94 ACACIA SENEGAL 



the powder, or to a solution formed with boiling waier and. 

 cooled, there is no appearance of a violet or blue colour." 



Composition. Gum acacia consists essentially of an acid culled 

 arable acid, gummic acid, or arabin, in combination with lime, 

 magnesia, and potash. This salt or mixture of salts forms about 

 70 per cent, of the gum ; the remainder consists of water, and of 

 various saline and earthy matters. Gum acacia is soluble in both 

 hot and cold water, and its solution has an acid reaction. Sub- 

 acetate of lead, as already noticed, forms an opaque white jelly 

 when added to the solution ; but no precipitate is formed in a 

 solution of gum acacia by the neutral acetate of lead, in which 

 respect it differs from a solution of gum tragacanth, which yields 

 an abundant precipitate under the same circumstances. By the 

 action of nitric acid acacia gum is resolved into mucic acid and a 

 little oxalic acid ; and when boiled with diluted sulphuric acid it 

 is slowly converted into grape sugar. 



Medical Properties and Uses. Gum acacia possesses demulcent 

 and emollient properties, for which purposes it is sometimes 

 employed medicinally ; but it is chiefly used as a vehicle for the 

 exhibition of other medicines, thus, to suspend insoluble powders, 

 and in the formation of lozenges. In coughs gum often affords 

 much relief, when it is allowed to dissolve slowly in the mouth ; 

 and under the same circumstances it is frequently useful in allay- 

 ing irritation of the throat and air passages, by diluting the acid 

 secretions and sheathing the parts from the action of the air. It 

 is also used internally in inflammatory affections of the stomach 

 and bowels ; and its influence as a demulcent is supposed to 

 extend even to the urinary organs, and thus to be useful in 

 irritation of the bladder and urethra. But in the latter cases it 

 is probable that its beneficial effects are in a great measure due 

 to the quantity of fluid which is taken with it, diluting and thus 

 diminishing the irritating action of the urine. Gum has also been 

 recommended as a substitute for amylaceous food in diabetes, as 

 it is not converted into sugar ; but its use in this disease does not 

 appear to have been attended with any appreciable benefit. 



A thick mucilage of gum has also been recommended as an 



