METHODS OF COAGULATION. 73 



None of the native methods of coagulation enumerated by Dr. Weber 

 shows any provision for eliminating any part 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 }^et scrap rubber is 

 commonly deemed of good qualit} r . 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 which do not 

 coagulate, so that it is difficult to avoid the inference that the percent- 

 age of albuminous matter is not constant or that it has been incorrectly 

 determined. 



At La Zacualpa was witnessed still another method of coagulation 

 by which all the nonvolatile constituents of the latex are retained. 

 The latex is spread in a thin coating upon the large banana-like leaves 

 of a species of Calathsea, laid out on the hot bare ground in the open 

 sun. This exposure to heat, light, and air turns the milk dark with 

 great rapidity, and in a few minutes it has become firm enough to 

 permit a second layer to be spread on. Subsequently two of the leaves 

 have their rubber-covered faces pressed together by being trodden 

 upon, and the rubber adheres to form a single leaf -like sheet from 

 which the leaves themselves are easily stripped away. Three stages 

 of the process and the finished product are illustrated in Plate XVII. 



COAGULATION OF SCRAP RUBBER. 



Whether due to a varietal difference in the trees or to climatic or 

 other differences of the external conditions, it seems to be a general 

 fact that on the more continuously humid eastern slope of Central 

 America the milk of Castilla does not run from the trees in quantities 

 which can be collected and treated by improved methods of coagula- 

 tion, but hardens in the cuts made by the rubber gatherer, who does 

 not carry home the milk but returns in a day or two to pull out the 

 dried "scraps," as rubber obtained in this way is called in the trade. 

 As both the quality and the price of scrap rubber are satisfactory, the 

 chief objection to this method of harvesting is the greater number 

 of cuts in the tree and the greater amount of labor necessary to collect 

 it, though the latter objection is somewhat counterbalanced by avoid- 

 ing the work of coagulation. The principal point is the amount 

 obtainable, and this depends upon the question of climates and varieties 

 rather than upon that of coagulation. According to Professor H. 

 Pittier, 6 pounds of scrap rubber are sometimes taken from a single 

 wild tree in Costa Pica; but while this amount is considerable it is 

 much less than that claimed by Koschny for the same country. 



