646 Prof. E. Rutherford on Slow 
The old radium, however, showed (immediately after this 
treatment) an activity measured by the @ rays of about 8 per 
cent. of its original amount. The activity could not be 
reduced any lower by further boiling or aspiration of air 
through the solution. This residual 8 ray activity was due 
to the product radium D stored up in the radium. It could 
not have been due to 8 rays from radium (C, since there was 
« distinct difference in penetrating power for the two kinds 
of 8 rays. The @ ray activity due to radium D was thus 
about 9 per cent. of that due to radium C. Disregarding 
the differences in the absorption of the @ rays, when the 
activity of the product D in radium reaches a maximum 
valne, the 8 ray activity due to it should be the same as that 
due to C. Since D is half transformed in forty years, the 
amount present in the radium after four years should be about 
7 per cent. of the maximum amount ; 7. e., it should show a 
8 ray activity of about 7 per cent. of that due to radium C. 
The observed and calculated values (7 and 9 per cent. 
respectively) are thus of the same order of magnitude. The 
amount of 8 rays from radium D present in pure radium 
bromide about one year old was about 2 per cent. of the 
total. 
The amount of radium E present in old radium was 
measured by observations of the activity imparted to a 
bismuth disk left for several days in the solution. Radium EH 
is not deposited to an appreciable extent on the bismuth 
from a water solution of radium bromide. If, however, a 
trace of sulphuric acid is added to the solution, the radium HK 
is readily deposited on the bismuth. The addition of sul- 
phuric acid to the radium solution practically effected a 
separation of radium D and E from the radium proper ; for 
the latter was precipitated as sulphate and the products D 
and HK remained in solution, After fiitering, the solution 
contained a greater proportion of the products D and E and 
very little radium. 
The ratio «/8 for the old radium was found to be about 
twice that observed for radium C. This result is in agree- 
ment with the deductions made in the calculations of the 
periods of the changes; for it can be theoretically shown 
that the amounts of D and E in the radium continue to be 
approximately proportional to one another after five years’ 
production, assuming the periods of the changes are forty 
years and one year respectively. 
The amounts of radium D and E observed in the old 
radium are thus in good agreement with the results deduced 
from other data. 
