As is well known, various methods have been proposed for determining the optimum vulcanization of rubber. These methods depend either upon physico-chemical examination or upon mechanical tests. In routine control the mechanical method of determination is used for the most part, because it requires but little time, and in addition this method has the advantage of showing directly by mechanical tests whether the vulcanizate being tested passes the requirements or not. The results obtained by this method frequently do not agree with those obtained by other methods. Of the many common methods of testing, determinations of the tensile strength and of the ultimate and residual elongation are the methods most frequently used. These three properties are measured simultaneously by one determination with the apparatus in most widespread use, i. e., the Schopper and the Scott machines. In special cases the resistance to abrasion, bending strength, hardness, and other properties are determined in addition. Considerably less often the hysteresis and Young's modulus of elasticity are determined. All these determinations are of significance in only a limited way, for the conditions under which the tests are carried out in the laboratory are not comparable to the actual service of the products. For basic reasons, this fundamental shortcoming cannot be avoided in the laboratory, though a few of the measurements do approach the true properties found in service. Of course, the results obtained in the laboratory are greatly influenced and made less reliable by other secondary factors, among which are the phenomenon of aging under natural conditions, prolonged stressing, etc.

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