484 Mr. A. Schuster on the Spectrum of Nitrogen. [June 20, 



XVII. " On the Spectrum of Nitrogen." By Arthur Schuster, 

 Student at the Physical Laboratory of Owens College. Commu- 

 nicated by Balfour Stewart,, F.R.S. Received June 13, 1872. 



1. Introductory. — The formation of the different spectra which one gas 

 is said to exhibit, when examined under different conditions, still remains 

 one of the most obscure points of spectrum analysis. In 1864, when 

 Pliicker and Hittorf published their researches "On the Spectra of Ignited 

 Gases and Vapours, with especial regard to the different Spectra of the same 

 elementary gaseous substance"*, they drew attention to the close resem- 

 blance in character of the band-spectra which certain metals yield at a 

 comparatively low temperature to the band-spectrum of nitrogen and sul- 

 phur. Boscoe and Clifton, n their paper "On the effect of increased Tem- 

 perature upon the nature of the Light emitted by the Vapour of certain 

 Metals or Metallic Compounds" f, rendered it probable that the band-spectra 

 of the metals belonged really to the oxides. The two spectra of nitrogen 

 were not, however, examined from that point of view, but, on the contrary, 

 they were made the starting-point of new investigations by "Wullner, who 

 came to the conclusion that certain gases may give even more than two 



o 



different spectra. Angstrom J, expressing his doubts about the trust- 

 worthiness of Wiillner's experiments, says in a note : "As regards the spectra 

 which are usually attributed to nitrogen, I mention here, as a general fact, 

 that it is my conviction that the fluted bands which are so characteristic of 

 the oxides of metals are never found in spectra of elementary gases." 



I propose to show, in the present communication, (1) that pure nitrogen 

 gives only one spectrum ; (2) that this is the line-spectrum ; (3) that the 

 fluted spectrum of the first order is due to oxides of nitrogen, formed under 

 the influence of the electric spark. 



2. First experiment. — The first experiment which I made with respect 

 to the spectrum of nitrogen, was a repetition of an experiment of Secchi, 

 who found that in different sections of the same tube three different 

 spectra of nitrogen might be obtained. A vacuum-tube was made exactly 

 according to Secchi' s description, filled with nitrogen and exhausted. To 

 my astonishmemt the tube showed, even in its widest parts, only a spectrum 

 of lines. No accurate measurements were taken at the time, but the spec- 

 trum was no doubt that of the second order described by Pliicker. Sud- 

 denly, and while I was looking through the spectroscope, the spectrum 

 changed, and the well-known fluted bands appeared. The first spectrum 

 could now easily be obtained by introducing a Ley den jar in the circuit. 

 The spark very soon ceased to pass, and it was then found that the tube 

 was leaking. 



3. The behaviour of this tube at once suggested the idea that the pre- 

 sence of air was necessary for the formation of the fluted spectrum. It is 



* Philosophical Transactions, vol. civ. p. 1. t Chemical News, vol. v. p. 233. 



\ Compte3 Eendus, Aug. 1871. 



