398 



Mr. K. H. Kinodon on some 



T (brs.). 



n. 







27-0 



22 



25-2 



40 



24-1 



88 



211 



113 



19-S 



139 



18-0 



209 



16-7 



310 



16-0 



454 



15-4 



A curve plotted from these readings is shown in fig. 2. 



Fiar. 2. 



O 50 IOO 



Time in hours 



I5Q 2QO 250 3GO 350 400 4-50 500 



The decrease in the ionization clearly indicates the pre- 

 sence of some radioactive impurity in the gas. From the 

 shape of the curve it may be estimated that the number of 

 ions made per c.c. per second would finally fa]l to about 15. 

 From this the number of ions per c.c. per second initially due 

 to the radioactive impurity was about 12. As this number 

 of: ions had decreased to 6, or to one half, in about 90 hours 

 (3*8 days), it may be concluded that the impurity was radium 

 emanation. In the gas from the Prest-o-Lite tank this 



