SALTS OF NEODYMIUM, PRASEODYMIUM, AND ERBIUM. 71 



10 c.c. of the solvent. She found that, in general, the bands had a differ- 

 ent arrangement in the various solvents; and in order to identify the 

 bands, she worked with mixtures of the various solvents, so as to get what 

 she supposed was a gradual shift of the bands. Her plates, however, show 

 that instead of having a shift in the bands, she had two sets of bands 

 existing simultaneously. 



In the second part of her investigation she studied change in absorp- 

 tion with change in concentration; in other words, Beer's law. She found 

 that with decreasing concentration there is a shift of the yellow band 

 towards the violet. The most concentrated solutions with which she 

 worked contained about 30.5 grams of didymium nitrate in 10 c.c. water. 

 She concludes that all of the facts established by her investigation can be 

 accounted for in terms of electrolytic dissociation alone. 



An excellent piece of work on the absorption spectra of aqueous solu- 

 tions of neodymium chloride has recently been done by Rech. 1 The ab- 

 sorption bands were carefully measured as far down into the red as the 

 sensibility of his plates would permit. There is transmission farther down 

 into the red than could be detected by the plates which he employed. 



The absorption spectra of a number of the powdered salts of neo- 

 dymium and erbium were recently studied by Anderson. 2 These included 

 the chloride, nitrate, sulphate, and oxalate. He found that each salt has its 

 own definite absorption, which is different from that shown by any other salt. 



PREPARATION OF ANHYDROUS SALTS. 



When working in non-aqueous solvents, it is, of course, necessary to 

 have the dissolved salts perfectly anhydrous. A number of the salts used 

 in this investigation can not be dried in the air by simply raising the tem- 

 perature. Under these conditions the oxy-salt would be formed. This 

 applies to most of the chlorides and bromides, whose non-aqueous solu- 

 tions were studied in this work. 



In every such case the chloride in question was dried in a current of dry 

 hydrochloric acid gas. It was placed in a porcelain boat, which was then 

 inserted into a glass tube through which a current of dry hydrochloric acid 

 gas was passed. The glass tube was then heated in an air-bath to the tem- 

 perature required to remove all of the water from the salt. 



In removing all of the water from a bromide, the salt was treated in 

 every respect like the chloride, except that it was dried in a current of dry 

 hydrobromic acid gas. The usual methods for testing the purity of all of 

 the compounds employed, and of standardizing the mother-solutions of 

 these substances, were used. A detailed discussion of this subject would 

 be superfluous. 



The praseodymium and neodymium, in the form of the double nitrate 

 with ammonium, were furnished us, with their characteristic generosity, 

 by the Welsbach Light Company, and it gives us unusual pleasure to 

 express here our heartiest thanks to their chemist, Dr. H. S. Miner. The 



Dissertation, Bonn, 1906. J Astrophys. Journ., 26, 73 (1907). 



