174 On pure Caoutchouc. [1826. 



decomposition of oil, fat, and other substances by heat, and 

 have more command of the process, that this substance, among 

 others, may furnish the fuel for a lamp, which remaining a 

 fluid at the pressure of two or three atmospheres, but be- 

 coming a vapour at less pressure, shall possess all the advan- 

 tages of a gas lamp, without involving the necessity of high 

 pressure. 



Royal Institution, June 7, 1835. 



On Pure Caoutchouc, and the Substances by which it is accom- 

 panied in the State of Sap or Juice*. 



I HAVE had an opportunity lately, through the kindness of Mr. 

 Thomas Hancock, of examining the chemical properties of 

 caoutchouc in its pure form, as well as of ascertaining the 

 nature and proportions of the other substances with which it is 

 mixed, when it exudes as sap or juice from the tree. At 

 present much importance attaches to this substance, in con- 

 sequence of its many peculiar and excellent qualities, and its 

 increasing applications to useful purposes. I have thought, 

 therefore, that a correct account of its chemical nature would 

 possess some interest. 



The extensive uses, both domestic and scientific, to which 

 Mr. Hancock has applied common caoutchouc, in consequence 

 of his peculiar mode of liquefying it, are well known. Hence 

 he was fully alive to the importance of its applications, when in 

 its original state of division. When he gave me the substance, 

 he communicated many of his observations upon it, which, with 

 others of my own, form the present paper. 



The fluid, I understood, had been obtained from the southern 

 part of Mexico, and was very nearly in the state in which it 

 came from the tree ; it had been altered simply by the formation 

 of a slight film of solid caoutchouc on the surface of the cork 

 which closed the bottle. The caoutchouc thus removed was 

 not a 500th part of the whole. The fluid was a pale yellow, 

 thick, creamy-looking substance, of uniform consistency. It 

 had a disagreeable acescent odour, something resembling that 



* Quarterly Journal of Science, xxi. 19. , 



