342 Mr. F. Soddy on the 



for the period. This could readily be done with the prepara- 

 tion of thorium oxide described by Stefan Meyer and Egon 

 v. Schweidler ( Wiener Anzeiger, Sitzung. 11/6/09) which 

 has been separated by Auer v. Welsbach from the products 

 obtained by Haidinger and Ulrich ( Wiener Ber. 1908, cxvii. 

 p. 621) from the radium residues of 30 tons of Joachimsthal 

 pitchblende, and which is stated to contain about 0*25 per 

 cent, of ionium. This, however, appears to have been 

 obtained from measurements of the <z-ray activity, by 

 assuming for the substance a period the same as for radium, 

 whereas the period and also the percentage of ionium is at 

 least fifteen times greater. A maximum limit to the amount 

 of ionium present could be fixed by subtracting from its total 

 mass the mass of thorium oxide present. The latter could 

 be determined by comparing the amount of thorium emana- 

 tion generated in a solution, preferably boiling, of the 

 substance with that from a standard thorium solution of the 

 same age since preparation under the same conditions 

 (Rutherford and Soddy, Phil. Mag. 1902, iv. p. 378). The 

 maximum period of ionium required is simply given by 

 dividing the maximum limit that can be assigned to the 

 mass of the ionium by the mass of radium generated by 

 the preparation in one year. This would fix the period 

 between two limits, and however wide apart they proved at 

 first to be, a very valuable step would have been made. 



Physical Chemistry Laboratory, 

 University of Glasgow. 



XXX. The Rays and Product of Uranium X. — II. 

 By Frederick Soddy, M.A., F.R.S.* 



THE conclusions in the preceding paper as to the minimum 

 period of ionium modify essentially the deductions pre- 

 viously drawn from the behaviour of the uranium X prepa- 

 rations separated from 50 kilograms of uranium nitrate 

 (Phil. Mag. 1909, xviii. p. 858), and it is desirable to give 

 some account of the further progress of this work. It was 

 pointed out that the failure to observe the growth of an 

 a-radiation during the decay of these preparations was 

 inconsistent with the measurements of the rate of production 

 of radium from uranium if uranium X were really in the 

 uranium-radimu series. As, however, it has just been 

 shown that the period of ionium was probably greatly under- 

 estimated, this failure rather affords additional evidence 

 confirming the extremely long period of this body. Using 

 * Communicated by the Author. 



