126 Dr. Hans Schrader on the Existence of Chemical 



long life such as uranium, thorium, or radium. Their 

 electrochemical properties are similar to those of the common 

 metals*. They appear to be present in solutions as ions, 

 and it would, therefore, seem probable that they are capable 

 of forming chemical compounds in the same way as the 

 long-lived products. If these compounds do exist, evidence 

 of their presence can be obtained from a study of some of 

 their physical properties, a method usually employed in 

 differentiating between homogeneous bodies. In the present 

 case, where bodies present only in extremely small quantities 

 are under examination, recourse has been had to an investi- 

 gation of their volatility and their solubility. 



Makower t has made some experiments on this point, 

 and found that radium C, after being dissolved in hydro- 

 chloric acid and the solution evaporated to dryness, vola- 

 tilized from surfaces of platinum and quartz in air at the 

 same temperature as before such treatment. The result, 

 therefore, indicates that, under the circumstances, radium C 

 had not been changed chemically in such a manner as to be 

 more or less volatile. 



I. Volatilization of Active Material from Surfaces of 

 Different Substances. 



The amount of an active body which can be volatilized 

 at a fixed temperature depends on the nature of the surface 

 on which it has been concentrated. Thus Makower found 

 that only 85 per cent, of radium C is volatilized from a 

 quartz surface after heating it for 5 minutes to 1320°, while 

 from a nickel surface 99 per cent., and from a platinum 

 surface 96 per cent., is volatilized at 1200°. 



Such behaviour is easily explained if one takes into account 

 the fact that volatilization necessitates the separation of the 

 molecules of the active material from the molecules of the 

 plate on which they are deposited. So the process is influ- 

 enced not only by the vibrations and molecular attraction of 

 the volatilizing substance, but also by the corresponding- 

 forces of the molecules composing the surface from which 

 the volatilization takes place. A further acceleration of the 

 process may be produced by the gases and vapours, especially 

 water, which rapidly condenses on every solid surface on 

 which the active material may be deposited. The fact that 

 the volatility varies if the surface in question is heated very 

 strongly can be explained by these considerations. It is 

 improbable that there exists an action between the different 

 radioactive atoms themselves, for in the experiments 

 * v. Hevesy, Phil. Mag. xxiii. p. 628 (1912). 

 t Makower, Manchester Memoirs, Uii. No. 7 (1909). 



