CONTRIBUTIONS FROM THE T. JEFFERSON COOLIDGE, JR., 

 CHEMICAL LABORATORY OF HARVARD COLLEGE. 



A REVISION OF THE ATOMIC WEIGHT OF PRASEODY- 

 MIUM. 



THE ANALYSIS OF PRASEODYMIUM CHLORIDE. 



By Gregory Paul Baxter and Olus Jesse Stewart. 



Presented January 13, 1915. Received December 29, 1914. 



CONTENTS. 



Page. 



Introduction 171 



The Purification of the Praseodymium Material 174 



The Purity of the Praseodymium Material 177 



The Absorption Spectrum of Solutions of Praseodymium Salts . . 179 



The Preparation of Praseodymium Chloride 180 



The Purification of Silver and Reagents 181 



The Drying of Praseodymium Chloride 182 



The Method of Analysis 189 



Results and Discussion 191 



Introduction. 



Not many years ago the atomic weight of neodymium was investi- 

 gated in this laboratory by the analysis of the anhydrous chloride. 1 

 Since considerable success was met both in preparing pure material 

 and with the analytical method employed, the twin element praseo- 

 dymium was investigated in a similar fashion ; for, from the results of 

 the earlier investigations upon praseodymium, it can readily be seen 

 the value of its atomic weight is far from certain. 



After Auer von Welsbach 2 first separated the old didymium, he 

 determined the atomic weights of the constituents by Pmnsen's 

 method of converting oxide to sulphate. Apparently the results were 



1 Proc. Amer. Acad., 46, 213 (1911); Jour. Amer. Chem. Soc, 33, 1; Zeit. 

 anorg. Chem., 70, 1. 



2 Sitzungsb. Akad. Wiss. Wien, 92, 317 (1885). 



