728 Mr. A. S. Eve on the Amount of Radium Emanation 

 An example of the method followed is here given : — 



Division per minute. 



A. Natural leak of the electroscope *065 



B. Obtained from tubes after 3*7 days' rest . '2b 



C. Obtained from tubes after 3*7 days' run . "65 



C— B. Due to emanation in 8 cb.m. of air .... *40 



A standard solution, containing 10~ 9 gram of radium, was 

 then placed in a flask, and air was bubbled through the 

 solution, through drying-tubes, and through the three iron 

 pipes, at the same rate and for the same time as before. 



Division per minute. 



D. Due to the standard solution and to all 1 



causes under heading C J 



2-1 



D— C. Due to 10~ 9 gram radium 1*45 



Hence 10 ~ 9 gram of radium gave 1*45 D/m, and 8 cb.m. 



of air gave *40 D/m. Therefore, 1 cb.m. of air contained the 



40 10 -9 

 emanation from --t-= x or 35 X 10~ 12 gram of radium. 



This was the largest value obtained. The smallest was about 

 half this; and the mean value was 27 x 10~ 12 gram. 



This method was laborious, a complete observation requiring 

 nearly 4 days for pulling the air through the pipes, and 9 hours 

 for obtaining the concentrated gases and introducing them 

 into the electroscope. These experiments were made in the 

 month of May. 



A third method was now adopted. Glass tubes were taken, 

 25 cms. long and 2 cms. in diameter ; each was filled with 

 50 grams of freshly prepared charcoal. They were arranged 



Fig. 2. 



<^~e« 



in the manner shown in fig. 2. The air passed through A, 

 and then divided into two currents passing through B and C 

 respectively. It is obvious that the speed through B, or C, 

 is half that through A ; and it is known that the absorption 

 is a function of the speed. Each tube was heated by two 

 Bunsen burners held by hand, and the process of heating was 

 continued until the gases practically ceased to come from the 

 charcoal. The air in the tube was then blown out, and also 



