510 SCIENCE PROGRESS 



It will be noticed that the above formula is spoken of as 

 representing the " chemical " molecule of caoutchouc. The real 

 molecule of Para rubber, or, as Harries terms it, the " physical " 

 molecule, must still be expressed (C 10 H 16 ) X , and be regarded as a 

 sort of polymer of the chemical molecule. The polymerisation 

 must, however, take place through very simple or loose 

 additions, as the polymer is easily resolvable under the influence 

 of such agents as ozone into single Ci H 16 "chemical" molecules. 



Harries also indicates how a molecule, represented by the i : 5 

 dimethyl-cyclo-octadiene formula, might easily break down into 

 isoprene, or become converted into dipentene or di-isoprene, 

 the known products of the distillation of rubber : 



(1) CH 3 - C - CH, - CH, - CH CH 3 - C - CH 2 - CH, - CH 



Hi 11 -> 11 



CH - ICH, - CHH - C - CH, CH 2 



CH, = CH - C-CH 3 



Di-isoprene. 



(2) CH 3 - C - CH 2 - 



II 

 CH - CH 2 - 



CH, - CH CH 3 \ 



|| -> },C - CH = CH 2 



CH 2 - C - CH 3 CH,,// 



Isoprene (2 molecules). 



CH 3 . /CH.-CH. 



\C - CH N )C - CH 3 



CH// \CH 2 - CH./ 



Dipentene. 



This formula for the chemical molecule of Para rubber is also 

 in agreement with the observed facts (i) that for every complex 

 Ci H 16 there are two unsaturated linkings ; (2) caoutchouc is an 

 optically inactive hydrocarbon. It will be seen that the formula 

 proposed does not contain an asymmetric carbon atom. 



It might reasonably be expected that some of the depoly- 

 merised rubber molecules having the above structure would 

 be found in the distillation products, and Harries considers it 

 probable that such molecules are contained in the fraction 

 boiling between 160 and 170 C, especially as this fraction gives 

 an ozonide similar to the caoutchouc ozonide. 



Referring to the formation of rubber in the plant, isoprene 

 has been suggested as a possible starting point in the process 

 of polymerisation. Prof. Harries considers that this is not the 

 case, but that another hydrocarbon, pentadiene, 



CH 3 - C - CH 2 - CH 2 - CH 



