RADIOACTIVITY OF SOIL GASES 65 
one or two cases. This result can have little practical application in 
the direct location of oil. Practically all of the radiations from radio- 
active substances are absorbed by a few feet of soil and since oil 
usually occurs hundreds of feet below the surface of the earth, the 
radioactive minerals associated with oil are in practice much too deep 
to be detected. 
EXPERIMENTAL 
For the purpose of making relative measurements of the radon con- 
tent of the soil gases, an apparatus resmbling that of Elster and Gei- 
tel (7) was constructed as is shown in Figure 1. The gases are drawn 
out from a hole in the soil about 5 feet deep through the inside tube of 
a 3.5-inch iron casing driven into the hole. The circular flange at the 
top of the casing driven into the ground helps to give a better seal at 
the surface of the ground. The gases are passed through calcium 
chloride drying tubes into the 1o-liter ionization chamber of the 
electroscope which contains a phosphorus pentoxide drying dish. The 
gases are pulled through the system by a suction pump. 
The electroscope for measuring the Alpha-ray activity of the gases 
is of the Wulf type. In the upper chamber, the platinized quartz fibers, 
whose deflection is read with a reading microscope, are suspended at 
the top from an insulating quartz fiber bow. The fiber system is in- 
sulated from the case at the lower end by means of an amber plug. 
The air in the upper chamber is dried with phosphorus pentoxide. 
The fiber system is connected to the rod electrode in the lower 
chamber, the rod being held in an insulating ambroid plug. The charg- 
ing lever is shown at the top of the ionization chamber on the right. 
A bank of a dozen small 22.5-volt B batteries is used as a source of 
charging potential. 
Although the Elster and Geitel method of filling the ionization 
chamber would not seem to be as satisfactory as the later method used 
by Ambronn (8), since there is a possibility that the original air in 
the chamber may not be completely pumped out and the quantity of 
this air remaining may vary with each filling of the chamber, still the 
consistency of the results obtained by repeating measurements with 
gases from different holes at a given point would seem to indicate 
that the method was reliable enough for this type of measurement, 
in which consistency of repeated readings rather than precision of 
any particular reading seems desirable. 
The Wulf-type electroscope is quite suitable for field work in spite 
of the fact that it has a delicate suspension. This suspension will 
stand rather severe jars and the calibration remains essentially con- 
987 
