Gas from Crude Petroleum. 5O7 
currents and the abscissee times, illustrates the results in 
this table. From this curve it is seen that the conductivity 
decreases in a geometrical progression with the time, falling 
to one-half value in about 35 minutes. This phenomenon 
is exactly analogous to that which other investigators have 
found in working with the radioactive emanations from 
thorium and radium, ana which has been explained on the 
assumption that these emanations have but a transitory 
existence, and are gradually transmuted to a new substance 
which has a definite rate of decay and which is the cause of 
the so-called induced or excited radioactivity. On this view 
it is clear that, from the observations above, the active 
emanation from petroleum also produces the substance which 
is responsible for induced radioactivity, and that the pre- 
sence of this substance in the cylinder is the cause of the 
high conductivity of the fresh air which replaced that 
blown out. 
An experiment, giving similar results, was conducted 
under the same conditions as that just described, except that 
the cylinder was maintained for 22 hours before the emana- 
tion was expelled at a positive potential of 168 volts. This 
would show that the substance responsible for excited radio- 
activity was ieft in the cylinder in both cases when the air 
was blown out, and, as it is known that negatively- charged 
conductors in the presence of radioactive emanations become 
more active than those positively electrified, it is very 
probable that in the first experiment the excited radio- 
activity was deposited on the walls of the receiver, while in 
the second case it was concentrated upon the electrode C. 
A confirmation of this conclusion was obtained by exposing 
a conductor under negative electrification, and then under 
positive, to the petroleum emanation. The exploring electrode 
C was taken from the cylinder A and suspended in a large 
glass tube, through which air containing the radioactive 
emanation was drawn. It was connected for half an hour 
to the negative terminal of an electrical machine giving a 
potential of about 10,000 volts, and on being replaced in the 
receiver it increased the conductivity of the air to about three 
times its normal value. The conductivity in this case fell to 
a half value inthe same time as before. When the exploring 
electrode was suspended under a positive electrification of 
10,000 volts, for the same time, in the current of air con- 
taining the emanation, it did not acquire any appreciable 
activity. 
It has been shown by Mme. Curie, Rutherford, and others, 
that the induced radioactivity from the radium emanation 
