The interfer om et er method for the m easurem ent of small dimensio nal changes is a da pted here t o m easurements on soft rubber. A d etail ed description is given concernin g the prepar a ti on of specimens, the a pparatus, tlle procedure, and the calculations necessary for the application of thi s m ethod. P art icular emphasis is placed on the m eas urement of thermal expansivity and the dimensional changes in volved in transitions between the differ ent form s of rubber. The lower limit of temperature is set onl y by the refrigerating liquid, temperatures as low as -185 C b eing utilized. The upper limit of t emperature is set only by the rubber itself. R esults obtained in a study of the expansivity and transitions of " st ark" (fro zen) rubbcr ar e given a s an illustration of the application of t he method. Other possible app lications are the m eas urement of the swelling of rubber by vapors a.nd the det ermination of stress-strain relations under compr essive loads. The chi ef limitation of the application of this met hod t o rubber arises from the plastic flow of un vulcanized rubber a t elevat ed t emperatur es. The method also possesses the inconvenience of requiring continuous obser vatio n. As compa red with alternative methods of measuring small. dimen sional changes, the method possesses advantages arising from its high sensiti vity, from the small size of the specimens r equired, from the ease of obtaining temperature equili brium, from the absence of a confining liquid, and from the simplicity of t he calculations. I. II. III. IV.
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Wood et al. (1939) studied this question.