SALTS OF NEODYMIUM, PRASEODYMIUM, AND ERBIUM. 69 



The elaborate investigations of Muthmann l and his coworkers, Stiitzel, 

 Bohm, Baur, Hofer, and Weiss, call for special comment. They raise the 

 question as to the elementary nature of praseodymium and neodymium, 

 and point out certain lines of evidence based on spectrum analysis which 

 make it not impossible that these substances are mixtures. They show 

 that by spectrum analysis it is possible to determine approximately the 

 amounts of neodymium and praseodymium in a mixture of the two, a 

 fact which had earlier been utilized by Jones 2 in his work on the atomic 

 weights of these two elements. 



By the electrolysis of fused neodymium compounds Muthmann was 

 able to prepare the pure metal. He then studied the physical properties 

 not only of neodymium, but also of cerium, lanthanum, and praseodym- 

 ium, which were prepared in the same manner. 



An important and interesting investigation was carried out by Liveing 3 

 on the effects of dilution, temperature, nature of the solvent, etc., on the 

 absorption spectra of solutions of didymium and erbium salts. His eye 

 observations were made with an ordinary spectroscope, and the photo- 

 graphs also with a prism spectroscope. He obtained some very good plates, 

 indeed, considering the kind of apparatus employed. He studied the effect 

 on the absorption of increasing the dilution of the solution, and established 

 the four following facts: 



The spectra of the different salts of the same metal in dilute solution 

 are identical. The spectrum is constant for the chloride and sulphate in 

 different dilutions, as long as the thickness of the absorbing solutions is 

 proportional to the dilution. The spectrum of the nitrate is modified by 

 some cause with increasing concentration. 



The absorption of the short wave-lengths, which differ for different 

 salts, diminishes with increased dilution. 



The effect of rise in temperature from about 20 to 97 renders the bands 

 more diffuse, but does not increase their intensity. 



The addition of acid made the absorption in general more diffuse, but 

 did not weaken the absorption. 



From this fact, together with the fact that rise in temperature does not 

 increase the intensity of absorption, Liveing concluded that absorption 

 can not be accounted for on the basis of electrolytic dissociation. 



The work of Liveing on absorption in non-aqueous solvents is of special 

 interest in the present connection. 



He says that didymium chloride dried at a temperature above 100 is 

 quite insoluble in alcohol. This was doubtless due to the formation of the 

 basic chloride. This salt can be heated to 140 to 150 in a current of dry 

 hydrochloric acid gas, and the anhydrous salt is still perfectly soluble in alco- 

 hol. The salt with which he worked doubtless contained more or less water. 



Liveing says that the absorption spectrum of the alcoholic solution 

 shows the same bands as an aqueous solution, but they are somewhat 



'Ber. d. deutsch. chem. Gesell., 32, 2653 (1899); 33, 42, 1748, 2028 (1900); Lieb. 



Ann., 320, 231 (1902). 

 2 Amer. Chem. Journ., 20, 345 (1898). 

 3 Camb. Phil. Soc., 18, 298 (1900). 



