On Loss of Charge by Evaporation. 489' 



dihydrol. The latent heat of evaporation of water includes 

 also the heat of dissociation of the dihydrol and trihydrol of 

 water into the hydrol of steam. The specific heat of water 

 is not an ordinary specific heat but includes a certain amount 

 of heat of dissociation, Pressure dissociates trihydrol at 

 rates given in Table VII. 



In Table XIII. are the physical constants of the two ingre- 

 dients of water given in C.G.S. units unless it is otherwise 

 stated. 



These results have mostly been obtained by application of 

 the mixture formula on the assumption that no shrinkage or 

 analogous change of properties takes place, and several of 

 them depend on *88 the density of liquid trihydrol at 0°, 

 which has been merely estimated by analogy from the density 

 of ice. 



Melbourne, July 1900. 



XLV1T. Experiments to Determine whether a Liquid when elec- 

 trified loses any portion of its charge by Evaporation. By 

 W. Cratg Henderson, M.A., B.Sc, Trinity College 

 Cambridge, late 1851 Exhibition Science Scholar*. 



THE question whether the vapour rising from the surface 

 of an electrified liquid is itself electrified or not. has 

 received considerable attention during recent years ; but un- 

 fortunately the various physicists who have made experiments- 

 on the subject have not all arrived at the same conclusion. 



On the one hand a negative answer is given to the question 

 by Blake f, by Schwalbe f , and by Sohncke § ; while on. the 

 other hand Exner || and Pellat^f both answer the question in 

 the affirmative. Each of these two physicists proceeds to 

 apply this conclusion from his experiments to the case of 

 evaporation of water from the earth's surface, and seeks thus 

 to account partly for the electrification of the atmosphere. 

 On consideration of Pellat's paper it seemed to me not in- 

 advisable to make still one more investigation of the problem, 

 and this idea was approved of by Professor J. J. Thomson. 



In the experiments described below I have kept in view 

 Pellat's application to the case of atmospheric electricity, and 

 have therefore in the first place followed him in using only 



* Communicated by Prof. J. J. Thomson, F.R.S. 

 t Blake, Wied. Ann. vol. xix. 1883, p. 518. 

 % Schwalbe, Ibid, vol lviii. 1896, p. 500. 

 § Sohncke, Ibid. vol. xxxiv. 1888, p. 925. 



!| Exner, Sitznnysber. der Kaiserl, Akad. der Wissen. zu Wien, xciii. 

 p. 222 (1886). f Pellat, Journ. de Phys. 1899, May, p. 253.. 



