BAXTER AND STEWART. — PRASEODYMIUM CHLORIDE. 181 



and the salt was crystallized three or four times from concentrated 

 solution by "salting out" at 0° with hydrochloric acid gas made by 

 boiling the fuming solution and conducting the gas to the solution 

 through a quartz tube. The crystals were each time centrifugally 

 drained and rinsed in platinum Gooch crucibles. 15 The product was 

 preserved in quartz in a vacuum desiccator over fused potassium 

 hydroxide. 



The Purification of Silver and Reagents. 



The greater part of the silver used in this work was prepared by 

 Mr. W. H. Whitcomb for an investigation upon the atomic weight of 

 neodymium, which will be published shortly. No innovations were 

 made in the processes of purification which have been frequently 

 described in papers from the Harvard Laboratory. These processes 

 were in brief as follows: Crude silver was dissolved in nitric acid, and 

 the chloride precipitated with a large excess of hydrochloric acid. 

 The precipitate, after being washed, was dissolved in ammonia and 

 reprecipitated with nitric acid. Then the silver chloride was reduced 

 with sodium hydroxide and sugar, and the metal was fused on charcoal 

 before a blast lamp. The metallic buttons were cleansed by scouring 

 and etching, dissolved in distilled nitric acid, and the metal repre- 

 cipitated with ammonium formate made from distilled ammonia and 

 formic acid. After thorough washing the product was again fused on 

 the purest lime before a blast lamp. Electrolytic deposition, with 

 silver nitrate as the electrolyte and with a dissolving anode of the pure 

 silver buttons, followed and the electrolytic crystals were fused in a 

 current of electrolytic hydrogen on a pure lime boat. Adhering lime 

 was removed by etching with nitric acid, and the buttons were washed 

 with water and ammonia, dried, and heated to about 500° in a vacuum. 

 The silver was preserved over potassium hydroxide in a desiccator. 

 In some of the later analyses the silver used had been purified exactly 

 as described above by Mr. F. L. Grover for work upon the atomic 

 weight of lead, or by Dr. H. C. Chapin for the investigation upon 

 neodymium. 



In Analyses 1 and 2 silver nitrate was employed which had been 

 freed from chloride by repeated crystallization. This material was 



15 Baxter, Jour. Amer. Chem. Soc, 30, 286 (1908). 



