420 Mr. G. N. Antonoff on the 



Some irregularities ir> the behaviour o£ UrX have been 

 noted by several investigators. Variations of the ray activity 

 in uranium were observed by Meyer and von Schweidler* 

 in 1904. The question was examined later by Grodlewski t, 

 who ascribed the abnormal behaviour to the diffusion of UrX. 

 Meyer and von Schweidler also found a rapid decay in some 

 preparations, indicating the presence of a product with a 

 period of about 2 days. Becquerelf separated from uranium 

 by charcoal some radioactive substance whose activity grew 

 in 8 days to one and a half times its original value. Later 

 Levin § repeated Becquerel's experiment, but could not 

 separate anything but UrX. 



Soddy || found that during the first ten days of decay some 

 preparations of UrX decay faster than the normal rate. 



In all these investigations no evidence of the purity of the 

 uranium preparations has been given. The present research 

 was undertaken with preparations of uranium from which all 

 known radioactive impurities had been separated. 



An account of the literature about uranium and its products 

 may be found in a review by St. Meyer (see Jahr. d. Bad. 

 vi. .1909, p. 381). 



Experiments with Uranium X. 



As commercial uranium nitrate, even extra pure, generally 

 contains very many radioactive impurities, several methods 

 of purification were employed with the view of separating 

 radium, actinium, and thorium with their series of products. 

 These methods will be. fully described later in the paper, but 

 it may be mentioned here that special tests of the uranium 

 preparations have afforded a definite proof that all radioactive 

 impurities have been removed. The UrX was separated by 

 two methods. The first consists in precipitating barium in 

 the uranium solution as BaS0 4 , and the second in adding an 

 iron salt to the uranium solution and precipitating it by 

 boiling. These methods wall be hereafter called the barium 

 method and the ferric method respectively. 



It is known that UrX emits soft rays with an absorption 

 coefficient in aluminium yit = 500 (cm.) -1 , and hard rays with 

 /a = 14 (cm.) -1 . The activities of the UrX preparations were 

 measured first when uncovered, and afterwards through 

 0*01 cm. of aluminium. The first measurement gave the 



* Meyer and v. Schweidler, Wien. Sitzber. cxiii. p. 1057 (1904). 

 t Godlewski, Phil. Mag. x. p. 45 (1905). 

 t Becquerel, C. H. cxli. p. 87 (1905). 

 § Levin, Phi/s. Z. vii. p. 692 (1906). 

 jj Soddv, Phil. Mag-, xix. p. 847 (1910). 



