70 THE PREPARATION OF RUBBER 



completely arrested so as to be hardly perceptible. If 

 more acid be added, the globules commence to unite and 

 form files of greater or less length, which then join up to 

 produce a fine network of rubber. The particular form 

 which this network assumes varies with the coagulant used, 

 and in Henri's opinion the strength of the rubber is largely 

 influenced by the structure of the clot and hence by the 

 method of coagulation employed. A number of investi- 

 gators have published results which support the view 

 that the method of preparation has considerable effect on 

 the strength of the rubber ; but it seems impossible that 

 the physical properties of the vulcanised product can 

 depend on the structure of the crude rubber, as this 

 must be entii-ely destroyed in the mixing which precedes 

 vulcanisation. 



Methods of Coagulation. — Coagulation can be brought 

 about in very many ways, which, however, are not all 

 of universal application. A method which will readily 

 coagulate the latex from one plant may have no effect 

 whatever upon that from another, so that the process 

 employed must always be adapted to the particular latex 

 which is being treated. 



The principal methods of inducing coagulation, which 

 are of practical importance, are given in the following 

 account : 



(1) Spontaneoibs Coagulation. — Some latices undergo 

 spontaneous coagulation on exposure to the air for longer 

 or shorter periods. The latex of many Landolphia vines, 

 and frequently that of the Ceara tree, does not flow freely 

 from the incisions and coagulation quickly occurs upon 

 the stem, films of rubber being formed which are subse- 

 quently stripped off and made either into balls or loose 

 " scrap." 



Other latices which flow more freely from the plant so 

 that they can be collected in bulk also coagulate spon- 

 taneously more or less completely on standing. Natives 

 frequently pour latex into holes in the ground, or into a 

 hollow tree, or into vessels, and leave it to stand until 

 coagulation takes place. In those cases, however, in 

 which the coagulation does not occur rapidly the protein 

 constituents of the latex are liable to undergo decom- 

 position, with the result that the rubber acquires a very 

 disagreeable odom-. 



