Possibility of separating Isotopes. 529 



It is evident that no appreciable separation whatever 

 had been achieved, hence if neon is not homogeneous the 

 vapour-pressure of its constituents at the temperature em- 

 ployed^ must be very nearly the same. It is, however, 

 impossible to draw any definite conclusion from the above 

 experiment as to the homogeneity of the gas until further 

 fractionations have been performed at other and lower tem- 

 peratures, preferably without the use of charcoal. 



Diffusion. 



Lord Rayleigh (Phil. Mag. xlii. p. 493, 1896) has inves- 

 tigated the problem of the separation of gases of different 

 density by diffusion. He obtained as an expression for the 

 effect of a single operation 



x + y X Y 



where (X, Y) (a?, y) are the initial and final volumes of the 

 gases, v 1 v 2 the velocities of diffusion, and y the enrichment 

 of the residue as regards the second constituent. 



After the failure of fractional distillation described above, 

 an attempt was made to separate the hypothetical con- 

 stituents of neon by diffusion through pipeclay. In this 

 case, as the molecular weights given by positive rays are 

 apparently 20 and 22 respectively, v and fi only differ by 

 5 per cent., so the above equation may be written in the 

 simple form 



Residual Volume 



The first apparatus was similar to that described by 

 Ramsay and Collie (Roy. Soc. Proc. lx. p. 206, 1896). After 

 an extremely laborious and prolonged series of diffusions a 

 small but apparently real difference of density was detected 

 amounting to about 0*7 per cent. A much more elaborate 

 apparatus was designed and was started early in 1914. This 

 apparatus is on the see-saw principle and the volume ratio is 

 about 2000, so that given perfect mixing this should give an 

 enrichment of 1*4. Rather more than 200 c.c. of enriched 

 gas had been collected by the time the War interrupted the 

 experiment. It is hoped that the apparatus will soon be 



Phil. Mag. Ser. 6. Vol. 37. No. 221. May 1919. 2 O 



