PRESIDENTIAL ADDRESS. 517 



towards the latex, led to tlio conclusion that ' coagulation * can take j)lace after 

 removal of the proteids, and that in all pi'obability it is the result of the 

 polymerisation of a liquid which is held in suspension in the latex and on 

 polymerisation changes into the solid colloid which we know as caoutchouc. 

 Weber, by experiments conducted in South America with fresh latex, arrived at 

 a similar conclusion, which later workers have confirmed. Although the nature 

 of the process is not yet completely elucidated, there is little room for doubt that 

 the coagulation is due to the ' condensation ' or polymerisation of a liquid con- 

 tained in the latex. For the chemist the important question remains as to 

 the nature of this liquid from which caoutchouc is formed. 



The chemical nature of caoutchouc is a subject which has attracted the atten- 

 tion of distinguished chemists from the middle of the eighteenth century, among 

 them being Faraday, Liebig, and DaUon. Faraday was the first to examine the 

 constituents of the latex of Jlevea brasiliensis. It is only in recent years that our 

 knowledge of the constitution of organic compounds, and especially of the 

 terpene group, has rendered it possible to make any great advance. It is 

 interesting to record that Greville Williams, in 1860, made most important con- 

 tributions to this subject. He identified a new hydrocarbon, isoprene, as a 

 decomposition product of caoutchouc, and recognised its polymeric relation to 

 caoutchouc. 



The results obtained from the analytical side, and especially the formation of 

 di-penteue and isoprene by pyrogenic decomposition of caoutchouc, had pointed to 

 the fact that caoutchouc was essentially a terpenoid polymer of the formula Ciyllig. 

 Harries finds, however, that the ozonide of caoutchouc, when distilled with steam, 

 breaks up into lajvulinic aldehyde, lajvulinic acid, and hydrogen peroxide, and 

 he concludes from this that caoutchouc is a polymer of an 1:5 dimethyl 

 cyclo octadiene. Whilst Harries' work has brought us much nearer the goal, and 

 has led to the discovery of a new method of investigation through the ozonides, 

 which is obviously of wide application, it cannot yet be said that the constitution 

 of caoutchouc has been settled or its relation to the parent liquid substance of the 

 latex definitely established. It has still to be shown how a closed-chain hydro- 

 carbon such as Harries' octadien can undergo polymerisation forming the colloid 

 caoutchouc. 



There are strong arguments for the view that the constitution of the parent 

 substance present in the latex is nearly related to that of isoprene. This remark- 

 able hydrocarbon of the formula CjHg, first obtained by Greville Williams from 

 the dry distillation of rubber, is an unsaturated olefenic hydrocarbon which is 

 found among the products, resulting from heating caoutchouc. It readily 

 polymerises forming di-pentene. Bouchardat noticed that this hydrocarbon 

 obtained from the pyrogenic decomposition of caoutchouc furnished a substance 

 identical with rubber when acted on by hydrochloric acid and under other 

 conditions. To AVallach and also to Tilden is due the further important observa- 

 tion that when isoprene prepared from oil of turpentine is kept for some time, it 

 gradually passes into a substance having all the characteristic properties of 

 caoutchouc. 



I have very briefly drawn attention to the present position of our knowledge of 

 the chemistry of caoutchouc in illustration of the interest which attaches to the 

 examination of vegetable products, and also because of the immense importance 

 of the problem from the practical and commercial standpoint. Chemistry in 

 this case holds the premier position in reference to this subject, and to a large 

 extent may be said to hold the key to the future of the rubber industry in all its 

 phases. The discovery of better methods of coagulation, preparation, and purifica- 

 tion will be efiected through chemical investigation, as will also the determination 

 of the manner of utilising the various other plants which furnish rubber-like 

 latices. That the physical properties of raw rubber, on which its technical value 

 depends, are to be correlated with the chemical composition of the material there 

 can be no doubt. The chemical analysis of raw rubber, as at present conducted, 

 is, however, not always to be taken by itself as a trustworthy criterion of quality, 

 and more refined processes of analysis are now needed. Although the finest 



