A gummy exudation from the stems of one or more undetermined species of Acacia.

Characters and Tests. - In spheroidal tears, nearly colourless, and opaque from numerous minute cracks; or in fragments with shining surfaces; brittle; bland and mucilaginous in taste; insoluble in alcohol, but soluble in water.

Impurities. - Starch; detected by the iodine test. Gum resins; detected by smell and taste.

Incompatibles. - Alcohol and sulphuric acid, borax, persalts of iron, and subacetate of lead.

Composition. - Gum arabic consists chiefly of arabic acid or arabin, C36H66O33, combined with calcium, magnesia, and potash, and 17 per cent. of water.

Preparations.

Mucilago Acaciae. - Gum, 40; Water, 60. Dose, 1 to 4 fl.dr.

Gum Acacia is also contained in Mistura Cretae, Mistura Guaiaci, Pulvis Amygdalae Compositus, Pulvis Tragacanthae Compositus, and in all Trochisci.

Action And Uses

Acacia possesses very similar properties and physiological effects to those of tragacanth, and is employed for the same purposes. (See Tragacantha.) An objection to its pharmaceutical use is its liability to undergo fermentation, and cause indigestion, flatulence, and diarrhoea. Its principal application therapeutically is for cough in the form of lozenges and linctuses.

Indigo - C8H5NO. A blue pigment prepared from various species of Indigofera. From India. Use. - Indigo is employed in chemical testing.