250 



Dr. 0. Masson. On the Wetting of 



[Apr. 25, 



In Series V it was found that k = M in the neighbourhood of the 

 maximum temperature. Therefore, from the definition of k the heat 

 capacity of the instrument used = Mz, the heat liberated per milli- 

 gramme of water absorbed. A measurement of the volume of the 

 bulb and also of known lengths of the stem of the thermometer was 

 made by weighing it suspended in water before it was covered with 

 cotton, and the total volume of glass and mercury subsequently 

 covered was calculated from these data to be 0*60 c.c. If the volume 

 heats of glass and mercury be both taken as 0-45 cal. per c.c., which 

 is not far from true, the heat capacity of that part of the thermometer 

 which was directly affected was 0*27. The specific heat of cellulose is, 

 according to Fleury,* 0'366, and as the cotton used weighed very nearly 

 0-900 gramme, the total heat capacity of the dry instrument may be 

 taken as 0-27 + 0*33 = 0*60 cal. The addition for moisture already 

 absorbed at the maximum temperature is about 0*03 cal. Hence, the 



heat evolved per milligramme of vapour absorbed is -j-j- = 0'57 cal. 



This is practically equal to the heat liberated (0*576 cal.) when a 

 milligramme of vapour at 25 condenses to form liquid water at 37*7, 

 which were the experimental conditions. But the uncertainties 

 involved in the above calculation forbid any further conclusion than 

 that already given, viz., that the heat of absorption by cotton is 

 composed mainly of the heat of liquefaction of water. f 



Summary and Discussion of Results. 



In the preceding pages it has been shown (1) that the conspicuous 

 rise of temperature which cotton undergoes when immersed in water 

 and its subsequent slow fall follow the same course as the similar 

 change which results from its exposure to air saturated with water 

 vapour, and that both are affected in the same way by previous 

 moisture and other conditions ; (2) that in the latter case the heating 

 is the direct result of the absorption of the vapour by the cotton, and 

 that the two processes can be quantitatively connected ; (3) that both 

 absorption and heat production continue appreciably for many hours, 

 though the rise of temperature is soon succeeded by a fall because the 

 heating effect is counteracted by radiation, etc., and that the evidence 

 points to no- definite limit to the absorption process; (4) that the 

 heat produced by the absorption is of about the same magnitude as 

 the heat of liquefaction of the same quantity of water, but may be, 

 in fact, either rather more or rather less ; (5) that in the case of 

 immersion in water, though the absorption of vapour cannot be 



* ' Chera. Soc. Abstr.,' 1900, TO!. 2, p. 188. 

 t The phenomena evidently have their origin in a difference of physical 

 affinities, which implies some difference between their heats. 



