MR. W. CROOKES ON RADIANT MATTER SPECTROSCOPY. 
707 
These proceedings are tedious enough even in their narration, but no mere words 
can enable the reader to realise the wearisome character of these operations when 
repeated day by day, month after month, on long rows of Winchester quart bottles. 
131. I commenced the purification of didymia in the latter part of the year 1883, 
and the operations have been going on since almost daily in my laboratory. At 
intervals of some weeks the didymia in the then stage of purification w T as tested in 
the radiant matter tube, a little lime having previously been added to bring out the 
discontinuous phosphorescence. During the first month the intensity of the orange- 
band spectrum scarcely diminished. After this it began to fade, but the last traces 
of orange band were very stubborn, and not till the last few weeks could I obtain a 
didymia to show no trace of the orange-band spectrum ; and this result has not been 
accomplished without sacrifice. My 1000 grammes have dwindled away bit by bit, till 
now less than half a gramme represents all my store. 
132. Whilst in the midst of the operations of purifying didymium and samarium I 
had the pleasure to receive a visit from Prof. Cleve, to whom we owe so much of our 
knowledge of the chemistry of the samarskite and cerite metals, and especially of 
didymium and samarium. He gave me not only most valuable information, and 
suggestions respecting the work I was then engaged upon, but on his return to 
Upsala he munificently presented me with specimens of lanthana, didymia, samaria, 
yttria, and erbia—specimens at that time considered to represent a state of purity. 
According to any chemical tests these earths would be deemed absolutely pure, but 
the test of the phosphorescent spectrum proved too severe a trial, and the didymia, 
lanthana, and samaria all showed the orange band—the lanthana faintly, the didymia 
more strongly, and the samaria brightest of all. A subsequent lot of “samarium- 
free ” didymia, sent by Prof. Cleve, also gave a strong orange-band spectrum, though 
the samarium present probably did not amount to more than the one hundred 
thousandth part of the didymium. 
Purification of Samaria. 
133. The foregoing experiments left little doubt that x, the orange-band-forming 
body, was samarium ; the last problem was, therefore, to get this earth in a pure state. 
The general plan of operations was the same as I adopted in getting didymium free 
from samarium, only attention was now directed to the portions richest in samarium 
which had been formerly set aside (128, 129). On fractionation in highly dilute 
solutions with very weak ammonia the first precipitates are richer in samaria than the 
last. These first precipitates were re-converted into nitrates, and fractionation again 
proceeded with. 
Fusion of the nitrates with potassic nitrate (129), or precipitation by, and washing 
with, potassic sulphate (130), are of no use in the final purification of samarium. 
When the object is to separate a little samarium from a large quantity of didymium, 
