458 Royal Society : — Mr. H. C. Sorby on some Spectra 



amount of uranium be very small, and so much of other oxides be 

 present as to make the bead very dark, or too opaque from de- 

 posited crystals, before it is sufficiently concentrated for the com- 

 pounds with the oxides of uranium to crystallize out, it may be im- 

 possible to detect it. In order to apply the test in the case of complex 

 minerals, a bead of borax, boric acid, and pure zirconia should be 

 prepared, then a small quantity of the mineral added, and, after 

 fusion and sufficient concentration, the bead made to crystallize in 

 the manner already described. If needle-shaped crystals be not 

 deposited in the bead when very hot, and if it do not suddenly turn 

 opaque when reheated, the result may not be satisfactory. In this 

 manner it is easy to detect uranium in -g-J- grain of such minerals 

 as Fergusonite, tyrite, and yttrotantalite, even when they contain no 

 more than 1 or 2 per cent. If in such cases the spectrum of the 

 uranous compound cannot be obtained, the bead should always be 

 flamed and reexamined, to see if that of the uranic compound is 

 thereby developed. 



In a similar manner we may make use of a little oxide of uranium 

 to detect zirconia ; but the test is far less delicate than the converse, 

 because it is almost impossible to obtain the compound in a crystal- 

 line state, unless there be an excess of zirconia. Not more than 

 T Wo g ram °f uranic oxide should be employed, or the bead may be 

 too opaque. There is no difficulty in thus detecting zirconia in zir- 

 cons, or in katapleiite ; but the presence of so much of other bases in 

 minerals like eudialyte prevents our obtaining a satisfactory result. 

 There certainly could not be a more characteristic test to confirm the 

 results of other methods, or to identify such a small quantity of ap- 

 proximately pure zirconia as could not easily be distinguished in any 

 other way. 



The only other compound of uranic oxide of very abnormal cha- 

 racter which I have so far discovered is that with cericic oxide. So 

 much of both oxides should be fused with borax in the oxidizing flame 

 as will yield a bead which is perfectly clear, and of pale yellow colour 

 when rapidly cooled, but crystallizes when gently reheated. If the 

 constituents be present in a certain proportion, it then turns from pale 

 yellow to a deep blue, as though coloured by oxide of cobalt. In most 

 cases the bead is rendered nearly opaque by the number of crystals ; 

 but sometimes, though it turns deep blue, it remains transparent, 

 owing to the compound being set free in a state similar to that of 

 the red oxide of copper in a borax blowpipe-bead, with carbonate of 

 soda and oxide of tin, treated in the reducing flame. The spectrum 

 of these blue beads shows no absorption-bands, but merely a general 

 absorption at the red end ; and it is curious to find that the combina- 

 tion of two yellow substances gives rise to a deep blue, in much the 

 same manner as when the yellow ferrocyanide of potassium is added 

 to a yellow ferric salt. The production of this blue colour on the 

 addition of a little uranic oxide might be employed with advantage to 

 identify moderately small quantities of cerium, even when mixed with 

 a number of other substances ; but unfortunately the presence of 

 much oxide of lanthanum, which is so commonly associated with it, 



