Gas from Crude Petroleum. 501 
of the observed phenomena lead to the conclusion that the 
air, in passing through the petroleum, becomes mixed with 
some radioactive gas or emanation. The initial portion of the 
curve leading up to the maximum corresponds exactly to that 
Current 
440 «166 
Hours. 
0 2 40 6) 8) 100 220 
of the curve given by Rutherford * for the emanation from 
radium, and also to that of the curve given by Strutt for the 
radioactive gas obtained by bubbling air through mercury 
and may be explained in the same way. The value of the 
conductivity immediately after the cylinder has been sealed 
measures the ionization due to the emanation itself. But, 
according to the disintegration theory proposed by Ruther- 
ford, the emanation is continuously producing by its decay 
the matter which causes excited radioactivity, and the 
ionizing power added by this latter material more than 
neutralizes, for a time, the decrease due to the decay of the 
emanation. Thus the conductivity of air freshly charged 
with this emanation gradually increases to a maximum state, 
which is reached when the loss in the ionizing power due to 
the decay of the emanation is just equalled by the gain con- 
tributed by the excited radioactivity produced in this process 
of decay. 
From this time the rate of change indicated gives the rate 
of decay of the emanation. The law which the rate of decay 
* Phil. Mag. vol. v. (April 1903) p. 445. 
