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 define 
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 iaw even when the ends were cut considerably wider than the 
middle 1 portion. Eventually the difficulty was got over by P unch, "S 
small rin^s which were stretched between smooth roupd iron hooks. 
The testing machine was constructed on the well-known pnnc.pleused 
in testin'' 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 rkume 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 ThJse prepared from hard cure Para were much darker 
and less transparent. When vulcanised for a short time the surface 
“fphured up Tn the ordinary manner. In the course ~k - 
far we have carried out over 150 vulcanisations. We have subjectea 
twenty separately vulcanised samples of Platoon rubber 
rmlv rubber and sulphur without mineral or other additions to tests to 
tensile strengA 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 ^ve an avemge 
strength of 3187 g^and an ebngatmn of ^3 cn g an 
products (K)containmg^5^per cent, p^ ^ while the 
sample vulcanised with 8 per cent, gave a tensile strength of 3324 grm^ 
nrr'ifinn of i2 Although the figures for tensile strength of K 
aid xTre somewhat higher than the average of the remainder (3187), 
Hn not IS great importance to this, as this latter average is 
gives a smaller elongation (12 o). 
We come now to vulcanising tests with fine hard cure Para. We 
are indebted to Mr. Devitt, jun., of the firm Lews ^d Peat for 
supplying us with a quantity of a good average sample of the above 
and valued early in March last at 5 s- xrf. per pound. The analysis of 
this sample is 
