Radium Emanation by Coconut Charcoal. 779 



I. 



Experiments to test the first point were made in Dec. 1907- 

 Jan. 1908 and July-Ang. 1908. The apparatus used was 

 that described in my earlier experiments *. Two radium 

 solutions were made up as follows : — 126 c.c. of a certain 

 radium solution was taken and divided into two parts of 

 43 and 83 c.c. (it was intended to be 42 and 84), so that the 

 radium contents were as 1 : 1*93. Each part was made up to 

 136 c.c. and placed in exactly similar bottles fitted with 

 inlet and outlet tubes so that air could be bubbled through 

 the solutions. Three exactly similar charcoal tubes, A, B, 

 (porcelain tubes 60 cm. long, 1*6 cm. 2 cross-section, central 

 foot filled with 39 gin. charcoal) were joined up in a circuit 

 as shown below : — 



Calcium-chloride m , . n „„ » 



" drying-tube. —Tube A Gauge A N 



N. 

 ,. „ , . , , ., \/ \To water 



r .btrong rad 1 um_Calcmm-cblonde_ T b fi G B— »-( Bottle. )_-> 



outside V_^\ B0lutl0U ' drying-tube. A y 



^ . . . / ^""^ 



\ Weak radium Calcium-chloride rv ■, n n n / 



i x- — i • l\. — lube C (jrauge L ' 



solution. drying-tube. *"«ov> ^ aLl= ^ v, 



Air was drawn through the three tubes by a water-pump. 

 The air-streams through the tubes were measured by means 

 of three gauges and adjusted to be of the same strength. 

 After the air-streams had been Mowing for some hours 

 they were stopped and the tubes t;iken and heated. The 

 amount of emanation the charcoal had absorbed was then 

 measured in the usual way. 



Let H = amount of emanation in the quantity of air that 

 passed along to tube A, 



and E = amount of emanation generated by the weaker 

 solution in ihe given time of exposure. 



Then the amounts of emanation arriving at tubes C and B 

 were H + E and H + 1*93E respectively. Let the amounts 

 of emanation caught bv the tubes A, B, C be denoted by 

 nH, 71,(11 + 1-93 E), r? 2 (H + E). Then, if 



n,( H + l-93E )-/zH_ 1-93 

 n 2 (H + E)-nfi ~ 1 ' 



it follows that n = n l = n 2 : i. e., the same fraction of the 

 emanation w r as absorbed in each case. 



Throughout the paper the amount of emanation is expressed 

 in the same arbitrary unit. The numbers are the leaks per 

 minute produced in my testing vessel by the emanation and 

 read on the scale provided to the electrometer. 



* See Phil. Mag. Oct. 1908 and July 1U10. 



