofan gum and contain occasional pieces of vermiform shape. Gum acacia for medicinal purposes should be in rounded or ovoid, colourless or pale yellowish, opaque, brittle, almost inodorous tears, or in small, angular, vitreous fragments, and have an insipid, mucilaginous taste.
Almost entirely soluble in water (1 in 1), forming a viscid neutral solution or mucilage. Insoluble in alcohol, but soluble in diluted alcohol in proportion to the amount of water present.
Constituents.—Gum acacia consists chiefly of diarabinan-tetragalactan-arabic acid (arabin) in combination with calcium, potassium, and magnesium. It also contains oxidising, peroxidising, and diastatic ferments; together with about 12 per cent. or more of water, and yields from 2.7 to 4 per cent. of ash, consisting chiefly of calcium, potassium, and magnesium carbonates. Gums that are of a yellow or brown colour usually contain tannin; and these, together with such as are incompletely soluble in water, or which yield ropy or glairy solutions, should not be used for medicinal purposes.
Action and Uses.—Gum acacia is employed medicinally as a demulcent, also in pharmacy as a suspending agent and pill excipient. It is administered in mixtures, cough syrups and linctuses in the form of mucilage, and in various pastilles, jujubes, and pastes. It is also used occasionally as a masticatory, either in the tears or in a firm pastille containing a little sugar. In dispensing it is used as a suspending agent in mixtures containing heavy insoluble powders, but it should not be used with bismuth salts, with which it is apt to form flaky masses. It is also employed, in the form of powder or freshly prepared mucilage, made from coarsely powdered acacia, for the emulsification of fatty and volatile oils and resinous tinctures. Finely powdered acacia is generally to be preferred as an emulsifier; it can be at once incorporated with the oil or oleoresin, the subsequent addition of twice as much water as gum producing the primary emulsion. The proportions requisite in the case of fatty oils and oleoresins are one part of powdered acacia to four parts of the oil. Volatile oils require one part to two parts of oil; but if the powdered gum be diffused in the oil, an equal volume of water added, and the mixture shaken, as little as 5 per cent. of gum may suffice to form a separable mixture in which equal distribution of the oil may be obtained by shaking. In the case of resinous tinctures mucilage of gum acacia should be used in the proportion of not less than one-sixteenth part of the finished mixture. Mucilage of gum acacia mixed with an equal quantity of syrup or glycerin is a useful excipient for pills. As a dry excipient powdered acacia is employed mixed in small proportion with powdered marshmallow root, or powdered liquorice root. A mixture Of equal parts of mucilage of gum acacia and syrup is used in the preparation of Unna's gum pastes; zinc oxide, mercuric oxide, and other medicaments being incorporated with it, as required. Gum acacia is incompatible with strong alcohol, borax, ferric salts, calomel, lead subacetate, and acids, unless well diluted.
- Mistura Acaciae, B.P.C.—ACACIA MIXTURE. Syn.—Mistura Mucilaginosa.
- Gum acacia (6 in 100), with syrup and diluted orange-flower water. Employed as a demulcent in cough syrups and linctuses. Dose.—4 to 15 mils (1 to 4 fluid drachms).
- Mucilago Acaciae, B.P.—MUCILAGE OF GUM ACACIA.
- Gum acacia, in small pieces, 40; distilled water, a sufficient quantity. Wash the gum by rinsing it quickly with a small quantity of distilled water, then dissolve in 60 of the water, and strain. Sterilisation, by heating at 100° for half an hour, enables the mucilage to be preserved for some time, especially if stored in well-filled bottles. Dose.—4 to 15 mils (1 to 4 fluid drachms).
- Mucilago Acaciae, U.S.P.—MUCILAGE OF ACACIA.
- Gum acacia, in small pieces, 34; lime water, 33 by weight; water, sufficient to produce 100 by weight; wash the gum with cold water, allow it to drain, add the lime water and water, stir occasionally until the gum is dissolved, and strain. Average dose.—15 mils (4 fluid drachms).
- Mucilago Acaciae Composita, B.P.C.—COMPOUND MUCILAGE OF ACACIA. Syn.—Pill-coating Mucilage.
- Gum acacia (1 in 10), with tragacanth, chloroform, and water. Used for moistening pills previous to coating.
- Potio Gummosa, Ph.Fr.—POTION GOMMEUSE.
- Gum acacia, in powder, to; syrup, 30; orange-flower water, to; distilled water, 100; all by weight.
- Pulvis Acaciae Compositus, B.P.C.—COMPOUND ACACIA POWDER.
- Gum acacia and tragacanth, in equal parts. May be used sparingly as an absorbent pill excipient.
- Syrupus Acaciae, B.P.C.—SYRUP OF ACACIA.
- Mucilage of gum acacia, 1; syrup, 3. Used chiefly as a demulcent in cough mixtures; should be freshly prepared as required. Dose.—4 to 15 mils (1 to 4 fluid drachms).
- Syrupus Acaciae, U.S.P.—SYRUP OF ACACIA.
- Gum acacia., in selected pieces, 10; refined sugar, 80; distilled water sufficient to produce 100. Dissolve the gum in about 43 of distilled water, add the sugar, heat on a water-bath till solution is effected, strain if necessary, and make up to the required volume with distilled water. Store the resulting syrup in small tightly-stoppered bottles, in a cool place. It is a useful demulcent, but is chiefly employed as an agent for suspending powders in mixtures.
- Syrupus Gummi, Ph.Fr.—SIROP DE GOMME.
- Gum acacia, washed, 10; sugar, 56; distilled water, 34.
The British Pharmaceutical Codex, 1911, was published by direction of the Council of the Pharmaceutical Society of Great Britain.