RUBBER MANUFACTURE. IOI 



intermixed with it, the coagulum forming a solid, white in 

 appearance, and quite distinct from the apparently homogeneous 

 mass of which it previously formed a part. 



In Mexico and Central America the latex of Castilloa is 

 boiled, and the rubber rises to the surface, resembling that 

 formed on animal milk when similarly treated. 



The collectors in the Amazon valley prepare rubber from 

 Para latex by submitting it to the smoke of burning Urucuri 

 palm nuts, which contains acetic acid and creosote. 



The West African natives prepare rubber from the latex of 

 Funtumia elastica by adding to it either the juices of various 

 plants having acid properties or salt water, and from the latex 

 of the Landolphia vines by smearing it over their naked bodies, 

 where the rubber is coagulated by the secretions from the skin, 

 or by treating it with lime juice. 



The principal acid coagulants employed on rubber planta- 

 tions are : acetic, sulphuric, hydrochloric, nitric, oxalic, citric, 

 and tartaric. Of these, sulphuric acid is the most powerful 

 coagulant, and citric acid is the weakest. 



The commonest alkaline coagulants are : mercuric chloride 

 (corrosive sublimate), sodium chloride (common salt), and alum. 



If an excess of either an acid or an alkaline solution be 

 applied to the latex no coagulation occurs, and the requisite 

 quantity of any coagulant varies in direct proportion to the 

 amount of pure latex present ; however much a given quantity 

 of latex may be diluted with water, the amount of the coagulant 

 required to bring about coagulation will remain constant. 



Quite recently Biffen discovered that the rubber in latex 

 could be separated from the other constituents by centrifugal 

 force. This process is quite distinct from coagulation, as by 

 centrifugal force the rubber globules are separated in a like 

 manner to cream when animal milk is churned, and their com- 

 position is not altered. 



" Rubber prepared by this method is reported to lack ' nerve,' 

 and there is a very remarkable difference in the vulcanisation 

 results obtained with coalesced and coagulated rubber respec- 

 tively. The difference is certainly not in favour of the coalesced 

 rubber " * 



* India-rubber Journal, 23rd June 1902. 



