206 On some Spectra of Compounds of Zirconia and Uranium. [Feb. 10, 



substances ; but unfortunately the presence of much oxide of lanthanum, 

 which is so commonly associated with it, interferes, as though the eerie 

 oxide had a stronger affinity for the oxide of lanthanum than for uranic 

 oxide. 



The most characteristic peculiarity of the compound of yttria and uranic 

 oxide is that it will not crystallize out from a borax blowpipe-bead, and 

 that the affinity of the uranic oxide for yttria is stronger than for zirconia. 

 Perhaps erbia may prove to act in the same way, but I have not been able 

 to examine that earth quite free from yttria. On adding yttria to a bead 

 with zirconia and a little uranic oxide, and gently naming it in the oxidizing 

 flame, the uranic oxide combines with the yttria and rises to the surface as 

 an orange-coloured scum, which has a great tendency to collect on the 

 platinum wire ; and if sufficient yttria be added, the crystallized borate 

 of zirconia is left in the interior almost colourless, and so free from uranic 

 oxide that no absorption-bands can be seen in the spectrum. We may 

 take advantage of this circumstance to detect yttria in small quantities of 

 compound minerals like Gadolinite and Fergusonite ; and 1 may here say 

 that by combining such means with the observation of the spectra of the 

 transparent or crystalline beads, and of the form of the crystals when 

 slowly deposited, with or without the addition of suitable reagents*, we may 

 often detect twice as many constituents in minerals as could be accomplished 

 by the ordinary methods of blowpipe chemistry — an advantage which I am 

 sure will be appreciated by those engaged in the study of rocks, when it is 

 often so important to obtain satisfactory results with small quantities of 

 material. I have also found these methods of great practical use in exa- 

 mining small residues in the qualitative analysis of minerals, and have thus 

 unexpectedly discovered small quantities of comparatively rare elements. 



I have tried the effect of many other substances along with zirconia and 

 the oxides of uranium, and find that most of them have no sensible influence, 

 unless they are present in considerable relative quantity. The most stri- 

 king effect is that of oxide of tin, which causes the two absorption-bands in 

 the yellow and yellow end of the green in the spectrum of the uranous oxide 

 compound to be nearly equally dark, whereas without the oxide of tin 

 that in the yellow is comparatively faint. This is another illustration of 

 the manner in which certain substances, having no special action on light, 

 influence by their presence the properties of another. The oxides of 

 uranium are unusually sensitive to such actions, and thus not only lend 

 themselves to us as blowpipe-reagents, but also seem more than any others 

 to afford the means of explaining the relation between the physical condi- 

 tions of compounds and their action on light. 



The only compound of zirconia with any other oxide to which I need 

 now draw attention is that with chromic oxide, as deposited from a borax 

 blowpipe-bead. After treatment in the deoxidizing flame, when the cooled 

 very pale-green bead is gently reheated, this compound crystallizes out 

 * See my paper, Monthly Microscopical Journal, vol. i. p. 349. 



