PARA-RUBBER CULTIVATION 609 



difference in analysis, the slight increase in protein and resin 

 being too little to account for the great difference in physical 

 properties. Thus the gross chemical composition, as revealed 

 by the ordinary methods of analysis, is no criterion as to the 

 physical properties of caoutchouc. There may be many varieties 

 of this substance, differing in elasticity and strength, but 

 identical as far as their chemistry can be pushed. 



Synthetic Rubber 



The possibility of the production of a commercial synthetic 

 caoutchouc to compete with the natural article has at times 

 perturbed the rubber-planter. A few years ago the forthcoming 

 of an artificially prepared product looked more hopeful than it 

 does now. In the first place a distinction must be drawn 

 between a laboratory prepared and a commercial synthetic 

 rubber. The former has been an accomplished fact 1 for a 

 number of years, and credit is due to Prof. Tilden 2 for 

 his work in this direction ; no one since apparently has 

 advanced further than he did. A synthesis of caoutchouc 

 occurred in his laboratory by accident. Engaged at one time 

 in researches on the terpene series of hydrocarbons, he noticed 

 that some liquid isoprene which had been laid aside in bottles 

 for several years had formed clots of solid substance which 

 had the composition and properties of india-rubber. He set 

 to work to investigate the matter and found that isoprene 

 could be changed into caoutchouc in two ways : either by very 

 slow polymerisation in the presence of a trace of acid, such as 

 had occurred in his laboratory by chance, or by bringing 

 isoprene into contact with strong aqueous or moist gaseous 

 hydrochloric acid. The first method is not a practical one on 

 account of the long period required, and the second could not 

 be made a commercial success, as the caoutchouc is merely a 

 small by-product in the formation of isoprene hydrochloride ; 

 and further the yield of isoprene from turpentine — the starting 

 point of the synthesis — does not probably exceed ten per cent, 

 under favourable conditions. Tilden confesses that after two 

 years' experimentation he had to reluctantly abandon the sub- 



1 Bouchardat as far back as 1878 had noticed that a tough elastic solid, 

 resembling india-rubber, was produced by the action of strong acids on isoprene. 

 {Compt. Rend. 1878, 87, 654, and 89, 361 and 11 17.) 



2 Tilden, Proc. Birmingham Phil. Soc. 1892, 8, 182 ; Report Brit. Association 

 [York], 1906, 525 ; India-Rubber Journal, 1908, 38, 321. 



39 



