MOISTURE IN TEXTILES 233 



The ranges of application of Equations 2 and 3 are evident from 

 Figs. 2 and \-B, respectively; but since the resistivity of cotton 

 becomes enormously high as the moisture content approaches zero, 

 it has been difficult to verify the application of equation 1 below 

 about 2 per cent. However, a recent study along somewhat different 

 lines has provided us with information on this portion of the moisture 

 content curve down to as low as 0.04 per cent M. C. It will be seen 

 from Fig. 3 that equation 1 holds between 1 per cent and 6 per cent 

 M. C. Below 1 per cent M. C, however, the resistance increases 

 more rapidly with decreasing moisture content than is consistent 

 with equation 1. 



The data from which Fig. 3 was secured completes a chain of 

 evidence upon which is based a theory of moisture adsorption which 

 appears adequate to explain many properties of cotton. This theory 

 involves, in addition to the data just discussed, a rather specific 

 picture of the cotton hair structure. 



2. Structure of the Cotton Fiber 



According to Balls,^ the cotton hair is formed by the outward 

 extension of a single cell from the epidermis of the seed-coat; this 

 extension, unaccompanied by any cell division may continue until the 

 hair is 2000 times as long as it is broad. Up to about half maturity, 

 the cell wall remains very thin but the hair attains most of its length; 

 during the remaining half of the growth period (about one month) the 

 wall thickens from the outside in until it appears to consist of about 

 30 to 35 concentric "growth rings" (see Fig. 4). Each growth ring 

 consists, further, of parallel strands of fibrils, which run continuously 

 in spiral form from end to end of the hair making one complete turn 

 around the hair in about three diameters, and with periodic reversals 

 in the direction of this spiral. Balls also suggests that side by side 

 in each growth ring, there are about 100 fibrils, each separated from 

 its neighbor by an air space. These fibrils are described by Balls as 

 "dominoes" laid down one on top of the other in a pile-up of growth 

 rings extending from the wall of the central canal or lumen to the 

 outer wall of the fiber. Thus the front and back of each domino are 

 growth ring boundaries, and each domino is separated from its neighbor 

 by an air space. There are also air spaces between each domino in a 

 growth ring. These air spaces are identified as the so-called pits in 

 the wall structure. They are visible under a microscope, and appear 

 to extend from the outer surface of the cotton hair down to the lumen. 

 These air spaces are far larger in magnitude than those separating 

 the front and back of each domino. Only by swelling the fiber in 



