THE CHEMISTRY OF INDIARUBBER 505 



the results of disruption caused by the somewhat drastic 

 conditions to which the rubber molecules are subjected in the 

 process of distillation at atmospheric pressure. 



From a comparison of the above distillation products we can 

 also form the following conclusions : 



(1) That the caoutchouc is in some way connected with the 

 terpenes, and any constitutional formula advanced should be 

 capable of explaining the transition of rubber into such com- 

 pounds as isoprene and dipentene. 



(2) That in the indiarubber molecule we have at least five 

 carbon atoms arranged in the order — 



CH 3 - C - C - C 



since this arrangement is found in all the known distillation 

 products. 



Derivatives of Caoutchouc 



Probably the first chemical derivatives of indiarubber 

 obtained were the vulcanisation compounds. Goodyear 1 in the 

 year 1839 seems to have been the first to apply the process 

 of heating rubber with sulphur. He found that after such 

 treatment the indiarubber lost its stickiness and maintained its 

 elasticity between wider ranges of temperature. For many 

 years, however, the chemistry of vulcanisation was but im- 

 perfectly understood ; the sulphur was generally said to be 

 " absorbed," whilst some workers regarded the process as one 

 of substitution, the sulphur replacing the hydrogen atoms of the 

 indiarubber "resin." 2 C. O. Weber 3 pointed out that this 

 hypothesis was improbable as only a comparatively small 

 quantity of sulphuretted hydrogen is liberated during the 

 vulcanising process. He further demonstrated that the process 

 is much more probably one of addition than of substitution, 

 the sulphur attaching itself at the double bonds or ethylenic 

 linkings in the molecule. 



Using sulphur chloride as a vulcanising agent, he prepared 

 an interesting series of compounds, the composition of which 

 supports the "additive" theory. Thus a completely vulcanised 



1 Chemistry of Indiarubber (Weber), 1902, p. 41. 

 • Thorpe's Dictionary of Applied Chemistry, vol. ii. p. 312. 



3 Chemistry of Indiarubber (Weber), 1902, p. 47 ; Journ. Soc. Chem. Ind. 1894 

 p. II. 



