THE GUMS. 245 



and A. arabica furnished nearly all the gums of commerce, 

 but it has lately been determined that A. verelc yields the 

 largest quantity. That coming from Senegambia is also 

 furnisbed by this species. The gums from different coun- 

 tries usually have different names, as Gum-Arabic, Cape 

 Gum, Gum-Senegal, Australian Gum, etc., and differ much, 

 too, in quality. As found in commerce, the pieces are 

 generally roundisb, with an irregular surface, ■which, upon 

 fracture, is vitreous in appearance. They may be transpar- 

 ent or cloudy, and are often more or less colored. All the 

 varieties, except the Cape Gum, are readily and completely 

 soluble in both hot and cold water. The Cape Gum is not 

 completely so. They are easily pulverized, and yield a 

 white powder — even the impure and colored masses. The 

 latter, therefore, are generally used for the powdered gum 

 found in the shops. The several kinds of Gum- Acacia are 

 heavier than water; their specific gravity varying from 1.3 

 to 1.6. Upon analysis they are found to contain, besides 

 the constituents mentioned above, about twelve to seven- 

 teen per cent, of water, a small quantity of sugar, resin, 

 and tannin. They yield about three per cent, of ash, 

 which consists largely of calcic carbonate. Some kinds, for 

 example, the Gum-Arabic, were used in remote antiquity. 

 In medicine it is employed on account of its demulcent 

 property. As a mucilage its use is very general, but the 

 largest quantity is consumed in stiffening fabrics, and pro- 

 ducing a glazed surface upon them. It is often added 

 to fluids to increase their density, so that they will hold in 

 suspension pigments, or other substances contained in them, 

 A common example of the kind is presented in writing-ink. 

 209. Feronia Gum, or East India G^im, is from Fero- 

 nia elephantum, a plant belonging to the Orange tribe 



