900 
MR. W. CROOKES ON RADIANT MATTER SPECTROSCOPY: 
filtrate for some time. The flask then corked was set aside for twenty-four hours and 
filtered. The filtrate was evaporated to a small bulk, nearly neutralised with 
ammonia, and then boiled for some time with excess of sodic thiosulphate. This 
precipitated the thorina, alumina, zirconia, and titanic acid, whilst it left in solution 
the metals of the cerium and yttrium groups. The filtrate was boiled down to a 
small bulk, when a further precipitation took place : this was filtered off and added to 
the first thiosulphate precipitate. To the clear filtrate excess of ammonic oxalate was 
added, and the whole allowed to rest twenty-four hours. The precipitated oxalates 
were filtered, washed, ignited, dissolved in hydrochloric acid, and the excess of acid 
evaporated off. The aqueous solution was then mixed with a large excess of freshly 
precipitated baric carbonate, and set aside for twenty-four hours with frequent 
shaking (29). This would precipitate much of the cerium, and any iron or alumina 
which might have escaped previous treatment. The liquid was filtered from the 
precipitate produced by baric carbonate, and the clear solution, which would contain 
nothing but barium, and some of the yttrium and cerium metals, was treated as 
described further on (30). 
28. The thiosulphate precipitate tested in the radiant matter tube gave no citron 
band, nor did it seem possible to detect this band on testing the purified thorina 
obtained from this precipitate, nor from the alumina or zirconia from the same 
precipitate. This confirmed the results obtained when working up zircons, that sodic 
thiosulphate did not precipitate the citron band-forming body. 
29. The barium precipitate (27) was dissolved in hydrochloric acid, the baryta 
separated with sulphuric acid, and the solution precipitated with ammonic oxalate. 
The ignited precipitate, which amounted to 0 - 223 per cent, of the mineral taken, 
contained the cerium metals. On testing in a radiant matter tube it gave the citron 
band only moderately well—-not nearly so strong as the original thorite and orangite. 
The iron and alumina in the filtrate from the ceric oxalates were likewise precipitated 
and tested; they showed a faint trace of citron band. 
30. The solution (27) filtered from the barium precipitate was freed from baryta by 
sulphuric acid, precipitated with ammonic oxalate, and the precipitate washed and 
ignited ; it amounted to only 0T25 of the mineral taken. Tested in the radiant 
matter tube it showed the citron band about as well as the corresponding earth from 
the barium precipitate. 
This was disheartening, for after having started with a mineral which gave the 
citron band well, and having hunted the citron band as it were into a corner, the 
only residt was two trifling precipitates showing the citron band less intensely than 
did the raw material itself. The experiment, however, proved one thing : the band¬ 
forming substance was not thorina. The occurrence of this spectrum must therefore 
be due to some other element present in small quantity in thorite and orangite. 
31. The two mixtures of earths—the one from the barium precipitate (29) and the 
other from the barium filtrate (30)—which showed the citron line moderately well, 
