Dillon, Clarke, and Hinchy — Sefaraiion of the Isotopes of Lead. 57 



If we omit No. 3 of the first series, the maximum difference between two 

 samples of the same kind in either series is '08 c.c per gram ; whereas the 

 minimum diffei'ence between two diflerent samples is O'lS. 



If we assume that the atomic weight of the lead /3 is 207'1, the mean ratio of 

 the silver nitrate required per gram of lead /3 to that required per gram of lead B 

 would give for the lead B an atomic weight of 207'4 in the first series, and of 

 207*3 in the second series. 



Samples of the original lead chloride, togetlier with the B and /3 chlorides, 

 were sent to Professor John ISToIan, of University College, Dublin, who very kindly 

 examined their radio-activity, and reported that, while this property was weak hi 

 all three, the radio-activity of the /3 chloride was much greater than that of either 

 the original or the B chloride. This confirms the observation of Hofi'manu and 

 Wolf. 



Unless there is an unknown source of error, the relative atomic weight 

 determinations indicate that the different isotopes of lead are not identical in 

 their chemical behaviour towards the Grignard reagent. If this is so, a con- 

 tinuation of the process of chemical fi'actionation described above should produce 

 such a difference in the atomic weights as would leave no doubt that a separation 

 had taken place. Experiments in this direction are in progress. 



SCIENT. PROC. R.D.S., VOL. XVII., NO. 6. 



