October 1, 1911.] 



THE INDIA RUBBER WORLD 



Rubber Testing at Gross-Lichterfelde. 



WHILE in German technical circles there no longer exists 

 any doubt with regard to the value of the mechanical 

 testing of rubber, there seems to be a conflict of opinion 

 as to the manner in which such tests should be carried out. To 

 this circumstance has been attributed the lack of their general 

 recognition and application. 



Much attention has been paid to the subject during the last few 

 years. 



WORK OF 1909. 



The testing of india-rubber and insulating materials elec- 

 trically, constructionally and thermally, was taken up at 

 the Testing Bureau of Gross-Lichterfelde, Germany, during 

 the working year 1909. Appliances were procured for the wash- 

 ing and vulcanizing of crude rubber and for compounding, with 

 the aid of which the bureau was enabled to make a practical 

 study of the process of vulcanization and the influence of the 

 chemical and physical processes therein employed. 



For conducting tests of the strength of rubber, L. Schopper's 

 (Leipzig) perfected testing machine, as w-ell as a Martens- 

 Schoppcr durability testing machine, were installed, the two 

 first named being in regular operation. 



The German cable factories had combined and in order to 

 control the supply of insulated wire, had formulated conditions 

 as to the quality of the rubber employed. The methods to be used 

 in the analyses were drawn up by the chemists of the different 

 factories interested, in co-operation with the Bureau. 



In very many instances tests were made to determine the 

 resistance of insulating substances to the chemical action of 

 water, acids, alkalies, etc. This work is being continued during 

 the current working year and methodical tests made of various 

 insulating substances. 



The elaboration of processes for the analysis of rubber, in 

 compliance with the requests of the United Manufacturers of 

 Insulated Wire, was another important phase of the work con- 

 ducted by the Bureau. It was at once evident that the end 

 desired would soonest be attained by a process for determining 

 the amount of pure rubber actually present in rubber compounds, 

 and for this purpose the method described by Axelrod, based on 

 the precipitation of rubber as tetra bromide, seemed best 

 adapted. A thorough test of the process, however, showed, in 

 the original form, several sources of error, which reflected doubt 

 on its reliability. 



For determining the percentage of sulphur, a process had been 

 elaborated by J. Rothe; in many instances a process devised 

 by Hinrichsen, based on the electrolytic oxidization of the or- 

 ganic substances in the presence of nitric acid, was also used. 



COMPARISON OF TESTING METHODS. 



In advance of the ofiicial report for 1910, the fourth number of 

 the 1911 "Communications" of the Bureau contains an interesting 

 article by Dr. K. Memmler and Herr A. Schob. both of that 

 institution, dealing with "The General Character of the Mechani- 

 cal Testing of Soft Rubber," to some extent reviewing what has 

 been done in the past. This paper supplements that read at 

 Copenhagen in 1909 by the experts in question and forms an 

 appropriate starting point for new investigations on the subject. 



As an initial proposition, it is stated that two forms of 

 mechanical testing call for discussion : 



(a) A simple test of quality, such as is employed for metals, 

 cement, etc. This test will of necessity be confined to determin- 

 ing the strength and elastic pjoperties of a rubber compound, 

 apart from the nature of the requirements, to which articles made 

 from such compound (hose, discs, rings, buffers, molded pieces, 

 etc.), may be liable in practice. 



(b) A test in which either finished articles or samples obtained 

 from them will be subjected to the same requirements to which 

 the articles will subsequently be exposed in practice. 



The latter method of testing, while possibly the more desirable 

 from a practical standpoint, will be found upon consideration to 

 be attended by manifold difficulties. As it is remarked, the 

 extensive variety of rubber manufactures renders difficult the 

 establishment of uniform bases for tests. Uniformity of testing 

 methods cannot, however, be dispensed with, if it is desired to 

 compare results obtained at different points. It is added, that 

 from the experience acquired with other materials, the attainment 

 of the desired object is more probable by the use of the first- 

 named plan, a simple test of quality. Care must, however, be 

 taken to establish this test in such a way that it may (without 

 taking up too much time, or using an excessive quantity of 

 material) be applied as a uniform standard to all rubber products 

 It must likewise not involve complicated testing arrangements. 



QUALITY TESTS FOR RUBBER. 



It is then deduced, that with systematic procedure it ought 

 not to be difficult to collect detailed results as to the exaci 

 strength (resistance to fracture, changes of form, elastic reaction, 

 etc.) of any description of rubber, with a view to its adaptability 

 to a given purpose. Manufacturers and consumers, it is urged, 

 will soon become accustomed to require, for instance, of a rubbeJ 

 for automobile tires, certain recognized fixed degrees of strength 

 or other properties. An automobile tire can, it is true, be fot 

 experimental purposes attached to a shaft with a certain burden 

 and a fixed number of revolutions, rotating upon a surface 

 representing a given paving material.* But, it is asked, who will 

 stand the expense involved by such a test of the comparative loss 

 in weight of tires, when usually only a small order is involved? 



The other manifold products of rubber, it is remarked, are in 

 the same position as automatic tires, although less affected by 

 considerations of expense than in the latter case where, if tests 

 are to be made with direct reference to prospective uses, there 

 will necessarily be a number of special trials. 



WHY NOT CHEMICAL TESTS? 



It is further remarked that an opinion prevails that a test for 

 quality alone can be furnished by chemical analysis of rubber 

 compounds. Against this contention it is, however, pointed out 

 that such chemical analysis has not yet reached a position where 

 generally recognized methods can be spoken of. Moreover, even 

 with the hoped-for perfection of analytical processes, it will be 

 difficult to deduce in all cases from its chemical composition, 

 reliable conclusions as to the elastic and mechanical qualities of 

 the rubber. In the same way the results of the chemical analysis 

 of iron afford but limited guidance as to its mechanical properties. 



With a view to the most exhaustive possible determination of 

 the quality of rubber, efforts are recommended for the reciprocal 

 expansion of the scope of both chemical analysis and mechanical 

 tests of strength. 



From these various considerations it is deduced that nothing 

 remains but to try to build up mechanical rubber testing in the 

 sense explained, on the basis of a simple test for quality. The 

 chief question is then, whether the quality of the rubber is to be 

 judged according to the samples cut out from the manifold 

 products of the article, or according to types drawn from a 

 compound already prepared. 



With regard to this question, it is pointed out that tests on a 

 large scale will be necessary to determine in what degree the 

 strength of a rubber compound, or of various sized vulcanized 



•See "Accurate Tests of Tire Efficiency," I.n-dia Rubber World, August, 

 1911, p. 443. 



