|HENDERSON] DEPOSITS OF RADIUM, THORIUM AND ACTINIUM 159 
of the total activity collected by the cathode. The percentage of 
the total positively charged is obtained by subtracting from 100° 
twice the percentage found on the anode, as there is also deposited 
on the cathode by diffusion an amount of activity equal to that de- 
posited on the anode. 

TABLE I, 
Volts per cm. Percentage. | 
Cathode Activity. 
13 92-7 
25 93-5 
80 94-8 
150 94-9 
1,000 96-2 
2,000 96-4 
4,000 96-9 
12,000 97-8 | 




A few experiments were carried out in hydrogen, carbon dioxide 
and sulphur dioxide, with the results shown in Table II. 





TABLE II. 
Volts per cm. Percentage Cathode Activity 
He | CO: SO2 
| | 
150 95-3 | 89-9 —— 
4,000 96-2 93-1 93-2 
12,700 — | 93-9 | —— 



The results obtained in air show how much more difficult it is 
to bring over to the cathode the rest-atoms of radium than of thorium, 
under similar conditions. To obtain 97-8% of the thorium rest- 
atoms on the cathode a potential gradient of only about 30 volts 
per, cm. would be required, compared with a potential gradient of 
12,000 volts per cm. in the case of radium. The ionization between 
the plates was of the same order of magnitude in the two cases. At 
the higher potential gradient a considerably larger percentage was 
found positively charged than the results of Wellisch would indicate, 
and there appeared to be no limiting value to the percentage brought 
over to the cathode, but as the potential gradient was increased 
this percentage gradually though slowly increased. Thus, in spite 
