if Common Lead could he separated into Isotopes. 375 



VY -:-B. 



Experiment. ^ " ■ — ^ Bemarks. 



Bottom Bullet. Top Bullet. 

 XV 3-4015 3-4033 Top Bullet 0-05 per cent, denser. 



XVI 3-4092 3-4094 Top Bullet 0-006 per cent, denser. 



XVII 3-4112 3-4111 Top Bullet 0-003 per cent, lighter. 



XXII 3-4090 3*4090 No difference. 



XXIII 3-4085 3-4069 Top Bullet 0*01 per cent, denser. 



It will be seen from these results that there is absolutely 

 no evidence for any separation effect. The density of the 

 upper and lower bullets agree as well as could be expected, as 

 a difference of -tV mgrm. in B which weighed about 3 grms. 

 would cause an error of 0*003 per cent, in the density. The 

 slight variation of the density from day to day is probably 

 due to the variation in the temperature of the methylene 

 iodide, and may also be caused by small variations in the 

 casting conditions. This point was not fully investigated as 

 the method is essentially a comparison one. 



It is rather difficult to form an idea of the separation we 

 might hope to obtain on theoretical grounds, owing to our 

 ignorance of the equation of state for a liquid. Since these 

 experiments were inaugurated, how T ever, Drs. Lindemann 

 and Aston have shown, in a paper entitled " The Possibility 

 of Separating Isotopes/' that if we neglect compression, and 

 assume equal atomic volumes for both leads, and then treat 

 one lead as simply dissolved in the other, we might expect 

 to get a concentration of thorium lead at the edge nearly 

 50 per cent, greater than that at the centre, if the peripheral 

 velocity was about 10 5 cm. per sec. In our case, however, 

 a peripheral velocity of only about 10 4 cm. per sec. could 

 be attained, which would only lead to a difference in con- 

 centration of about ^ per cent. This would only give a 

 difference of '005 per cent, in density, which is too small to 

 be detected by the method of determining the density used. 

 On these grounds, then, it is not surprising that with the 

 centrifuge at our disposal no positive results were obtained. 

 It would seem, however, certainly possible that with a 

 specially constructed centrifuge some definite result might 

 be obtained. 



Ivea£)i Laboratory 



Trinity College, Dublin. 



