MR. W. CROOKES ON RADIANT MATTER SPECTROSCOPY. 
703 
Analysis of Cerite. 
118 . The first necessity was to get the earths ceria, lanthana, and the mixture hitherto 
called didymia, in a pure state, for my so-called pure earths of this group all showed 
the orange band in more or less degree. 
About 14 lbs. of cerite were finely ground, made into a thick paste with strong 
sulphuric acid, and heated to drive off excess of acid. The mass became of a white or 
pale grey colour. This was digested in cold water, filtered, and the residue well 
washed with cold water. 
To the filtrate oxalic acid was added, which precipitated all the earths, with any 
lime, &c., that might be present, as oxalates. It saves time at first only to aim at a 
partial separation of the mixed earths, and for this purpose it is well to proceed as 
follows :—The dried oxalates are boiled with strong nitric acid till completely decom¬ 
posed, the nitrates are evaporated to dryness, mixed with three times their weight of 
nitre, and fused at the lowest temperature at which nitrous fumes come oft'; the 
residue is digested in water, filtered, and washed. The insoluble residue, of a pale 
yellow colour, consists of ceric oxide and basic ceric nitrate, with a little of the other 
oxides, whilst the filtrate contains the bulk of the lanthanum, didymium, and samarium. 
Separation of Ceria, Lanthana, Didymia, and Samaria. 
119. To free the lanthanic, didymic, and samaric nitrates from the last traces of 
cerium it is necessary to fuse them again very gently with three or four times their 
weight of potassic nitrate, at a temperature just sufficient to cause slight decomposition. 
The operation of fusing must be repeated on the evaporated filtrate many times to 
throw out all the cerium. 
The ceric oxide, or basic nitrate obtained, is freed from any didymium by re¬ 
treatment with nitric acid and fusion as above ; the presence of didymium being 
indicated by its brown colour or by the absorption spectrum of the solution. 
120. The separation from each other of lanthana, didymia, and samaria is a most 
laborious process, and the amounts of these earths, obtainable in anything like a pure 
state, is small, compared with the mass of material worked up. The solution of the 
nitrates of these elements is made perfectly neutral, diluted to such a strength as to 
contain about 1 per cent, of the oxides, and a very dilute solution of ammonia is added, 
about 0’1 gramme NH 3 in 500 cubic centimetres, the precipitation being conducted in 
large vessels, as ordinary Winchester quart bottles. The first precipitates formed are 
rich in samarium, and also contain much didymium; these are followed by didymium, 
with some lanthanum and samarium ; and the final precipitates consist almost wholly 
of lanthanum. By this method there are obtained three portions of hydrates, which 
must be again worked up separately by precipitation ; the first for samarium (133), 
the second for didymium (127), and the third for lanthanum (125), the process of 
fractional precipitation being repeated on each portion fifty or a hundred times. 
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