1872.] Mr. A. Schuster on the Spectrum of Nitrogen. 485 



well known that the oxides of nitrogen are formed on passing the electric 

 spark through air, and the resemblance which this spectrum bears to 

 the spectra of the oxides of metals rendered this view probable. In order 

 to test it, a series of experiments were made, showing that, — 



(a) Whenever the fluted spectrum appeared, it could be shown that 

 traces of oxygen were present ; 



(b) Whenever there was a certainty of no oxygen being present, the 

 spectrum of the second order appeared under all pressures and in all tem- 

 peratures. 



In order to free the nitrogen from every trace of oxygen, I adopted, at 

 Dr. Stewart's suggestion, the plan of heating a small piece of sodium placed 

 in the vacuum-tube. This proved in each case perfectly satisfactory ; for 

 when every trace of oxygen had thus been absorbed, the line-spectrum alone 

 was invariably obtained*. 



4. Wave-length of the tivo spectra. — There is no possibility of con- 

 founding the two spectra. The fluted spectrum is well known by its 

 beautifully shaded violet bands ; but in order to exclude any possibility of 

 error, their position was read off on the reflecting scale of the spectroscope ; 

 the measurements were reduced to wave-lengths, and the following numbers 

 obtained for the least refrangible end of the bands in tenth metres f: — 



Fluted Spectrum. 



5129 4436 



4981 4390 



4649 4318 



4556 4237 



As the measurements were taken merely for the sake of reference, they 

 do not lay claim to great accuracy. 



The true spectrum of nitrogen is easily recognized by a very bright green 

 line followed at a small distance towards the more refrangible parts by a 

 green band ; it also contains some violet bands, which are not shaded. The 

 position of the principal lines was read off ; their wave-lengths, as determined 

 by Dr. Marshall Watts from the measurements made by Pliicker, are as 

 follows : — 



Line-spectruru. 



band 



214 I 



6176 5666 4199 J 



6087 5164 (the green line) 



6051 4894 

 5908 4644 



4184 1 

 4170/ 



* The formation of the fluted spectrum does not imply that all the nitrogen in the tube 

 has been oxidized ; it has been remarked by different observers, and especially noticed 

 by Pliicker, that when the spark passes through a mixture of two gases, the spectrum 

 of* one only is often seen. 



f A tenth metre, according to Angstrom, means a metre divided by 10 10 . 



