470 Scientific Intelligence. 



observed when the preparation was uncovered. The activity of 

 the uranium-X thus prepared, when measured through - 01 cm or 

 more of aluminium, decayed exponentially with the same period 

 as the preparations obtained by the barium method. The absorp- 

 tion curves of the ferric preparations show the presence of a 

 much larger quantity of soft /3-rays than is found in the barium 

 preparations. 



The decay curves for the new radio-active substance were 

 derived in the following manner : First the decay curves for the 

 uncovered ferric preparation and for the pure uranium-X through 

 o-01 cm of aluminium were plotted to the same scale on the same 

 sheet. By multiplying the ordinates of the latter curve by the 

 empirical constant 2*15 a curve was obtained which corresponded 

 theoretically with the activity of pure uranium-X when uncov- 

 ered, that is, this curve would have coincided throughout with 

 the decay curve for the uncovered ferric preparation if the laiter 

 had contained no radio-active element other than uranium-X. In 

 fact, these two curves do coincide sensibly for points whose 

 abscissae represent 10 or more days. Therefore, by subtracting 

 the ordinates of the theoretical barium preparation curve from 

 the corresponding ordinates of the experimental ferric curve the 

 decay curve for the newly discovered product was obtained at 

 once. 



The new substance was always found to be present in the ferric 

 preparations. It is characterized by the emission of soft /3-rays. 

 All attempts to separate uranium-Y in large quantities from 

 uranium were unsuccessful. Furthermore, owing to the very 

 similar chemical properties of uranium-X and the new product, it 

 was not found possible to isolate the latter, for it was always 

 accompanied by uranium-X. The half -value period of uranium-Y 

 came out consistently from all the decay curves as about 1*5 days. 



Scintillation experiments indicated both that uranium-Y emits 

 some a-rays, and also that the half period was about 1*5 days, as 

 before. It should be remarked that the number of a-particles 

 observed was small compared with what would be expected from 

 the /3-ray activity of the product. A study of the initial por- 

 tions of the absorption curves of uranium-Y also leads to the 

 conclusion that a-rays are emitted. The absorption coefficients for 

 the a- and /3-rays are given respectively as y, = 2500 (cm.) -1 and 

 fi = 300 (cm.) -1 . Finally, as regards the position of uranium-Y 

 in the radio-active series, Antonoff concludes from all the experi- 

 mental evidence that uranium-Y is a lateral disintegration product 

 of uranium and is produced in small quantity as compared with 

 uranium-X.— Phil. Mag. (6), xxii, 419. h. s. it. 



9. On a Method of making Visible the Paths of Ionizing 

 Particles through a Gas: — It has been found by C. T. R. Wilson 

 that the tracks of individual a- or /3-particles, or of ionizing rays 

 of any kind, through a moist gas may be made visible by con- 

 densing water upon the ions set free. Not only is it possible to 

 see the paths of the particles, but Wilson has even succeeded in 

 photographing these paths. 



