37 ° 
rous. Methods of treatment depending or. a knowledge of the 
other constituents of the latex have led to the t .eduction 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 fhe 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 18th 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 
0 f the constitution of organic compounds and especially of the ter- 
nene group, ha? *-■*' lered it possible to make any great advance. 
It is interesting ~ ~ord 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 
• nn L P . To Wallach and also to Tilden is due the 
