84 SYNTHETIC RUBBER 



products such as the tetrabromide CioHieBii. Many 

 attempts have been made to devise a constitutional 

 formula for the CioHie group in caoutchouc which shall 

 agree with all the known facts regarding its chemical 

 behaviour and its close relation to isoprene and the ter- 

 penes. Harries, as the result of his work on the ozonide 

 which he obtained from caoutchouc, has suggested that 

 the C10H16 group in caoutchouc is a derivative of an 

 eight-carbon ring compound, viz. dimethylcyc^ooctadiene. 

 Other suggestions regarding the constitution of caoutchouc 

 have been based on the fact that isoprene and the aUied 

 hydrocarbons containing two conjugated double Imkages 

 readily polymerise with the formation of rubber-like sub- 

 stances. This change may, however, take place in several 

 different ways, and it is therefore impossible to draw 

 definite conclusions as to the constitution of the resultmg 

 product. 



The constitution of caoutchouc, therefore, remains an 

 open question at the present time, though much informa- 

 tion which will be of value in determinmg the matter 

 is being gradually accumulated. 



Synthetic Rubber. — The possibility of manufacturing 

 rubber synthetically by chemical means has attracted 

 much attention during the last few years, but it will only 

 be possible here to give a very brief statement regarding 

 the present position of the problem. In the first place 

 it may be pointed out that what is called " synthetic 

 rubber " is actually rubber, identical with or closely 

 resembling natural caoutchouc in composition, physical 

 properties, and behaviour, but produced chemically, and 

 that it must not be confused with the group of products 

 known as " rubber substitutes." 



The preparation of rubber synthetically on a com- 

 mercial scale has been a possibility, or even a probability, 

 since it was first recorded by Bourchardat and Tilden, in 

 1879 and 1882 respectively, that the hydrocarbon iso- 

 prene, C5H8. polymerises under certam conditions to 

 form a rubber-like substance. Tilden in particular 

 showed that the product thus obtained behaved exactly 

 like natural rubber and could be vulcanised. These 

 discoveries were the starting-point of the subsequent 

 attempts to prepare synthetic rubber, and the early 

 work in connection with the subject was devoted to 



