644 BOTANY AND PHARMACOGNOSY. 



Acacia is not soluble in alcohol, but is completely soluble in 

 water ; the solution is adhesive, gives an acid reaction with litmus 

 paper, yields a gelatinous precipitate with basic lead acetate solu- 

 tion (Ghatti gum giving but a slight precipitate), ferric chloride 

 or concentrated solution of sodium borate (Mesquite gum is not 

 precipitated by any of these reagents), does not give a bluish 

 or reddish color with iodine (absence of artificial g^ms con- 

 taining starch or dextrin), or a brownish-black precipitate with 

 ferric chloride (absence of gum of Australian species), and does 

 not reduce Fehling's solution (absence of artificial gums con- 

 taining sugars). 



The powder contains few or no altered or unaltered starch 

 grains or vegetable tissues. 



Constituents. — A crystalline glucoside, which is apparently 

 arabic acid (arabin or gummic acid) in combination with cal- 

 cium, magnesium and potassium, and which constitutes the greater 

 part of the gum ; water, 12 to 17 per cent. ; ash 2.7 to 4 per cent. 



Allied Plants. — The best grade of gum Arabic (gum Sene- 

 gal) is obtained from Acacia Senegal and A. glaucophylla, both of 

 tropical Africa. Gums with a brown or red color are obtained 

 from A. arabica, A. Seyal, A. stenocarpa and A. Ehrenbergiana. 

 There are a number of gums which have many of the properties 

 of gum Arabic, as Cape gum, from A. horrida and A. Giraffw; 

 Australian or wattle gum, from the golden wattle (A. pyc- 

 nantha), tan wattle (A. decurrens) and A. homalophylla; Amrad 

 gum, from A. arabica; Gedda gum, from A. gummifera; Talca 

 gum from A. modesta of India. Gums are also obtained from 

 other genera of the Leguminosae, as Mesquite gum, from Pro- 

 sopis juliflora, of the Southern United States and Mexico ; Sassa 

 gum from Albizzia fastigiata, of Abyssinia ; Barrister gum, from 

 Mesoneurum Scortichinii, of Australia. A gum resembling acacia 

 is found in Flindersia maculosa, of Eastern Australia, and Chlo- 

 roxylon Swietenia, of Farther India and Ceylon, both plants of 

 the Fam. Rutaceae. Other gums are obtained from the plants of 

 the following families: Rosaceae (p. 290); Burseraceae (see 

 Myrrha), Anacardiaceae (p. 322) ; Guttiferae (p. 336). 



Adulterants. — Various species of Acacia indigenous to trop- 

 ical Africa and Australia, as well as Anogeissus latifolia (Fam. 



