Schlundt—Radioactivity of Some Spring Waters . 1247 
radioactive equilibrium the emanation present per liter of water. 
In the table of results the activities are expressed in terms of 
both uranium and radium. The radium values were obtained 
by multiplying the uranium values by 3.8 x 10 -7 , the equi¬ 
librium ratio, Ra/^ 
On the continent of Europe the activity of waters is expressed, 
as a rule, in absolute units. The saturation current, in elec¬ 
trostatic units, produced by the emanation per liter of water ex¬ 
presses its activity. The constants required in this system of 
units were determined for the electroscope used in the tests. 
The last column of the table of results gives the values of the 
activities in electrostatic units. 
The electroscope used in these experiments is of the C. T. R. 
Wilson type. It is rectangular in form,—6.4 x 10.1 x 14.7 cms. 
inside measurements,—and is securely fastened on a wooden 
base which also carries the reading microscope for noting the 
rate of fall of the leaf. Its rectangular brass frame is fitted in 
the front and back with pieces of plate glass, and is provided 
with two good brass stopcocks. On the top is a circular opening 
with a threaded brass ring into which screws a brass cap having 
a central opening. Through this hole projects the brass rod to 
which is fastened below the blade that carries the aluminium 
leaf. This leaf system is fastened into the cap by means of a 
sulphur cast which also serves to insulate it from the case of the 
instrument. To protect the sulphur insulation the electroscope 
is provided with a small cap that slips over the screw cap. 
The capacity of the electroscope was found to be 952 cc. A 
fall of the leaf of one division per minute represented 7.5 x 10" 4 
gram uranium or 28.5 x 10" 11 gram radium. Each division of 
the ocular of the microscope, in the space where readings were 
always made, represented a fall of potential of 1.7 volts, and the 
electrostatic capacity of the leaf system was found to be 9.4 cms. 
the latter constant was determined by means of a Harms stand¬ 
ard condenser whose capacity was 42.5 cms. The procedure 
given by Harms was carefully followed. 1 The calibration of 
iPhysik. Z. 5, pp. 49-50. 
