might be a product of the disintegration of the radio-elements.
Sir William Ramsay and Mr Soddy in 1903 undertook an investigation of the radium emanation, with the purpose of seeing if it were possible to obtain any spectroscopic evidence of the presence of a new substance. First of all, they exposed the emanation to very drastic treatment (section 158), and confirmed and extended the results previously noted by Rutherford and Soddy that the emanation behaved like a chemically inert gas, and in this respect possessed properties analogous to the gases of the helium-argon group.
On obtaining 30 milligrams of pure radium bromide (prepared about three months previously) Ramsay and Soddy33 examined the gases, liberated by solution of the radium bromide in water, for the presence of helium. A considerable quantity of hydrogen and oxygen was released by the solution (see section 124). The hydrogen and oxygen were removed by passing the liberated gases over a red-hot spiral of partially oxidized copper-wire and the resulting water vapour was absorbed in a phosphorus pentoxide tube.
The gas was then passed into a small vacuum tube which was in connection with a small U tube. By placing the U tube in liquid air, most of the emanation present was condensed, and also most of the CO2 present in the gas. On examining the spectrum of the gas in the vacuum tube, the characteristic line D3 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 CO2 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-lengths 6677, 5876, 5016, 4972, 4713 and 4472. There were also present three other lines of wave-lengths 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 this investigation, of the refined methods of gas analysis, previously employed by Sir William Ramsay with so much skill in the separation of the rare gases xenon and krypton, which exist in minute proportions 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