506 
CHEMISTRY: RICHARDS AND WADSWORTH 
by filtration through a Gooch-Munroe crucible with platinum mat, the 
resulting solution was concentrated and crystallized once more as ni- 
trate. The pure crystals were electrolyzed, and the pure radio-lead 
treated exactly as in the case of the other samples previously described.^ 
As the amount of substance at hand was very small, the work could 
not be done quite so accurately as before. The density determinations 
were made in the same pycnometer as before, by the second method 
described on page 223 of our previous publication, the volume of the 
pycnometer having been redetermined because its tip had been broken 
in the meantime. Four identical determinations gave 5.7200 as the 
weight of water in the pycnometer at 19.94°, weighed in air. There- 
fore, the volume of the pycnometer was 5.7361 cm. 
TABLE 1 
Density of Lead from Cleveite 
OBSERVED 
WEIGHT 
WEIGHT IN 
VAC. {W) 
OBSERVED 
WEIGHT WATER 
NOT DISPLACED 
COEIRESPONDING 
VOLUME 
VOLUME OF 
PYCNOMETER 
VOLUME {V) 
OF WATER 
DISPLACED 
DENSITY 
{W/V) 
4.4252 
4.4250 
5.3287 
5.3437 
5.7361 
0.3924 
11.277 
4.4252 
4.4250 
5.3286 
5.3436 
5.7361 
0.3925 
11.274 
4.4252 
4.4250 
5.3285 
5.3435 
5.7361 
0.3926 
11.271 
4.4252 
4.4250 
5.3285 
5.3435 
5.7361 
0.3926 
11.271 
Average 
, 11.273 
The density of this sample, presumably a nearly pure isotope, is thus 
11.273, distinctly less than 11.289, the density of the Australian radio- 
lead, and still less than the density 11.337 found for ordinary lead. The 
decrease is almost exactly proportional to the decrease of the atomic 
weight in these samples; for the atomic weight of the Australian lead 
was about 206.35, and that of this sample 206.085. Thus the atomic 
volume of the isotope, 18.281 (equal to 206.08/11.273), is almost iden- 
tical with that of pure lead, as indicated by our previous experiments. 
Thus 18.281 is essentially equal, within the Hmit of error of experiment, 
to the value 18.277, found for ordinary lead, and to the value 18.279, 
found for Australian radio-lead. It is interesting to note that Austra- 
lian radio-lead would be essentially duplicated as to these properties by 
a mixture consisting of three parts of pure isotope to one of ordinary 
lead. 
1 Honigschmid, Sitzungsber. Wiener Akad., 123, II a, 20 (1914). 
2 Richards and Wadsworth, /. Amer. Chem. Soc, 38. 221 (1916). 
2 Baxter and Grover, /. Amer, Chem. Soc, 37, 5 (1915). 
' Forbes, /. Amer. Chem. Soc, 33, 1937 (1911). 
^ Richards and Wadsworth, loc. cit., p. 224. 
