910 
MR. W. CROOKES OX RADIANT MATTER SPECTROSCOPY: 
Preparation of mixed erbia, holmia, and thulia free from other earths. 
60. The filtrate from the terbic formate (57), rich in erbia, and containing besides 
terbia, holmia, thulia, and yttria, was now treated by converting it into nitrates, 
evaporating to dryness, and submitt ting the mass to careful fusion, stopping the 
operation when the liquid mass began to evolve nitrous fumes. The erbic, holrnic, 
and thulic nitrates decomposing before the yttric nitrate, extraction with water gave 
an insoluble residue rich in erbia, holmia, and thulia, and a filtrate rich in yttria. 
The insoluble residue was dissolved in nitric acid, again evaporated to dryness, and 
fused. These operations were repeated eight or ten times, with the result of raising 
the TI equivalent of the erbium metals to about 5 6'8, but the citron-band spectrum 
remained strong for some time after. It, however, ultimately disappeared. A 
concentrated solution of this erbic, &c., nitrate showed a beautiful and intense 
absorption spectrum. I did not attempt any separation of erbium, holmium, and 
thulium from each other, as the evidence here obtained is sufficient to show that the 
element giving the citron-band spectrum is not one of these three metals. Likewise 
I had far too little material to enable me to enter on a work of such difficulty with 
any prospect of success. 
Philippia. 
61. The so-called philippia was sought for in the portion of earths intermediate 
between the terbia and yttria (54). These were dissolved in dilute formic acid, and the 
solution, filtered from some terbic formate which would not dissolve, was carefully 
evaporated down to a small bulk, filtering off the terbic or other difficultly soluble 
formates as they deposited. The clear concentrated solution was then set aside over 
sulphuric acid to crystallise. In the course of a few days brilliant rhombic prisms 
crystallised out, having exactly the appearance described by Delafontaine.* The 
finest of these crystals were picked out, dried on blotting-paper, and analysed. The 
hydrogen equivalent was found to be M = 38'2. The citron-band spectrum in the 
radiant matter tube was very brilliant. The solution decanted from these crystals 
was evaporated to a syrupy consistency, filtered from insoluble terbic formate which 
deposited, and treated for yttria (65). 
Some of the best rhombic crystals were added to cold water acidulated with formic 
acid, and gently heated, but all attempts to dissolve and re-crystallise them failed. A 
large quantity of an insoluble formate separated, and the mother-liquor on concen¬ 
tration again deposited shining rhomboidal crystals. On attempting to re-crystallise 
these, they again deposited an insoluble white powder. The mother-liquor was found 
to contain a large quantity of yttria, and the white insoluble formate on ignition gave 
an earth having the atomic weight and chemical behaviour of terbia. This entirely 
* ‘ Comp'es Rendus,’ vol. 87, p. 559 ; 1 Chemical News,’ vol. 38, p. 202 ; ‘ Journ. Chem. Soc.,’ vol. 36, 
p. 116. 
