at the Royal Institution, 1908-1916 773 



of change in the two directions — from the coloured to the coj our less 

 systems and vice versa. 



Sulphur being an element allied to oxygen, it is also conceivable 

 that a like change may occur in its vapour. So far as I am aware, 

 all known cases of chemical change in which luminosity is developed 

 are cases of oxidative change. 



The sequel to Sir James Dewar's lecture is remarkable. At the 

 ■close of the abstract, it is stated that : — " Nitrogen obtained from 

 the liquefied gas gives only a feeble and very diffused glow. This 

 gas contains oxygen, a few per cent, of which causes the glow, as pure 

 nitrogen gives no visible luminosity with this kind of electric dis- 

 <;harge." 



Further experiments with nitrogen, made by Professor Strutt in 

 the course of 1912, led him to discover that nitrogen, like oxygen, is 

 ■converted into a highly active form when subjected to an electric 

 discharge of a peculiar character. In principle the apparatus he 

 used does not differ from Sir James Dewar's but he differs from Sir 

 James in his account in asserting that the gas becomes brilliantly 

 luminous even in absence of oxygen. This conclusion was called in 

 <,[uestion by certain German chemists but was long maintained by 

 Professor Strutt ; latterly he has been inclined to retreat from this 

 position and to admit that the glow may be dependent upon the 

 presence of oxygen. Professor Strutt has not ascertained what pro- 

 portion of the active form of nitrogen is produced nor whether the 

 "Change be associated with any change in volume, as in the case of 

 ozone ; the volume should be doubled if change take place in ac- 

 <3ordance with the equation 



No ^-F 2N 



If the appearance of phosphorescence be in any way associated with 

 reversible change in a system containing a coloured component, there 

 is no reason to expect the production of a glow in nitrogen under the 

 ^circumstances considered. 



Prof. Strutt has stated that on cooling the activated gas, in a 

 spherical bulb provided with an elongated, narrow tubular neck, 

 by plunging the neck into liquid air, the period of luminosity is 

 shortened. Hence he concludes that " the reunion of nitrogen 

 atoms occurs more quickly the lower the temperature," discarding 

 the obvious explanation that the more rapid change is due to the 

 more local concentration of the gas in the cooled limb of the tube. 

 Finally, he adds, " this is a unique instance of a chemical action 

 being quickened by cooling " : as a matter of fact, not a few gaseous 

 interactions are quickened, within certain limits, by cooling ; the 

 case is in no way peculiar. 



