352 Mr. J. B. B. Burke on the 



observed (see Carnb. Phil. Soc. Proc. 1897), the glow pre- 

 sents a totally different appearance according as there is 

 carbon, nitrogen, or sulphur present with oxygen. When 

 there is carbon present the glow is white, when there is some 

 nitrogen present yellow, and when there are traces of sulphur 

 blue. In cyanogen the glow is white, as in mixtures of 

 oxygen and carbon. In air it is yellow, as in mixtures of 

 oxygen and nitrogen. In pure electrolytic oxygen, as has 

 been said, it is difficult to get the glow, but when a small 

 quantity of air is introduced into the tube so that some 

 nitrogen is also present, the glow becomes intensely bril- 

 liant. 



The best phosphorescence I have ever obtained has been 

 with air, in a tube which contained a number of sealing-wax 

 joints and in which there was just a very slight leak ; and 

 with it on two or three days I have been able to get a glow 

 of great brilliancy that lasted two minutes without much 

 diminution in intensity, and I should say lasted altogether 

 about five or six minutes. 



The conditions which give rise to the maximum effects are 

 extremely difficult to determine. Hydrogen, whether pure or 

 with a small proportion of oxygen of about 5 per cent., does 

 not give any phosphorescence. 



It is very singular also, that in a bulb with an aluminium 

 window, as described in Art. (17), the glow in air was a bluish- 

 green, indicating that a disintegration of particles from the 

 surface of the aluminium had taken place by the passage of 

 the discharge through the gas, and that these had taken part 

 in the production of the glow. 



Dewar has shown (Joe. cit.) that ether and scents in 

 very small quantities destroy the glow and render it quite 

 impossible to reproduce the phosphorescence, which tends 

 further to support the view that the glow depends upon some 

 part played by slight impurities. 



(9) If the phosphorescence is the result of chemical com- 

 bination attending the passage of a discharge of electricity 

 through a mixture of gases, it is very singular that at 

 ordinary pressures the glow is not produced, but only in high 

 vacua, and then only within a comparatively narrow range 

 •of pressures. Thus it would not be unreasonable to expect 

 that some process analogous to chemical combination, but 

 unknown at ordinary pressures, is facilitated by the passage 

 of a discharge in high vacua, and manifested by the phe- 

 nomenon of phosphorescence. For it is quite conceivable, 

 that at certain pressures a mixture of gases may enter into 

 combination, of a somewhat unstable kind, by the passage of 



