124 DISTRIBUTION OF THE ACTIVE DEPOSIT OF RADIUM 



The only apparently satisfactorj'- results which remained 

 were those of Wellisch^. He found that there was a limiting 

 value to the fraction of the rest-atoms which could be con- 

 centrated on the cathode, as the strength of the field was 

 increased. Later"', he gave .882 as the value (corrected for 

 diffusion) of this limiting fraction when the radium emanation 

 was in an atmosphere of drj^ air. He found similar limiting 

 values of .882 and .789 when the emanation was in atmospheres 

 of hydrogen and carbon dioxide respectively. He also found 

 that all the rest-atoms were uncharged in an atmosphere of 

 ether vapor, as was found by the writer in the case of thorium. 

 Several experimenters, Wellisch and Bronson^, Wellisch^, and 

 Walmsley^, have shown quite conclusively that no appreciable 

 fraction of the rest-atoms is negatively charged. Hence, 

 according to Wellisch's results, 11.8% of the rest-atoms are 

 formed uncharged in dry air. 



In the writer's experiments on thorium it was found 

 that the charged condition of al the rest-atoms was the 

 same in a pure gas (i. e. either all positive or all neuk-al), 

 and that in a mixed atmosphere the fraction of the rest- 

 atoms positively charged depended on the relative propor- 

 tions of the constituents of the mixture. The explanation 

 of this seemed to be that the charged condition of the rest- 

 atom depended on what kind of molecules surrounded it. 



No such simple explanation seemed applicable to the 

 results of Wellisch. It, therefore, seemed desirable to investi- 

 gate further the behavior of the rest-atoms of radium. 



It was suggested by the writer in the previous paper 

 that the fact that there seemed to be a limit to the fraction 

 of the rest-atoms one could collect on the cathode was due 

 to the fact that air was a mixture. This formed the starting- 

 point of the present investigation. It might perhaps be 



3. Wilmsley. Phil. .Mag., Oct., 1014. 



4. Wo;i.sch, A.-n. Journ Sc:., Oct. 1913. 



5. Wellisch, Atii. Journ. Sci., Oct. 1914. 



. Wellisch and Bronson, .\ni. .Journ. Sci., May, 1912. 



