520 



SMITHSONIAN MISCELLANEOUS COLLECTIONS 



VOL. 54 



In 1901 Braiiner' gave a preliminary notice of an investigation upon 

 the atomic weight of praseodvmium, but without details. He has since 

 published his data in Abegg's Handbuch der anorganischen Chemie,' 

 as follows : 



First, tlio oetoliydratcd sulphate was dehydrated at 500°, then calcined 

 to oxide, and tlie latter finally analyzed iodometrically to determine the 

 true proportions of Pr203. Percentage A in the next table is that of 

 Pr.Os in the hydrous sulphate, and P. refers to tbe anliydrous salt: 



Pr„(80,),.SH,0. 

 1.29269 

 1.27990 



Pr-ASO,),. 

 1.03242 

 1.02193 



.59747 

 .59137 



Per cent. A. 

 46.219 



46.204 



Mean, 46.211, 

 ± .0050 

 Pr = 141.09 



Per cent. B. 

 57.871 

 57.868 



57.8695 



Secondly, four samples of praseodymium oxalate were analyzed by the 

 method already described under cerium and lanthanum. I give the ratio 

 computed from the percentages, in the form SCoOg : Pr.Og : : 100 : a;; 



Eacli value for the ratio is here weighted according to the number 

 of the CoOg determinations. The mean of all, thus weighted, is 152.720, 

 ±.0148. 



Hence Pr = 140.95. 



Finally, Brauner affected the synthesis of the anhydrous sulphate. 

 Praseodymium oxalate was calcined, and the composition of the oxide 

 produced Avas ascertained by iodometric titration. It was then converted 

 into sulphate, witli the correction, described under lanthanum, for excess 

 of sulphuric acid. The corrected data are these: 



^ Proc. Chem. Soc, 17, 65. 

 -Bd. 3, .Abth. 1, pp. 263-26.5. 



