Weiffhts oj Radium and Thorium Emanations. f>< 



the value *100, which gives a molecular weight correspond- 

 ing with the lower limit given by Kuthertbrd and Brooks 

 (Joe. cit.). It is possible, however, that the value '100 is 

 somewhat too high, since no precautions seem to have been 

 taken to insure that temperature conditions were steady. 

 In the experiments to be described below, the emanation was 

 made to diffuse through porous plugs, and its rate of diffusion 

 compared with that of other gases of known molecular weight. 

 Assuming Graham's law. that the rate of diffusion of a gas is 

 inversely proportional to the square root of its density, it is 

 possible from such a comparison to calculate the molecular 

 weight of the emanation. 



2. Description of Apparatus, and Method of Experimenting 



with the Emanation. 



The air containing the emanation, the rate of diffusion of 

 which was to be determined, was confined over mercury in 



Fie. 1, 



I 



-0/9 



"l5rj=[f==-> To Water Pump 

 t 



the glass vessel A (fig. \). which will be referred to as the 

 •• diffusion-vessel," and which was 3 centimetres in diameter 

 and graduated downward- in cubic centimetres from to 200. 

 The volume of the "dead-space" from the tap T to the firsi 



