289 
welehe den Zweck hatten zu eruieren, ob nach Einwirkung der Ra- 
diumstrahlen auf die Speicheldrüse (Glandula submaxillaris) irgend 
welche Störungen der Tätigkeit derselben auftreten. Es wurde näm- 
lieh nach längerer Bestrahlung der Drüse durch die dieselbe be- 
deckende Haut der Speichel beiderseits gesammelt, gewogen und 
auf Trockengehalt und Asche, auch auf dessen Gefrierpunkt unter- 
sucht. 
Diese Versuche ergaben indessen keine positiven Resultate. 
22. M. TADEE GODLEWSKI O niektörych wlasnoscia promieniotwörczych 
Uranu. (Some Radioactive Properties of Uranium). (Sur certai- 
nes propriétés radioactives de U Uranium). Mémoire présenté par M. L. Na- 
tanson m. t. 
1. The discovery of UrX. 
In 1900 Sir William Crookes!) showed that it is possible to 
separate from uranium by a single chemical operation a small 
amount of a radioactive substance to which he gave the name UrX. 
This substance was, weight for weight, many hundred times more 
active photographically than the uranium from which it had been 
separated. The uranıum deprived of this substance was almost 
inactive. 
Similar results were afterwards observed by Becquerel?) who 
also noted the important fact that uranium recovered its activity 
with the time, while the activity of the separated substance de- 
cayed. This phenomenon was then quantitatively investigated by 
Soddy *), by Rutherford and Grier 4) and by Rutherford and Soddy 5). 
These investigations proved that the activity of UrX, when 
measured by ß rays, decayed with the time according to an expo- 
nential law, falling to half value in 22 days. In the same period 
uranium which, by removal of UrX, was deprived of all its ß 
activity retovered it, and the recovery eurve was complementary 
to the curve of decay of UrX. From the point of view of the 
1) Crookes: Proc. Roy. Soc. 66 p. 409, 1900. 
2) Beequerel: C. R. 131 p. 137, 1900; 133 p. 977, 1901. 
°) Soddy: Trans. Chem. Soc. 81 p. 860, 1902. 
1) Rutherford and Grier: Phil. Mag. Sept. 1902 p. 315. 
5) Rutherford and Soddy: Phil. Mag. Apr. 1903 p. 411. 
