644 BOTANY AND PHARMACOGNOSY. 



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

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

 litmus paper, lo c.c. of a lo per cent, solution does not yield 

 a gelatinous precipitate with 0.2 c.c. of normal lead acetate test 

 solution, but is precipitated with o.i c.c. of a test solution of 

 ferric chloride (Mesquite gum is not precipitated) ; a cold solu- 

 tion does not give a bluish or reddish color with iodine (absence 

 of artificial gums containing starch or dextrin), or a brownish- 

 black precipitate with ferric chloride (absence of gum of Aus- 

 tralian species). A 10 per cent, aqueous solution of acacia when 

 examined by the polariscope should show but a slight Isevoration. 



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. glancophylla, both of 

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

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

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

 of gum AralDic. as Cape gum, from A. horrida and A. Giraffcc; 

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

 nantha), tan wattle {A. dccurrens) and A. homalophylla. Gums 

 are also obtained from other genera of the Leguminosse, as 

 Mesquite gum, from Prosopis juMora, of the Southern United 

 States and Mexico. 



Giiatti gum or Indian gum is an exudation from the wood 

 of Anogcissus latifolia (Fam. Combretaceas) a tree indigenous 

 to India and Ceylon. It occurs in yellowish-white tears with a 

 dull rough surface and a vitreous fracture. It is entirely soluble 

 in cold water, forming a very viscous mucilage. 



An artificial gum has been prepared by heating starch with 

 sulphuric acid in an autoclave, the resulting product being neu- 

 tralized, washed and then dried. It is said to resemble acacia in 

 appearance and adhesiveness. 



The powder, while sometimes adulterated with dextrin and 



