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LXXIIL The Production of Radium from Uranium. 

 By Frederick Soddy, M. A. * 



SINCE the theory was brought forward that radioactivity 

 is accompanied by the change of the atom of the radio- 

 element (Rutherford & Soddy, Phil. Mag. [6] v. 1903, p. 576), 

 it has been recognized that the rate of change of radium is 

 sufficiently rapid to cause the practically complete disappear- 

 ance of any initial quantity of radium during the course of 

 at most a few tens of thousands of years, so that the theory, 

 if correct, must be able to account for the continued existence 

 of this element. The rate of change of an element, like 

 its atomic weight, seems to be a completely invariable and 

 unvarying constant of nature, and there is no evidence to 

 justify the view that the processes which accompany radio- 

 activity have commenced at a late and recent period of the 

 earth's history. On the other hand, the case of radium is 

 essentially similar to that of all the other types of radio- 

 active matter. It is changing much more rapidly than the 

 elements uranium and thorium, but far slower than polonium. 

 Any initial quantity of polonium would, according to the 

 recent accurate determinations of the rate of change of this 

 element {Ber. d. D. Chem. Gesell. 1905, p. 592) be reduced 

 to less than one-tenth per cent, after the lapse of only five 

 years, while the times for the same to occur in the case of 

 the emanations of radium, thorium, and actinium respectively 

 are 40 days, 10 minutes, and 37 seconds. To these cases, the 

 idea of the comparatively recent origin of radioactive pro- 

 cesses is of course inapplicable. From the first it was obvious 

 that the conception of the continuous reproduction of the 

 more rapidly changing types from the slower-changing so- 

 called " parent-elements," which was arrived at by the study 

 of the radioactive emanations and other similar types, 

 embraced also the cases of radium and polonium. If, for 

 example, radium and polonium are themselves intermediate 

 or transition forms of elementary matter, which are being 

 reproduced as fast as they themselves change, by the exces- 

 sively slow disintegration of some parent element of higher 

 atomic weight, not only the continued existence, but also the 

 extremely minute quantity in which radium and polonium 

 occur in nature is at once explained. As only two elements, 

 thorium and uranium, are known with atomic weight greater 

 than that of radium, the choice of a possible parent was 



* Communicated by the Author. 



