46 Dr. T. Godlewski on some 



who also noted the important fact that uranium recovered its 

 activity with the time, while the activity of the separated 

 substance decayed. This phenomenon was then quantitatively 

 investigated by Soddy *, by Rutherford and Grier f , and by 

 Rutherford and Soddy %. 



These investigations proved that the activity of UrX, when 

 measured by ft rays, decayed with the time according to an 

 exponential law, falling to half value in 22 days. In the same 

 period uranium which, by removal of UrX, was deprived of 

 all its ft activity recovered it, and the recovery curve was 

 complementary to the curve of decay of UrX. From the 

 point of view of the disintegration theory, this fact indicated 

 that UrX is a successive product of uranium, and the change 

 of UrX into its successive product was accompanied by the 

 emission of ft particles. 



2. The Experiments of Meyer and Schweidler on Uranium. 



In 1904 Meyerand von Schweidler § repeated the quantitative 

 measurements of Rutherford and Soddy with the difference, 

 that while the latter used for separation of UrX the method 

 of Becquerel, they made use of Grookes's method. 



The aqueous solution of uranium nitrate was shaken with 

 ethyl ether, and then the ether and water portions were 

 separated from one another. The ether portion contained 

 uranium nitrate deprived of UrX, and the ft activity of this 

 portion increased according to the theoretical curve, to half of 

 its total value in 22 days. The uranium nitrate, however, 

 when crystallized from the remaining water portion, lost its 

 ft activity at a different rate, decaying to half value in 2 days 

 instead of 22 days. This unusual fact, that the recovery and 

 decay curves of a radioactive product were not complementary 

 to one another, either pointed to the existence of a new product, 

 or indicated some unknown radioactive phenomenon. In order 

 to elucidate this question, Meyer and Schweidler started a series 

 of investigations on the radioactive properties of uranium 

 nitrate freshly crystallized from the water solutions. They 

 substantiated the fact that uranium nitrate crystallized from 

 the hot-water solutions in the form of compact plates exhibited 

 a peculiar radioactive behaviour. The activity of these 



* Soddy, Trans. Cliem. Soc. lxxxi. p. 860 (1902). 



f Rutherford and Grier, Phil. Mag. Sept. 1902, p. 315. 



X Rutherford and Soddy, Phil. Mag. April 1903, p. 411. 



§ Meyer and v. Schweidler, " Untersuchungen iiber radioaktive Sub- 

 stanzen, II. : Ueber die Strahlung des Uran." Sitzher. der Wiener Akad. 

 Mathem.-natunviss. Klasse, Bd. 113. Abt.II. a. pp. 1057-1079, Juli 1904. 



