Volatility of Radium C. 137 



It is seen that there is a sudden increase in the activity 

 between the 14th and the loth minute. This is due to the dis- 

 tillation of radium C to the cooler end of the tube as soon as 

 the hotter end has reached 360°. 



When the hottest part of the furnace was kept at 380° a 

 similar experiment gave a similar set of results, the sudden 

 increase occurring in this case after eight minutes. At 300° 

 and at 200° no such effect was found. Radium C begins, 

 therefore, to volatilize in considerable amount from a quartz 

 surface in an atmosphere of hydrogen at about 360°. It is 

 at this temperature also that it condenses entirely when 

 volatilized at higher temperatures. 



Experiments show that provided hydrogen is present with 

 the emanation in excess of impurities such as carbon dioxide 

 or traces of water, radium C volatilizes at the lower tempera- 

 ture; if oxygen is in excess, volatilization takes place at the 

 higher temperature. Impurities such as dust or grease, 

 which would undoubtedly hinder volatilization, can have no 

 effect in these experiments, siuce the experiments are con- 

 ducted in thoroughly cleaned, sealed quartz tubes. 



The assumption of Schrader, that two different compounds 

 of radium C are formed in the two sets of experiments, is 

 the simplest explanation of a difference of more than 800° 

 in the volatilization points of a body present only to the 

 extent of about 7 x 10 ~ 10 of a gram. 



Summary. 



1 . In presence of oxygen, radium A, radium B, and 

 radium C are all non-volatile from a surface of quartz 

 below 700° ; the volatilization point of radium C is higher 

 than 1200°. 



2. In presence of hydrogen, radium A, radium B, and 

 radium C are completely volatile from a quartz surface 

 below 650° ; the volatilization point of radium C is about 

 360°. 



I have to thank Prof. Rutherford for his advice and help 

 throughout this investigation. 



Physical Laboratories, 



University of Manchester. 



