210 32 



we get, 



which wilh sufficient accuracy may be transformed into 



d-d' 



E =-- E 



■1'+" =.-) 



inasmuch as the quantity p. , , in the experiments in question, never exceeds 



0.02. All the measurements of emanation are corrected according to the last formula. 

 After having thus determined the amount of emanation, E, introduced into the 

 ionisation chamber, the emanation, Ct, contained in 1 ccm. spring gas at 760 mer- 

 cury and 20" C. is computed by simple proportion, when the reduced volume, V, of 

 the gas employed in the experiment, is known. 

 Therefore, „ 



Ct -= ^, 



Ct denoting the emanation contained in 1 ccm. of spring gas at the moment the 

 gas was inlroduced into the ionisation chamber. 



Supposing that the gas has been t seconds in the collecting tube, the emana- 

 tion Co contained in 1 ccm. of spring gas at the time the gas was collected, is given 



by Ihe formula 



C, = Co e- 216x10-"' 

 or 



Co - C,e2i«xio-«*. 



When Ct and / are known, Co can be calculated by means of this formula. Of 

 course, the formula is not applicable except when the gas contains only radium 

 emanation. Cq is the emanation per gram of uranium per second contained in 

 1 ccm. of spring gas at the moment the gas was collected from the spring. From 

 the foregoing it is obvious that the ultimate determination of the emanation con- 

 tained in the spring gases is only to be obtained by somewhat prolonged calcula- 

 tions. As examples showing how these calculations are carried out, I cite here in 

 extenso the measurements of the emanation of two samples of Icelandic spring 

 gases, with the necessai'y calculations. 



Reykir No. 5, Skföastaöalaug. 



Sample of gas collected on 16th. August 1906 at 5 p.m. Barometer: 746 mm. 

 mercury. Temperature: ITC. The volume of the collecting bottle, 102.2 ccm. 



The sample was introduced into the ionisation chamber on the same day at 

 8.30 p.m. Barometer 746mm. Air temperature 6° C. 



