1870.] On some Spectra of Compounds of Zirconia and Uranium. 197 



I. " On some remarkable Spectra of Compounds of Zirconia and 

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

 December 27, 1869. 



When a scientific man lias been led into an error and afterwards dis- 

 covers 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 question, 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-^, 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 compara- 

 tively 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 didymium 

 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, yet in no case are they so considerable as to 

 prevent our recognizing at once that the spectra are all due to didymium. 

 It is also important to notice that the amount requisite to give a most 

 splendid spectrum when the bead is crystalline will scarcely show any trace 

 of bands when it is in a vitreous condition, dissolved in the borax. This is 



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

 vol. xx. p. 9. 



t See also Bunsen's paper, Pogg. Ann. vol. exxviii. p. 100, 



