Mr. A. Schuster on the Spectrum of Nitrogen. 539 



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 measure- 

 ments made by Pliicker, are as follows: — 



Lme-spectrum. > 



band 

 band 



5. Description of apparatus. — The tubes generally used had two 

 pockets, A and B, into which small pieces of metallic sodium were 

 introduced by means of the tubes G and D. The tube was con- 



6243 



5767 



4214 1 

 4199/ 



6176 



^Q^)Q 



6087 



5164 (the green hne) 



4184 1 

 4170 



6051 



4894 



5908 



4644 





nected with the receiver containing the nitrogen, whilst the tube D 

 was connected with the air-pump. The nitrogen was generally pre- 

 pared by the combustion of phosphorus in air. After a few hours' 

 standing, when all the phosphoric acid formed had been absorbed, the 

 gas became quite clear and was ready for use. This mode of pre- 

 paration, it is true, does not give the nitrogen very pure ; but as my 

 object was to get the nitrogen free from oxygen, and this was easily 

 obtained by means of the absorption by sodium, the method was 

 found sufficient. Other modes of preparing the nitrogen were tried, 

 such as passing air over red-hot copper or the decomposition of 

 ammonia by chlorine, but the same results w^re invariably obtained. 

 The air-pump used was that of Carre's freezing-machine, with which 

 pressures down to 2 millims. could be easily obtained. When the 

 pressure was measured, a f-shaped tube was employed, one side of 

 which was connected with the Geissler's tube, the other with the 

 pump, while the mercury was drawn up in the longer part of the tube ; 

 its height was read off and compared with a barometer. I now pass 

 to the description of the experiments. 



6. Method of experimenting . — When the air in the vacuum-tube 

 had been exhausted, the communication with the receiver containing 

 the nitrogen was opened, and the gas was allowed to pass through it 

 for some time while the pump was being worked. The tubing con- 

 necting the tube with the receiver vi^as then clamped air-tight, and 

 the tube was exhausted. 



