Dirj.ON, Clarkk, and HmcuY—Sepai-atton of the Isotopes of Lead. 55 



slowly into water, and the aqueous mixture was extracted several times with 

 ether. The ether solution was dried over calcium chloride ; the ether evaporated, 

 and the lead tetraethyl distilled in vacuo. A small residue of lead iodide remained 

 in the distilling ilask. 



The lead tetraethyl was next converted into lead nitrate by dropping 

 it slowly into hot dilute nitric acid ; and the lead was precipitated from 

 the solution as sulphate by adding sulphuric acid and alcohol. The lead 

 sulphate was filtered off, washed, and dissolved in ammonium acetate ; and the 

 solution was saturated with sulphuretted hydrogen. The precipitated lead 

 sulphide was filtered off, washed, and dissolved in hot hydrochloric acid ; and the 

 lead chloride which crystallized out was recrystallized from water containing 

 hydrochloric acid. This lead chloride was dried and labelled " Lead chloride A." 



The residue from the extraction of the lead alkyl compound, consisting of 

 basic iodide of magnesium, metallic lead, and traces of the chloride and iodide of 

 lead, was repeatedly boiled with a solution of sodium carbonate until the carbonate 

 solution gave no reaction for halides with silver nitrate. It was then dis.solved in 

 nitric acid, treated with sulphuric acid and alcohol; and the resulting lead sulphate 

 was converted into lead chloride by exactly the same process as that described 

 above. It was recrystallized from water containing hydrochloric acid, dried, and 

 labelled " Lead chloride a." 



The A and the a chlorides were again made to react separately with the 

 requisite quantities of magnesium ethiodide ; and the oigano-lead compound was 

 in each case extracted as before. The metallic lead from the lead chloride a and 

 the lead tetraethyl from the lead chloride A were then treated for coiiversion 

 into their respective chlorides in exactly the same manner as had been done 

 previously, and the two samples were labelled 'respectively " Lead chloride j3 " and 

 "Lead chloride B." 



Our next step was to find whether there was any appreciable difference 

 between the atomic weights of the lead in the two samples. The method adopted 

 for this purpose was that of relative atomic weight determination as used by 

 Soddy and Hyman^ in their comparison of the atomic weights of ordinary and 

 thorite lead. A platinum boat was heated in a current of hydrochloric acid gas ; 

 and when the boat had cooled, the hydrochloric acid was displaced by dry air. 

 The boat was weighed, and a quantity of the lead chloride under examination (a 

 little over a gram) was placed in it. The lead chloride was fused in a current of 

 dry hydrochloric acid ; the hydrochloric acid was displaced by air when cold, and 

 the boat and contents were weighed. The boat was then dropped into a stoppered 

 bottle containing one litre of water and 5 c.c. of nitric acid (which had previously 

 been distilled over silver nitrate), .and the bottle was placed in a water bath kept 

 at 60" C, and was shaken frequently. In this way all the lead chloride was 

 brought into solution in about three hours. The boat was removed from the 

 bottle, washed several times with distilled water, 100 c.c. of water being used 

 altogether, and the washings being poured each time into the bottle. The boat 

 was then dried in the steam oven, heated in dry hydrochloric acid, which on cooling 

 was displaced by air, and was finally weighed again. A set of bottles, each 

 containing one of the samples, was made up in this way, the same platinum boat 

 being \ised throughout. In the first series of experiments three solutions of lead 

 B and two of lead /3 were used. In the second series there were two of each kind. 



When a set of solutions had been prepared, 200 c.c. of the same silver nitrate 

 .solution were added to each from the same pipette. The bottles were well shaken, 



'J. C. S. 105(1914), 1402. 



