
328 RADIO-ACTIVE PROCESSES [CH. 
the radio-active minerals and is an invariable companion of the 
radio-elements. In addition the presence of a light, inert gas like 
helium in minerals had always been a matter of surprise. The 
production by radium and thorium of the radio-active emanations, 
which behaved like chemically inert gases of the helium-argon 
family, suggested the possibility that one of the final inactive 
products of the disintegration of the radio-elements might prove 
to be a chemically inert gas. The discovery later of the material 
nature of the a rays added weight to the suggestion; for the 
measurement of the ratio e/m of the @ particle indicated that if 
the a particle consisted of any known kind of matter, it must either 
be hydrogen or helium. For these reasons, it was suggested in 
1902 by Rutherford and Soddy? that helium might be a product 
of the disintegration of the radio-elements. 
Sir William Ramsay and Mr Soddy in 1903 undertook an in- 
vestigation 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 149), 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 (pre- 
pared about three months previously) Ramsay and Soddy? ex- 
amined 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 
116). 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 by a phosphorous 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 CO, present in the gas. On examining the spectrum 
1 Phil. Mag. p. 582, 1902; pp. 453 and 579, 1903. 
2 Nature, July 16, p. 246, 1903. Proc. Roy. Soc. 72, p. 204, 1903. 
