A weighted averaging method for tensile data on vulcanizate, has been dopted in JIS. This is based on the fact that the distribution of tensile data is considered to be a kind of doubly exponential theory by Kase. But the author thinks the median method agree with the results of the tests than above mentioned one by the improvement of testing process. The author has proved inductively the truth of normal type of the frequency-distribution by many experiments and moreover, deductively from the established facts of many other substances; i.e.
(1) The main factor of the rupture of specimens is not always attributed to the largest flaw or the smallest cross-section in the parallel part. So that the tensile strength should be calculated by dividing the breaking force by the median cross sectional area as the representative value.
(2) In the case of bending the bench marks at break, we must measure the mean distance, excepting the maximum between the marks.
Hereby, if we adopt median value, the distribution of the data may be nearly normal. So that the calculation is very simple and convenient on the statistical analysis of the data. As the result, it is more efficient and moreover, the value is closer to the true value.

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N, N'-polythiobis (dimethylamine), N, N'-polythiobis (diethylamine) and heptasulfuryl imide were found to be effective curing agenst for natural rubber. These agents were characteeized by apparent non-blooming and delayed scorching. Only 1.5 phr of these agents is enough to cure natural rubber tightly without accelerators under usual vulcanization condition. The scorch time of the compounds is longer than that of Ncyclohexylbenzothiazyl-2-sulfenamide and sulfur system (I). The tensile properties of the vulcanizates seem to vary with sulfur content of N, N'-polythiobis (dimethylamine) (II). The highest tensile strength of te vulcanizates was attained by the use of (II), sulfur content of which was about four atoms of sulfur per molecule. The strength was found to be higher than that of the vulcanizate cured with (I). The valcanizates cured with these organic polysulfides possessed poor resistance to heat aging, but this defects was improved by using common vulcanization accelerators together with antioxidant.

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N, N'-Dicyclohexyl-1, 2, 4, 5-tetrathia-3, 6-diazine (CTS), especially its effect as vulcanizing agent and vulcanization accelerator on rubbers was investigated. The vulcanizates of natural gum and SBR-ISAF black stocks cured with 5.04 phr of CTS (equivalent sulfur moles to 2 phr of sulfur) were found to exhibit not only high tensile strength but also high resistivity to heat aging. It was also found that CTS is an effective vulcanization accelerator for the natural and the SBR stocks and gives vulcanizates having a high tensile strength.

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