Bands in the Spectrum of Active Nitrogen. 827 



In discussing the phenomenon, I was inclined to the 

 opinion that the afterglow might be the result of the 

 presence of infinitesimal traces of oxygen or of nitric oxide, 

 partly because, in spite of the utmost precautions, it seemed 

 unlikely that the nitrogen used by me was entirely free from 

 these impurities, but more particularly because of the usual 

 presence in the spectrum of the third group of " nitrogen " 

 bands, attributed by Deslandres and others, apparently with 

 good reason, to nitric oxide. The nitrogen was prepared by 

 heating a solution of sodium nitrite and ammonium sulphate, 

 and was then passed through pyrogallic acid solution and 

 drying-tubes. When the gas was first admitted to the tube 

 while a feeble discharge was passing, the glass fluoresced 

 brilliantly for several seconds, but this effect soon died out, 

 apparently as the result of some chemical reaction. The 

 spectrum taken during the fluorescent stage showed the 

 third group of bands of remarkable intensity, and this ultra- 

 violet radiation produced the fluorescence. These bands were 

 also usually present in the spectrum of the afterglow. 



Strutt and Fowler are of the opinion that the afterglow' 

 occurs only in nitrogen entirely free from oxygen, and that 

 both the third group and the new bands are due to nitrogen. 

 Recently, however, Comte * has made some experiments 

 from which he has concluded that the afterglow is not found 

 in pure nitrogen, but only when minute quantities of oxygen 

 are present. 



In my photographs, reproduced in the ' Astrophysical 

 Journal ' for July, 1904, it may be sepn that in some cases 

 the new ultra-violet bands appear, in others there is no trace 

 of them, the only features of this region being the mercury 

 lines and some bands apparently due to cyanogen. The 

 visual bands in the green, yellow, and red were invariably 

 observed. At the time the cause of these differences was not 

 apparent. More recent attempts to reproduce the original 

 results invariably failed, the cyanogen bands and visual 

 bands always appeared, but there was no trace of the ultra- 

 violet bands. It may be noted that in the later experiments 

 nitrogen was used which had for some time been standing in 

 the storage system, which consisted of bottles of pyrogallic 

 acid and caustic potash solutions and drying-tubes containing 

 caustic potash and phosphorus pentoxide. 



Recently, while studying the spectra of mixtures of 

 nitrogen and ox}^gen, the explanation has been found. 

 With no kind of discharge, strong or weak, could the 

 spectrum of the third group be obtained when approxi- 

 mately pure nitrogen was used ; but when a small quantity 

 * Pki/s. Zeit. xv. p. 74 (1913). 



