408 



Mr. Frederick Soddy 



[March 15, 



curves labelled I, II, III, refer to these preparations. No. Ill was 

 the last prepared, after experience with the others, and contained 

 both the greatest quantity of uranium and the least radium initially. 

 No. IV refers to a much later experiment with no less than 6 kilo- 

 grams of uranyl nitrate, purified by repeated crystallization in the 

 course of other work. In all, there has been a distinct growth of 

 radium, but it is so small, and the period over which the measurements 

 extend is so prolonged, that the errors of the individual measurements 

 are relatively great. The general scope of the curves, as indicated in 

 the figure, are, however, probably not far wrong. A conservative 

 view to take is that in all cases the curves are straight lines. There 



Fig. 9.1 



is some indication in No. I of an increasing slope, but it is negatived 

 by tlie evidence of Nos. II and III. 



The quantity of uranium in the four preparations differs widely. 

 In Fig. 11 the curves are replotted in a different way to eliminate 

 this difference. The ordinates represent the quantities of radium 

 formed in terms of the amounts of radium in equilibrium with the 

 uranium. The equilibrium amount is the amount that theoretically 

 Bhould be formed after the lapse of sufficient time, if uranium is the 

 ultimate parent of radium. It will be seen that the slopes of the 

 four curves are all different and diminish in order, the growth in the 

 first being the greatest, and in the last, after all the experience in 

 methods of purification, the least. This is additional evidence that, 



