the Diffusion of Uranium, 417 



(3) Diffusion velocity o£ 1/6 molar U(SOJ 2 in water. 

 Diffusion constant calculated from the weight of material, 



0*480 sq. cm. per day. 



Same calculated from the activity, 



0-480 + 0-004 sq. cm. per day. 



In these experiments diffusion was allowed to take place for 

 periods of from two to eight days. 



The results show clearly that the differences in the diffusion 

 constant calculated from the amount of material used and 

 from the activity lie wholly within the error of experiment. 

 If uranium 2 differs in valency from uranium 1 by two units, 

 the diffusion constants calculated from the two sets of data 

 should show a difference of about 30 per cent. 



The fact that the diffusion constant of the quadrivalent 

 urano salts is only about 20 per cent, lower than that of the 

 bivalent uranyl salts may seem to contradict the conclusions 

 of the preceding paper. In these experiments, however, not 

 only does diffusion take place in excess of the anion, but the 

 solution used is so concentrated (1/6 molar) that the disso- 

 ciation of the U(S0 4 ) 2 into its quadrivalent ions is incom- 

 plete, and it is to be expected therefore that it has a 

 correspondingly greater diffusion constant. 



It is difficult at present to say whether or not the results 

 of these experiments contradict the hypothesis that loss of 

 an a-particle from an atom causes the valency of the resultant 

 atom to differ by two from the parent one. The existence 

 of uranium 2, though rendered probable by the work of 

 Geiger and Nuttall * and of Marsden and Barrett | , is riot 

 established with certainty. Again, its position in the dis- 

 integration series is at present uncertain. It may lie either 

 between uranium 1 and uranium X, or between uranium X 

 and ionium. The experiments of Soddy on the growth 

 of radium from uranium X indicate that it comes after 

 uranium X ; though naturally these results are capable of 

 another interpretation. If this were so, uranium (hexa- 

 valent) produces uranium X (quadrivalent), and the latter, 

 uranium 2 (hexavalent). The transformation of uranium 1 

 into uranium X, and that of uranium X into uranium 2, 

 would then result in the valency changing by two units in 

 each case. It is not improbable that this is really what takes 

 place, for the expulsion of an a-ray should change the nature 



^ JuOC. Ctt. 



t Proc. Phys. Soc. 1911, vol. xxiii. p. 367. 



