273 
probably the y rays are emitted also by AcX itself. For instance, 
the eurves of decay of activity of AcX measured by @ and f rays 
are throughout identical even from their beginning; and further, 
the activity of AcX measured by £ rays, 5 minutes after strong 
heating, when all the volatile exeited activity should be driven 
off, exhibits a very great initial value, which could not be the 
case if the  rays were emitted only by exeited activity. 
It is thus most probable that AcX itself gives rise to all three 
kinds of rays. 
Source of the actinium emanation. 
In the case of thorium the produet ThX was intermediate be- 
tween thorium and its emanation. In order to see if AcX oceupies 
the same position in actinium, I measured the rate of change with 
time both of the emanating power of AcX and of actinium from 
which AcX was removed. The measurements of activity of the 
emanation were made in a eylindrieal brass testing vessel!) in the 
interior of which three insulated electrodes were placed; during 
the measurements one of the electrodes was connected with an 
electrometer and the other two were earthed. 
Both actinium X and actinium deprived of AcX were placed 
in solutions of ammonium chloride in two bubbling flasks, and 
these could be successively connected with the testing eylinder in 
which the amount of emanation was measured. For the purpose of 
comparison with a substance of a standard emanating power the 
following arrangement was used. 
The current of air passed through the bubbling bottle and 
carried with it the emanation of the product to be investigated. 
It thus passed through the testing eylinder in which the activity of 
the emanation was measured. On leaving the eylinder the current 
of air entered a glass tube 2 cms in diameter and about 2 meters 
long. At the end of this glass tube some fresh solid actinium was 
placed and the emanation from this was carried into the second 
testing cylinder where its activity was measured. 
In this manner the same current which carried the emanation 
from the product under investigation, also carried the emanation 
from the standard aetinium. In passing through the long and wide 
!) See Rutherford: Radioactivity p 199 and Fig. 37. 
