694 
CHEMISTRY: RICHARDS AND WADSWORTH 
ton, as represented by changes in the total ash of the body, which pro- 
ceeded for a time at the expense of other tissues while the animal was 
held at constant weight, does not now, in the active growth which 
accompanies refeeding, keep pace with this rapid gain in body weight, 
and consequently in a few days the normal relation is almost re- 
established. 
FURTHER STUDY OF THE ATOMIC WEIGHT OF LEAD OF 
RADIOACTIVE ORIGIN 
By Theodore W. Richards and Charles Wadsworth, 3d 
WOLCOTT GIBBS MEMORIAL LABORATORY. HARVARD UNIVERSITY 
Read before the Academy, November 14, 1916. Received, November 27, 1916 
The recent independent and almost simultaneous investigations 
upon the atomic weight of lead from radioactive minerals have proved 
with very little room for doubt that the substance derived from this 
source has a much lower atomic weight than ordinary lead.^ This 
conclusion is so important in its theoretical relations that its every 
aspect should be carefully investigated. Accordingly, the present 
paper represents further research in this direction, embodying deter- 
minations of the atomic weight of new samples of varied origin. The 
outcome entirely supports the earlier conclusion. 
Four samples from widely separated sources were studied in the 
present research, namely, lead from Australian carnotite, from American 
carnotite, from Norwegian cleveite, and Norwegian broggerite. 
The first of these samples was obtained in large quantity through 
the kindness of Mr. S. Radcliff and Mr. E. R. Bubb, of New South 
Wales. 
The preliminary purification of the sample was carried out in Aus- 
traHa.2 Our subsequent purification was briefly described in a recent 
paper,^ but some additions to the account are needed. The metallic 
lead was dissolved in nitric acid, leaving practically no residue. A 
portion of the nitrate thus obtained was precipitated with 20% hydro- 
chloric acid from dilute solution. Lead sulphide was precipitated 
from the warm acidified solution of this chloride by pure hydrogen 
sulphide, and after separation and washing was dissolved in pure 
nitric acid. The small portion oxidized to sulphate during this process 
was boiled with sodium carbonate and the lead carbonate, washed 
free from sodium, was dissolved in nitric acid and united to the main 
portion of the nitrate, which was recrystallized four times from pure 
water and precipitated as chloride from a warm solution in a quartz 
