Page 307 - Pharmacognosy 2 PG303

Pharmacognosy-2 (PG303) Level 2 Clinical Pharmacy-Pharm D

4- lead sub-acetate test: To 5 ml of an aqueous solution of gum Arabic (1/50), add
1 ml of lead sub-acetate solution; a flocculent white precipitate is formed (c.f.
Gum Tragacanth).

5- Iodine test: To 1 g of powdered gum Arabic add 1 ml of N/.50 iodine, a
yellowish-brown colour is produced (c.f. Agar and Gum Tragacanth).

Constituents
Acacia consists principally of Arabin which is a complex mixture of calcium,

magnesium, and potassium salts of arabic acid. On hydrolysis, arabic acid yields 1
molecule of L-rhamnose, 2 molecules of D-galactose, and 3 molecules of L-
arabinose and an aldobionic acid. Gum Arabic also contains diastase and oxidase
enzymes, and hence readily turns powdered guaiacum resin, or the tincture diluted
with water, blue.

Uses
It is used in medicine as a demulcent, and as suspending and emulsifying

agent.

Gum Tragacanth

Syn.: Tragacanth; Tragacantha; Gummi Tragacanthae, Gum Dragon

Gum Tragacanth is the dried gummy exudation obtained by incision from
Astragalus gummifer Labill., and some other Asiatic species of Astragalus (Fam.
Leguminosae, Papilionoideae). It contains not more than 1 % of foreign organic
matter.

The plants are small, branching, thorny shrubs about a metre in height and
are natives of southern and eastern Europe and, especially of Asiatic Turkey and
Persia, where they form one of the most characteristic forms of vegetation.

Preparation
When the stem is incised, the gum exudes and dries. The form that it assumes

being dependent on the form of the incision. Vertical slits yielding flat, ribbon-

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