CHEMISTRY: BAXTER, GROVER AND THORVALDSON 
75 
cause the atomic weight of radioactive lead has recently been found to 
differ from that of ordinary lead- we also undertook the examination 
of inactive lead from widely different geographical sources. Lead 
nitrate was prepared from the various minerals, and after crystallization 
was converted to lead chloride. The latter in turn was several times 
crystallized from dilute hydrochloric acid solution, fused and analyzed 
by comparison with silver. Each specimen of lead nitrate was carefully 
examined spectroscopically as previously described, and not the slightest 
difference could be detected between the different specimens. Further- 
more the radioactivity of all the minerals was tested in a sensitive gold- 
leaf electroscope and no one of them was found to increase the normal 
leak of the instrument by a measurable amount. 
In the experiments with lead chloride no attempt was made to collect 
the silver chloride obtained in the comparisons with silver. Instead, 
in separate experiments with new portions of the chloride, silver chloride 
was precipitated with an excess of silver nitrate and the precipitate was 
collected and weighed. 
The analyses in the following table were made by Grover. 
The Atomic Weight of Lead 
PbCl2 : 2Ag PbCl2 : 2AgCl 
Ag = 107.880 CI = 35.457 
SOURCE OF MATERIAL 
GRAMS OF 
PbCb 
GRAMS OF 
Ag 
RATIO 
PbCl2: 2Ag 
ATOMIC 
WEIGHT OF 
Pb 
GRAMS OF 
AgCl 
RATIO 
PbCla: 
2AgCl 
ATOMIC 
WEIGHT OF 
Pb 
Commercial 
Nitrate 
5.63567 
5.58730 
6.86319 
4.37200 
4.33427 
5.32402 
1.28904 
1.28910 
1.28910 
207.21 
207 . 22 
207.22 
Joplin, Mo, 
U. S. A.i 
4.70770 
4.20222 
3.65223 
3.25968 
1.28908 
1 . 28899 
1.28915 
207.22 
207.20 
207.23 
Average 
Wallace, Id. 
U. S. A.2 
7.04688 
5.88935 
5.46691 
4.56868 
1.28907 
1.28901 
1.28907 
207 . 22 
207.20 
207.22 
Average 
Wallace, Id. 
U. S. A.2 
6.96370 
6.89046 
1 . 28904 
207.21 
7.17754 
7.10231 
0.97021 
0.97017 
207.22 
207.21 
Average 
Tucson, Ariz., 
U. S. A.3 
4.90083 
5.79300 
3.80171 
4.49404 
1.28911 
1.28904 
207.22 
207.21 
0.97019 
207.21 
1 Galena; 2 Cerussite; ^ Vanadinite and Wulfenite. 
