59 



of the product to any very marked degree. On the other hand, care, 

 of course, must be taken to keep the temperature within certain denned 

 limits. 



For tensile strengths much difficulty was experienced in testing 

 small strips, owing to the tendency of the rubber to tear and rupture 

 in the jaw, even when the ends were cut considerably wider than the 

 middle portion. Eventually the difficulty was got over by punching 

 small rings, which were stretched between smooth round iron hooks. 

 The testing machine was constructed on the well-known principle used 

 in testing cement and other materials, where a regular stream of 

 water or shot is allowed to run into a vessel and the supply cut off 

 automatically the moment of rupture. All figures given are the mean 

 of at least ten tests. 



Having briefly described the experimental methods employed we 

 now proceed to give a short resume of the results so far obtained. 



The products prepared from plantation rubber were of a beautifully 

 clear transparent yellow to brown shade when viewed through sheets 

 i mm. thick. Those prepared from hard cure Para were much darker 

 and less transparent. When vulcanised for a short time the surface 

 sulphured up in the ordinary manner. In the course of our work so 

 far we have carried out over 150 vulcanisations. We have subjected 

 twenty separately vulcanised samples of plantation rubber containing 

 only rubber and sulphur without mineral or other additions to tests for 

 tensile strength and elongation at the moment of rupture, details of 

 which are given in Table II. 



Taking first the tensile strength in grms. required to rupture the 

 rings, the average of the whole series works out to 3203, and the 

 elongation at the moment of rupture 13*1. Of these samples, sixteen 

 were vulcanised with 6 per cent, of sulphur, and gave an average 

 strength of 3187 grms. and an elongation of 13*0. Three vulcanised 

 products (K) containing 5 per cent, of sulphur were tested, and gave an 

 average tensile strength of 3245 grms. and elongation 14, while the 

 sample vulcanised with 8 per cent, gave a tensile strength of 3324 grms. 

 and elongation of 12. Although the figures for tensile strength of K 

 and X are somewhat higher than the average of the remainder (3187), 

 we do not attach great importance to this, as this latter average is 

 pulled down by the uniformly low results obtained with mixing Q, and 

 due to some irregularity in the mixing process. On the other hand, it 

 is noteworthy that K (with 5 per cent, sulphur) gives a greater elonga- 

 tion (14-0) than the average (13*0), while X (with 8 per cent, of sulphur) 

 gives a smaller elongation (12*0). 



We come now to vulcanising tests with fine hard cure Para. We 

 are indebted to Mr. Devitt, jun., of the firm of Lewis and Peat, for 

 supplying us with a quantity of a good average sample of the above, 

 and valued early in March last at 5s. id. per pound. The analysis of 

 this sample is : — 



