Gas from Crude Petroteum. 505 
appear that there is present in crude petroleum an active 
substance more persistent than the emanation from radium, 
perhaps a minute quantity of radium itself. If this be so, 
the air drawn through the oil might possibly carry with it 
into the cylinder a slight trace of this substance. Such a 
condition would explain the departure from the law of decay 
I,=I,e— exhibited by the increasing values of 1/X in column 1 
of Table II. 
Induced Radioactivity—Hach time the gas containing the 
emanation was blown from the cylinder, the conductivity of 
the ordinary air admitted from the room was found to be 
still very high. Repeated tests showed that the initial con- 
ductivity of this fresh air was about 35 per cent. of that of 
the displaced gas, but in every case it quickly fell, until 
after about two hours the conductivity reached the normal 
value of 16:5. In expelling the emanation, a blast of air 
was sent through the cylinder continuously for five minutes 
by means of a small foot-pump, after which the receiver was 
again sealed. | 
Measurements were then made on the conductivity at short 
