x] RADIO-ACTIVE PROCESSES 329 
of the gas in the vacuum tube the characteristic line D, of helium 
was observed. 
This experiment was repeated with 30 milligrams of radium 
bromide about four months old, lent for the purpose by the writer. 
The emanation and CO, were removed by passing them through a 
U tube immersed in liquid air. A practically complete spectrum 
of helium was observed, including the lines of wave-length 6677, 
5876, 5016, 4972, 4713 and 4472. There were also present three 
other lines of wave-length about 6180, 5695, 5455 which have not 
yet been identified. 
In later experiments the emanation from 50 milligrams of the 
radium bromide was conveyed with oxygen into a small U tube, 
cooled in liquid air, in which the emanation was condensed. Fresh 
oxygen was added and the U tube again pumped out. The small 
vacuum tube, connected with the U tube, showed at first no 
helium lines when the liquid air was removed. The spectrum 
obtained was a new one, and Ramsay and Soddy considered it 
to be probably that of the emanation itself. After allowing the 
emanation tube to stand for four days, the helium spectrum appeared 
with all the characteristic lines, and in addition, three new lines 
present in the helium obtained by solution of the radium. These 
results have since been confirmed. The experiments, which have 
led to such striking and important results, were by no means easy 
of performance, for the quantity of helium and of emanation released 
from 50 mgrs. of radium bromide is extremely small. It was 
necessary, in all cases, to remove almost completely the other gases, 
which were present in sufficient quantity to mask the spectrum of 
the substance under examination. The success of the experiments 
has been largely due to the application to the investigation of the 
refined methods of gas analysis, which had been previously employed 
by Sir Wilham Ramsay with so much success in the separation of 
the rare gases xenon and krypton, which exist im minute pro- 
portions in the atmosphere. The fact that the helium spectrum 
was not present at first, but appeared after the emanation had 
remained in the tube for some days, shows that the helium must 
have been produced from the emanation. The emanation cannot 
be helium itself, for in the first place, helium is not radio-active, 
and in the second place, the helium spectrum was not present at 
