184 PROCEEDINGS OF THE AMERICAN ACADEMY. 



three gases could be delivered to the bottling apparatus at will. This 

 apparatus is identical with that used by Baxter and Hartmann 25 for 

 the drying of cadmium chloride, and by Baxter and Grover 26 for the 

 drying of lead chloride. After the fusion of the neodymium chloride, 

 the hydrochloric acid was displaced by nitrogen and the nitrogen in 

 turn by air. Then the boat and contents were transferred to the 

 weighing bottle, which was allowed to stand in a desiccator near the 

 balance for some hours before being weighed. 



A solution of praseodymium chloride which has been fused in this 

 way, sometimes contains a small amount of insoluble glistening 

 particles, practically invisible unless examined in a strong light in a 

 vessel whose curvature magnifies their apparent size. A similar 

 difficulty was met by Baxter and Chapin in the preparation of pure 

 anhydrous neodymium chloride. Under unfavorable conditions, 

 which will be described shortly, the amount of this insoluble material 

 may be considerably augmented, but when prepared under the most 

 favorable conditions the salt dissolves rapidly without leaving even a 

 trace of insoluble matter. Even when a small amount of insoluble 

 material is formed, a clear solution is usually obtained after a day or 

 two. The conditions under which the extent of the difficulty is too 

 small to have an appreciable effect upon the results, have been found 

 to be very careful preliminary dehydration of the salt, and a very 

 short period of fusion. These conditions were maintained in the 

 preparation of all of the specimens of material which were analyzed, 

 but only in Analyses 5, 6, 9, 10, 16, 24, 25, 30, 31, 38 and 39 was the 

 solution of the salt absolutely clear at the start. 



Many experiments were carried out, however, first, to find out the 

 nature of the insoluble matter, and second, to discover the extent of the 

 difficulty. At the outset there seemed to be three possibilities as to the 

 nature of the substance. The most probable one was that the sub- 

 stance is a basic chloride, but it was possible that it might be either an 

 insoluble allotropic form of the trichloride or a lower chloride, i. e. 

 praseodymium dichloride. The fact that prolonged fusion of the salt 

 invariably resulted in the formation of relatively large amounts of 

 insoluble material seemed to point toward one of the last two explana- 

 tions, although there seems to be no certain evidence of the existence 

 of such compounds in the case either of praseodymium or of other rare 

 earths. 



25 Jour. Amer. Chem. Soc, 37, 113 (1915). 



26 Investigation not yet published. 



