240 BELL SYSTEM TECHNICAL JOURNAL 



(plot of Collins' data). Using the following equation formulated in 

 accordance with the calculations in section 4, 



n = {^ X 125000^)7.6 X 33 X 2 = 12 molecular layers. (4) 



Since a layer one molecule thick on the fibril surfaces is equivalent 

 to 0.42 per cent moisture content, 12 such layers are equivalent to 

 5 per cent M. C. The observed moisture content at 50 per cent 

 R. H. is 5.5 per cent. If to this 5 per cent M. C. thus calculated, is 

 added the 0.7 per cent-0.8 per cent held within the fibril structure, 

 a total of 5.7 per cent to 5.8 per cent is obtained, which checks re- 

 markably well with the observed value (5.5%), considering the method 

 of computation. 



Collins reported swelling values for cotton exposed to 100 per cent 

 R. H. (some condensation was visible on the cotton), and for cotton 

 immersed in liquid water. Moisture contents calculated from these 

 data as in equation 4 give 21 per cent and 23 per cent respectively, 

 a surprisingly good agreement with observed values at saturation, 

 which, as reported by various observers, lie between 20-25 per cent, 

 depending upon the degree of wetness of the material, as indicated by 

 condensation of moisture on the surface. 



6. Moisture Required to Fill Pits and Lumen. 

 From Fig. 4-a, it appears that cotton may hold considerably more 

 moisture than corresponds to the saturation values calculated under 

 Section C. The total moisture calculated to fill the pits and lumen in 

 addition to covering the fibril surfaces is more than 140 per cent. 

 Coward and Spencer^* have shown that wet cotton retains about 50 

 per cent of its weight of water after centrifuging, and these authors 

 expressed the opinion that the water was not interstitial, but contained 

 in the hairs themselves. The above calculations indicate that not 

 only 50 per cent but much more than 100 per cent may be retained 

 in the cotton hair, and it is possible that the amount retained after 

 centrifuging or pressing may be some function of the treatment and 

 the surface energy relations of the sorbed moisture. 



7. Reduction in Moisture Sorption of Cotton by Acetylation 

 New ^^ has shown that the equilibrium moisture content of cotton 

 is progressively reduced as the acetyl (CH3CO) content is increased. 

 Below 21 per cent CH3CO content, acetylation can be carried out in 

 a mild way without appreciable effect upon the strength or physical 

 structure of the hair. Above this value the fiber appears to be 



