490 



Mr. W. Craig Henderson on 



water, negatively charged, as the liquid to be evaporated, 

 and in making all the experiments at the ordinary tempera- 

 ture of the room. Following these experiments I have made 

 further experiments with water heated up to the boiling- 

 point, thus ensuring rapid evaporation; and, lastly, experi- 

 ments were made in which ether was used as the liquid to be 

 evaporated. 



It may be stated here that the result of my experiments is 

 in opposition to that of Pellat's, as they show no loss of 

 charge from the liquid by evaporation. 



1. Evaporation of Water at Ordinary Temperature 

 of Room. 



The method of experiment used by Pellat was to insulate 

 a shallow vessel on a block of paraffin, connect it to the in- 

 sulated quadrants of an electrometer, charge it to a known 

 potential noting the deflexion on the electrometer scale, and 

 then observe the leakage of this charge during a certain 

 time. The experiment was then repeated with the vessel full 

 of water. In this way Pellat found that the leakage was 

 somewhat greater when the vessel was full of water than 

 when it was empty. The results of four sets of experiments 

 are given and are as follows : — 





Potential 

 in Volts. 



Time between 

 beginning and 

 end of experimt. 



Electrometer Deflexion 



(a) witb J (b) without 



Water in vessel. 



Excess of 

 (a) over (b). 



I. ... 



155 



h. m. 

 1 25 



301-9 



278-2 



23-7 



II. ... 



116 



1 39£ 



145-0 



135-5 



9-5 



III. ... 



116 



1 44* 



172-8 



159-3 



13-5 



IV. ... 



116 



1 45 



182-9 



170-4 



12-5 



It will be seen that in these experiments the excess of 

 leakage when water was present over that when there was 

 no water is in no case more than 8'5 per cent, of the leakage 

 observed without any water in the vessel. The presence of 

 so large * a leakage when the vessel is empty would seem to 

 introduce a possible ambiguity into the result when water is 



* The percentage of the loss of charge without water in the vessel to 

 the total charge given to the system, as denoted by the deflexion on the 

 electrometer scale, is as follows : — 



In Expt. I. above, 56*8 per cent. 



» » ■"■• » O0".u „ „ 



„ ,, III. ., 70-5 „ „ 



»» n IV. .. o9'o ,, ,, 



