210 Prof. F. Soddy and Miss A. F. R. Hitchins on the 



a connected account of the whole work up to that date was 

 given in a lecture at the Royal Institution (March 15th, 

 1912)*, and the conclusions then drawn may be briefly 

 restated. 



In the following table particulars are given of the four 

 uranium preparations studied : — 



No. 



Grams of 

 Uranium. 



Date of 

 purification. 



Method of 

 purification. 



Initial rate of growth 

 of radium per year per 

 kilogram of uranium. 



I. ... 



255 



21/10/05 



Ether. 



I3xl0~ 12 g. 



II. ... 



278 



14/ 8/06 



Ether. 



8xl0" 12 g. 



nr. ... 



408 



13/12/06 



Ether. 



3-5xl0~ 12 g. 



IV. ... 



3000 



4/ 6/09 



Henry stallization. 



25 xlO -12 g. 



The methods of purification of the uranium adopted, ex- 

 traction with ether in the case of the first three preparations 

 and repeated recrystallization from water in the case of the 

 fourth, are those generally employed to remove uranium X 

 from uranium, and, since uranium X is now known to be 

 isotopic with ionium, the best possible methods for removing 

 ionium had unknowingly been employed, A very slow rate 

 of growth was apparent in all four preparations, diminishing 

 in order from J3xl0~ 12 gram of radium per year per 

 kilogram of uranium in the case of the first, to about one- 

 fifth of this rate in the case of the fourth. These differences 

 can only be due to the more successful elimination of initial 

 ionium in the successive preparations, and prove that, in the 

 first two preparations at least, the growth of radium is to be 

 ascribed mainly to initial ionium . As Rutherford has pointed 

 out, the growth of radium from uranium, if ionium is the 

 only long-lived intermediate product, must proceed initially 

 according to the square of the time. But in 1912 there was 

 no evidence that the growth of radium in any of the pre- 

 parations was proceeding other than linearly with the time. 

 That is to say, it was certainly due, for the most part, at 

 least in the case of the first preparations, to initial ionium 

 that had survived the purification processes, and there was 

 in 1912 no positive evidence that uranium was producing 

 radium at ail. On the assumption that the whole of the 

 radium came from the uranium, the minimum possible period 

 of average life of ionium can be found. This was deduced 

 * Trans. Royal Institution, 1912. 



