[ 53 ] 



No. 6. 



PEELIMINAEY EXPERIMENTS ON A CHEMICAL METHOD OF 

 SEPARATING THE ISOTOPES OF LEAD. 



By THOMAS DILLON, D.Sc, EOSALIND CLARKE, D.Sc,. 



AKD 



VICTOR M. HINCHY, B.Sc. 

 (Chemical Department, University College, Galwa.y).' 



[Read June 27. Printed July 27, 1922.] 



The usual methods used for the separation of the elements from one another 

 depend upon reactions between ions, such as fractional crystallization and fractional 

 precipitation. Eeactions of this type are common to nearly all the elements, and, 

 as the property of solubility of salts, upon which such reactions depend, 'often 

 varies gradually among the elements, it is perhaps not surprising that there 

 should be atoms which, while differing slightly in atomic weight, are so alike in 

 all their chemical properties that they must be placed in the same position in the 

 periodic table. Once, however, it is admitted that the atoms of any body have a 

 different weight, it is difficult to imagine that they are absolutely identical in all 

 chemical properties ; and it would seem to be only a matter of finding the particular 

 chemical reaction in which they show an appreciable difference in order to be able 

 to effect their sepai'ation. 



Now there is one property of the metallic elements which is of a very specialized 

 cliaracter, and that is the property of forming organo-metallic compounds. This 

 property is possessed by comparatively few metals, and elements standing close to 

 one another in the periodic table show marked differences in the ease of formation 

 and stability of their organic derivatives. Furthermore, the process of formation 

 of the lead organic compounds is peculiar. Frankland and Lawrence' found that 

 lead chloride reacts with zinc alkyl, half of the lead being precipitated, and 

 the other half forming alkyl derivatives of tetravalent lead. Pfeiffer and Truskier- 

 were the first to substitute the Grignard reagent for the organo-zinc compounds in 

 this reaction, and they prepared various alkyl and aryl derivatives of lead by this 

 means. 



The reaction between lead chloride and the Grignard reagents is represented by 

 the following equation : — 



2 PbCL + 4 MgRX = PbR, + 2 MgCl, + 2 MgX. + Pb. 

 Here, some of the lead atoms change their valency from two to four, while 

 others pass into the elemental state. It occurred to us that it would be worth 

 while trying whether the lead atoms of different weights showed any appreciable 



1 J. C. S. 35 (1879), 244. ^ Ber. 37 (1904), 1125. 



SCIENT. PBGC. R.D.S., VOL. XVII, NO. 6. K 



