CHEMISTRY. 299 



from the contaminations derived from the utensils used in crystal- 

 hzation. The atomic weights of the samples so obtained from the 

 crystal (A) and the mother liquor (B) ends of the series, respectively, 

 agreed within the experimental error of 6 parts in 100,000 parts of the 

 chloride. The results are given in the preceding table, two control 

 determinations of the atomic weight of ordinary lead being appended 

 for comparison. 



The jS-ray activity of these samples was also studied with great 

 care by means of an aluminum-leaf quantitative electroscope, having 

 taken especial precautions to eliminate any outside source of ioniza- 

 tion and to treat each sample in precisely the same fashion. The /J-ray 

 acti\dties of the end samples were thus found to agree with one another 

 within the experimental error of 1 per cent. Evidently, neither the 

 atomic weight nor the ionizing power of the end fractions give any 

 e\idence that an appreciable amount of separation had occurred 

 through the agency of the thousand crystallizations. 



2. Melting-Points of Ordinary and of Isotopic Leads. 



This investigation also was carried out with the help of Dr. Norris 

 F. Hall. The comparison was made by means of a multiple copper- 

 constantan thermocouple. Much time was spent in securing con- 

 ditions as satisfactory as possible, but the results were not entirely 

 definite, on account perhaps of the low latent heat of melting of 

 lead. As a general average of 44 experiments by means of the cooUng 

 curve, a difference of 0.05° between the melting-points of the Australian 

 radioactive lead and ordinary lead were observed, the radioactive 

 lead having the higher melting-point. This difference was confirmed 

 by differential measurements taken when each sample was partly 

 melted. It is probable that the shght divergence was due to the fact 

 that the ordinary lead was not of the very highest degree of purity, 

 but it may have contained a trace of some unknown contamination. 

 The lead from carnotite had been so completely purified as to leave no 

 suspicion of this kind. In any case, the result, which we regard as 

 merely preliminary, is enough to show that the difference between the 

 melting-points of ordinary lead and radioactive lead is very slight. 



3. The Thermoelectric Behavior op Isotopic Lead. 



Dr. Norris F. Hall assisted also in this investigation, in which a 

 sample of pure isotopic lead was placed in contact mth pure ordinary 

 lead and the junction treated as a thermoelement. No electromotive 

 force whatever was thus developed. The electrical conductivity of 

 the two samples have not yet been measured with a sufficient degree of 

 accuracy to predicate complete equality of this property because of the 

 difficulty of preparing a wire of even gage, but this matter will receive 

 further attention. 



