Density Measurements on Synthetic Rubbers

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Abstract
For many purposes the density of a material need be known with an accuracy of only a few per cent. For many materials the density of one sample may differ from that of another by this amount, and no useful purpose may be served by making more precise measurements on individual samples. In natural rubber, the densities of different samples have been shown, in a compilation of twenty-one values, to lie with two exceptions between 0.905 and 0.919 gram per cc. at 25° C. The variations probably represent real differences in the samples and not accidental errors of observation. Since one can seldom know exactly the origin and subsequent treatment of a sample of natural rubber, there is little value in increasing the precision of measurement. Synthetic rubbers, on the other hand, can be regarded as usually produced under conditions which are much better controlled and known. It is logical, then, to measure the density with greater precision and to hope to be able to ascribe significance to its variations from one sample to another. The present work is concerned with the development of a method for preparing specimens of synthetic rubber in a form suitable for precise measurements of the density, the actual measurement by the method of hydrostatic weighings, and a presentation of the results for most of the varieties of synthetic rubber now of commercial importance in the United States.

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