370 BELL SYSTEM TECHNICAL JOURNAL 



A brief review of these formulae is given together with a brief account 

 of the results of experimental investigations on the dielectric behavior 

 of mixtures. A rather extended bibliography is given. 



The Effect of Moisture on the Electrical Properties of Insulating 

 Waxes, Resins and Bitumens? J. A. Lee and Homer H. Lowry. 

 The results of measurements of dielectric constant and effective 

 conductivity at 1,000 cycles and resistivity are reported for 31 waxes, 

 resins and bitumens, including not only naturally occurring products 

 but also commercial dielectrics and mixtures. The measurements 

 were made on the materials initially in a thoroughly dry condition, 

 after six months' immersion in a salt solution corresponding qualita- 

 tively to exposure to 98 per cent relative humidity, and after having 

 been redried. All the insulating materials studied absorbed water 

 under the conditions of experiment. The absorption was least with 

 the hydrocarbons and greatest with shellac and bayberry wax. In 

 general, the greatest increase in capacity and conductivity and the 

 greatest decrease in resistivity were shown by the materials which 

 absorbed the most water. The percentage change was much greater 

 in the conductivity and resistivity than in the dielectric constant, 

 as was to be expected. 



The Mechanism of the Absorption of Water by Rubber}^ H. H. 

 Lowry and G. T. Kohman. Data are reported which show the 

 influence of the various factors which determine the amount of water 

 absorbed by any given sample of rubber. From a consideration of 

 the results obtained, it was concluded that, at a given temperature, 

 the most important external factor determining the amount of water 

 absorbed by a given sample of rubber is the vapor pressure of water 

 with which it is in equilibrium. The data show further that the water- 

 soluble constituents within the rubber are responsible for most of the 

 water absorbed at high hurrtidities, that increasing the rigidity of a 

 rubber compound decreases greatly the amount of water absorbed, 

 and that aging increases the water absorption. It is pointed out that 

 all the experimental facts are consistent with the view that the absorp- 

 tion of water by rubber consists of two processes: the formation of a 

 true solution of water in rubber and the formation of solutions internal 

 to the rubber of the water-soluble constituents of the rubber which 

 can be removed by washing. 



^ Jr. of Industrial and Engineering Client., 19, 302-306, 1927. 

 i°7/-. of Physical Chemistry, 31, 23-57, 1927. 



