1904.] Cotton by Water and by Water Vapour. 249 



case also the calculation is independent of any purely empirical 

 formula. 



The Influence of the Bath Temperature. 



The only experiments designed to test this question were those 

 summarised in Table IV and illustrated in fig. 4. The 6 curves 

 are there seen to cross one another on the down slope in such a 

 way as to suggest that the rates of absorption, originally higher at 

 the higher bath temperature, reverse their order of magnitude not 

 long after passing the maximum 6. This conclusion would necessarily 

 follow from Equation (IV) if c were a constant for the three experi- 

 ments at 12, 18, and 25, for then cO must be equal for any pair 

 at the moment of crossing, and kdOjdt is manifestly of larger negative 

 value there for the curve belonging to the higher bath temperature. 

 But c, though essentially a constant unaffected by temperature, is 

 known to be susceptible to change if the amount of water vapour 

 in the air be altered, as is the case in passing from an experiment at 

 one bath temperature to one at another, and, as a matter of fact, 

 measurement of the areas of the curves for 12, 18, and 25, and 

 comparison of them with the actual m values at 65 minutes, show 

 that c must be given the approximate values 0*22, 0'25, and 0'27 

 respectively. And when this difference is allowed for, it appears 

 that the rates of absorption in the three experiments originally 

 different approach the same value, but do not reverse their order. 

 For a proper investigation of this question complete series of experi- 

 ments would be required at different bath temperatures, all other 

 conditions being the same. 



Magnitude of the Heat Development. 



In the preceding tables there is sufficiently good agreement between 

 the found and calculated values of m to justify the statement that 

 the two assumptions on which the calculation is based are sub- 

 stantially correct. It is tolerably certain that neither of them is 

 rigorously true, but it may be taken as proved that the heat liberated 

 during the immersion of cotton is, for practical purposes, directly 

 proportional to the weight of moisture absorbed. This does not 

 necessarily mean that there is nothing else to be considered than the 

 simple heat of liquefaction. It may be so, but the condensation of 

 vapour may be supplemented by some other process, either exothermic 

 or endothermic. The experimental method that has been employed 

 cannot properly test the question thus raised, but the following 

 rough calculation shows that there can be no very large difference 

 between the heat of liquefaction and the heat of absorption by 

 cotton : 



VOL. LXXIV. u 



