CHEMISTRY: RICHARDS AND WADSWORTH 
699 
tive conclusions previously reached by Richards and Lembert is sup- 
ported, namely, that this isotopic lead possesses the same spectrum as 
ordinary lead. The present outcome is especially interesting because 
the isotopic lead obtained from the preparations of Dr. Gleditsch was 
probably almost pure — certainly much purer than that examined in 
1913. 
Since the atomic weight is variable, but the spectrum and atomic 
volume^ of these samples all the same, one can hardly avoid concluding 
that a part of the atom exercising an important effect upon the atomic 
weight is without influence upon the spectrum or volume. The dual 
nature thus postulated is, of course, in accord with the interesting 
hypothetical assumptions which have been advanced by various au- 
thors concerning the possible makeup of the atom; but our present 
research can go not further than support the idea of duahty without 
defining exactly of what the two parts may consist. 
We are glad to acknowledge our indebtedness to the Carnegie Insti- 
tution of Washington for generous support in this investigation. 
Summary. — In this paper the atomic weight of four different samples 
of isotopic lead not hitherto tested, as well as one sample of ordinary 
lead (used to control the others), was determined. The results were as 
follows : 
Ordinary lead 207.18 
Isotopic lead (Carnotite, Colorado) 207.00 
Isotopic lead (Carnotite, Australia) 206 . 34 
Isotopic lead (Broggerite, Norway) 206. 12 
Isotopic lead (Cleveite, Norway) 206.08 
That the most carefully selected sample should give the lowest result 
is'^strong (although not absolutely conclusive) evidence that the higher 
results obtained from other samples were due merely to the accidental 
admixture of ordinary lead. No new lines were found either in the 
ultraviolet or visible spectrum of any of these samples. Each, except the 
ordinary lead, possesses radioactivity, but the magnitude of this radio- 
activity seemed to bear no relation to the lowering of the atomic weight. 
1 Richards and Lembert, /. Amer. Ghent. Soc, 36, 1329 (1914); Honigschmid and St. 
Horovitz, Paris, C. R. Acad. Sci., 158, 1798 (1914); M. Curie, Ibid., 158, 1676 (1914); 
Soddy and Hyman, London, J. Ghent. Soc, 105, 1402 (1914); also especially, Honigschmid, 
Sitz. k. Akad. Wiss., Wien, Ila (Dec, 1914). 
2 A description of the details is to be found in the paper by S. Radcliff, /. Proc. R. Soc, 
New South Wales, 47, 145 (1913). 
3/. Amer. Ghent. Soc, 38, 223; these Proceedings, 2, 505 (1916). 
^Loc. cit., these Proceedings, 2, 505 (1916). 
^ A fuller description is given in our paper published in the December, 1916, number of 
/. Amer. Ghem. Soc. 
