45O COMPOUND PRODUCTS. CHAP. I. 



tion of the caoutchouc is owing to the absorption of 

 oxygene. 



Properties. Caoutchouc, when pure, is of a white colour, 

 without taste and without smell. The black colour 

 of the caoutchouc of commerce is owing to the 

 method of drying the different layers upon the 

 moulds on which they are spread. They are dried 

 by being exposed to smoke. The black colour of 

 the caoutchouc therefore is owing to the smoke or 

 soot alternating with its different layers. It is soft 

 and pliable like leather and extremely elastic, so 

 that it may be stretched to a very great length, and 

 still recover its former size. Its specific gravity is 

 0*9335. Mr. Gough of Manchester, has made some 

 curious and important experiments on the con- 

 nexion between the temperature of caoutchouc and 

 its elasticity, from which it results that ductility as 

 well as fluidity is owing to latent heat.* 



Caoutchouc is not altered by exposure to the air. 

 It is perfectly insoluble in water ; but if boiled in 

 water for some time its edges become so soft that 

 they will cement, if pressed and kept for a while 

 closely together. ) 



It is insoluble in alcohol, but soluble in ether.;}: 

 It is soluble also in volatile oils and in alkalies. 

 And from the action operated upon it by acids, it 

 is thought to be composed of carbon, hydrogene, 

 oxygene, and azote. 



* Manch. Trans, vol. vi. f Ann. de Cbim. vol. xi. p. 153. 



t Thomson's Chera. vol. iv. p. 337. Ibid. 





