172 RUBBER AND 



determine by rule of thumb methods. A simple and 

 uniform method of testing commercial samples is there- 

 fore greatly to be desired. At the present time there is 

 little doubt that differences in the original samples, and 

 differences which arise during transport and storage, are 

 often to some extent discounted by slight inaccuracies 

 in the methods of testing. The determination of the 

 best form of plantation rubber is thus further delayed. 



It is therefore not surprising that the opinions of 

 experts seem to differ as regards the precise effect of 

 almost every factor which is capable of influencing the 

 quality of the manufactured rubber. Thus rubber from 

 young trees was formerly regarded as markedly inferior 

 to that obtained from old trees. Recent experiments 

 have not invariably confirmed this conclusion, although 

 some appear to do so, and the question is not finally 

 settled. In a similar way opinions differ widely as 

 regards the effect of smoking or the use of vacuum 

 driers. At present the general opinion is that plantation 

 rubber is on the whole less satisfactory and less durable 

 than fine Para. Thus it is commonly stated that plan- 

 tation rubbers are unsuitable for the manufacture of 

 elastic thread, a use which is generally admitted to 

 represent one of the most stringent tests of quality. 



As the crops on Eastern estates increase, and larger 

 and larger bulks of rubber are turned out, a steady 

 increase in uniformity is to be expected. Already many 

 samples of plantation rubber have been produced which 

 are indistinguishable in quality from the best Para by 



