1870.] 



of Zirconia and the Oxides of Uranium, 



203 



depended upon the presence of some substance which either reduced the 

 uranic oxide or prevented the oxidization of the uranous. 



These facts thus clearly show that the various spectra which seemed to 

 indicate the presence of a new element existing in three different physical 

 conditions, are in reality only characteristic of the two oxides of uranium 

 combined with zirconia, or not in combination. Perhaps some may think 

 that my having been thus led astray shows that little or no reliance can be 

 placed on the method of investigation employed ; but I contend that the 

 mistake was due to its being such an unexpectedly delicate test for uranium ; 

 and, as explained above, the error was ultimately corrected by a further 

 development of the same method. As far as the interests of science are 

 concerned, there is no need to regret the general result. We have lost 

 what appeared to be good evidence of a new earth, but have gained an 

 almost entirely new system of blowpipe testing, which enables us to detect 

 such a minute quantity of some substances as could not be recognized 

 by the ordinary means. I shall not now attempt to give anything like a full 

 account of this subject, since it would be much better to let it form part of 

 a paper on various improvements in blowpipe chemistry, but will merely 

 mention a few facts which have a special bearing on the question before us. 



In the first place, I would say that zirconia and the oxides of uranium 

 are most useful reagents in detecting the presence of certain substances 

 with which they unite to form compounds having very special characters. 

 The most striking of these are the compounds already described, which 

 are distinguished by the spectra, and not by any well-marked colour, — the 

 compound of eerie oxide with uranic oxide, which is of a splendid deep 

 blue colour, but shows no absorption-bands ; and that of yttria with uranic 

 oxide, which is characterized by a deep orange-colour and extreme fusibility. 

 Thorina and oxide of lanthanum form with uranous oxide compounds 

 which give spectra with absorption-bands in special positions, but of the 

 usual type, and not of such a marked character as to be useful in detecting 

 minute quantities of those substances in mixtures. 



In order to see the spectra of the zirconium-uranium compounds, it is 

 requisite that both elements should be combined in a crystalline condition. 

 When both constituents are melted in borax and are held in solution, or 

 if when crystals are deposited any other substance replaces either the 

 zirconia or the oxides of uranium, the characteristic spectra cannot be seen. 

 The most simple application of this test for uranium is in the case of various 

 zircons. As much of the powdered mineral as will dissolve should be melted 

 with borax in a circular loop of platinum wire about J inch in diameter, so as 

 to give a bead of moderate thickness. A little boric acid should then be 

 added, which not only tends to keep the uranium in the state of protoxide, 

 but also facilitates the crystallization of the borate of zirconia, which is far 

 less soluble when there is excess of boric acid. The bead should then be 

 kept at a bright red heat, just within the deoxidizing flame, until so much 

 borax has been volatilized that small needle-shaped crystals begin to be 



