CHEMISTRY: RICHARDS AND WADSWORTH 
505 
DENSITY OF RADIO-LEAD FROM PURE NORWEGIAN 
CLEVEITE 
By T. W. Richards and C. Wadsworth, 3d 
WOLCOTT GIBBS MEMORIAL LABORATORY. HARVARD UNIVERSITY 
Received by the Academy, August 4, 1916 
Through the kindness of Prof. Ellen Gleditsch of the University of 
Kristiania we have been so fortunate as to receive a specimen of lead 
sulphide from carefully selected Norwegian cleveite. According to Dr. 
Gleditsch, ^'The Norwegian uraninites are very old and very unaltered. 
They are found in well developed crystals and occur in connection with 
the pegmatite dykes in southeastern Norway." The sample in question 
occurred in cubic crystals near Langesund. 
As Honigschmid has already pointed out^ the properties of radio-lead 
(this name being used provisionally to designate lead produced by radio- 
active transformations) obtained from pure minerals of this sort are 
far more interesting and significant than those of lead obtained from 
ordinary uranium ores, which doubtless contain some admixture of 
ordinary lead. Honigschmidt has shown that the lead from pure 
cleveite has an atomic weight as low as 206.06, and our own experience 
with the sample referred to above essentially confirms this result, as 
will be shown in another communication. So far as we know, however, 
the density of lead of this kind has not yet been determined, and ac- 
cordingly the present paper recounts such a determination, which 
forms an interesting sequel to the recently published results on the 
density of Australian radio-lead.^ 
The purification of the sulphide, which doubtless contained traces of 
sulphides of other metals was carried out as follows : The specimen was 
dissolved in nitric acid and crystallized three times with centrifuging 
as nitrate, — a process which Baxter's experience has shown to be an ex- 
cellent one for the purification of lead from other metals.^ From this 
purified nitrate the chloride was precipitated by pure hydrochloric acid, 
and this salt was crystallized three times. The final crystals, after 
draining on the centrifuge, were stored in a vacuum desiccator over 
caustic soda. The chloride thus prepared was used for the determina- 
tion of the atomic weight, the density being determined in the material 
saved from the filtrates from that determination. These filtrates con- 
tained excess of silver, therefore enough hydrochloric acid was added 
to bring the concentration of the dissolved chloride ion to 0.01 normal, 
because at this concentration silver chloride is most nearly insoluble.^ 
When the precipitated silver chloride had settled and had been removed 
