450 BELL SYSTEM TECHNICAL JOURNAL 



it appears likely that adsorption of moisture is largely a function of 

 free hydroxyl groups. From our data it appears that when wet 

 cotton is dried rapidly at high temperatures, the internal or micelle 

 surface contains a minimum of hydroxyl groups. As the cotton is 

 permitted to absorb more and more moisture, the hydroxyl groups 

 which were oriented into the interior of the micelles by the drying 

 process where their hygroscopic property is, in effect, neutralized by 

 attraction of associated molecules, are attracted to the surface to 

 hold the absorbed moisture. On drying, these hydroxyl groups do 

 not return readily to the interior and a greater number of water 

 molecules are held at any relative humidity, thus accounting for the 

 normal hysteresis effect observed in the moisture content-relative 

 humidity relation. 



Practically all of the experimental data discussed in this paper were 

 secured during 1928 and 1929, and the above theory was proposed 

 at that time. Apparently at about the same time Urquhart questioned 

 the explanation offered some years previously by Urquhart and 

 Williams ^^ to account for hysteresis in the moisture relations of cotton, 

 depending upon a modification of the Zsigmondy pore theory. In 

 June 1929 "^ Urquhart proposed a theory comprising the essential 

 features of the orientation of hydroxyl groups as offering a better 

 explanation than the pore theory' for the moisture-adsorbing properties 

 of cotton. The general outline just given in connection with the 

 study of the electrical properties of cotton is much the same as the 

 more complete theory discussed by Urquhart. 



However, further consideration of our experimental data led to 

 the conclusion that neither the pore theory nor the orientation of 

 hydroxyl groups completely accounts for the hysteresis effect in the 

 log I.R. — log per cent M.C. relation. 



As mentioned above, rapid drying of wet cotton under proper 

 conditions is assumed to give internal surfaces containing a minimum 

 of hydroxyl groups. This idea can be qualified as follows: Either 

 such drying conditions are conducive to the presence of a minimum of 

 hydroxyl groups on the internal surfaces, or they are conduciv'e to a 

 less imijorm distribution of these groups on these internal surfaces. 



Consequently, on initially absorbing moisture from such a dried 

 condition, the moisture associated with hydroxyls will not be uni- 

 formly distributed and the conduction of current through the cotton 

 along these internal surfaces will be somewhat discontinuous. On 

 desorption from saturation, moisture will be removed in a more regular 



-^ Urquhart and Williams, Jour. Text. Inst., 15, T433, 1924; also Shirley Inst. 

 Mem., 3, 197, 1924. 



" Urquhart, Jour. Text. Inst., 20, T125, 1929. 



