Bands in the Spectrum of Active Nitrogen. So 1 



to nitrogen appears to be the same, both for the uncondensed 

 discharge and the afterglow. There is strong fluorescence 

 of the glass at first when either nitrons or nitric oxide is 

 admitted to the uncondensed discharge, accompanied by a 

 strong flaring-up of the third group. There is no strong 

 fluorescence when oxygen is admitted, although there is 

 enough to be observed. 



These results show that the third positive group of bands 

 always appear when very small traces of oxygen are present, 

 and are absent when the nitrogen is freed from oxygen as 

 far as possible. The /3 group of bands always appear with 

 the third group, but have a greater relative intensity in the 

 spectrum of the afterglow. Both appear with the condensed 

 discharge in a large tube, but not in a small one. where the 

 current density is greater. No characteristic difference can 

 be observed between the effects of adding small quantities of 

 oxygen, nitrous oxide, or nitric oxide, but the inference is 

 inevitable that these bands are in some way dependent upon 

 oxygen. 



It appears that the only invariably characteristic part of 

 the afterglow spectrum are the bands with heads at 6322, 

 5854, 5M2, and 5053, belonging to the first positive group. 

 In my experiments the afterglow continuously increased in 

 intensity as the proportion of oxygen was reduced ; but I 

 doubt whether in any case the nitrogen was completely freed 

 from oxygen or nitric oxide. The origin of the afterglow 

 seems, therefore, an open question ; it may be an attribute 

 of pure nitrogen, or it may be caused by traces of oxygen or 

 other impurity. When so much oxygen is mixed with the 

 nitrogen that there is no trace of afterglow with a moderate 

 discharge, it may be set up brightly by an intense discharge ; 

 and it seems possible that with a sufficiently strong dis- 

 charge it might be produced with large quantities of oxygen 

 present. 



I have so far failed to determine the conditions under 

 which Strutt and Fowler's " fourth group of positive bands " 

 appear. They were first obtained by me in the spectrum of 

 the condensed discharge in nitrogen in which the afterglow 

 could be maintained only with difficulty on account of leakage 

 of air, and since I have been able to obtain them with clear- 

 ness only when air was introduced. There are faint indica- 

 tions of their presence on films taken with a slight admixture 

 of oxygen, but no trace of them on photographs of the 

 spectrum of nitrogen free as far as possible from oxygen. 

 There were some indications that they are due to enhance- 

 ment of certain lines of the third group of bands, but this is 



