696 
CHEMISTRY: RICHARDS AND WADSWORTH 
in the preparation of Sample A, the material was treated exclusively 
in vessels of platinum or quartz. All the weighings were reduced to 
the vacuum standard and all other precautions usual in this sort of 
work were carefully maintained. 
The analysis was essentially similar in every way to the method 
described so often in Harvard contributions. The lead chloride was 
fused in a platinum boat in pure hydrochloric acid; this gas was dis- 
placed with nitrogen while the substance was cooling; and finally the 
pure dry salt in its boat was pushed into the weighing bottle, stoppered 
in pure dry air with the help of the familiar Harvard bottling apparatus' ' 
and weighed at leisure. The weighed salt was placed in a large Erlen- 
meyer flask with glass stopper very carefully ground. Enough water 
was then added to form a fiftieth normal solution of the saJt and the 
flask and contents, with the addition of a drop of pure nitric acid to 
prevent the formation of basic salt, were gently warmed on an electric 
stove, at about 50°C., until complete solution was obtained. The 
boat was then removed, and the residue filtered off, both boat and 
residue being carefully washed and the filtrate being collected directly 
in the precipitating flask. 
The chlorine contained in this solution was then precipitated in the 
usual fashion by an amount of silver calculated from preliminary trials 
to correspond with it as nearly as possible. Any slight deficiency or 
excess was corrected by adding silver nitrate or chloride, and testing 
in the nephelometer; and the finally corrected weight is given in the 
table. The precipitation was carried on in a dark room, under red 
light, and all the usual precautions were taken. 
The first two determinations of ordinary lead were only preliminary, 
in order to gain practice with the method, and are not included in the 
table below. They yielded values for the atomic weight respectively 
207.15 and 207.16. All the other analyses which were brought 
forward to conclusion are recorded in the tables, which are self- 
explanatory. 
The atomic weight of ordinary lead 
SAMPLE 
CORRECTED 
WEIGHT PbCb 
CORRECTED 
WEIGHT Ag 
ADDED 
RATIO 
PbCl2 : Ag. 
ATOMC 
WEIGHT Pb 
3 
3.72918 
2.89325 
1.28892 
207.179 
4 
5.35111 
4.15151 
1.28896 
207.188 
Average 
207.183 
