6 1 



rigorous conclusions from these series of tests, and we do not infer that 

 caoutchouc in the plantation Para is superior to that in the Amazonian 

 hard cure Para merely because in an average of a number of tests we 

 have obtained slightly better figures with the former. It should be 

 remembered that a certain treatment in mixing and vulcanising which 

 would bring out the best qualities of plantation rubber might require 

 some modification when applied to the hard cure product. On the 

 other hand, we have avoided such objections as far as possible by 

 varying the conditions, such as the duration and temperature of 

 vulcanisation so as to bring out the best results in both cases. 



A considerable amount of work on these lines is in progress,, and 

 we hope before long to be in position to publish the results of further 

 tests ; we think, however, that with the results so far obtained we are 

 justified in concluding that the actual rubber or caoutchouc contained 

 in the plantation products will prove to be at least as good if not 

 superior to that of the Amazonian product. So far, we find that the 

 statements frequently made in some quarters that plantation rubber is 

 wanting in "nerve" is not justified by tests we have made on the 

 vulcanised product obtained from the best prepared block. 



We have examined the distensibility of vulcanised plantation 

 rubber under increasing strain, and the results are plotted in the forrm 

 of a curve. 



As in the tensile strength tests, a sheet of rubber i mm. thick 

 was cut in the form of a ring 40 mm. in diameter and 2*5 mm. wide. 

 It was stretched vertically between smooth iron hooks, the upper one 

 being fixed and the lower one carrying a scale pan. Two marks were 

 made on the band, and the distance between them measured as 

 weights were put into the pan. 



We have also made some preliminary tests on sheets of block 

 rubber containing mineral matter, two of which we give below. 

 Mixing M consisted of 50 grms. caoutchouc, 4 grms. sulphur, 10 

 grms. zinc oxide, 25 grms. lithopone, and 1 grm. pitch; that 

 is, approximately: — 



Caoutchouc ... ... ... 56 per cent. 



Zinc oxide ... ... ... 11 ,, 



Lithopone ... ... ... 28 „ 



Pitch ... ... ... ... 1 



and sulphur, 8 per cent., reckoned on the caoutchouc. 



Mixing J consisted of 50 grms. of plantation block caoutchouc, S 

 grms. sulphide of antimony, and 2 grms. sulphur. The results 

 obtained are given in Table IV. 



