ELASTIC GUM. 2Q5 



in great abundance over the vast extent of Africa, yet gum arabic 

 is produced chiefly by those trees which are situated near the equa- 

 torial regions ; and we are told that in Lower Egypt the solar heat 

 is never sufficiently intense for this purpose. The gum exudes in a 

 liquid state from the bark of the tree, in a similar manner to the 

 gum which is often produced upon the cherry-trees, <&c. in this 

 country ; and by exposure to the air it soon acquires solidity and 

 hardness. In Senegal the gum begins to flow when the tree first 

 opens its flowers ; and continues during the rainy season till the 

 month of December, when it is collected for the first time. Ano- 

 ther collection of the gum is made in the month of March, from in- 

 cisions in the bark, which the extreme dryness of the air at that 

 time is said to render necessary. Gum arabic is now usually im- 

 ported into England from Barbary, in large casks or hogsheads. 

 The common appearance of this gum is well known ; and the vari- 

 ous figures which it assumes seem to depend upon a variety of ac- 

 cidental circumstances attending its transudation and concretion. 

 Gum arabic of a pale yellowish colour is most esteemed; on the 

 contrary, those pieces which are large, rough, of roundish figure, 

 and of a brownish or reddish hue, are found to be less pure, and 

 are said to be produced from a different species of mimosa ; but 

 the Arabian and Egyptian gum is commonly intermixed with pieces 

 of this kind, similar to that which comes from the coast of Africa 

 near the river Senegal. 



Gum arabic does not admit of solution by spirit or oil ; but in 

 twice its quantity of water it dissolves into a mucilaginous fluid, of 

 the consistence of a thick syrup. 



\Labat, Mutis. Wildenow. 



SECTION IX. 



Elastic Gum. Caoutchouc or Indian Rubber. 



Sipbonia Elastica. Linn. 



The caoutchouc, elastic gum, or Indian rubber, is obtained 

 chiefly from the siphonia, a genus that possesses but one known spe- 

 cies, the elastica, a tall tree, indigenous to Guiana, and other parts 

 of South America. It is possessed of the most singular properties : 

 no substance is yet known which is endued in so great a degree 



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