206 Sir W. Rainsay and Mr. F. Soddy. Radioactivity [July 28 r 



the eye in a darkened room. On opening a stopcock between a tube 

 containing the emanation and the pump, the slow flow through the 

 capillary tube can be noticed ; the rapid passage along the wider tubes ; 

 the delay caused by the plug of phosphorus pentoxide, and the 

 sudden diffusion into the reservoir of the pump. When compressed, 

 the luminosity increased, and when the small bubble was expelled 

 through the capillary it was exceedingly luminous. The peculiarities 

 of the excited activity left behind on the glass by the emanation could 

 also be well observed. When the emanation had been left a short 

 time in contact with the glass, the excited activity lasts only for a short 

 time ; but after the emanation has been stored a long time the excited 

 activity decays more slowly. 



The emanation causes chemical change in a similar manner to the 

 salts of radium themsehes. The emanation pumped off from 

 50 milligrams of radium bromide after dissolving in water, when 

 stored with oxygen in a small glass tube over mercury turns the glass 

 distinctly violet in a single night ; if moist the mercury becomes 

 covered with a film of the red oxide, but if dry it appears to remain 

 unattacked. A mixture of the emanation with oxygen produces 

 carbon dioxide when passed through a lubricated stopcock. 



3. Occurrence of Helium in tJie Gases Evolved from Radium Bromide. 



The gas evolved from 20 milligrams of pure radium bromide 

 (which we are informed had been prepared three months) by its 

 solution in water and which consisted mainly of hydrogen and 

 oxygen* was tested for helium, the hydrogen and oxygen being 

 removed by contact with a red-hot spiral of copper wire, partially 

 oxidised, and the resulting water vapour by a tube of phos- 

 phorus pentoxide. The gas issued into a small vacuum-tube which 

 showed the spectrum of carbon dioxide. The vacuum tube was in 

 train with a small U-tube, and the latter was then cooled with liquid 

 air. This much reduced the brilliancy of the C0 2 spectrum, and the 

 D 3 line of helium appeared. The coincidence was confirmed by 

 throwing the spectrum of helium into the spectroscope through the 

 comparison prism, and shown to be at least within 0'5 of an Angstrom 

 unit. 



The experiment was carefully repeated in apparatus constructed of 

 previously unused glass with 30 milligrams of radium bromide, pro- 

 bably four or five months old, kindly lent us by Professor Rutherford. 

 The gases evolved were passed through a cooled U-tube on their way 

 to the vacuum-tube, which completely prevented the passage of carbon 

 dioxide and the emanation. The spectrum of helium was obtained and 

 practically all the lines were seen, including those at 6677, 5876, 5016, 

 * Cf. Giesel, ' Ber.,' 1903, 347. 



