70 ABSORPTION SPECTRA OF SOLUTIONS. 



modified. The positions of maximum absorption are all moved towards 

 the red. The shift of the different bands is not equal. The bands in the 

 yellow and green in the alcoholic solution are so shifted as to suggest the 

 appearance of new bands, but Liveing says that by studying solutions of 

 different concentrations he has convinced himself that no new bands ap- 

 pear. We shall see that this is an error. 



Liveing found the same modifications of the spectrum in aqueous solu- 

 tions produced by glycerol as by alcohol. Liveing 1 concludes thus: 



On a review of the whole series of observations, I conclude that the characteristic 

 absorptions of didymium compounds, namely those which are common to dilute aqueous 

 solutions, and are only modified by concentration, by heat, and by variations of the solvent, 

 are due to molecules which are identical in all cases, though their vibrations are modified 

 by their relations to other molecules surrounding them. 



Urbain 2 devised a new method for separating the rare earths, using 

 ethyl sulphate. 



Drossbach, 3 in his work on absorption in the region of the ultra-violet, 

 measured a number of the bands of praseodymium and neodymium; and 

 Hartley, 4 in his work on the absorption spectra of metallic nitrates, included 

 the nitrate of erbium. In discussing his results, Hartley calls attention to 

 the fact that Bunsen 5 found that didymium salts in the crystallized state 

 and in solution show absorption bands that vary in width with the thickness 

 of the absorbing medium and with the quantity of the salt. Solutions of 

 the chloride, sulphate, and acetate, each containing the same weight of di- 

 dymium, yielded different spectra, the bands being shifted towards the red 

 end of the spectrum with increase in the molecular weight of the salt. 



Hartley calls attention to the fact that more recently Becquerel 6 ob- 

 served similar variation in the absorption spectra, both in crystals and in 

 solutions, while Muthmann and Stiitzel 7 found marked differences between 

 the spectra of solutions of the different salts of neodymium, such as the chlo- 

 ride, nitrate, and carbonate. As Hartley points out, these facts can not be 

 reconciled with the theory that the absorption spectra of solutions of neo- 

 dymium salts are due to the neodymium ion, since the solutions of the 

 above-named salts contain, for comparable concentrations, practically the 

 same number of neodymium ions. 



Among the more recent investigations made upon the salts of the rare 

 earths is that of Miss Helen Schaeffer. 8 She attempted to test Kundt's 

 law for the nitrates of certain rare earths such as neodymium and cerium. 

 She employed the following solvents : Water, methyl alcohol, ethyl alco- 

 hol, propyl alcohol, isobutyl alcohol, amyl alcohol, allyl alcohol, glycerol, 

 and acetone. Solutions were studied containing 1 gram of the salt in 



1 Camb. Phil. Soc., 18, 314 (1900). 



2 Compt. rend., 126, 835, 127, 107 (1898). 



3 Ber. d. deutsch. chem. Gesell., 35, 1486 (1902). Ann. Chim. Phys. (7), 19, 184 (1900). 

 Journ. Chem. Soc., 83, 221 (1903). 



6 Pogg. Ann., 128, 100 (1866). 



8 Compt. rend., 104, 777, 1691 (1887). 



7 Ber. d. deutsch. chem. Gesell., 32, 2653 (1899). 



8 Phys. Ztschr., 7, 822 (1906). 



