EXnCRIMENTS IN RADKVACTIVITY. 205 



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

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

 capilhir}^ 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 bul)ble was expelled through 

 the capillar}' it was exceedingly luminous. The peculiarities of the 

 excited activit}' left behind on the glass by the emanation could also 

 be well observed. When the emanation has 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 activit}^ 

 decay's more slowly. 



The emanation causes chemical change in a similar manner to the 

 salts of radium themselves. The emanation pumped off from 50 milli- 

 grams 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 HELHTM IN THE GASES EVOLVED FROM RADIUM BROMIDE. 



The gas evolved from 20 milligrams of pure radium l)romide (which 

 we are informed had been prepared three months) ])y its solution in 

 water and which consisted mainly of hydrogen and oxygen (cf. Giesel, 

 Ber. , 1!»03, 347) Avas tested for helium, the hydrogen and oxygen 

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

 tially oxidized, and the resulting water vapor l)y a tube of phosphorus 

 pentoxide. The gas issued into a small vacuum tul)e which showed 

 the spectrum of car))on dioxide. The vacuum tul)e was in ti'ain with a 

 small U-tube, and the latter was then cooled with liquid air. This 

 much reduced the brilliancy of the COj spectrum, and the D^ 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 

 previouslv unused glass with 30 milligrams of radium bromide, prob-. 

 ably four or five months ok' kindly lent us by Professor Rutherford. 

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

 to the vacuum tube, which compictel}' prevented the passage of carl)on 

 dioxide and the emanation. The spectium of lielium was obtained, 

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

 5016, -tlK^S, 4713, and 44-72. There were also present three lines of 

 approximate wave lengths, 6180, 5695, 5455, that have not yet been 

 identified. 



