Disintegration Products of Uranium. 423 



to a half period of 23*5 days. The points marked on the 

 curve show the values obtained experimental!}'. It is seen 

 that they agree with the theoretical curve within the limits 

 of experimental error. There is thus no evidence of any 

 intermediate change between uranium and UrX*. 



Experimental Method. 



Before discussing the results obtained with ferric prepara- 

 tions, it is necessary to describe briefly the method employed 

 to detect the soft radiations when mixed with the radiation 

 of UrX. As UrX separated from pure uranium by the 

 ferric method is accompanied by some soft radiation, a 

 special experimental arrangement was adopted to measure 

 all soft and hard rays under the same conditions. A /3 ray 

 electroscope with its opening covered with thin aluminium 

 sheet of 0"00025 cm. thickness was employed. The radio- 

 active preparation was clamped to the bottom of the electro- 

 scope so as to be directly under the opening, and always in 

 the same position. The sheets of absorbing material were 

 placed between the opening and the radioactive preparation, 

 and were thus compressed by the clamp. Special care was 

 taken to avoid any displacement of the radioactive prepara- 

 tion when large thicknesses of foil were used. In this way 

 it was possible to obtain practically the full effect in the 

 electroscope of the hard and soft /3 rays. The a ray effect 

 is, however, diminished more than that due to the (3 rays, 

 because they have to pass through about 0*8 cm. of air 

 before reaching the aluminium foil, whose thickness is equi- 

 valent to 0*5 cm. of air, or in other words, the loss of a ray 

 activity is that due to a shortening of the range by 1*3 cm. 

 of air. This experimental arrangement is convenient for 

 taking absorption curves because the aluminium foil prevents 

 air currents in the electroscope. In some cases, how 7 ever, 

 when a stronger effect from the a rays was desired, the 

 measurements were taken in an identical electroscope v^thout 

 an aluminium foil. In this case there was no absorption of 

 the radiation, and the ionization produced corresponds to the 

 whole path of the a. rays. The absorption curves for the pre- 

 parations of pure UrX show that if the film is very thin, 

 the ratio of the total activity to that of the preparation 

 measured through a standard sheet of O'Ol cm. of aluminium, 

 which allows only the hard rays of UrX to pass, is invariably 

 2*15 under the experimental conditions. If UrX is accom- 

 panied by some additional soft rays this ratio is much higher, 



* The meaning- of the clotted curve 2 will be exnlained later, 



2 F 2 



