Boltwood — Salts of Radium. 



413 



of the emanation formed from the radium was actually re- 

 tained by the solid salt. In the following table (Table III) 

 the per cent of the total emanation contained in each film is 

 given in the first column, the per cent of the total emanation 

 which would have been found after the stated time had elapsed, 

 if uone had escaped, is given in the second column, and the 

 ratio of these, or the per cent of the emanation actually formed 

 which was retained by the film, is given in the third column. 



Film No. 



1 



2 

 3 



Table III. 

 1. 



35-9^ 

 il-5fc 

 66-5$ 



1000 



95$ 



3. 



71-50 



70*00 



It is apparent from these numbers that in the films used the 

 radium salt retained only from 7/0 to 71*8 per cent of the total 

 radium emanation formed within them. 



Since the increase in the activity due to the accumulation 

 of definite proportions of emanation and products is given in 

 Table I, it is possible to calculate the activity which the films 

 would have ultimately attained if no emanation had escaped 

 from them. Thus in the case of film No. 1, the difference 

 between the initial activity and the activity at the end of 3 

 days 22 hours was 1*88. This represents the activity due to 

 35*9 per cent of the emanation and active products of rapid 

 change. One hundred per cent of the emanation and active 

 products would therefore have an activity of 5*23 div. per 

 minute, and the maximum value of the activity would be 1*14 

 plus 5*23, which is 6'37. Dividing 6*37, the maximum activ- 

 ity, by 1/14, the initial activity, gives the value 5*59 for the 

 ratio of these two numbers. The corresponding data for all 

 three of the films is given in the following table (Table IV). 









Table IV. 







umbei 

 of 



Initial 

 activity 



End 

 activity 



Per cent of 

 emanation 



Activity 

 of 100$ 



Activity if 

 all emanation Eatio 



film 



retained 



emanation 



is retained 



1 



1-14 



3-02 



35-9 



5*23 



6-37 5-59 



2 



1-20 



5-21 



7 1 '5 



5-61 



6'81 5-68 



3 



1-12 



4-60 



66-5 



5-23 



6*35 567 



The average value of the ratio of the activity of the salt free 

 from emanation to the activity of the salt containing all of its 

 radium emanation is, from the above, 5*64. 



The increase in the activity of a film of pure radium bromide 

 was also determined by evaporating a solution of pure radium 

 bromide containing a little hydrochloric acid to dryness in one 

 of the glass dishes. The activity of the freshly prepared film 



