HISTORICAL SKETCH OF CHEMISTRY OF RUBBER 7 



for isoprene, CH 2 : C(CH 3 ) . CH : CH 2 . Two years later he 

 showed that isoprene can be obtained by the destructive dis- 

 tillation of turpentine, indicating the first possible process for 

 the commercial preparation of rubber. He noted that poly- 

 merisation took place most readily after a preliminary heating 

 which yielded an oily body, and suggested that the analogues 

 of isoprene, C 4 H 6 , C 6 Hi , etc., might be made to polymerise 

 to a series of rubber hydrocarbons. In 1887 Wallach showed 

 that isoprene changed to a rubber-like body under the action 

 of light alone, thereby anticipating Tilden's independent 

 discovery five years later. In a paper published in 1892 

 Tilden remarks : " I was surprised ... at finding the bottles 

 containing isoprene from turpentine entirely changed in appear- 

 ance. In place of a limpid, colourless liquid, the bottles con- 

 tained a dense syrup in which were floating several large masses 

 of solid, of a yellowish colour. Upon examination this turned 

 out to be indiarubber. . . . The artificial rubber unites with 

 sulphur in the same way as ordinary rubber, forming a tough 

 elastic compound." Tilden was thus the first to show that 

 synthetic rubber can be vulcanised like natural caoutchouc. 

 Tilden's and Bouchardat's work was confirmed by Weber in 

 1894, so that the scepticism expressed by Klages and Harries 

 as to the methods employed, and the identity of the product 

 obtained, is remarkable. 



The constitution of rubber has been considerably elucidated 

 by the extensive researches of Harries, dating from 1901 and 

 onwards . He had found that when unsaturated substances were 

 treated with ozone, a molecule of ozone added itself at each 

 double bond, yielding an ozonide, which, on treatment with 

 steam, split up into two fractions at the point of addition. In 

 this way he determined the constitution of oleic acid. From 

 rubber he obtained a body of the molecular weight indicated 

 by the formula C 10 H 16 O 6 . This was decomposed by steam 

 into laevulinic aldehyde, CH 3 . CO .CH 2 . CH 2 . CHO, laevulinic 

 acid, CH3.CO .CH 2 .CH 2 .COOH, and laevulinic aldehyde 

 superoxide, CH 3 .CO .CH 2 .CH 2 .CHO. Harries explained the 

 II II 



O— — — O 



action by the following structural formulae : 



