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XLI. The Diffusion of Uranium. By G. VON Hevesy, 

 Ph.D., Hon. Research Fellow of the University of Man- 

 chester, and L. YON Putnoky *. 



BOLTWOOD found that uranium in disintegrating emits 

 twice as many a-particles as the other bodies in the 

 uranium-radium series, each of which emits one a-particle 

 only. To explain this result we may assume, either that a 

 uranium atom expels two a-particles on disintegrating, or 

 that there is present with the uranium a second long-lived 

 body which also expels an a-particle. Geiger and JSuttall f 

 have shown recently that there are two different a-particles 

 emitted by uranium, one having a range about 4 mm, greater 

 than the other. The emission of an a-particle of definite 

 range is a characteristic property of a radioelement. The 

 obvious deduction, therefore, from Geiger and Nuttall's 

 experiments is that ordinary uranium consists of two bodies, 

 uranium 1 and uranium 2, each of which expels one a-par- 

 ticle. The same authors have shown further that there is a 

 linear relation between the logarithm of the range of the 

 a-particle in air and the logarithm of the transformation 

 constant. From this relation they have deduced that the 

 period of uranium 1 is 5 X 10 9 years, and that of uranium 2 

 2 x 10 6 years. Hence in 2500 parts of commercial uranium, 

 there is one part of uranium 2, and the activity of this body, 

 weight for weight, is 1250 times that of the uranium. The 

 isolation of uranium 2, therefore, would be of considerable 

 practical interest. 



In the preceding paper it is shown that after expulsion of 

 an a-particle, the resultant product in many cases has a 

 valency which differs by two from that of the disintegrating 

 atom. It is of interest, therefore, to ascertain whether 

 uranium 2 differs in valency from uranium 1. If it does 

 it would diffuse at a different rate, and should therefore be 

 capable of being partially separated from it. 



With this object in view the diffusion rates of the com- 

 plex bivalent ion U0 2 ++ and the quadrivalent ion U ++++ 

 have been compared. The bivalent ions are produced by 

 dissolving uranyl salts in water, and the quadrivalent ions 

 by dissolving the urano-salts. 



The diffusion constant either of the uranyl ion or of the 

 urano ion may be obtained in two different ways : — 



(1) By determining the weight of uranium in equal 



volumes of the solution in the various layers. 



(2) By determining the activity of the uranium in equal 



volumes of the solution in the various layers. 



* Communicated by Prof. E. Rutherford, F.R.S. 

 t Phil. Mag. vol. xxiii. p. 439 (1912). 

 2F 2 



