12 



DISTRIBUTION OF THE ACTIVE DEPOSIT OP 



anode, and hence was electrolytically saturated with hydrogen. 

 To test if a similar effect took place with thorium in air, ex- 

 periments were made, using as cathodes plates previously 

 used as anodes, and vice versa. No effect was detected within 

 the limits of observational error. 



It was found by Wellisch and Bronson that in the case of 

 radium a much greater proportion of the rest atoms were 

 uncharged in an atmosphere containing water vapor than in 

 dry air. The effect of water vapor on the distribution of 

 the rest atoms of thorium was accordingly tried. In order to 

 obtain the maximum effect possible with water vapor ex- 

 periments were made with air saturated with water vapor 

 at room temperatures. This was accomplished by substitut- 

 ing water for the sulphuric acid of the previous experiments 

 so that the plates stood over water. As the temperature of 

 the laboratory varied from day to day the conditions under 

 which the different results were obtained were not identical. 

 The general effect however is seen in table 2, and is plotted 

 in curve B, Fig. 4. 



Table 2. 



Volts. 



Percentage 

 cathode activity. 



6.4 



66.5 



14.1 



73.7 



20.3 



78.8 



40.0 



84.8 



99.7 



93.4 



196. 



96.0 



313. 



97.2 



The effect of water vapor is evidently to greatly increase 

 the ralre of recombination. The^question of its effect on the 

 initial charged condition of the rest atoms will be referred to 

 after the effects of ether vapor have been discussed. 



