Oe =e 
Transformation Products of adium. 645 
this is not realized in practice. The 6 rays of radium D 
are slightly less penetrating than those of radium ©, while 
the a rays of radium H have only about half the penetrating 
power of those of radium C. Our knowledge of the mechanism 
of absorption in matter is, however, too imperfect to correct 
for these differences with any certainty. 
The above methods of calculation, though.somewhat com- 
plicated, certainly serve to give the right order of magnitude 
of the periods of the two changes. It will be shown, too, 
that the calculated periods agree approximately with the 
amounts of radium D and H present in old samples of radium. 
The chief uncertainty in the methods of calculation lies in the 
difficulty of ascertaining the relative electrical effect produced 
by the a and @ particles compared with those emitted from 
radium C, 
The time T required for each transition product of radium 
to be half transformed is shown in the following table :— 
Transition Time 'T' to be 
products of radium. half transtormed. 
RaApIvumM. about 1000 years. 
EMANATION. 4 days. 
Rapium A. 3 minutes. 
ceoron ise 21 minutes. 
Rapium C. 28 minutes. 
are D. about 40 years. 
Rapium E. about one year. 
Keperiments with Old Radium. 
Since the substance radium D is produced from radium at 
a constant rate, the amount present mixed with the radium 
will increase with its age. I had in my possession a small 
quantity of my first specimen of impure radium chloride, 
kindly presented to me by Professors Elster and Geitel four 
years ago. ‘the amount of radium D present in it was 
tested in the following way :—The substance was dissolved 
in water and kept continuously boiling for a period of about 
six hours. Under these conditions the emanation is removed 
as rapidly as it is formed, and the @ rays from the radium, 
due to the product radium C, practically disappear. A newly 
prepared specimen of radium bromide under these conditions 
retains only a fraction of 1 per cent. of its original @ radiation. 
