are usualf 



Possibility of separating Isotopes. 

 large compared with 



527 



r T d? C 1 



Jo^Jo 



ZcpdT 



at all ordinary temperatures, the difference in the constant 

 of the law of mass action would probably be imperceptible 

 unless suitable equilibria were examined under favourable 

 conditions. Thus isotopes could not be separated by an 

 ordinary precipitation, t. e. what used to be called an irre- 

 versible reaction, anv more than nitrogen and oxvgen could 

 be separated by dropping liquid air into a red-hot flask. 



Fractional distillation was the first method used by Aston 

 in attempting to separate the two hypothetical constituents 

 of Neon (''Homogeneity of Atmospheric Neon,'' Brit. Assoc. 

 Birmingham Meeting, 1913). The gas was fractionated 

 over charcoal cooled in liquid air. The apparatus used 



Diagram of Fractionation Apparatus. 



is illustrated in the accompanying figure; the method of 

 working was as follows : — 



The gas was admitted in a, one of the small charcoal 

 bulbs abed all cooled in liquid air. After a reasonable 

 •time had elapsed the first fraction was pumped off by lowering 



