BAXTER AND STEWART. — PRASEODYMIUM CHLORIDE. 179 



weighed. In this way fraction 4365 was found to contain 2.5 percent, 

 fraction 4368, 0.4 percent and fraction 4371, 0.1 percent of cerium. 

 Besides the small and unimportant percentage of cerium in fractions 

 4368 and 4371, which were analyzed, the rapid falling off of the 

 cerium percentage is worth noting. 



The Absorption Spectrum of Praseodymium Chloride. 



The absorption spectrum of praseodymium chloride prepared from 

 fraction 4181 was measured in the region of the visible spectrum by 

 means of a Hilger wavelength spectroscope, provided with an extra 

 dense prism and achromatic lenses. The accuracy of measurement 

 with this spectroscope was not far from 0.1 h/j, even for the longer 

 wavelengths. Of the four broad absorption bands shown by con- 

 centrated solutions, only the one in the yellow visibly resolves into 

 two narrower ones as the dilution increases. The wavelengths of the 

 middle of each band at the lowest concentration at which it could be 

 plainly seen are given below, together with observations by some other 

 observers. 11 Praseodymium nitrate was found to give an exactly 

 similar absorption spectrum. 



Baxter and Stewart Aufrecht Auer Bohm 



Photographs of the absorption spectrum also were taken with a 

 Fery quartz spectrograph. When the source of illumination was a 

 Nernst filament, no absorption bands beyond the visible region could 

 be found with any exposure or any" concentration of solution. When 

 the spark from " Nichrome" wire was employed, however, it was found 

 that the light is completely cut off at from X 280 to X 270 according to 

 the concentration of the solution, and that the solution is opaque up to 

 the extreme limit of the spectrograms, about X 210. In these spectro- 



11 Kayser, Handb. d. Spectr., Ill, 440. 



