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On some Properties peculiar to Caoutchouc, and their 

 Applications. By Mr Brockedon.* 



Caoutchouc is a vegetable constituent, the produce of se- 

 Teral trees ; the most prolific in this substance are, Siphonia 

 Caoutchouc^ Urceola elastica, Ficus elastica, §fc» ; of these 

 the Siphonia Caoutchouc extends over a vast district in Cen- 

 tral America, and the caoutchouc obtained from this tree is 

 Ijest adapted for its manufactures. Over more than 10,000 

 square miles in Assam the Ficus elastica is abundant. The 

 Urceola elastica (which produces the Gin ta wan of the Malays,) 

 abounds in the islands of the Indian Archipelago. It is de- 

 iScribed as a creeper of growth so rapid, that in five years it 

 extends 200 feet, and is from 20 to 30 inches in girth. This 

 tree can, without being injured, yield by tapping, from 50 to 

 60 lb. of caoutchouc in one season. A curious contrast is 

 exhibited in the tardy growth of the tree from which the 

 Gutta Percha is obtained. This tree does not come to its 

 prime in less than from 80 to 120 years. The produce can- 

 not be obtained but by the sacrifice of the tree. It is found 

 in a concrete state between the bark and the wood after the 

 tree has been cut down, and it is in this condition that, hav- 

 ing been scraped out, it is sent to our market. 



When coagulated by evaporation or agitation, caoutchouc 

 separates from the aqueous portion of the sap of the trees 

 which yield it. This solid and fluid cannot afterwards be 

 reunited, any more than butter is capable of mixing with the 

 milk from which it is separated. Caoutchouc is a hydro- 

 carbon. This chemical character belongs to all varieties of 

 the substance, and many other vegetable constituents, though 

 they differ materially in physical qualities. Some specimens 

 are harder than Gutta Percha itself, while others never solid- 

 ify but remain in the condition of bird-lime or treacle. 



The process termed the vulcanizing of caoutchouc was dis- 

 covered by Mr Thomas Hancock in 1843. — A sheet of caout- 

 chouc immersed in melted sulphur absorbs a poHion of it, 

 and at the same time it undergoes some important changes 



* Abstract of a Communication read to the Royal Institution, March 21, 1851. 



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