THE DETECTION AND WIDE DISTRIBUTION OF YTTRIUM. 
909 
the gadolinite earths. This process is the only one known for separating ytterbia from 
yttria. 
Selection mast be made of these methods according to the mixture of earths under 
treatment, changing the method as one earth or the other becomes concentrated on 
one side or thrown out on the other. Each operation must be repeated many times 
before even approximate purity is attained. The operations are more analogous to 
the separation of members of homologous series of hydrocarbons by fractional 
distillation than to the separations in mineral chemistry as ordinarily adopted in 
the laboratory. 
Preparations of pure terbia. 
56. The mixture of high equivalent earths (54) richest in terbia, erbia, holmia, and 
thulia was treated as follows :— 
The earths were dissolved in dilute formic acid, and the solution heated for some 
time. A white powder of terbic formate separated. This was filtered off, the solution 
containing the more easily soluble formates evaporated to dryness, and ignited. In 
this way the M = 48 earths were separated into two lots, one rich in terbia and the 
other rich in erbia, &c. The treatment with formic acid was again repeated on both 
lots, and the crude terbia finally purified as follows :— 
57. The crude terbia from all the operations was systematically treated by the 
formic acid process, keeping the liquid so dilute that only a portion of the terbic 
formate separated out each time. The syrupy solution of formates was treated as 
described further on (60). The hydrogen equivalent of the terbium was taken each 
time; latterly it kept pretty constant at 49‘5. The terbia was also tested in the radiant 
matter tube. At first the citron spectrum was very strong; gradually, however, it 
got fainter and fainter under the repeated formic treatment, until finally the spectrum 
became so weak as to satisfy me that it was due only to impurity in the terbia, and 
that, had the material been sufficient to stand against the extravagant process of 
purification adojffied, I should finally have got a terbia giving no citron-band spectrum. 
(Subsequent examination (87) showed me that this terbia did not contain more than 
l-5000th part of yttria.) 
58. A concentrated solution of the purest terbia obtained in this way, when 
examined by the spectroscope, showed no absorption lines whatever: proving the 
absence of erbium, holmium, and thulium. 
59. The hydrogen equivalent (4 9'5) would not definitely show the absence of ytterbium 
(57*9) and yttrium (29’7); but these would have been separated by the formic acid 
treatment, terbic formate requiring 30 parts of water for its solution, whilst yttric and 
ytterbic formates dissolve in less than them own weight of water. Moreover, it was 
not probable that the terbia contained an appreciable quantity of any of these earths 
as an impurity, for neither the oxalic acid, the fusing nitrate, nor the formic acid 
process of fractionation produced any change in the atomic weight, 49‘5. 
MDCCCLXXXITT. 6 A 
