CHEMISTRY: BAXTER AND STEWART 
79 
previous to fusion. Careful analysis of this material showed it to be 
praseodymium oxychloride. By exercising every precaution in the 
drying of the salt and by fusing the salt as rapidly as possible, formation 
of the oxychloride can either be avoided completely or kept within a 
limit so small as to produce no important effect upon the final result. 
These precautions were taken in drying all the specimens of chloride. 
The solution of the praseodymium chloride was precipitated in dilute 
solution with a solution of a weighed amount of the purest silver very 
nearly equivalent to the chloride. By examination of the miother-liquor 
with a nephelometer it was determined whether the amount of silver used 
was exactly equivalent to the chloride, and an initial deficiency or ex- 
cess was made up with very dilute standard solutions. Finally the silver 
chloride was collected and weighed. Corrections were applied for moisture 
retained by the silver chloride and for the silver chloride dissolved in the 
washings. 
The following table gives a comparison of the results obtained with 
the various fractions of the last series, as well as with the one selected 
from series 174, Fraction 3474. Of the others. Fraction 4383 is the 
mos 4368 the least soluble. As a rule 5 to 6 gram portions of the 
chloride were used. Vacuum corrections were applied to the apparent 
weights of praseodymium chloride, silver, and silver chloride. 
It is apparent that the variations among the different fractions are 
chiefly fortuitous; for the extreme fractions examined show a difference 
which is hardly beyond the experimental error of analysis. The atomic 
weight of praseodymium seems to be very nearly 140.92, if silver is taken 
The Atomic Weight of Praseodymium 
Ag = 107.880 
CI = 35.457 
FRACTION 
PrCl3:3Ag 
PrCls: 3AgCl 
AVERAGE VALUES 
3474 
140.913 
3474 
140.939 
3474 
140.943 
140.923 
3474 
140.924 
3474 
140.914 
140.941 
Average 
140.927 
140.929 
140.928 
4383 
140.910 
140.909 
4383 
140.914 
140.902 
Average 
140.912 
140.906 
140.909 
4381 
140.908 
140.937 
4381 
140.920 
4381 
140.915 
140.925 
4381 
140.921 
