COMPOUND PRODUCTS. CHAP. I. 



of a clear, viscid, and tasteless fluid, that gradually 

 hardens upon being exposed to the action of the 

 atmosphere, and condenses into a solid mass. This 

 exudation is known by the name of Gum. It issues 

 copiously from many fruit-trees, but especially from 

 such as produce stone-fruit, as the Plum and 

 Cherry-tree, in which it exudes chiefly from fissures 

 in the bark, though it sometimes exudes also even 

 from the fruit. From plants, or parts of plants, 

 containing it, but not discharging it by spontaneous 

 exudation, it may be obtained by the process of 

 maceration in water. It has been found by che- 

 mists to consist of several varieties known by the 

 names of Gum Arabic, Gum Tragacanth, Cherry- 

 tree Gum, and Mucilage. 



Gumara- Gum Arabic, which is the most plentiful of all 

 the gums, is the produce of the Mimosa nilotica, a 

 native of the interior of Africa and of Arabia whence 

 its name. In its concrete state, in which it generally 

 assumes the shape of irregular globules, it is con- 

 siderably hard as well as somewhat brittle ; and is 

 destitute both of smell and taste. When pure it is 

 colourless and transparent, though sometimes it is 

 tinged with yellow, varying in its specific gravity 

 from 1300 to 14gO.* 



It is insoluble in alcohol ; but is readily soluble 

 in water ; and if the solution is exposed to the ac- 

 tion of the atmosphere, the water is gradually 

 evaporated, and the gum again left in a solid mass. 



* Davy's Agric. Chem. Lcct. iir. 



