558 



Professor Deivar 



[June 8, 



action, and that such conditions should favour chemical changes is 

 contrary to what might have been expected. 



In order to carry out the following experiments a good and 

 powerful air-pump is required, and the Institution is fortunate in 

 possessing a specially constructed instrument generously presented 

 by the inventor, William Anderson, Esq. M.I.C.E. Director-General 

 of Ordnance Factories. 



Fig. 



Phosphorescent Gases Apparatus. 



The more essential part of the apparatus is represented in 

 Fig. 1. Common air is first dried and purified by passing through 

 one vessel containing calcium chloride, and another containing caustic 

 potash ; the latter absorbs the carbonic acid. The air is next filtered 

 by passage through a U-tube filled with cotton wool, after which it 

 enters through a carefully adjusted small tap, the two-bulbed vacuum 

 tube represented in the cut. The narrow channel between the bulbs 

 is necessary ; the glow is concentrated thereby, and this seems to 

 have something to do with the efi'ects obtained. It makes no dif- 

 ference whether platinum, charcoal, or aluminium poles be used 

 inside the vacuum tube. The lower part of the tube opens into a tall 

 glass vessel, connected below with the exhaust pump and a mercurial 

 pressure gauge. 



When the current of highly attenuated air blows downwards 

 through the vacuum tube (which is surrounded by a box to prevent 

 any light being seen from the electrical discharge) a luminous glow, 



