Transformation Products of Radium. 643 
more than the initial part of the a ray curve. The results, 
however, show that an interval of two months is very short 
compared with the time required for the product D or E to 
be half transformed. 
Although the times of observation have been too short to 
determine experimentally either the value of 4 or Ay, it is 
possible, on certain assumptions, to form a rough estimate of 
these values. 
Tt has been experimentally observed that each of the 
products of radium which emit a rays supplies about an 
equal proportion of the activity of radium when in radio- 
active equilibrium. Since, when equilibrium is reached, the 
sume number of particles of each of the successive products 
must break up per second, this is an expression of the fact 
that every atom of each product breaks up with the expulsion 
of an equal number (probably one) of @ particles. Now 
radium D is directly derived from radium C, and since the 
rate of change of D is very slow compared with that of C, 
the number of particles of D initially present must be very 
nearly equal to the number of particles of radium C which 
break up during the time that radium D is being formed. 
Now, suppose that each atom of radium C and D emits one 
8 particle with the same velocity. The ionization produced 
by each particle will be the same under the same experimental 
conditions, and the integrated value of the saturation current 
due to the B rays over the time that the body is exposed to 
radium C must equal the corresponding integrated value 
for the @ rays during the life of radium D. Suppose, for 
example, that a quantity of emanation is introduced into 
a glass tube and left to stand for a month. During that 
interval the emanation has nearly all been transformed. 
The activity due to the 8 rays from it will reach a maximum 
several hours after the introduction of the emanation, and 
will then decay with the time falling to half value in four 
days. Let 7, be the maximum saturation current due to the 
8 rays, measured in a suitable testing vessel. The total 
quantity Q, of electricity passing between the plates of the 
testing vessel during the life of the emanation is approximately 
given by 
is be: ? 
a=| ia= | e™dt= >> 
0 v0 
where X is the constant of change of the emanation. 
In a similar way, if 7, is the initial current due to the @ 
rays from the radium D deposited in the tube (measured 
