35 213 



As many investigators, especially German, have employed of late the unit of 

 emanation in spring gas proposed by Mache and Meyer, it is important to be 

 able to compare this nnit directly with the one employed in these experiments. 



This may be done in the following manner. According to equation (7) on 

 page 207 the relation between the leakage in the ionisation chamber and the ema- 

 nation expressed in the units of Mache and Meyer is given by 



A = 4.74 X 10-ßa„. 

 In some experiments I made special efforts to measure the ionisation imme- 

 diately after the introduction of the radioactive gas into the ionisation chamber. 

 From these experiments I deduced 



a„ = 0.6 am 



consequentlv 



' ' A = 2.84 X 10-6o„,. 



If, in measuring rim, v ccm. is used instead of 1 litre of^the spring gas, the above 

 equation is transformed to 



A ^2-:^i^^^^„. = 2.84x10-3^. 

 o V 



1000 



On the other hand, 1 calculated the emanation in accordance with the formula 



C = \Ml""^. 

 I' 



Hence it is clear that my unit may be transformed to the unit of Mache and Meyer 



by multiplying the amount of emanation expressed in my units, by the factor 



2 84 

 f-^fjX^O-^ - 2.11 X 10-3. 



Accordingly, the emanations of the two samples quoted, expressed by the 

 units of Mache and Meyer, are 



Reykir No. 5 2.66 x 10"^ (E. S. E.) 



Hveravellir No.27 . . . 27.6 x lO^s (E. S. E.) 



It was important to ascertain how far the radioactive emanation contained in 

 the Icelandic spring gases is due exclusively to radium, and whether the gases 

 contain some other radioactive emanations. I shall now mention two methods by 

 which I endeavoured to ascertain this point, viz. (1) by examining the ionisation 

 curve, which shows how the ionisation in the ionisation chamber increases during 

 the first hour after the introduction of the active gas; (2) by determining the coef- 

 ficient of decay for the emanation contained in the spring gases. A third method, 

 especially applicable to the investigation of rapidly changing emanations, will be 

 mentioned later. 



If, in determining the nature of the emanation, one bases one's observations 

 only on the ionisation curve, great care must be taken in the filtration of the gas 

 before introducing it into the ionisation chamber. The slightest quantity of dis- 

 integration products of the emanation, escaping into the ionisation chamber with 



28* 



