of Electrification by Evaporation. 401 



(The sign indicates the charge apparently carried away by the 

 vapour.) 



No correction has been made in the above figures for the 

 deflections obtained with the dry dish. These were more vari- 

 able, but usually of the same sign as when a liquid was evapo- 

 rating, and of a magnitude not very different. Making this 

 necessary correction, 



Alcohol gavea potential \ __^ io ^ m that of a DanieIFs 

 iroiu • • • • . j r n 



Cotton wet with alcohol 1 rtr .»o.i n a-a L ce ' 



x j.- i j? }■ —0-028 to— O'OoO 

 gave a potential from J " " 



In the above observations the rate of evaporation was not 

 measured. 



The earlier observations on water and salt water gave deflec- 

 tions about 0*1 that given by a Daniell's cell, the deflections 

 with the dry dish being nearly the same (see Table I.). Though 

 the dish was insulated for five minutes or more, the position 

 of the spot of light was read every thirty seconds. Far the 

 greater part of the deflection was attained in the first minute 

 or two ; and after five minutes scarcely any further deflection 

 could be discovered. 



The observations thus indicated that the small deflections 

 obtained were mainly due to leakage from electrified parts of 

 the apparatus. The sources of this leakage were carefully 

 investigated ; and three principal ones were discovered, viz. 

 the charged needle of the electrometer, the vulcanite posts 

 supporting the electrodes of the electrometer, and the glass 

 cup of the commutator. In the later experiments care was 

 taken to eliminate these sources of leakage as far as possible. 

 The connexions were so made that the electrodes and commu- 

 tator were not touched for clays before the experiments, and 

 the charge on the needle was not replenished within about 

 twenty-fours of the experiment. When these precautions 

 were taken the deflections became less than 0*01, and gene- 

 rally less than 0-005 of a Daniell's cell (see Table II.). 



In contrast with these deflections, Tait and Wanklyn ob- 

 tained, by dashing liquids on red-hot platinum, for 



solution CuS0 4 a potential + 300 times that of a Daniell's cell, 



solution NaCl „ „ +120 ., „ „ , 



distilled water „ „ + 21 „ „ „ , 



alcohol „ „ + 3 „ ,, „ 



