34 VEGETABLE DRUGS WITHOUT ORGANIC STRUCTURE. 



the microscope. A few cell walls, occasionally some 

 fragments of detached corky tissues, and some crystals. 

 In adulterated powdered gum arable the microscopic 

 pictures will naturally vary according to the adulterant. 

 Various flours are often employed as adulterants. Their 

 characteristic starches are readily recognized. 



Adulterations. — The gum is frequently adulterated 

 with other kinds of gum, as cherry, Bdelbin, a gum resin. 

 These, being dark gums, are bleached by means of sulphur 

 or chlorine gas. 



The powdered gum is mixed with a great variety of sub- 

 stances, most of which, if of organic structure, are readily 

 detected by the microscope. Other adulterants must 

 be detected by chemical means. Dextrin is a very 

 common adulterant of the powder. A mixture of this 

 latter in gum may be detected by moistening with a 

 few drops of ammonium molybdate and potassium 

 nitrate which when heated gives a blue color. 



Uses. — In medicine as a demulcent. In the arts gum 

 arable has a wide range of usefulness. 



Other Gums of Similar Characters. — There are a great 

 number of these, and only the most important can be 

 mentioned. Their chemical composition has been con- 

 sidered. 



Cherry and plum gums, from the cultivated and wild 

 cherry and plum trees, are extensively gathered. They 

 exude from natural breaks in the bark of the tree and 

 occur as roundish irregular masses up to one and one- 

 half inches in diameter. Plum gum is lighter in color, 

 cherry gum being more reddish. Both are insoluble in 

 water, but form emulsions. Senaar gum (Talca or 

 Souakim gums) is from North Africa, probably from 

 Acacia fistula and A. Stenocarpa, Hocht. Jesire gum is 

 from the same general region. Cape gum or South 

 African gum, from Acacia horrida, Willd., is a darker, 

 cloudy gum, soluble with difficulty in water. It is 



