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



passed into a crystalline state ; for the spectrum then shows four 

 absorption-bands, and is more like the 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 car- 

 bonate-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 would 

 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 characteristic absorption-bands, 

 whereas, when present along with zirconia in the crystalline beads, 

 oTTOlTo" g ram gives an equally well-marked spectrum ; and ^Vo g ram 

 shows it far better than a larger quantity, which makes the beads too 

 opaque. These very minute quantities were obtained by the re- 

 peated 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 either in 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 of 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 flaming the crystalline bead, the spectrum is entirely altered, 

 and becomes like No. 6, which seems to be characteristic of a com- 

 pound of borate of zirconia with uranic oxide. This gives a spec- 



* Figs, 1 and 2 of my former paper, at p. 67 of the present volume. 



