THE ASSAM RUBBER TREE 231 



cuts are arranged in vertical rows, G in. apart, and a cup 

 is fixed at the base of each row. In trials of this method 

 during the dry season (November to March) it was found 

 that two-thirds of the total yield of rubber was obtained 

 from the latex collected in the cups, whilst the remainder 

 coagulated on the stem. 



In Java the latex of Ficus elastim quickly coagulates 

 spontaneously on the stems, and until recently the whole 

 of the rubber was collected in the form of scrap which 

 was made into balls. In 1911, however, machinery was 

 introduced for treating the scrap rubber, and some of 

 it is now prepared in the form of crepe or block. 



In the Malay Penmsula the latex of Ficus elastica usually 

 flows much more freely than in Assam and Burma and 

 can be easily collected in bulk. A number of different 

 methods of tapping have been tried, including herringbone 

 incisions, V incisions, and vertical incisions, as well as 

 several pricking systems. A method of making the 

 incisions which has been recommended is to cut shallow 

 grooves in the bark in the first instance and then to liberate 

 the latex by means of a sharp thm-bladed knife or by a 

 pricker. 



Coagulation of the Latex. — It is a curious fact that 

 when the latex of Ficus elastica flows sufficiently freely 

 to be collected in bulk it does not readily coagulate, 

 whereas in other cases it coagulates so quickly on ex- 

 posiu-e to the air that the rubber can only be obtained 

 in the form of scrap. 



The latex is not affected by the addition of acetic acid, 

 and methods of chiurning which have been suggested are 

 not very successful. It can, however, be coagulated by 

 boiling, but this method is not very satisfactory, as the 

 rubber only separates slowly, and the heating must con- 

 sequently be continued for a long time. Biu-gess re- 

 commends the use of tannic acid as the best coagulant 

 for Ficus elastica latex, and has proposed the following 

 process. The latex, which should not be diluted with 

 water, is warmed to 40° C, and a solution of tannic acid 

 of known strength is then added until there is 1 per cent, 

 of tannic acid in the latex. Thus, using a 20 per cent, 

 solution of tannic acid, one part of the solution would 

 be added to nineteen parts of latex. The latex is then 

 gently churned, avoiding violent agitation, and in one or 



