D08 A Radioactive Gas from Crude Petroleum. 
decays to one-half value in about 30 minutes, and Adams 
has found that the induced radioactivity from the gas in 
Cambridge tap-water falls to half value in about 35 minutes. 
These values are practically the same as that determined in 
the present investigation, and confirm the conclusion already 
arrived at, that the active gas from crude petroleum is very 
co) 
probably identical with the emanation from radium. 
Conclusion. 
Summarizing the results given in the foregoing paper we 
have the following :— 
1. Fresh crude petroleum has been found to contain a 
strongly radioactive gas which is similar in its rate of decay 
and also in the rate of decay of the induced radioactivity 
which it produces to the emanation from radium and to the 
emanations obtained by a number of experimenters from 
mercury and from certain waters fresh from the earth. 
2. This radioactive gas decays approximately according to 
an exponential law, falling to half value in 3:125 days. 
3. It produces ‘an. induced radioactivity whose rate of 
decay is such that it falls toa half value in about 35 minutes. 
4. There are indications of the existence in crude petroleum 
of slight traces of a radioactive substance more persistent 
than the radium emanation, 
In a paper published during the progress of the experiment 
by Elster and Geitel* reference is made to a recent investi- 
gation by Himstedt on the radioactivity of petroleum, but 
up to the present time this communication has not been 
received, so that a comparison with his results cannot be 
made here. 
In conclusion I desire to express my thanks to Professor 
J. C. McLennan for suggesting the research and for his 
invaluable aid and advice at all times. I also wish to 
acknowledge my indebtedness to Mr. L. Gilchrist and to 
Mr. 8. Dushman for kindly aiding me in making some of 
the observations. 
Physical Laboratory, 
University of Toronto, 
March 31, 1904. 
* Archives des Sct. Phys. et Nat. sér. 4, t. xvii. (Jan. 1904) pp. 5-22. 
