2 MakOWER, Volatility of Radium A and Radium C. 



is due to the decay of radium A which has a time period 

 of three minutes. If, therefore, radium A were in any 

 way prevented from depositing on the rod, we should 

 expect that not only would the activity of the rod after 

 exposure to the emanation be much less, but on examining 

 the deposit on the rod, the initial fall of activit}- should be 

 entirely absent. These conditions would be fulfilled if 

 the rod, exposed to the emanation, were kept above the 

 volatilisation point of radium A ; and, therefore, by 

 examining the activity of a rod after exposure to the 

 emanation at different temperatures, it should be possible 

 to infer the volatilisation point of radium A by finding 

 the temperature above which the product ceased to be 

 deposited on the rod. 



The apparatus used for carrying out the experiment 

 is shown in Fig. i, and was as follows. The nickel rod A, 



^^:^-r^h-} 



Fiz. I. 



the activity of which was subsequently to be examined, 

 was held in position along the axis of an iron tube T by 

 the iron rods B and C, supported respectively in the 

 rubber stopper D and the glass tube E which was itself 

 held in position by the rubber stopper F. On the central 

 portion of the tube T was wound a coil of nickel wire G, 

 insulated from the tube by asbestos. The iron tube was 

 contained in a larger porcelain tube P which was filled 

 with kieselgur for heat insulation. By passing an electric 



