182 PROCEEDINGS OF THE AMERICAN ACADEMY. 



prepared by Dr. Grinnell Jones for work on the atomic weight of 

 phosphorus. 16 



In the preparation of reagents the precautions usual in exact work 

 were taken. The ordinary distilled water of the laboratory was twice 

 redistilled, once from alkaline permanganate and once alone, through 

 block-tin condensers. Hydrochloric and nitric acids were distilled 

 through quartz condensers, in the case of the hydrochloric acid the 

 first and last running being rejected, in the case of the nitric acid two 

 distillations being carried out, the first third being rejected in each 

 distillation. Nitric acid distilled in this way does not contain more 

 than the merest trace of chlorine, if the original acid is nearly free from 

 the latter element. 



Quartz or platinum utensils were employed wherever glass would 

 have introduced objectionable impurities, and electrical heaters were 

 used whenever the products of combustion of illuminating gas were 

 to be avoided. In the crystallization of solids centrifugal drainage 

 was always used to assist in the mechanical removal of mother liquor 

 from crystals, except in the fractional crystallization of the praseo- 

 dvmium material where it would have been of little assistance. 



The Drying of Praseodymium Chloride. 



The drying of the chloride for analysis was effected according to the 

 recommendations of Matignon 17 and in very much the same way that 

 neodymium chloride was dried by Baxter and Chapin, except that 

 while the neodymium salt was not fused, and hence retained a trace 

 of water, which was subsequently determined, the praseodymium 

 chloride was rendered anhydrous by fusion. Bearing in mind the 

 earlier experience with neodymium chloride, that the dehydration 

 of the salt must be made as complete as possible before the actual 

 fusion occurs, in order to prevent the formation of basic salt, the salt 

 was caused to lose its crystal water by a process of efflorescence in a 

 current of dry nitrogen and hydrochloric acid gases at gradually 

 increasing temperatures. Richards 18 has pointed out that a hydrated 

 salt may be freed from moisture much more effectively in this way than 

 when melting is allowed to take place. We found the transition tem- 



16 Proc. Amer. Acad., 45, 137 (1909); Jour. Amer. Chem. Soc, 31, 298. 



l7Compt. rend., 134, 427 (1902). 



18 Zeit. physik. Chem., 46, 194 (1903). 



