ON THE PRESENT POSITION OF THE CHEMISTRY OF RUBBER. 249 



must be assumed in the rubber molecule, as it occurs in all the examined 

 decomposition products. 



(3) Isoprene and dipentene do not occur in the rubber molecule as 

 such, but are produced by the disruption of a larger or more physically 

 complex molecule at a high temperature, for, as Fisher and Harries have 

 shown, if the distillation is conducted at as low a temperature as possible 

 these compounds are not produced in any considerable quantity. 



We will now pass on to a consideration of the compounds which have 

 been obtained by the direct action of various reagents on the caoutchouc 

 itself. 



Direct Derivatives of Caoutchouc. 



Comparatively speaking, very little work had been done until quite 

 recently in the direction of obtaining direct derivatives of indiarubber 

 which could be regarded as definite compounds, or throw any light on the 

 constitution of the molecule. 



Vulcanisation Comjwunds. 



In 1839 Goodyear first definitely established the fact that indiarubber 

 on treatment with sulphur at high temperatures became vulcanised ; that 

 after such treatment it maintained its elastic properties between wide 

 ranges of temperature. He also discovered ebonite, the final product of 

 the action of sulphur on rubber. Subsequently Hancock discovered the 

 process independently in England, and since that time many investigators 

 have been engaged in work on vulcanisation both with sulphur and with 

 sulphur chloride. For many years, however, no definite compounds were 

 described ; nor, in fact, does anything definite with regard to the true 

 nature of the process seem to have been known. In most cases sulphur 

 was simply said to be absorbed. 



Burghardt^ regarded vulcanisation as consisting in the replacement of 

 the hydrogen of the caoutchouc ' resin ' by sulphur, but no experimental 

 evidence was brought forward of such being the case. Weber pointed 

 out that the small amount of sulphuretted hydrogen liberated during 

 the process of vulcanisation was not reconcilable with a process of 

 substitution. 



In 1894 2 C. O. Weber prepared from indiarubber, by vulcanisation 

 with sulphur chloride, a yellowish white compound, CkjHkjSoCL-, in the 

 form of friable flakes or of horny granules. This was insoluble in all 

 organic solvents in the cold, but dissolved with decomposition in hot 

 solutions of aromatic hydrocarbons and terpenes. On analysis it gave 



Weber termed the compound polyprene sulpho- chloride. No sul- 

 phuretted hydrogen or hydrogen chloride was evolved during the formation, 



' Chemistry of Indiarubber (Weber), 1902, p. 47 ; Thorpe's Liet. Api)d. Chcm. 

 vol. ii. 312. ' " Ibid,., p. 97 ; also J. S. C. I., 1894. p. 11. 



