[ 450 ] 

 LXVI. Proceedings of Learned Societies. 



ROYAL SOCIETY. 

 [Continued from p. 383.] 



Feb. 10, 18/0.— Lieut.-General Sir Edward Sabine, K.C.B., Presi- 

 dent, in the Chair. 

 HPHE following communications were read : — 



-^ " On some remarkable Spectra of Compounds of Zirconia and 

 the Oxides of Uranium." By H. C. Sorby, F.R.S. 



When a scientific man has been led into an error and afterwards 

 discovers his mistake, I think it a matter of duty that he should 

 take an early opportunity to correct it. I therefore now write the 

 following notice of certain remarkable peculiarities in the spectra of 

 some compounds of the oxides of uranium with zirconia which led 

 both myself and others* to conclude that they were due to a new 

 elementary substance. 



Though the spectra of the different salts of those bases which show 

 well-marked absorption-bands often differ in detail, yet they usually 

 resemble each other so much that there is no difficulty in recognizing 

 each particular element. This is so constantly the case in the various 

 compounds of erbium, didymium, and cobalt, and in the ordinary 

 salts of uranium, that for a long time the more I studied this ques- 

 tion, the more did it appear to be a general rule, and there seemed 

 to be no reason to suspect that a few special compounds of uranium 

 would give spectra with absorption-bands as unlike as possible those 

 of all others. Such, however, turns out to be the fact when its 

 oxides are combined with zirconia. 



As an excellent illustration of important differences in mere detail, 

 but general correspondence, I would refer to the spectra of didymium 

 in different states of combination f, and would especially refer to the 

 most distinct of the numerous absorption-bands, which occurs in the 

 yellow. The various compounds agree in showing this band in the 

 same general position ; but by careful management, and by the use 

 of sufficient dispersive power, it may be resolved into a very variable 

 number of narrow bands or black lines. For example, in the case of 

 the crystallized sulphate containing comparatively little lanthanum 

 it can be resolved into seven narrow lines, two of those near the 

 centre being the darkest ; whereas when much lanthanum is present, 

 one line on the side next the green is so much darker than the rest 

 that the others are comparatively absent. On fusing the mixed 

 oxides with borax, the same spectrum is seen as with oxide of di- 

 dymium alone, and I can resolve the above-named band into only two 

 narrower bands ; whereas when the saturated bead is made to deposit 

 crystals by being kept some time at a very dull red heat, this band can 

 easily be resolved into eight equal and very distinct black lines. 

 Although these and similar differences in detail are of much interest, 



* Professor Church, ' Chemical News,' vol. xix. p. 121, and Professor Loew, 

 ib. vol. xx. p. 9. 

 f See also Bunsen's paper, Phil. Mag. Sept. 1866, p. 177. 



