CONTRIBUTIONS FROM THE CHEMICAL LABORATORY OF 

 HARVARD COLLEGE. 



A REVISION OF THE ATOMIC WEIGHT OF NEODYMIUM. 



FIRST PAPER.— THE ANALYSIS OF NEODYMIUM CHLORIDE. 



By Gregory Paul Baxter and Hahold Canning Chapin. 



Presented October 12, 1910. Received September 21, 1910. 



Contents. 



Introduction 215 



Separation of Neodymia from Other Rare Earths 219 



Absorption Spectrum of Aqueous Solutions of Neodymium Salts . . . 227 



Preparation of Neodymium Chloride 230 



Preparation of Pure Silver 231 



Drying of Neodymium Chloride 232 



Method of Analysis 235 



Determination of the Moisture Retained by the Neodymium Chloride . . 236 



Specific Gravity of Neodymium Chloride 239 



Results and Discussion 240 



Summary 243 



Introduction. 



Investigations bearing upon the rare earths have always been par- 

 ticularly attractive on account of some unusual chemical and physical 

 properties of these substances, their peculiar relations to the Periodic 

 System, and in particular the important position which some of them 

 have taken with relation to artificial illumination. To be sure any re- 

 search involving the preparation of even one of the earths in a state of 

 approximate purity is sure to be protracted, if not tedious. The very 

 proof of the purity of a preparation is by no means easy to secure. The 

 chief guides which have served in the determination of the purity of 

 material have been the spectra, both absorption and emission, and the 

 atomic weights. For a quantitative determination of purity the atomic 

 weight is perhaps more frequently used than any other test. Hence 

 for this reason as well as from theoretical considerations an exact 

 knowledge of the atomic weights of the rare earths is very desirable. 



