410 



FOREST PRODUCTS 



system. Daily incisions are made at 45° until the trunk is nearly covered 

 with scars. When the bark of the trunk is almost completely covered 

 with cuts to induce the flow of latex, a period of years is generally allowed 

 to elapse before beginning to retap the tree. Small sharp knives are 

 employed in making the incisions instead of the axes or large cutters 

 used in Brazil. 



Instead of the primitive and wasteful method of reducing the latex 

 to crude rubber, as followed in the forests of Brazil, the fluid is collected 

 in large tanks or casks. It is coagulated by the admixture of an acid, 

 usually acetic acid or lime juice. The coagulation gradually separates 

 as a soft, white, or yellowish mass. This is washed by first passing 

 through washing machines, and then through other machines, which 

 compress it in thin sheets or long ribbons called cr6pe. These are hung 

 up and dried. Plantation rubber enters the market either in the form of 

 crepe in sheets or biscuits or in the form of large blocks made by com- 

 pressing the sheets of crepe together. 



Plantation rubber formerly did not bring the same prices on the 

 English and American markets as that commanded by the Para or " wild " 

 rubber, but it now brings about the same or even slightly better price. 

 It is much cleaner and freer from impurities than the wild rubber and 

 contains only i per cent of water as against 15 per cent for the latter. 

 It is generally regarded, however, that plantation rubber has not the 

 tensile strength of the Para rubber. This may be due to the fact that the 

 plantation rubber is generally procured from much younger trees. 



The following table shows the relative importance of plantation 

 rubber and the product of native forests of Brazil and other portions of 

 the tropics: 



PRODUCTION OF RUBBER FROM PLANTATION AND N.'VTIVE SOURCES IN 

 TONS FROM 1911 TO 1918, INCLUSIVE 



