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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 & partieles. 
2. The experiments of Meyer and Schweidler on Uranium, 
In 1904 Meyer and Schweïdler !) repeated the quantitative mea- 
surements Of Rutherford and Soddy with the difference, that while 
the latter used for separation of UrX the method of Becquerel, 
they made use of Crookes’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 ß 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 ß 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 erystallized from the water solutions. They suhstan- 
tiated the fact that uranium nitrate erystallized from the hot water 
solutions in the form of compact plates exhibited a peculiar radio- 
active behaviour. The activity of these plates decayed in the first 
few days after erystallization to about half of its original value, 
reaching a minimum after four or five days, and then increased 
slowly for a very long time. The time in which the minimum was 
reached and the initial form of the eurve were both dependent on 
the thiekness of the plate. As regards the meaning of this pheno- 
menon, the authors suggest two possibilities; either that there is 
a change in the activity itself, or that the absorption of the rays 
is modified by the physical alteration of the crystallized pla- 
1) Meyer und Schweidler: Untersuchungen über radioaktive Substangen IT: 
Über die Strahlung des Urans. Sitzber. der Wiener Akad. Mathem-naturwiss. 
Klasse Bd. 113 Abt II a. p. 1057—1079 Juli 1904. 
