232 



Dr. 0. Masson. On the Wetting of 



[Apr. 25, 



organic, and showed that the property is a general one, that the state 

 of division and previous dryness of the material are important, and 

 that the phenomenon is much better marked with animal and vege- 

 table substances than with mineral powders. His experiments, how- 

 ever, can hardly be regarded as quantitative, for the temperature 

 rises, of which he records a long list, have no real significance apart 

 from the special conditions under which they were observed, nor do 

 they by themselves throw light on the nature of the process which 

 causes them. Later observers seem to have confined their attention 

 to inorganic materials such as silica and glass, and the recent work of 

 G. J. Parks, which will be referred to later, is specially notable in this 

 connection. But the author is not aware of any previously recorded 

 thermometric investigation on the lines he has adopted, having the 

 following objects in view : 



1. To map the whole course of the observed change of temperature 

 of cotton due to its immersion in water, tracing both the rise to the 

 maximum and the subsequent fall. 



2. To do the same for the case of immersion in air saturated with 

 water vapour, and to compare the two results. 



3. To examine the effect of varying conditions and particularly of 

 the initial dryness or dampness of the cotton. 



4. To determine, in the case of immersion in saturated air, the 

 course of the hygroscopic absorption. 



5. To ascertain the relation between this absorption and the 

 temperature change. 



6. To examine the information so obtained as to its bearing on the 

 nature of the Pouillet effect. 



Apparatus and Methods. 



The thermometers required to fulfil the two conditions of being 

 short enough to be weighed on an accurate balance and of yet 

 having a sufficient length of scale. As they were likely to be used 

 at various temperatures, a very open scale was out of the question. 

 Those chosen were graduated in whole degrees only, reading from 

 below zero to 100 C. Eeadings were always made by a telescope with 

 a micrometer scale in the eyepiece. In all the earlier experiments 

 this micrometer scale was used merely for subdividing the degrees, 

 but in those described as Series V it was employed so as to make the 

 readings altogether independent of the thermometer graduations. 



Comparison of the instruments with a standard thermometer at 

 various temperatures showed that the capillary was of practically 

 uniform bore, and as all the readings in any experiment were referred 

 to the initial one, so as to give temperature differences, any zero-point 

 error of the thermometer was of no importance. 



