130 DISTRIBUTION OF THE ACTIVE DEPOSITS OF RADIUM 



by Wellisch, must be ascribed to the fact that in the earlier 

 types of vessels there was no means of preventing the recom- 

 bined rest-atoms from diffusing into the vessel proper and 

 settling on the plates. That such an effect was appreciable, 

 even in the present vessel where there was little space between 

 the edges of the guard-rings and the bell-jar, was shown in 

 the following manner. Two tinfoil screens were arranged to 

 slip over the plates while in the electroscope. One exposed 

 only the outer part of the anode plate, while the other exposed 

 an equal area at the centre of the anode. If diffusion of 

 recombined rest-atoms took place from outside one would 

 expect to find more activity per unit area near the edge 

 than near the centre of the plates. This would of course be 

 noticeable on the positive plate only. Experiments were 

 performed, leaving out the cotton wadding previouslj^ referred 

 to. It was found that the activity near the edge of the anode 

 plate was about 1.4 times that on an equal area near the 

 centre. Similar experiments carried out with ths wadding in 

 place gave the activity near the edge practically the same 

 as that on an equal area near the centre. 



A few experiments were carried out in atmospheres 

 of hydrogen, carbon dioxide and sulphur dioxide, with the 

 results shown in Table II. 



Table II. 



Potential 

 gradient 



Percentage Cathode Activity. 



Volts per 

 cm. 



Ho. 



CO.. 



SO2. 



150 



4000 



12000 



95.3 

 96.2 



89.9 

 93.1 

 93.9 



93.2 



