422 Diffusion of Actinium and Thorium Emanation. 



thorium and actinium emanations which have been determined' 

 by other observers under different experimental conditions. 



For thorium emanation we have two sets of experiments : 

 those of Rutherford* giving a diffusion coefficient *09 and 

 those of Makowerf giving # 109. In the case of actinium 

 emanation there has, up till now (as far as the author is aware), 

 been only one determination of its diffusion coefficient, namely, 

 that of DebierneJ, who obtained the value '112. Taking the 



mean of the two values quoted for thorium as '99 we obtain 



for the ratio of the molecular weights I -^r- \ = 1'28. 



It will be seen, on reference to Tables III. and IV., that 

 the mean value of PxK does not show as much as 5 per cent, 

 variation from any one of the values themselves, this would 

 indicate that the number given for the ratio of the molecular 

 weights, namely, 1*42 is not subject to as much as a 10 per 

 cent, error. 



The conclusion arrived at that actinium emanation is of 

 considerably lower molecular weight than thorium (and 

 therefore also than radium) emanation, is quite in agreement 

 with much of the recent work which has been done, showing' 

 that actinium is not one of the products in the direct line of 

 descent from uranium to radium § . 



Summary, 



1. The diffusion of actinium emanation in gases such as 

 air, hydrogen, carbon dioxide, sulphur dioxide, and argon 

 shows no considerable deviations from the ordinary laws of 

 diffusion. 



2. The variation with pressure of the coefficients of dif- 

 fusion of the actinium and thorium emanations appears to be 

 quite regular down to pressures of a few centimetres. 



3. A comparison of the diffusion coefficients of the actinium 

 and thorium emanations in air under similar experimental 

 conditions gives the ratio of their molecular weights as 1*42, 

 that of thorium being the heavier. 



In conclusion I have much pleasure in thanking Professor 

 Hutherford for several suggestions during the course of the 

 work, and Mr. J. N. Pring for assistance in preparing the 

 argon. 



* ' Radioactivity,' p. 276. 

 f MakoAver, Phil. Mag. 1905, p. 56. 

 j Debierne, Le Radium, 1907, p. 21.3. 



§ Rutherford, Phil. Mao-. 1907, vol. xiv. p. 733; Boltwocd, 'Nature/ 

 1907, p. 544. 



