﻿Ultra-violet Light on Chlorine. 763 



very simple construction and thence into a large carboy 

 containing slaked lime, and from tins away into the open air. 

 An electric fan was employed to maintain a strong draught 

 and remove such chlorine as might leak into the air. 



The series o£ curves show the kind of result obtained : — 



Experiments on Air. 



Curve I. — Represents the results of one of the earliest 

 experiments using ordinary pure dry air. It shows how all 

 the negative ions produced by 10 seconds'' illumination were 

 caught by a potential difference of two volts, but that with 





Curve I. 





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CONOENSER PQT£NTJAL 



Effect of duration of illumination on the number and mobility 

 of negative ions in air. 



three times the illumination larger ions had been formed 

 requiring four volts before the saturation potential was 

 reached, only about 90 per cent, of the ions being caught at 

 2 volts. 



From the formula deduced for his condenser by Becker *, 

 the velocity of the ion corresponding to a saturation potential 

 of two volts works out to 0*28 centimetre per second for 

 one volt per centimetre, and for four volts half that velocity, 

 The formula is, however, only an approximation unless a 

 radial field is secured inside the condenser and the stream of 

 gas is free from eddies, whereas in these experiments such 



* A. Becker, Ann. dc Thys t vol. xxxi. p, 98 (1910). 



