﻿760 Dr. E. B. Ludlam on the Action of 



In this way the nuclei have the effect of conserving the 

 ions, damping their velocity and so preventing their rapid 

 recombination and diffusion to the walls*. 



Ozone. — Is produced even in air which has been purified 

 by cold and must be a consequence of the direct action of 

 the light on the molecules of oxygen ; its production is 

 caused by wave-lengths longer than 200 /jljul, and is not 

 associated with airy photoelectric effect. 



Effect on the Walls of the Vessel. 



All the experiments on ionization of gases are complicated 

 by the action of the light on the walls of the containing 

 vessel. No conductor is available for the walls which does 

 not either give out ions itself, or contaminate^ the gases. 

 The wave-length at which the wall-effect begins is longer 

 than that at which the gas effect first takes place ; further, 

 the ions produced are always negative, whereas the gas effect 

 produces an equal number of positive and negative ions ; 

 consequently, the excess of negative ions over positive is 

 throughout these experiments ascribed to the action of light 

 on the walls of the vessel. 



Wave-length. — A careful study of the effects observed 

 through different media leads to the conclusion that the 

 difference in properties between visible violet and the ad- 

 joining ultra-violet is less than between some portions of the 

 ultra-violet region, and this may account for numerous dis- 

 crepancies between the results of different observers who 

 have unwitting!}- been experimenting with light of different 

 wave-lengths. 



Experimental. 



The source of light employed was a spark of about one 

 centimetre in length produced between alunrnium terminals 

 connected to a coil of special construction, w r ound with a 

 secondary of low resistance and provided with a condenser 

 of great capacity. The coil was supplied with a current of 

 20 amperes broken by a Wehnelt interrupter. The coil and 

 spark-gap were both enclosed in tin boxes connected to 

 earth. 



Chlorine is a difficult gas to work with. Accordingly, the 

 plan followed was to commence with air, to observe the 

 effects already established with regard to it and proceed to 

 examine the effect of an increasing proportion of chlorine, 

 until pure chlorine itself was under investigation ; then, to 

 add intentionally certain vapours and note their effect. 



* The reverse action, destruction of ions, lias been observed in cases 

 where the concentration of the nuclei was verv QTeat. 



