474 



Sir W. Eamsay and. Prof. J. K Collie. [May 18, 



When the spectrum was examined two days later, besides the 

 hydrogen and mercury lines, there were seen: — 5595, feeble; 5105, 

 feeble ; 4985, very feeble ; this was with a jar and spark-gap inter- 

 posed ; the ordinary discharge showed only the primary and secondary 

 spectra of hydrogen, and that of mercury. 



Eleven days later, the emanation from the same stock of radium 

 bromide was collected, and treated in exactly the same manner. This 

 time, however, an excess of conscientiousness made us continue to 

 extract gas with the pump from the bulb C containing the frozen 

 emanation, surrounded by liquid air, for too long a time. Every two 

 or three strokes of the pump collected a minute bubble, occupying 

 about the tenth of a millimetre in length of the very narrow fall-tube 

 of the pump, which was really a fine-bore capillary. The yield of gas 

 appeared to be continuous ; and when these bubbles were examined in 

 the dark they were brilliantly luminous. This gas was really the 

 emanation, which possesses a feeble vapour pressure even at the 

 temperature of liquid air. Needless to say, on attempting to examine 

 the spectrum, little was seen, for the pressure of gas in the vacuum- 

 tube was too low. 



The tube was therefore washed out with the gas which had been 

 pumped off, and the process was repeated. The minute bubbles which 

 passed down the capillary fall-tube of the pump were examined, and 

 pumping was stopped when they showed a very faint luminosity in 

 the dark. On compressing the emanation into the spectrum-tube, the 

 spectrum was again brilliant, and measurements were made. It was 

 found possible to read the lines several times, for although the 

 spectrum faded in less than a minute, it appeared to recover on 

 ceasing to pass the current. But this recovery soon failed and, as 

 before, nothing could be detected after 5 minutes but the primary 

 and secondary spectra of hydrogen. Now the tube was practically 

 vacuous before warming the bulb containing the emanation ; no 

 current would pass ; but it is, of course, possible that the gas carrying 

 the emanation had not been perfectly dried in passing through the 

 tube B, containing phosphoric anhydride; any water- vapour would 

 have condensed in the cooled bulb C, and would only slowly have 

 vaporised into the vacuum-tube. On arriving there, it would give 

 the hydrogen spectrum. Another possibility is that it may have 

 come out of the electrodes ; for it has been frequently noticed in 

 glowing out a vacuum-tube with aluminium electrodes that even after 

 all trace of hydrogen has been removed by passing the discharge so as 

 to heat the electrodes, and by pumping, the hydrogen spectrum has 

 reappeared on admitting a trace of one of the gases of the argon group, 

 and passing the discharge for a longer time ; but the intensity of the 

 spectrum which replaced that of the emanation may perhaps warrant 

 the supposition that hydrogen as well as helium is one of the products 



