of Compounds of Zirconia and the Oxides of Uranium. 459 



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 flaming 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 ad- 

 vantage of this circumstance to detect yttria in small quantities of 

 compound minerals like Gadolinite and Fergusonite ; and I 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 re- 

 agents*, we may often detect twice as many constituents in minerals as 

 could be detected 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 satis- 

 factory results with small quantities of material. I have also found 

 these methods of great practical use in examining small residues in 

 the qualitative analysis of minerals, and have thus unexpectedly dis- 

 covered 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 striking 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 pre- 

 sence 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 conditions 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 so as to give a fine red-pink colour by 

 transmitted light, even when so little chromium is present that the 

 glassy bead is scarcely at all green. If too strongly heated, the pink 

 tint is lost. This compound is of interest in connexion with the 

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



