On the Separation of the Isotopes of Mercury. 31 



satisfying this relation 



C 2 Gs + C3C4 + C * C 2 = 



and whose sum is unity * we have that 



(d*y = (^l) 2 + %?* (fc) 2 4 X^(dx Z ) 2 + CC^d^Y 



will satisfy Einsteiu's equations G> s = 0. However, a 

 detailed examination of all possibilities is out of place here. 

 It will suffice if we have shown that the Einstein 

 differential equations are of a regular character and are 

 exactly integrable in a large variety of cases. 



III. On the Separation of the Isotopes of Mercury, 

 By J. N. Br^nsted and Gr. Hevesy f. 



1. Introduction, 



THE hypothesis, based on various considerations, that 

 isotopy, hitherto found only within the domain of the 

 radioactive elements, may be finally proved to be a general 

 property of matter, has been established by Aston's % brilliant 

 experiments. The question of the separation of isotopes, 

 already much discussed in radio-chemistry, has become 

 thereby a problem of still more general importance. We 

 have already elsewhere § given brief accounts of the results 

 of some experiments made in this laboratory on the separation 

 of isotopes. The present paper contains a closer description 

 of the principles and the methods used, together with the 

 results of further experiments. 



2. On some methods of separating of Isotopes. 



On account of the chemical properties of the atom being 

 materially independent of its mass, only a few methods of 

 separation come into consideration — chiefly, those which 

 make use of the difference in the molecular velocities (atomic 



* The units of measurement of x 2 , x z , x 4 can be so chosen that C 2 , C 3 , 



^2 , 



C 4 in the equations H 2 = C 2 ■r 1 C2+C3+C4 etc. above all equal unity and 

 this necessitates c 2 +c 3 +c.i=l since C2C3C4 =c 2 4-c 3 +c 4 . 



f Communicated by the Authors. 



% Aston, Phil. Mag. xxxviii. p. 707 (1919) j xxxix. pp. 449, 611 (1920) ; 

 xl. p. 628 (1920). 



§ < Nature,' cvi. p. 144 (1920) ; cvii. p. 619 (1921). 



