Abstract
THE presence of water is one of the principal causes of electrical instability in dielectric materials, often resulting in large variations in direct current resistance, dielectric constant, and power factor. A knowledge of the laws governing the sorption of water is therefore of considerable interest to the electrical and communications industries. The various investigators in the field of sorption of water by rubber have not reported their findings in a manner which will permit of consistent interpretation and correlation for engineering uses. Insufficient attention has been given to the effect of such factors as shape of test specimen, temperature control, variations in vapor pressure, chemical changes in the test specimen, etc. Consequently no sorption coefficient suitable for application to practical problems and no measure of the rate of sorption which will permit an adequate comparison of one material with another is now available. The purpose of this article is to describe the relation between rate of sorption and some of these variables, such as thickness of test specimen, temperature, and vapor pressure, and to show how sorption tests can be applied to certain practical problems. It is not the purpose to present a survey of the literature. The word “sorption” is used in conformity with current phraseology to mean the combined effect of adsorption and absorption.