RUBBER 449 



bly, the increased flow when the second incision is made near the first is 

 because latex has flowed to the wound in order to repair it. 



Though Hevea seems to be in general the best rubber-producing tree, 

 there is a little doubt whether it should be everywhere introduced; for 

 instance, in Africa, where another species is native. African labor is 

 less intelligent than that in the Malay States and the African natives 

 can not tap the trees so successfully. The native trees and vines are 

 usually cut down. 



Moreover, experiments should be made with plantations of from 

 three to five thousand trees before a decisive judgment is given, for it is 

 possible that in large plantations diseases might rise and spread which 

 have not appeared in small plantations. In very large estates, protective 

 belts of other trees either of the original forest or of another genus of 

 planted rubber should be made use of to prevent spread of diseases. 



While, as stated above, in the Amazon valley five pounds of latex con- 

 taining approximately two pounds of caoutchouc is considered a large 

 yield, on the plantations trees ten years old are expected to yield three or 

 four pounds of rubber. During 1908 nine thousand trees in the Cicely 

 estate, one of the older Malay companies, gave an average of six pounds 

 per tree, though the trees were between five and ten years old. In the 

 Perah State there were eight trees seventeen years old, of an average 

 girth of 55 inches, which yielded 28£ pounds of rubber each. From the 

 economic point of view the yield per acre is of more importance than 

 the yield per tree. Six-year-old trees will yield about a hundred pounds 

 per acre, while ten-year-old trees will yield three or four times as much. 



In the East, rubber is coagulated from the latex by acetic acid. 

 Smaller quantities of other acids would serve the same purpose, but an 

 excess prevents coagulation, while with acetic acid the quantity may vary 

 within fairly wide limits. When coagulation is brought about by acetic 

 acid either pains must be taken to dry the rubber very thoroughly or 

 some antiseptic must be put in. The method of smoking carried out in 

 the Amazon district provides both acetic acid and the antiseptic 

 fumes of creosote. Coagulation could be brought about by simple drying, 

 but in this case the rubber is apt to become moldy and putrid. The 

 precise cause of coagulation by acid is not certain. It has been ascribed 

 to the small amount of protein in the latex, but, on the other hand, it is 

 claimed that if the protein is removed the rubber can still be coagulated. 

 The rubber produced has a composition something like the following: 

 94 per cent, caoutchouc, 3 per cent, resin, 2.5 per cent, protein, and 0.5 

 per cent, each of moisture and ash. One should perhaps add that what 

 is usually called protein may not really be that substance, but some other 

 which contains nitrogen. 



The competition between Amazon hard Para rubber, which is so far 

 the standard, and plantation rubber is keen. The latter is the purer, but 

 vol. lxxxv.— 31. 



