436 BELL SYSTEM TECHNICAL JOURNAL 



boiled cotton, designated A and B respectively. These raw and 

 water-boiled samples initially came from the same lot of raw insulating 

 cotton. 



The arrangement of the data in these tables shows the sequence in 

 which the equilibrium values were obtained. 



On Fig. 1 are plotted curves showing the relations between (a) per 

 cent M.C. and per cent R.H., and {b) log I.R. and per cent R.H. 

 for the raw cotton data in Table I. Fig. 2 contains a single curve 

 showing the relation between log I.R. and log per cent M.C. for the 

 raw cotton. Fig. 3 contains all three of these different types of 

 curves for the two samples of water-boiled cotton. Since the data for 

 these two water-boiled samples checked with one another so well, 

 only one curve of each type was necessary to express the relations 

 for both samples. Fig. 4 shows the relation between log I.R. and 

 per cent M.C. for only the lower range of the experimental data for 

 raw cotton, since up to about 5 per cent moisture content this relation 

 as expressed by equation I on page 432 appears to hold better than 

 equation II. 



Discussion of Experimental Data 

 Moisture Content-Relative Humidity Data 



Exposure of raw cotton to a saturated atmosphere causes a reduction 

 in the area of the moisture content-relative humidity hysteresis loop '- 

 (Fig. 1). Conversely, no reduction in the area of the loop on successive 

 cycles is observed in the case of water-boiled cotton, perhaps due to 

 this previous water treatment. 



Sheppard and Newsome ^^ found reductions in the area of this type 

 of hysteresis loop for a treated cotton on successive cycles of exposure 

 to high and low humidities. Our data show — (a) no change occurs 

 in the position of the absorption curve for water-boiled cotton during 

 two absorption cycles; (b) identical desorption curves for two different 

 water-boiled samples; (c) identical desorption cur^^es for raw cotton 

 in three cycles, as well as a suggestion that the third absorption curve 

 (only one point obtained — at 26 per cent R.H.) coincides with the 

 second absorption curve; (d) a reduction in area in the raw cotton 

 hysteresis loop on the second absorption cycle; (e) this reduced area 

 for the raw cotton differs but little, both in area and location, from the 

 hysteresis loop for the water-boiled cottons. 



12 This type of hysteresis loop in the moisture adsorption properties of cotton has 

 been discussed at length by Urquhart and Williams, Jour. Text. Inst., 15, T138, 1924; 

 also Shirley Inst. Mem., 3, 49, 1924. 



"Sheppard and Newsome, Joiir. Phys. Chem., 33, 1819, 1929. 



