MancJicstcr Meiiioi} s. Vol. liii (1909), No. 7. 5 



this temperature the curves show a slight increase after 

 the first rapid fall of activity, instead of inereiy becoming 

 constant. This is what would be expected if the radium B 

 were volatilised as sooi^ as formed from the radium A 

 deposited on the rod. This result is in agreement with 

 the experiments of Curie and Daune,* who found for the 

 volatilisation point of radium B the temperature 600^^ C. 

 The 3rd, 4th, 5th, and 6th curves show the results obtained 

 when the rod was exposed to the emanation at the higher 

 temperatures. It will be noticed that already at 840° C. 

 the initial drop of activity after removing from the emana- 

 tion is less marked than at lower temperatures. At 

 885° C, the initial drop has almost disappeared, while at 

 925° C. there is practically no initial rapid drop of activity 

 at all, showing that at this temperature no radium A was 

 deposited on the rod. We may therefore infer that 

 radium A begins to have an appreciable vapour pressure 

 at 800" C, and that at 900" C. it is completely volatilised. 



Volatility of Radium C. 



The experiments on the volatility were undertaken 

 not only to redetermine the volatilisation point with 

 accuracy, but, as has already been mentioned, to investi- 

 gate whether the environment of radium C had any 

 influence on its volatility. The active deposit from 

 radium was collected on plates of various materials by 

 exposing them to radium emanation for several hours. 

 After removal from the emanation and the lapse of 

 sufficient time for the radium A to have decreased to an 

 inappreciable amount, the material was subjected to any 

 required temperature by inserting it in an electrically 

 heated platinum - strip furnace for five minutes. The 



* Curie and Daune, Coinptes Rciuius, 138, 1904. 



