250 REPORTS ON THE STATE OF SCIENCE. 



and the compound was evidently an additive one. On boiling with alco- 

 holic potash two molecules of HCl were split off and a compound obtained 

 having the formula C10H14S2. Analysis : — 



which was termed polyprene sulphide. It was identical in its properties 

 with perfectly vulcanised rubber. It was then found that a homogeneous 

 vulcanised compound could be obtained containing only 4-8 per cent, 

 sulphur, and to explain the constitution of this compound Weber was 

 forced to assume that the molecule of caoutchouc was at least CsoHgo- 

 The compound formed he supposed to have the composition — 



CsjHgo — S — S— CsuH^o 



\ / 



CI CI 



He further considered that the vulcanisation consisted in the addition 

 of sulphur chloride at the ethylenic linkings in the rubber molecule, and 

 that thus between the compound first obtained, which he now regarded as 

 CiooHi6oS;oCl2n) and the compound above described, CiooHiggSaClj, 

 there were eight other possible vulcanisation products. The various 

 degrees of vulcanisation of manufactured rubber would thus correspond 

 to the formation of one or other of these intermediate compounds. 



From observations made subsequently Weber came to the conclusion 

 that for the rubber molecule the formula C^oHg^ was well within the 

 range of possibility. 



In 1888' attempts were made to elucidate the constitution of 

 caoutchouc by Gladstone and Hibbert, in the first place from physical 

 considerations, afterwards by means of its halogen derivatives. 



These investigators observed the refraction and dispersion equivalents 

 of purified indiarubber in benzene solution, and on reviewing the results 

 obtained, came to the conclusion that for every C|oH,g molecule there are 

 three pairs of doubly-linked carbon atoms. Further, they endeavoured 

 to estimate the molecular weight of caoutchouc by Raoult's depression-of- 

 freezing-point method. The observed depression was so small, however, 

 that if the method holds good in this case the molecule must be at least 

 ^loooHieoo- 



Halogen Compounds of Caoutchouc. 



Gladstone and Hibbert also prepared a chlorine compound by passing 

 chlorine gas into a solution of indiarubber in chloroform. Hydrogen 

 chloride was given off during the process, indicating that some substitution 

 was taking place, and a compound was obtained which gave results on 

 analysis agreeing with the formula 0,oH|4Cl8, thus indicating a formula 

 CioHigClg for a purely additive compound. This result would seem to 

 support their view with regard to the presence of three double bonds in 

 the caoutchouc molecule. 



A brom compound, CioH,gBr4, was also prepared by the action of 

 bromide on a chloroform solution of caoutchouc, and also another brom- 



' Jov/rn. Ckem, Sue, 1888, p. 680. 



