269 
present is so minute that it precludes the possibility of a direct 
chemical investigation of its properties. 
We see from table I that the activity of AcX increases in 
the first day after removal to about 150}, of its original value, 
100 
80 
D 
© 
Activity 
+ 
© 
20 
Fig. 1. 
Time in days. 
reaches a maximum, and then decays with the time according to 
an exponential law falling to half value in 102 days. This expo- 
nential law of decay is clearly seen in Fig. 2, where the ordinates 
represent the logarithms of the activity of the product AcX, and 
the abseissae the time after separation. On subtracting from the 
quantities given in the table I the number 2:70, which represents 
the activity of the residue which did not decay with the time 
the points fall accurately on a straight line as in the figure. This 
non decaying residue comes probably from the small amount of 
actinium, which is not preeipitated and is therefore present in the 
filtrate. 
The activity of actinium, from which actinium X was removed, 
increased so that the recovery curve was approximately compli- 
mentary to the decay curve of AcX. The small difference between 
the experimental and the theoretical eurve, as expressed by the 
