Decembee 3, 1915] 



SCIENCE 



807 



The most active source thus far recorded 

 was found in mine water at Joachimstlial, 

 Bohemia, and contained per liter an amount of 

 emanation equivalent to that in equilibrium 

 with 700 X 10'^° gram radiiun. 



Fig. 1 shows the type of electroscope used in 

 the present experiments. The gold leaf was 

 mounted on a brass rod passing through a sul- 

 phur plug into the ionization chamber. The 

 leaf was used at a fairly high sensibility. 

 Since it was not convenient to use a guard ring, 

 the natural leak of the instrument was large, 

 varying from .25 to .40 divisions per minute 

 on different days. No suitable constant source 

 of potential was available and the leaf was 

 charged with an ebonite rod by removing the 

 metal cap at the top. The ionization chamber 

 was gas tight and was of approximately 725 c.c. 

 capacity. 



Samples of water to be tested were collected 

 in suitable boiling flasks at different localities. 

 The contained emanation was removed by boil- 

 ing and allowed to cool. The ionization cham- 

 ber was then partially exhausted, and the mix- 

 ture of air and emanation allowed to flow 

 slowly into it through a drying tube of calcium 

 chloride with end plugs of cotton wool. The 

 rate of motion of the gold leaf in divisions per 

 minute after three hom-s was used in compar- 

 ing the activities of different samples. All 



readings were corrected for the natural leak 

 of the instrument and for the decay of the 

 emanation itself during the time elapsing be- 

 tween collection and examination. After three 

 hours the emanation was pumped off by means 

 of a foot bellows through a long pipe into the 

 open air far outside the laboratory. The ioni- 

 zation then decayed with the half value period 

 of active deposit. 



A diagram of the apparatus used for boiling 

 out the emanation which is but a slight modi- 

 fication of that described by Makower and 

 Geiger^ is shown in Fig. 2. The burette was 

 filled with water previously boiled in the flask 

 A. The water under investigation in flask B 

 was boiled from ten to fifteen minutes. Ema- 

 nation still remaining in the connecting tube c 

 after the burette had been emptied was car- 

 ried over into it by air let in through the side 

 tube d. 920 c.c. of water was collected for each 

 test. 



Standardization of the Readings of the 

 Electroscope 



In order to standardize the readings of the 

 electroscope 10 c.c. of a standard solution con- 

 taining 1.57 X 10"^ mg. radium was diluted 

 to 250 c.c, and 60 c.c. of this solution boiled 

 thoroughly and allowed to grow emanation for 

 31 days. This emanation, the equivalent to 

 that in equilibrium with 3.77 X 10"" gram 

 radium, was introduced into the electroscope. 

 The ionization after three hours was 57.11 

 divisions per minute. 



The results obtained from a number of 

 sources are given in the following table : 



Column 5 in the above table records the 

 amounts of radium emanation found in the 

 different sources. These values are compara- 

 tively large. The maximum activity found in 

 spring water by Shrader* near Williamstown, 

 Mass., was 2.12 X 10"^" gram radium. The 

 most active sources found during this inves- 

 tigation were in Arlington, E. I. Both the 

 springs examined flowed out of Fenner's Ledge. 

 This contains deposits of graphite mixed 

 with a low-grade soft coal. The geological 



3 "Practical Measurements in Radioactivity," 

 Longmans, 1912, p. 114. 



i Physical Beview, May, 1914, pp. 339-345. 



