37o 



rous. Methods of treatment depending on a knowledge of the 

 other constituents of the latex have led to the production of rubber 

 in a purer condition. Much still remains to be elucidated by che- 

 mical means as to the nature of the remarkable coagulation of the 

 latex. As is well known the latex is a watery fluid resembling milk 

 in appearance which contains the rubber, or as I think more pro- 

 bable the immediate precursor of rubber together with proteids and 

 other minor constituents. The constituent furnishing rubber is in 

 suspension and rises like cream when latex is at rest. On the 

 addition of an acid or sometimes of alkali or even on mere exposure 

 coagulation takes place, and the rubber separates as a solid, the 

 other constituents for the most part remaining dissolved in the 

 aqueous liquid or serum. The first view of the nature of the coagu- 

 lation process was that like the coagulation of milk by acids it is 

 dependent upon a process of proteid coagulation, the separated 

 proteids carrying down the rubber during precipitation. This 

 explanation cannot, however, be considered complete by the chemist 

 and there are peculiarities connected with the coagulation of the 

 latex which are opposed to the view that it is wholly explained by 

 the associated proteids. The experimental investigation of the 

 question on the chemical side is beset with many difficulties which 

 are increased if access cannot be had to fresh latex. A number 

 of experiments were made at the Imperial Institute with latex for- 

 warded from India. The difficulties contended with in preventing 

 coagulation during transit were great, but in the case of the latex 

 derived from certain plants there were to some extent surmounted 

 and the results obtained especially with reference to the behaviour 

 of certain solvents towards the latex led to the conclusion that 

 coagulation can take place after removal of the proteids and that 

 it is in all probability the result of the polymerization of a liquid 

 which is held in suspension in the latex and on polymerization 

 changes into the solid colloid which we know as Caoutchouc. 

 Although the nature of the process is not yet completely elucidated 

 there is little room for doubt that the coagulation is due to the 

 polymerization of a liquid and probably of a liquid hydrocarbon 

 contained in the latex. 



The chemical nature of Caoutchouc is a subject which has 

 attracted the attention of distinguished chemists from the middle of 

 the 1 8th century, among them being FARADAY, LiEBIG and DALTON. 

 Faraday was the first to examine the constituents of the latex of 

 Hevea braziliensis. It is only in recent years that our knowledge 

 of the constitution of organic compounds and especially of the ter- 

 pene group, has rendered it possible to make any great advance. 

 It is interesting to record that GREVILLE WILLIAMS in i860 made 

 the most important contributions to this subject. He identified a 

 new hydrocarbon isoprene as a decomposition product of Caout- 

 chouc and recognised its polymeric relation to Caoutchouc. 



There are strong arguments for 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 



