916 
MR. W. CROOKES ON RADIANT MATTER SPECTROSCOPY: 
former place 3028 to 3049 being quite dark. The appearance is shown in line 
No. 4. On superposing this spectrum and that from the ignited sulphate the 
displacement of the citron bands was clearly observed ; with a very narrow slit the 
two bands were seen not to touch. The two green bands were visible, but very hazy 
and indistinct, and only to be resolved into bands with difficulty. The yttria was 
now removed from the tube, ignited to a bright red heat, and re-tested. The 
spectrum was a little stronger than that given by the yttria ignited at. a lower 
temperature, but in other respects the general appearance and measurements were 
unchanged. No alteration was caused by subsequent ignition to a white heat. 
77. Pure yttric sulphate ignited to a bright white heat gave a spectrum corre¬ 
sponding to the oxide (76); the sulphate having been decomposed by the high 
temperature. 
78. Yttric phosphate was precipitated, washed, and dried at a heat below redness, 
and introduced into the radiant matter tube. It phosphoresced faintly, giving the 
citron band hazy and faint, extending from about 3010 to 3060. The red bands were 
faint, and the green bands, especially the first one, were stronger than usual. The 
salt was now removed from the tube, and heated to redness. It became of a grey 
colour, and now phosphoresced with a beautiful green light. The citron band was still 
broad and faint, but the green bands were very bright and distinct, and the red band 
between 2610 and 2627 was also stronger. The sjiectrum No. 5 shows the appearance. 
Heating the phosphate before the blowpipe made little change in the character of 
the phosphorescence. It was moistened with sulphuric acid, heated to a dull redness, 
and then tested, but no further change was produced in the spectrum. This 
experiment shows that the citron-band test for yttrium is far less delicate in the 
presence of phosphoric acid than in its absence. 
Occurrence of yttria in Nature. 
79. It is an old and probably a true saying that every element could be detected 
everywhere had we sufficiently delicate tests for it. Early observations (10, 16) had 
prepared me for the wide distribution of the element giving the citron band, and no 
sooner had the exquisite sensitiveness of this spectrum test forced itself on my notice 
than I sought for yttrium in other minerals.- Facts which I had noticed in connexion 
with the variation of the appearance of the citron spectrum, according to the quantity 
of yttrium present, showed that it might be possible to devise a process for the rough 
quantitative estimation oi yttrium, and after several experiments this was ultimately 
carried out in the following' manner :— 
The calcic carbonate which was found to give no citron band (12) was boiled in a 
quantity of nitric acid insufficient to dissolve it. The solution was filtered from the 
insoluble residue, diluted to a convenient bulk, and standardised: 14'91 grains of 
