152     Dr.  H.  L.  Bronson  :  Effect  of  High  Temperatures  on 
easily  calculated  that  the  final  period  of  decay,  that  is  the 
period  of  radium  B,  is  about  25'$  minutes.  The  experimental 
results   are  not    accurate    enough    to    make   the  last    figure 
WQ/lt//OI/y  JG    AJ/S/SJJA//  JO   30? 
certain,  and  a  mean  of  a  large  number  of  other  values  obtained 
would  indicate  that  25'$  minutes  may  be  a  trifle  too  small. 
It  seems  certain,  however,  that  the  period  of  radium  B  is  very 
nearly  26  minutes. 
The  theoretical  values  in  the  following  table  were  obtained 
by  assuming  that  only  two  changes  take  place  in  the  active 
