822 On separating Mercury into its Isotopic Forms. 



Let Jc= — . d 1 = density of isotope A, 



n 2 



d 2 = „ „ B. 



Then ~ = — 1 = 1*02 verv nearly. 



4 M 2 - J 



And the density of the mixture 



= 1 4 I "(M 1 + ^) 



= T ^,,(/.-l-02 + l). 



Putting & ==1-003 and &=1 respectively, we find that the 

 difference of the densities at the outer end of the tube and 

 at the centre equals 'OOOOlo^- The difference between the 

 densities at the outer and inner ends will of course be 

 double this, but still it only amounts to one part in 30,000 t 

 It would probably be extremely difficult to detect this differ- 

 ence with any certainty, and thus experiments with this 

 centrifuge would not lead to any really satisfactory results. 

 In this connexion it is of interest to note that J. N. Bronsted 

 and G. Heresy (Nature, 106. p. 144, 30 Sept. 1920) claim to 

 have effected a certain separation in mercury of about this 

 magnitude by fractional distillation at low pressures. They 

 state that their density determinations can be trusted as 

 accurate to 1 in a million, but it would be difficult to deal 

 with so large a quantity of mercury, as they did, in centri- 

 fuging experiments. However, it would certainly seem 

 quite feasible to construct a centrifuge in the form of a 

 hollow disk which could be run up to at least 60,000 revs, 

 per minute ; and such a centrifuge, if its other dimensions 

 were approximately the same, would give a difference of 

 density of about 1J parts in 1000, which should be quite 

 easily detectable. The amount of separation might further 

 be increased by successive experiments, but the results 

 obtained would apparently hardly justify the expense entailed 

 in constructing the special centrifuge. 



Ireagh. Geological Laboratory. 

 January, 1921. 



Note. — It might be possible to separate liquid neon by 

 this method, if a centrifuge could be run at a sufficiently low 

 temperature. The case of neon is rather more hopeful as 

 there is a difference in density of about 10 per cent, between 

 the two isotopes, and working at such a low temperature 

 would, of course, increase the separation effect very largely. 



