MOISTURE IN TEXTILES 231 



cotton. With silk the corresponding change in resistance is somewhat 

 greater, and although silk sorbs materially more moisture than cotton 

 at any equivalent atmospheric condition, it is much the better insu- 

 lating material. Small amounts of naturally-occurring, water-soluble 

 salts in cotton, such as NaCl and K2SO4, seriously impair the resistance 

 of this textile. Traces of acids or alkalies left after degumming have 

 a similar effect on silk. By washing these materials in water, their 

 electrical properties are greatly improved. 



Figure \-A shows the familiar equilibrium relation between relative 

 humidity and moisture content for cotton, including the hysteresis 

 loop. A similar hysteresis characteristic, Fig. 1-B, in the relative 

 humidity-resistance relation has been discussed in previous publica- 

 tions.^- ^ Figure 2 shows more clearly, as suggested by a comparison 

 of the two types of curves in Fig. 1, that the resistance of cotton is 

 critically dependent upon its moisture content. The curves in Fig. 2 

 show another important fact. The resistance of cotton may have, 

 not one, but a range of resistance values for a single moisture content, 

 depending upon the previous treatment or "history" of the sample. 



This fact, which is one of great practical importance, is illustrated 

 in Table I. Eleven samples of cotton, taken successively from the 

 same spool, were dried to constant weight at 100° F., in a current of 

 dry air, then equilibrated together under very carefully controlled 

 conditions, first at 87.7 per cent R. H., then re-dried as before and 

 re-equilibrated at 84.3 per cent R. H. several days later. The moisture 

 contents of these samples were as follows: 



TABLE I. 



% Moisture Contents 

 Sample No. at 87.5% R. H. at 84.3% R. H. 



1 10.95 10.1 



2 10.8 10.0 



3 10.7 9.9 



4 10.8 9.8 



5 11.1 10.2 



6 11.0 9.9 



7 11.8 10.8 



8 10.7 10.1 



9 10.85 9.8 



10 11.0 10.0 



11 10.7 9.9 



The moisture contents of these samples showed small but definite 

 differences, persisting even between tests several days apart. One of 

 the samples had apparently been treated slightly differently from the 

 others in preparation, since it preserved a marked difference in moisture 

 content in both tests. Since a change of only 0.1 per cent in M. C. 



