CHEMISTRY: RICHARDS AND WADSWORTH 
695 
dish with hydrogen chloride. The precipitate was centrifuged, dis- 
solved in water and recrystallized four times, each time having added 
a few drops of hydrochloric acid to prevent the formation of basic 
salt. The second mother liquid gave no test for nitrate. This chloride 
formed Sample A, and after two additional recrystallizations a similar 
specimen constituted Sample B. 
The second portion of the original nitrate made from the Australian 
sample was purified in a m.uch simpler fashion. Avoiding the trouble- 
some precipitation with hydrogen sulphide, the nitrate was recrystal- 
lized five times successively by adding concentrated nitric acid to its 
aqueous solution; then the lead was converted into chloride, and by 
precipitation with excess of hydrochloric acid this salt also was re- 
crystallized five times. This was Sample C of the chloride, a portion 
of which before the last crystallization had served to prepare Sample 
D of the metallic isotopic lead used for determining the density.^ 
The next sample, derignated F, was prepared from American car- 
notite and came to us in a considerably purified state through the 
kindness of Dr. C. H. Viol of Pittsburgh, of this company, and of Prof. 
W. D. Harkins. The method of further purification was essentially 
like that just described.^ 
Two other samples of especial value and significance were obtained 
through the kindness of Dr. Ellen Gleditsch, of Kristiania. Both came 
from primary rocks — Norwegian pegmatite dykes. The purification 
of one of these, from cleveite, has already been described;^ the source 
of this material, which occuired in cubic crystals and was carefully 
selected, was near Langesund, Norway. It was recrystallized first 
as nitrate and then as chloride three times, each in the usual manner, 
and the pure substance was designated as Sample G. 
Yet another sample, designated H, was prepared from lead sulphide, 
also kindly sent by Dr. Gleditsch, obtained from selected crystals of 
Norwegian octahedral broggerite from Roade, near Moss, Norway. 
This was purified in precisely the same way as lead from cleveite. 
In addition to these four samples containing isotopic lead enough 
ordinary lead was carefully purified to serve as the basis of control 
analyses. The purest ''test lead" of commerce, free copper, was 
dissolved in nitric acid and recrystallized four times as nitrate and 
four timds as chloride. 
Throughout this work the usual care taken in atomic weight in- 
vestigations was not forgotten. The nitric acid, hydrochloric acid, 
water and silver were all purified in methods already often described, 
and throughout the work on the nitrate and chloride of lead, except 
