Fluorescence of Iodine and Mercury. 



317 



vapour is strongly electro-positive, and its fluorescence should 

 therefore be very sensitive to the presence of an electro- 

 negative gas. 



Our results confirm this view, for in oxygen at a pressure 

 of only 3 mms. we obtained no fluorescence at all, though 

 the quartz bulb was heated to a temperature sufficient to give 

 us mercury vapour at 30 cms. pressure. The apparatus is 

 shown in fig. 1. A quartz bulb with a double neck was 

 used, one sealed to a vertical tube with sealing-wax, the 

 other serving for the introduction of the high temperature 

 thermometer, also sealed in with wax. The quartz necks of 

 the flasks were kept cooled with wet cotton, and the portion 

 of the bulb containing the mercury heated with a burner. 



Fiflr. 1. 



Quartz Ie/vs 



II To Pump aho 

 If Gas /?ss£i/o//73 



The temperature of the mercury, the coolest part of the 

 system, was measured, and this gave the pressure of the 

 vapour. At the beginning of the experiment the stop-cock A 

 was opened and the mercury allowed to sink below the lateral 

 tube B, by lowering the mercury reservoir 0. 



The stop-cock A was then closed and the bulb thoroughly 

 exhausted. The cock A was then opened, D being closed, 

 and the mercury allowed to rise until the bulb of the 

 thermometer was just covered. The cock A was now closed 



