Boltwood — Life of Radium. 499 



This is the form of the expression used in calculating the 

 results of the experiments. Two curves with the time in days 



taken as the 'abscissas, one for the values of 1 — e~ and the 

 other for the values of 1 (1— e ' ), were plotted on 



AC , 



squared paper and afforded a convenient means for quickly 

 obtaining the values of these quantities for different periods 

 of time. 



If, after testing a solution, a second test was made less than 

 30 days later, the value obtained for the amount of emanation 

 in the second case was increased by an amount equal to Ie~ 2 ' 

 where I was the activity of the emanation found in the first 

 test and £ 2 was the interval between the times of testing. 



The method followed in calculating the results of the 

 experiments will be illustrated by the following example : A 

 solution of ionium (Solution 3) was prepared and was sealed 

 up, after thorough boiling to remove all emanation. Five 

 daj^s and twenty-two hours later the gases were boiled out and 

 tested in the electroscope. The leak due to radium emanation 

 was found to be equal to 0*094 divisions per minute. Eighteen 

 days later (23*9 days from the start) the gases were again 

 removed and the activity of the emanation then obtained was 

 equal to 0*613 div. per min. in the electroscope. The value 

 found in the first test was 0*094, and 0*094Xe~ 18;i is 0-004; 

 this quantity was therefore added to 0*613, giving 0*617 div. 

 per min. for the activity of the emanation at the second time 

 of testing. The equations then had the form 



(For 5-9 days) 0*65^ + 2*25^ = 0*094 



(For 23-9 days) 0*986^ + 18*36^ = 0*617 



and from these equations the values a = 0*0317 and q = 0*034 

 were obtained. The sensitiveness of the electroscope was 

 such that a leak of 1*00 div. per min. corresponded to the 

 equilibrium amount of emanation from 1*05 XlO -9 gram of 

 radium. The amount of radium produced per day was there- 

 fore 0*0333 XlO" 9 gram and the amount present in the solution 

 at the start was 0*0357 XlO -9 gram. 



Ionium /Solution 1. 



The preparation of this solution has already been described 

 in a previous paper.* The mineral used consisted of about 

 one kilogram of a crude carnotite ore containing approximately 

 nine per cent of uranium and a total quantity of radium equal 

 to about 3*1 XlO -5 gram.f 



*This Journal, xxv, 371, 1908. 



f This is the solution mentioned in an earlier paper, this Journal, xxii, 537, 

 1906, where the content of uranium in the mineral taken and the amount of 

 radium produced in the first 193 days are incorrectly given. 



