Effect of Atmospheric Humidity and Temperature on the 



Relation between Moisture Content and Electrical 



Conductivity of Cotton * 



By ALBERT C. WALKER 



THE data given in this paper show the effect of successive equi- 

 librium humidity cycles on the relation between (a) relative 

 humidity and moisture content; (b) insulation resistance and relative 

 humidity; and (c) insulation resistance and moisture content, for raw 

 and water-boiled cotton at constant temperature (25° C). These 

 data have been of considerable assistance in explaining the behavior 

 of cotton, particularly the fact that its d.-c. insulation resistance, 

 when measured at some definite test condition,^ is dependent, to a 

 surprising extent, upon previous treatment, e.g. the manner in which 

 wet cotton is dried, temperature of drying, and the atmospheric con- 

 ditions to which it is exposed after drying, before being measured 

 under the comparable test condition. 



The information secured as a result of this investigation has been 

 valuable in improving the practical methods of inspection used to 

 control the quality of textiles for electrical insulation in telephone 

 apparatus. 



Previously it was shown ^ that the relation between the insulation 

 resistance (I.R.) and percentage moisture content (per cent M.C.) of 

 cotton can be expressed by the equation 



log I.R. = - A log per cent M.C. -f B. 



It is now known that a single value of the slope A of this linear 

 function does not suffice for all cottons, nor even for one sample of 

 cotton. The slope may have values between 10 and 12 for the same 

 sample depending upon the previous treatment of the cotton. Further, 

 this equation holds only between about 3 per cent and 10 per cent 



* This is one of three papers by Walker and Quell, published in the March and 

 April 1933 issues of The Journal of the Textile Institute. Abstracts of the other two 

 papers appear in the Abstracts section of this issue of the Bell System Technical 

 Journal In the April 1929 Bell System Technical Journal there are two papers by 

 R. R. Williams and E. J. Murphy, and E. B. Wood and II. II. Glenn, respectively, 

 dealing with the problem of textile insulation. ,. r .-r. . ., 



1 It is the practice to compare the electrical insulatmg quality of different cotton 

 samples by measuring the d.-c. insulation resistance after bringing the samp es to 

 equilibrium with 75 per cent relative humidity at 25° C or at 85 per cent relative 

 humidity at 37.8° V. (100° F.), equilibrium being approached from a lower humidity. 



2 Murphy and Walker, /. Phys. Chem., 32, 1761, 1928. 



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