MR. W. CROOKES ON RADIANT MATTER SPECTROSCOPY. 
709 
sure. The colour of samaria, as pure as I have been able to prepare it, is white with 
the faintest possible tinge of yellow. The absorption spectrum of samarium salts is 
much more feeble than the spectrum of didymium salts. 
The accompanying drawing (fig. 2) shows the absorption spectra of solutions of 
didymic and of samaric nitrates. It will be observed that the strongest bands of the 
samarium absorption spectrum are almost covered by strong absorption bands of 
didymium. Unless, therefore, the samarium is decidedly in excess, it will be difficult 
for any but a very practised observer to detect its presence. Fortunately the 
marvellous delicacy of the phosphorescent spectrum of samarium renders any other 
spectrum test of little value. 
136. I have already mentioned (117) that the cerite earths are supposed to contain 
a fifth member, which has been provisionally called Ya.* Not much is known 
respecting the properties of this earth, but from the little I can glean it would appear 
to become concentrated with the samarium, from which a partial separation may be 
effected either by continuing the operation of fractional precipitation or by taking 
advantage of the different solubilities of their double potassic sulphates in potassic 
sulphate ; the potassio-samaric sulphate being almost insoluble in a saturated solution 
of potassic sulphate, whilst the corresponding salt of Ya is soluble in 100 to 200 
volumes of the same solution. By persevering in this mode of treatment I ultimately 
obtained a small quantity of a white earth which gave no samarium spectrum in the 
radiant matter tube. Whether or no it was Ya I cannot say, as the quantity 
obtained was insufficient to enable me to determine its atomic weight. 
The Phosphorescent Spectrum of Samarium. 
137. Pure samaric sulphate by itself gives a very feeble spectrum. Some of the 
pure salt was heated to redness,! sealed in a radiant matter tube, and carefully 
exhausted. The coil was adjusted so as to give a powerful spark ; the room was well 
Fig. 3. 
darkened, and the eye kept shielded from extraneous light. It was difficult to hit the 
exact moment of exhaustion between the disappearance of gas and non-conductivity, 
but by careful watching at the spectroscope a point was reached at which the 
* Maeignac, ‘ Comptes Rendus,’ vol. 90, p. 899 ; ‘ Chemical News,’ vol. 41, p. 250. 
t Samaric stilphate is not decomposed at the temperature employed. 
MDCCCLXXXV. 4 Y 
