898 
MR, W. CROOKES ON RADIANT MATTER SPECTROSCOPY: 
19. For many years chemists have suspected that what is known as zirconia might 
be a compound. Svanberg* found that zircons from different localities varied in 
specific gravity, and the earth or earths obtained by fractional precipitation with 
oxalic acid had not the same properties, the hydrogen equivalents of the metals of the 
earths of the different fractions varying from 17 , 01 to 27'3, the metal of the earth 
hitherto recognised as zirconia being 22 - 4.+ He considered zirconia to contain two 
different earths, the oxalate of one being less soluble in acid than that of the other, 
and their sulphates differing in crystalline form and solubility. He proposed the name 
“ noria ” for one of the earths, retaining that of zirconia for the other. The researches 
of Berlin, on the other hand, seem to disprove this. 
20. Remembering the remarkable result produced in the absorption spectrum of 
some jargons by the presence of a minute trace of uranium,J I tried numerous 
experiments with this metal, adding small quantities of it to zirconia, lime, thoria, 
ceria, &c., but in no case could I educe the citron-band spectrum by this means. 
I may condense a year’s work on zircon,—more than ten pounds weight of crystals 
from North Carolina having been worked up—by stating that the result was comprised 
in about 300 grains of an earthy residue (IS), and about two ounces of oxalate, chiefly 
calcium ; the former gave the citron hand very well. The process as detailed above is 
given, since by this means a very large quantity of zircons was worked up, affording 
me the material which ultimately enabled me to solve the problem which at one time 
seemed almost hopeless. 
The zirconia prepared from these zircons when tested sometimes showed the 
citron band, especially after precipitation as an oxychloride. Zirconia precipitated 
as thiosulphate did not yield the citron band (28). A zirconia rich in citron band, 
fractionally precipitated by ammonia, yielded precipitates of increasing richness, the 
last fraction showing the citron band strongly. 
21. The calcic oxalate obtained from zircon gave unsatisfactory results, so attention 
was directed to the earthy residue (18). This was found to be of highly complex 
character, containing thoria (which had escaped precipitation as thiosulphate), ceria, 
lanthana, didymia, yttria, and probably some of the newly-discovered rarer earths. 
Examination of cerite for the citron band. 
22. The position of the citron band in the spectrum falls exactly on the strongest 
absorption band of didymium, so that a piece of didymium glass or cell of solution of 
the nitrate entirely obliterates the citron band. This naturally suggested that the 
band was due to didymium. 
* Pog. Ann., vol. 65, p. 317. 
f Svanberg’s numbers for these earths are 938 to 1320 (M 2 0 3 ), the earth hitherto recognised as 
zirconia being 1140 ; oxygen being 100. For the sake of uniformity I have recalculated his equivalents 
for the metals on the O = 16 scale, taking the formula as M 2 0 (see note 1, par. 40). 
t ‘ Chem. News,’ vol. 19, pp. 121, 142, 205, 277; vol. 20, pp. 7, 104; vol. 21, p. 73. 
