

TRAGACANTH 243 



several selections have been made, the remaining colored pieces con- 

 taining 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 South- 

 western America and South America. Quite abundant in some por- 

 tions 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. Ace- 

 tate of lead, with ammonia added subsequently, yields a gelatinous 

 precipitate. These reactions, however, differ to some extent in dif- 

 ferent samples. 



CONSTITUENTS. Arabic acid, Ci 2 H 22 Oii, combined with calcium, mag- 

 nesium, and potassium, to the presence of which its solubility is due; 

 boiled with dilute acid it yields arabinose or arabin sugar. A solu- 

 tion 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 b % y adding alcohol to acidified (HC1) 

 mucilage, and drying the precipitate. It yields arabiose in prismatic crystals 

 when boiled with acids and possibly also galactose. 



Powder. Not more than i 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. 



OFFICIAL PREPARATIONS. 



Mucilago Acaciae (34 per cent.). 



Syrupus Acaciae (10 per cent, of acacia), . . Dose: i to 8 fl. dr. (4 to 30 mils). 



Pulvis Cretae Compositus (20 per cent.), used as an excipient. 



256. TRAGACANTHA. TRAGACANTH 



GUM TRAGACANTH 



The spontaneously dried gummy exudation from Astra'galus gum'mifer Labillar- 

 diere, 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. 



