THE CHEMISTRY OF INDIARUBBER 4 97 



and Apocynacece. The caoutchouc is suspended in the latex in 

 the form of minute transparent globules averaging about ia gao in. 

 in diameter, much in the same way as the oily particles are 

 suspended in milk. On coagulation of the latex, which can 

 be brought about by heating or by treating with certain 

 chemicals, a clot or coagulum is formed, which consists chiefly 

 of caoutchouc, always mixed, however, with varying quantities 

 of resinous and albuminous impurities. 



Chemically, caoutchouc is a hydrocarbon of the empirical 

 formula C 5 H 8 . Its molecule is, however, much larger than such 

 a formula would indicate, and in the absence of accurate data 

 we are compelled to make use of the rather vague representa- 

 tion, (C 5 H 6 ) n or (C 10 H 16 ) n . It is an unsaturated hydrocarbon, 

 containing one double bond or unsaturated linking for every 

 complex C 5 H 8 . When pure, caoutchouc is an almost colourless 

 elastic substance, transparent in thin sheets, and it has a 

 specific gravity varying, in different samples, between '91 

 and '93. 



It is insoluble in many of the usual solvents, but in chloro- 

 form, benzene, and several other organic liquids it dissolves in 

 a rather remarkable manner. Up to a certain point it swells up 

 and seems to absorb the solvent, then it goes gradually into 

 solution ; but even moderately dilute solutions are quite gelati- 

 nous in character. Indiarubber thus behaves as a colloid, and 

 it is principally this fact that makes its investigation a matter 

 of such great difficulty. The known methods for ascertaining 

 the molecular weights of compounds are useless in the case 

 of caoutchouc. The difficulty of the problem is also increased 

 by the fact that it is impossible to distil indiarubber, or, in fact, 

 to heat it to much above ioo° C, without effecting a decomposition 

 of the molecule. Further, the substance is a hydrocarbon, and 

 the absence of reactive radicles such as hydroxyl or carboxyl 

 groups precludes the possibility of obtaining a number of 

 derivatives which might otherwise have been useful for purposes 

 of characterisation. 



On heating caoutchouc to temperatures above ioo° C. it begins 

 to get viscous and sticky, and on cooling it does not again 

 recover its elastic properties. If the heating is continued in a 

 distilling flask, the whole mass becomes liquid, and eventually 

 a very pungent-smelling distillate collects in the receiver. That 

 the process is not one of simple distillation, but rather of 



