SECT. XIX. CAOUTCHOUC. 44Q 



to most people in this country by the name of 

 Indian rubber. 



It is obtained chiefly from Hcevea Caoutchouc 

 and Jatropha elastic a, trees indigenous to South 

 America ; but it has been obtained also from several 

 trees which grow in the East Indies, such as Ficus 

 indica, Artocarpus integrlfolla and Urceola elastica. 



If an incision is made into the bark of any of 

 these plants a milky juice exudes which, when it 

 is exposed to the air, concretes and forms caout- 

 chouc. As the object of the natives in collecting 

 it had been originally to form it into vessels for their 

 own use, it is generally made to concrete in the 

 form of bags or bottles. This is done by applying 

 the juice when fluid in thin layers to a mould of 

 dried clay, and then leaving it to concrete in the 

 sun or by the fire. A second layer is added to the 

 first, and others in succession, till the vessel acquires 

 the thickness that is wanted. The mould is then 

 broken and the vessel fit for use, and in this state it 

 is generally brought into Europe. It has been 

 brought, however, even in its milky state by being 

 confined from the action of the air.* 



If the milky juice is exposed to the air, an elastic 

 pellicle is formed on the surface. If it is confined 

 in a vessel containing oxygene gas, the pellicle is 

 formed sooner. If oxymuriatic acid is poured into 

 the milky juice, the caoutchouc precipitates imme- 

 diately. This renders it probable that the forma- 

 * Connais. Chim. vol. viii. p, 37. 



VOL. i. 2 G 



