Ratio between Uranium and Radium in Minerals. 345 



uranium X loses its activity completely without the formation 

 of any product possessing a detectable radioactivity. We 

 must therefore suppose either (1) that uranium X is not in 

 the uranium-radium series, (2) that long-lived new rayless 

 products must exist in the series, or (3) that if uranium X 

 changes directly into ionium the period of the latter must be 

 greater than 30,000 years. There is good reason to believe 

 that the last explanation may prove correct ; so that to achieve 

 the object for which the investigations were commenced still 

 larger quantities of uranium must be dealt with, or the 

 methods must in some way be greatly improved. 



Physical Chemistry Laboratory, 

 University of Glasgow. 



XXXI. The Ratio between Uranium and Radium in Minerals. 

 By Frederick Soddy, M.A., F.R.S., and Ruth Pirret, 

 B.Sc* 



Mlle. Gleditsch (Compt. Rend. 1909, cxlviii. p. 1451 ; 

 cxlix. p. 267), in a reexamination of the ratio of uranium 

 and radium in minerals, found small but distinct variations 

 in the ratio for Ceylon thorianite, Joachimsthal pitchblende, 

 and French autunite. Thorianite being probably a very old 

 mineral and autunite a very recent one, the results sug- 

 gested that the older the mineral the greater the ratio of 

 radium to uranium. Neither Boltwood nor Strutt in their 

 original determinations of this ratio refer to autunite, but 

 the latter included thorianite (Phil. Mag. 1905, ix. p. 599 ; 

 Proc. Roy. Soc. 1905, A. lxxvi. p. 88). Mile. Gleditsch first 

 separated the radium chemically from the minerals before 

 estimating it ; and it seemed very desirable to repeat the 

 work, determining the radium in the usual way, without 

 carrying out this separation. This has been done for speci- 

 mens of the three minerals mentioned, the radium having 

 been estimated by comparison of the amount of radium 

 emanation generated, after periods of accumulation of a 

 month or longer, in solutions of the minerals containing a 

 fraction of a milligram of uranium preserved in sealed 

 flasks. For Joachimsthal pitchblende we employed standards 

 I. and V., previously used for calibrating the electroscope, 

 and described by one of us in an earlier paper (Phil. Mag. 

 1909, xviii. p. 849), where a full description of the method 

 of estimating the radium is given. So far attention has 

 been mainly directed to thorianite ; for, as Mile. Gleditsch 



* Communicated by the Authors. 

 Phil. Mag. S. 6. Vol. 20. No. 116. Aug. 1910. 2 A 



