CHAPTER VI 



THE PREPARATION OF RUBBER 



Coagulation of the Latex. — In order to obtain rubber from 

 latex, it is necessary to induce the change known as 

 coagulation. When coagulation takes place, the caout- 

 chouc globules present in the latex coalesce to form a 

 white clot of soft porous rubber which separates from 

 the Uquid and rises to the surface, leaving the serum 

 perfectly clear if the process is complete. In the case 

 of some latices an intermediate stage can be obtamed in 

 which the rubber globules separate from the liquid without 

 coalescing, and rise to the surface as a " cream," which 

 can be agaui diffused through the liquid on shaking. 

 This behaviour, which is termed " creaming," is, however, 

 not general, and is only sJiown by certain latices, such 

 as that of Castilloa elastica. If the creamed globules 

 are separated from the liquid and submitted to pressure 

 or allowed to dry, they coalesce to form a mass of rubber 

 similar to that obtained by direct coagulation. 



The exact nature of the change which takes place during 

 the coagulation process is not fully understood, but the 

 most reasonable hypothesis appears to be that some alter- 

 ation occurs m the substance composmg the globules of 

 the latex. It seems probable that the globules do not 

 consist of solid particles of rubber, but of a liquid sub- 

 stance, and that when coagulation occurs this liquid 

 undergoes polymerisation or condensation with the produc- 

 tion of solid rubber (see Dunstan, Bull. Imp. Inst., iv. 323). 



A careful study of the physical changes which take 

 place during the coagulation of latex has been made by 

 Victor Henri, who has obtained very interesting results. 

 He has found, for example, that when acetic acid is added 

 to Para latex in insufficient amount to produce coagula- 

 tion, the Brownian movement of the globules is almost 



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