1870.] of Zirconia and the Oxides of Uranium. 



201 



ordinary type ; but this change does not occur if a little borax has been 

 added. The addition of more and more borax causes the absorption-band 

 to become more and more faint, and to advance towards the blue end, until 

 we obtain a spectrum with very faint bands but of the usual character. 



In examining the various products into which I separated jargons in 

 order to study the supposed new earth in a state of purity, I obtained a 

 small quantity of a dark-coloured substance, apparently zirconia containing 

 some oxide which communicated a green tint to a glassy, borax blowpipe- 

 bead, but yet not sufficiently distinct to show that it was due to uranous 

 oxide. I therefore thought that the carbonate-of-soda method might throw 

 light on the question ; and though the presence of zirconia prevented 

 solution by pure carbonate of soda, the addition of a little borax enabled 

 me to prove that uranic oxide is really present in some jargons. Such, 

 then, being the case, it seemed desirable to ascertain whether the oxides of 

 uranium w r ould give rise to any special spectra when present along with 

 zirconia in crystalline blowpipe-beads. To my astonishment I found that 

 the spectra were precisely the same as those obtained in the case of what 

 I had thought to be an approximately pure new earth*. When, however, 

 I had ascertained the quantity of oxide requisite to give this result, I was 

 no longer surprised that I had not suspected its presence. In the case of 

 transparent blowpipe-beads of borax with microcosmic salt, it is requisite to 

 have as much as about grain of uranous oxide to show faintly the charac- 

 teristic absorption-bands, whereas, when present along with zirconia in 

 the crystalline beads, ^jo-orr grain gives an equally well-marked spectrum ; 

 and -g-oVo" g ram shows it far better than a larger quantity, which makes the 

 beads too opaque. These very minute quantities were obtained by the 

 repeated division of a small known weight, either before or after fusion 

 with borax. This spectrum also differs very considerably from the spectra 

 of the usual salts or blowpipe-beads of uranous oxide. On comparing 

 them side by side, the only common peculiarity is the fact of there being 

 numerous absorption-bands distributed over a large part of the spectrum, 

 but they do not correspond in either number or position. On the contrary, 

 they differ almost as much as possible, and the darker bands in the 

 spectrum of this zirconia compound occur where the transmitted light is the 

 brightest in other cases. 



The oxide cf uranium is so easily reduced at a high temperature to the 

 state of protoxide in a borax-bead, with excess of boric acid, and is so 

 readily peroxidized at a dull-red heat, when crystallized along with borate 

 of zirconia, that there seemed good reason to refer the change in the 

 spectra to temperature rather than to the state of oxidization, until after it 

 was found that they were due to uranium. By gently naming the crystal- 

 line bead, the spectrum is entirely altered, and becomes like No. 6, which 

 seems to be characteristic of a compound of borate of zirconia with uranic 

 oxide. This gives a spectrum with five well-marked absorption-bands, 

 * Figs. 1 and 2 of my former paper. 



Q2 



