256. Tragacantha.—Tragacanth. Gum Tragacanth.
The spontaneously dried gummy exudation from Astra'galus gum'mifer Labillardiere, or from other Asiatic species of Astragalus.
BOTANICAL CHARACTERISTICS.—A small, tangled, spiny bush of compact growth, the petioles being converted into long spines. Flowers yellow, in axillary clusters. Legume partially two-celled.
DESCRIPTION OF DRUG.—The flake tragacanth comes in transversely lined, curved, and contorted bands, somewhat resembling fragments of oyster shell, but tough and horny; color whitish or yellowish, translucent. Taste insipid, sometimes faintly bitterish; inodorous. It is difficult of pulverization, made less so, however, by the use of a warm mortar. It does not dissolve in water, but swells up and forms a thick, gelatinous mass.
VARIETIES.—Very narrow bands or strings variously coiled. Tragacanth in sorts-stratified or nodular, conical and subglobular pieces, more of less brown, often adulterated with the gum of the almond and plum trees.
Powder.—Elements of: See Part iv, Chap. I, B.
CONSTITUENTS.—Traganthin or bassorin, C6H10O5, constituting about 43 per cent., swelling up in water, but not dissolving; and arabin, the calcium salt of gummic acid, soluble in water, but not identical with the arabin or arabic acid of acacia. Ash, not more than 3.5 per cent.
ACTION AND USES.—Used as a demulcent, but rarely, however, on account of its insolubility. Chiefly used in pharmacy to give consistence to lozenges, etc.
Mucilago Tragacanthae (6 per cent.).