36 



especially with reference to thebehaviourof certain solventstowards 

 the latex, led to the conclusion that ' coagulation' can take place 

 alter removal of the proteids, and that in all probability 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 poly- 

 merisation of a liquid contained 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 attention of distinguished chemists from the middle 

 of the eighteenth century, among them being Faraday, Liebig, and 

 Dalton. Faraday was the first to examine the constituents of the 

 latex of Hevea 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 

 i860, made most important contributions to this subject. He 

 identified a new hydrocarbon, isoprene, as a decomposition product 

 of caoutchouc, and recognised its polymeric relation to caout- 

 chouc 



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. 



To Wallach and also to Tilden is due the further important 

 observation 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 purification will be effected 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 caoutchouc for technical purposes is only yielded by 

 some half-dozen plants, under whose names these varieties of 



