-54 Scientific Proceedings, Royal Dublin Society. 



choice ill the direction they would take in this reaction, or, in other words, 

 whether a sepai-atioii of the isotopes of lead could be effected by its means. 



It should be mentioned in this connexion that Hoffmann and Wolf ' in 1907 

 acted on lead cliloride containing radium D with magnesium phenyl bromide, and 

 found that most of the radio-activity remained in the metallic lead. 



Our scheme of work will be clear from the following diagram : — 



PbCh 



/\ 



/ \ 



/ \ 



Pb PbRi 



I I 



^^ si/ 



PbCh (a) PbClj (A) 



/\ /\ 



/ \ / \ 



Pb PhR4 Pb PbRj 



. i I 



Sl/ si/ 



PbCh (5) PbClo (B) 



A quantity of lead chloride is treated with the Grignard reagent, and the lead 

 alkyl and the metallic lead are separated from one another, and converted into 

 lead chloride. The two quantities of lead chloride are again separately treated 

 ■with the Grignard reagent, and the resulting products separated as before. If 

 there is any difference between the isotopes with regard to their tendency to form 

 <jrganic compounds, it will be seen that a repetition of this process, always using the 

 metal on the extreme left and the organo-metallie compound on the extreme right 

 of the diagram, will lead to an accumulation of one isotope at the extreme left 

 and the other at the extreme right and the lead salts marked B and /3 in the 

 ■diagram might possibly show a difference in the atomic weights of the lead which 

 they contain. 



As a result of some preliminary observations, we decided to use the ethyl 

 compound of lead as the basis of our experiments. The synthesis of the 

 magnesium compound with this group goes smoothly and easily without the 

 formation of troublesome bye-products, while tlie lead alkyl could be easily 

 purified as far as required hy us. Grutner and Krause,^ who first isolated the 

 lead tetraethyl by this method, found that it was contaminated with unsaturated 

 lead alkyls ; but for our purpose this was of no consequence. We found that a 

 quantitative yield of lead tetraethyl could be obtained by using one mol of lead 

 chloride to three-and-a-half mols of magnesium ethiodide. If the proportion of 

 lead chloride exceeded this, the yield diminished. 



The lead chloride used was a sample kindly given to us by Messrs. Hopkin, 

 Williams, & Co., London. It was recovered from the manufacture of meso- 

 thorium, and therefore consisted of a mixture of the chlorides of ordinary lead 

 and of lead from thorite. The salt was recrystallized and dried by heating in a 

 ■current of hydrochloric acid gas. 



Tlie Grignard reagent was prepared in the usual way, from 104 grams of ethyl 

 iodide and 16 grams of magnesium. Fifty-two grams of the dry lead chloride 

 were then added gradually. When the lead chloride had all been added, the 

 mixture was heated for four hours under a reflux condenser, air and moisture 

 being excluded by means of a mercury seal. The reaction product was poured 



' Ber. 40 (1907), 2425. 2 ^^^ 49 (]916), 1415. 



