1904] 



The Spectrum of the Radium Emanation. 



471 



Fig. 1. 



the pump was caused to flow past the stop-cock by raising the reservoir 

 of the pump and closing the exit tube at its lower end ; the mercury 

 slowly leaked past the valve of the pump, passed the tap (which was 

 then shut), and so confined the space above the radium bromide by 

 means of mercury. As radium bromide yields electrolytic gas, 

 containing an excess of hydrogen, the pressure gradually rose ; the 

 mercury in contact with this gas remained perfectly bright, and 

 showed no tendency to adhere to the glass ; the presence of ozone 

 thus appears to be excluded, but this excess of hydrogen will form the 

 subject of a future communication. 



The emanation was allowed to accumulate for 14 days. The pump 

 was exhausted until no trace of a bubble passed down the capillary 

 exit tube. But as even then a 

 trace of air must have remained 

 in the barrel, the tap leading to 

 the bulbs containing the radium 

 bromide was turned, rapidly, so as 

 to admit a trace of the electrolytic 

 gas into the pump and "wash it 

 out." This gas was rejected. The 

 remaining electrolytic gas with the 

 emanation was collected in a tube 

 which had previously been heated 

 to redness, and then twice washed 

 out with pure oxygen. The mer- 

 cury in the collecting tube was 

 then boiled, and the bubble of gas 

 removed. It was hoped thereby 

 to have eliminated every trace of 

 nitrogen. The gas was then intro- 

 duced into the gas-burette, shown 

 in the figure, through the inverted 

 syphon. All the mercury was 

 freshly filtered and pure. The 

 apparatus, too, was freshly con- 

 structed and heated to redness to 

 burn out traces of dust. The gas- 

 burette had been washed out with 

 alkali and with nitric acid, and 

 then with a stream of distilled 



water; it was dried by drawing through it a stream of dust-free air, 

 Some slightly moist caustic potash was melted on to the glass, near the 

 sparking wires ; this was intended to absorb any trace of carbon dioxide 

 which might have chanced to be formed during the explosion o the 

 electrolytic gas by the burning of dust. The rubber tube was cemented 



