70 



Mr. W. Makower on the Molecular 

 Table V.— Plug III. 



Gas. 



I 



v . j v. 



t. 



Vo- 



V- 



X. 



X 



mean. 



Xx-3120. 



XVM 

 X -3120. 



1-49 



0., 



o: ...... 



o; 



44-9 

 644 

 68-3 



46-7 

 66-5 

 70-3 



64 

 54 

 56 



35-5 

 50-8 

 540 



10-8 

 25-3 

 276 



•852 

 •845 

 •831 



•843 



•263 



C0 o .;. 



co; .;. 

 co; ... 



SO., ... 



SO; .:. 



so ... 



so; ... 

 so; ... 



65-8 

 61-5 

 630 



72-2 

 66-6 

 69-4 



! 62 

 50 

 60 



65-8 

 61-5 

 630 



36-0 

 370 

 343 



•670 

 •650 



•678 



•666 



•208 



1-38 



55-6 

 57-4 

 62-4 

 51-1 

 50-3 



643 

 65-8 

 72-6 

 59-4 

 57'3 



I 53 

 54 



! 66 

 50 

 43 



556 

 57-4 

 62-4 

 511 

 50-3 



3495 



362 



38-4 



316 



33-5 



•526 

 •525 

 •495 

 •529 

 •508 



•517 



161 129 



Emana- 

 tion ; 



49-4 1 50-2 

 53-3 53-8 

 52-6 53-1 

 48-6 49-3 



: 85 



91 



88 

 ; 98 



272 

 206 

 222 

 274 



138 

 107 

 117 

 1235 



•395 

 •384 

 •383 

 •395 



•389 



121 



(1-205) 



Part II. 



The Molecular Weight of Thorium Emanation. 



7. Introduction and General Method. 



On account of the rapid rate of decay of thorium emana- 

 tion, it is not possible to measure its rate of diffusion by the 

 method used for radium emanation and described above. 

 Kutherford ('Radioactivity/ pp. 233, 234) has, however, 

 described a method by which the diffusion-coefficient into air 

 may be determined, and obtains the value K = # 09, from 

 which he concludes that " the two emanations do not differ 

 much from one another in molecular weight/'' In the 

 following pages an account is given of some experiments in 

 which the rate of diffusion of thorium emanation was com- 

 pared with that of radium emanation, and as a result of 

 which the above conclusion is fully confirmed. The method 

 used depended on maintaining, through a vessel with porous 

 walls, a constant current of air mixed with emanation, the 

 concentration of which was measured before and after passing- 

 through this vessel, which will be referred to as the diffusion- 

 vessel. 



To make the quantity of emanation which passed through 

 the walls of the diffusion-vessel as great as possible, it was 

 necessary to make the area of the porous walls great com- 

 pared with the volume of the vessel, which was therefore 

 constructed as follows : — two plates of porous porcelain 



