Boltvmod — Life of Radium. 497 



all it was produced at a very small fraction of the rate which 

 was to be expected from other considerations. It was possible, 

 however, that the transformation of uranium X into radium 

 was not a direct one, and that the atoms of uranium X disin- 

 tegrated to form atoms of an unknown intermediate product 

 with a slow rate of change from which radium was ultimately 

 produced. 



The indications were all in favor of the presumption that 

 this intermediate product, if it existed, had so slow a rate of 

 change that, for purposes of determining the rate of produc- 

 tion (and disintegration) of radium, it offered all the advan- 

 tages of a true parent. In a search for this possible interme- 

 diate product I finally found* that there could be separated 

 from uranium minerals a substance from which radium was 

 unquestionably produced at a readily measurable rate. This 

 substance was separated with thorium, with which it remained 

 very persistently, exhibiting a chemical behavior almost iden- 

 tical with that given by Debierne as characteristic for actinium. 

 It was, therefore, at first supposed that the radium-forming 

 substance was actinium, although the necessity of further in- 

 vestigation before reaching a definite conclusion was fully 

 appreciated. Further experiments were therefore undertaken 

 from the results of which it was established that the radium- 

 producing substance was a new radio-active element, to which 

 the name " ionium " was given. f In the mean time Rutherford 

 had found \ that, although radium was produced in a com- 

 mercial preparation of actinium which he had examined, the 

 substance from which the radium was formed could be par- 

 tially separated from the actinium and could not therefore be 

 identical with it. 



Experimental Part. 



The experiments which will be described in this paper w r ere 

 undertaken with the object of determining the rate of disinte- 

 gration of radium. The operations consisted in the separation 

 of the ionium from definite quantities of certain uranium min- 

 erals and the comparison of the amounts of radium produced 

 by the separated ionium in known periods with the amounts 

 of radium originally associated with it. 



The radium present in the minerals used was ascertained by 

 comparing the activity of the maximum or equilibrium amount 

 of radium emanation evolved from a small, average sample of 



* This Journal, xxii, 537, 1906. 

 \ This Journal, xxiv, 370, 1907. 



% Nature, lxxv, 270, 1907; ibid., lxxvi, 126, 1907; Phil. Mag., xiv, 733, 

 1907. 



