60 AMOUNT OF RUBBER IN LATEX 



the tappings, the effect is much less marked. Thus, for 

 example, Bamber and Lock in Ceylon found that the 

 amount of rubber in the latex of Para trees tapped every- 

 day or every second day rapidly fell from 50 per cent, 

 to about 30 per cent. ; if, however, an interval of four 

 five, six, or seven days was allowed between the tappings, 

 the proportion of rubber did not fall much below 40 per 

 cent. Beadle and Stevens have recorded that in the 

 Federated Malay States Para trees seven to eight years 

 old which were lightly tapped every other day fm-nished 

 latex containing an average of 37' 5 per cent, of rubber, 

 whereas the corresponding figure for similar trees which 

 were more heavily tapped at the same intervals was only 

 2 7" 5 per cent. In abnormal cases the latex of cultivated 

 Para trees has been found to contain such a small per- 

 centage of rubber that it could not be coagulated by the 

 usual methods, whilst, on the other hand, the latex of a 

 thirty-year-old tree in Ceylon has furnished as much as 

 64 per cent, of dry rubber. It will be seen, therefore, 

 that very considerable variations occur. 



Christy determined the amount of dry rubber in a 

 number of specimens of Funtumia latex obtained from 

 forest trees in Uganda. In twenty-six trees the propor- 

 tion of dry rubber in the latex ranged from 24' 4 to 46' 6 per 

 cent., whilst two other trees were abnormal, the latex 

 containing only 85 and 11 per cent, of dry rubber. 



Three specimens of the latex of Landolphia owariensis 

 examined at the Imperial Institute were found to contain 

 respectively 44' 1, 448, and 513 per cent, of dry rubber. 



The most important constituents of latex other than 

 the caoutchouc, so far as the preparation of rubber is 

 concerned, are the resin and protein, since these sub- 

 stances are always included in the coagulated product. 

 Some of the mineral matter of the latex is also invariably 

 present in crude rubber and occasionally small amomits 

 of the carbohydrates in addition. 



Resin. — The proportion of resin present in latex is 

 subject to very wide variation and the ratio of resm to 

 caoutchouc largely determines the value of a latex as a 

 som'ce of commercial rubber. The following analyses, 

 made at the Imperial Institute, will illustrate the varia- 

 tion which may occur in the composition of the product 

 obtained from different latices : 



