594 SCIENCE PROGRESS 



he accompanied as scientific adviser a small rubber-exploiting 

 expedition to tropical America, and when there experimented 

 on various latices with a cream separator. He found that the 

 machine answered admirably for Castilloa and claimed also that 

 he effected the separation of the caoutchouc of Hevea latex 

 by this means. The advantage of the centrifugal method lies 

 in the fact that the rubber can be extracted from the latex 

 in a state of great purity. 



The success of the centrifugal separator in the case of 

 Castilloa has been repeatedly confirmed. This latex, indeed, 

 creams readily on standing and good rubber can be prepared 

 in this way. With Hevea, however, confirmation has not been 

 forthcoming. No one in the East, as yet, has been able to 

 effect the separation of the caoutchouc globules of this latex 

 by centrifugal force, even with a speed of 11,000 revolutions 

 per minute. This latex, further, never shows the least sign of 

 creaming. It remains homogeneous as long as the slightest 

 acidity is prevented from arising. The difference in the be- 

 haviour of the two latices is probably due to the size of the 

 caoutchouc globules. These are most likely much larger in 

 Castilloa latex than in that of Hevea. 



Biffen's ingenious application appeared most promising 

 twelve years ago as a handy means of preparing first-class 

 commercial rubber. Since it has been proved to be impractic- 

 able with the latex of cultivated Para rubber trees in the East, 

 it is now of minor importance. 



Centrifugally separated caoutchouc is no doubt the purest, 

 as it is practically free from albuminous matter (protein) which 

 forms a small percentage of all other raw rubbers. Recent 

 investigation 1 suggests, however, that the small quantity of 

 cured protein contained in Para rubber is not without an 

 advantageous influence. The texture of the raw rubber appears 

 to depend to a large extent on the manner of coagulation — 

 a phenomenon depending upon the protein present. 



Coagulation 



To Biffen 2 is also due the first adequate explanation of the 

 nature of latex-coagulation. His view has been challenged 



1 Spence, D., Quart. Journ. Liverpool Instit. Commercial Research, 1908, 



3,47. 



2 Biffen, loc cit. p. 170. 



