310 B. B. Bamsey — Radioactivity of Spring Water. 



Where e = amount of emanation in electroscope. 



* mRI = maximum current, at end of three hours, in E. S. units. 

 V = volume of ionization chamber. 

 S = surface of ionization chamber. 



This formula applies to a cylindrical chamber whose volume is 

 about one liter and whose height is one to three times the 

 diameter. 



Accuracy of theformulce. — As a test of the Duane formula 

 the following test made by two students will serve. The two 

 electroscopes were connected together and filled with emana- 

 tion, care being taken to see that the emanation was the same 

 density in each electroscope. This experiment was carried out 

 under favorable conditions in the laboratory. 



Electroscope "Tin" Schmidt 



Observer F. G. T. W. D. S. 



Diameter of chamber 10*8 7*8 cm. 



Height of chamber 12 - 1 20-3 cm. 



Volume of chamber 1102" 968* cu. cm. 



Surface of chamber 594' 586*6 sq. cm. 



Capacity of electroscope.. 17* 6 '3 cm. 



Amount ©f emanation 206000- X 10 -13 200000- X 10 -13 curies 



Another test made in the field at the spring by the same 

 observers will give an idea of the accuracy under unfavorable 

 conditions. 



Illinois Central Spring, July 24th, 2 p. m. 



Water temperature, 12° -4 C Air, hot and Temperature 



windy. 1 04° F. in shade. 



Observer F. G. T. W. D. S. 



Electroscope "Tin" Schmidt. 



Curies per liter *f water 360- X 1 -13 300* X 10 -13 



The following test made at a spring will give an idea of the 

 accuracy of Schmidt's shaking method. The same electroscope 

 was used, but three different shaking cans were used. 



J. C. S. Spring, Aug. 5th, 1914. 



Water temperature, 12°-5 C. Air temperature, 30° C. 



I II III 



Time of beginning 11*03 a.m. 11-46a.it. 2-00 p.m. 



Vol. of water '107 3-000 5-000 liters. 



Vol. of air -943 4-100 2*100 liters. 



Mean deflection of electro- 

 scope per minute 16- 29-5 52-5 divisions. 



Curies per liter 425-X10' 13 435-XlO~ ia 443-X10" 12 



