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BELL SYSTEM TECHNICAL JOURNAL 



moisture content — corresponding to a range of relative humidity 

 (hereinafter written R.H.) from 15 per cent to 85 per cent at 25° C. 

 Nearly the whole range of moisture adsorption ' of cotton between 

 dryness and saturation may be characterized by three equations, as 

 follows: 



Below 3 per cent moisture content ^ 



log I.R. = - ^ per cent M.C. + B 

 Between 3 per cent and 10 per cent moisture content 

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



(I) 



(11) 



Between 10 per cent moisture content and saturation (about 25 per 

 cent M.C.) 



log I.R. = - ^ per cent R.H. + B (III) 



Different values of A satisfy these equations, depending, as noted 

 above, upon the previous treatment of the cotton and upon the 

 direction of approach to equilibrium; whether this approach is from 

 the dry state (along an absorption cycle), or from the wet state (along 

 a desorption cycle). The experimental data include results of tests 

 on one sample of raw cotton and two of water-boiled cotton. The 

 following tabulation gives some idea of the limiting values of A and 

 the conditions under which they will satisfy the equations: 



Experimental Method 



Samples of cotton were brought to equilibrium with a flowing stream 

 of air at 25° C, in which the partial pressure of water vapor could be 

 adjusted to any desired value and maintained constant within 0.0115 



' The word "absorption" is used to denote the taking up of a vapor, "desorption" 

 the giving up of a vapor, and "adsorption" the general process without special 

 indication of gain or loss. The use of these terms implies no assumptions with regard 

 to the mechanism of the processes they denote. 



•• Below 2 per cent M.C., the I.R. of even raw cotton is difficult to measure, since 

 it is above the limiting sensitivity (10'^ ohms/mm. at 100 volts) of the insulation- 

 resistance bridge used. Further tests are being made on this low range, using a 

 more suitable type of cotton sample. 



* Difficult to measure water-boiled cotton in the range where Equation I might 

 apply. 



