CHEMISTRY: RICHARDS AND WADSWORTH 697 
The atomic weight of "isotopic^' lead 
SAMPLE 
CORRECTED 
WEIGHT PbCl2 
CORRECTED 
WEIGHT Ag 
ADDED 
RATIO 
PbCl2 : Ag 
ATOMIC 
WEIGHT Pb 
1 
A 
Camotite, Australia 
4. 04U1U 
3 .Olllo 
1 . Zo4yv5 
O AA "210 
2 
B 
Camotite, Australia 
5.35517 
4.16711 
1.28512 
206.359 
3 
B 
Carnotite, Australia 
6.15608 
4.79072 
1.28500 
206.334 
4 
C 
Carnotite, Australia 
4.14770 
3.22748 
1.28512 
206.359 
Average 
206 . 342 
5 
F 
Camotite, U. S. A 
5.31585 
4.12670 
1.28816 
207.015 
6 
F 
Carnotite, U. S. A 
^ . oooyy 
O . Ol IK) 1 
1 . ZooUO 
Average 
207.004 
7 
H 
4.29104 
3.34187 
1.28402 
206.122 
8 
G 
3.92736 
3.05913 
1.28382 
206.079 
9 
G 
Cleveite, Norway 
4.45270 
3.46818 
1.28387 
206.090 
Average 
206.084 
The results of these analyses show that the different samples con- 
taining iso topic lead all give lower values for the atomic weights than 
ordinary lead, but that the material from each source gives a differ- 
ent value, precisely as had been previously found in the earlier investi- 
gations in this and other laboratories. Ordinary lead gave the maximum 
value (essentially equal to that found by Baxter^) and isotopic lead 
from Norwegian cleveite gave the minimum value (essentially equal 
to that found by Honigschmid in broggerite^ 206.06). 
It seems reasonable to suppose that the other samples were composed 
of mixtures of these two kinds of lead. The value 206.34 would be 
given approximately by a mixture of three parts of isotopic lead like 
that obtained from Norwegian cleveite with one part of ordinary lead — 
a reasonable supposition, since the AustraHan carnotite was known 
to have contained galena. The American carnotite. Sample F, had 
an atomic weight which would be given by a mixture of only one part 
of the pure isotope with 5 or 6 of ordinary lead, — a condition which 
seems to indicate the admixture of very large amounts of galena with 
the sample in question. 
Two physical properties of the several preparations under considera- 
tion have especial interest, namely, the magnitude of the radioac- 
tivity and the nature of the spectrum. Both were studied in the pres- 
ent research. We confirmed the outcome of earlier work^ that the 
radioactivity is not proportional to the decrease in atomic weight in 
samples containing isotope coming from different sources. If the 
radioactivity were dependent upon the presence of the isotope radium 
