229 



THE CULTURE OF THE CENTRAL AMERICAN 



RUBBER TREE, XIII.* 



{Continued from Bulletin for August.) 



By O. F. Cook, Botanist in charge of Investigations in Tropical 

 Agriculture, U. S. Department of Agriculture. 

 OTHER METHODS OF COAGULATION. 



The traditional method of treating Para rubber in Brazil is to 

 spread it in thin layers on wooden paddles, which are held over 

 burning palm nuts. The highest grades of commercial rubber 

 have been produced in this way, but the process is too slow, 

 laborious, and disagreable. There seems, however, to be ground 

 for a suspicion that some constituent of the smoke, which is 

 incorporated into the rubber, may have a beneficial effect upon 

 its mechanical properties and the previously cited adverse opinion 

 upon the pure but unsmoked Hevea rubber from the East Indies 

 seems to give further warrant for such a notion. The experiment of 

 smoking Castilloa rubber has been tried at La Zacualpa, but the 

 result was a hopelessly sticky mass. The difference of behaviour 

 is, however, more likely to be due to differences in the latex rather 

 than to differences in the rubber itself. 



It is not to be overlooked that, while the high percentage of 



albuminous impurities in Castilloa rubber has rendered the price 



lower and the removal of them should increase the price, yet it 



will reduce the quantity of the marketable product and will thus 



not be an unmixed advantage. All the methods of coagulation 



now in use bring about the incorporation with the rubber of a large 



amount of the albuminous substances of the latex. Dr. Weber 



claims that if none of the albumens are left out they will constitute 



over 25 per cent, of the solid product and adds : 



The native rubber collectors prepare the rubber from the latex in such away that 

 at least part of the aqueous vehicle of the latex is drained .away before coagulation 

 takes place, and consequently we never find a Central American rubber (crude) 

 which contains as much as the above-stated quantity (25 [ler cent, of albuminous 

 matter), but lots containing from 9 to 13 per cent are quite common. 



The meaning of this sentence is not obvious, and it becomes still 

 less so if we. read it in connection with one which follows a little 

 later. 



Therefore, whenever we coagulate the rubber, we can only do so by coagulating 

 it in conjunction with the albumen present, and we have at once a product possess- 

 ing all the inemediable drawbacks which above we discussed at some length. 



None of the native methods of coagulation enumerated by Dr. 

 Weber shows any provisionfor eliminating anypart of the albumen. 

 There is certainly nothing of this kind in connection with scrap 

 rubber, into which all the solid constituents of the milk are simply 

 dried down and little escapes except by evaporation, and yet scrap 

 rubber is commonly deemed of good quality. In coagulation by 

 the acid or alkaline juices of plants or by soap, salt, or alum, or by 

 the boiling of the juice, the only materials which escape are those 



* Extract from the U. S. Department of Agriculture, Bull. No. 49. Bureau of Plant 

 Industry. 



