INFLUENCE OF MOISTURE UPON INSULATORS 



233 



common to all. If any textile within our experience, including 

 cellulose acetate (or even glass), be brought in contact with two 

 electrodes of opposite polarity in the presence of atmospheric moisture, 

 the electrical properties of the material undergo a change with a 

 rapidity dependent on the current and in turn upon the voltage, the 

 length of path, and the humidity. Such a change in the properties 

 of insulating materials with continued application of voltage has been 

 discussed recently by Granier, who advanced the explanation ^^ that 

 it is due to the presence of electrolytic impurities in the materials. 

 However, the great magnitude of this change, which may occur in 

 textiles when freely exposed to ordinary atmospheres, seems to have 

 been very little appreciated. 



TABLE III 



Rate of Change of Resistance with Time of Application of 

 Voltage for Some Fibrous Materials 



Separation of Electrodes J^ in. Humidity 97 per cent (approx.) Voltage 275 



In our experiments the insulation resistance rises to a value perhaps 

 10 to 100 times the original value, depending on the nature and 

 condition of the fiber. A few typical cases are given in Table III. 

 This phenomenon will be referred to as polarization. This rise in 

 resistance appears to be largely due to substantial denudation of 

 some intermediate portion of the fiber of electrolytic impurities, 

 which in general tend to accumulate in the vicinity of the electrodes. 

 The phenomenon involves the possibility of chemical reactions between 

 the products of the electrolysis and the material of the electrodes, 

 as well as the evolution of gases and the conversion of soluble salts 

 into insoluble products. As regards the mineral constituents of 



" Granier, J., Soc.frangais Elec. Bull., 3, 480 (1923). 

 16 



