262 BEPOKT— 1880. 



formation o£ nitrogen dioxide can be proved by means of a solution of sul- 

 phate of iron. But the reasoning proves too much ; for oxides of nitrogen 

 are also formed under the influence of the jar discharge when the line 

 spectrum is visible, and we should, therefore, have an equal right to 

 assume that the line spectrum of nitrogen is due to an oxide. It is im- 

 portant to remark that the chemical compounds which are formed outside 

 the sjjark give us no information on the chemical origin of the spectrum 

 which is given by the spark itself. In the absence of any contradictory 

 proof, Salet's experiment that the band spectrum of nitrogen is seen in a 

 tube in which sodium is heated to its fusing point must be considered 

 conclusive that the spectrum is not due to an oxide. 



Compounds of Nitrogen and Hydrogen. 



Schuster: 'Brit. Ass.' Brighton (1872) p. 38; 'Nature,' vi. p. 



359. 

 Dibbits, Dr. : ' Spektraal- Analyse,' p. 127 ; ' Pogg. Ann.' cxxii. p. 518. 

 Hofmann : ' Pogg. Ann.' cxlvii. p. 95. 



The spectrum seen when a weak spark is taken in a current of am- 

 monia is neither that of nitrogen nor that of hydrogen, but must be due 

 to a compound of these two gases. The writer of this report could even 

 obtain a spectrum in a vacuum tube by maintaining a current of the gas 

 through the tube. The spectrum consisted of a single band in the 

 greenish yellow, standing on a faint continuous background. The wave- 

 length was approximately found to be 5686 to 5627 decimetres. If am- 

 monia and hydrogen are burnt together, either in air or in oxygen, a 

 complicated spectrum is obtained, the chemical origin of which has not 

 been satisfactorily explained as yet. Drawings of this sjiectrum are given 

 by Dibbits and Hofinann. 



Compounds of Nitrogen and Oxygen. — No emission spectrum has as 

 yet been found which can be with certainty referred to a compound of 

 nitrogen and oxygen ; though it is possible that the above-mentioned 

 spectrum of the flame of ammonia and hydrogen may in part be due to 

 an oxide of nitrogen. The absorption spectrum of the red fumes of 

 nitrogen tetroxidc has often been mapped ; the most perfect drawing is 

 given by Dr. B. Hasselberg (' Mem. de St. Pet.'xxvi. No. 4). According 

 to Moser (' Pogg. Ann.' clx. p. 177), three bands close to the solar line 

 disap23ear when the vapoiir is heated. 



III. Oxygen. 



o 



Angstrom : ' Pogg. Ann.' xciv. p. 141 (1855). 



Pliicker: ' Pogg. Ann.' cvii. p. 518 (1859). 



Huggins : ' Phil. Trans.' cliv. p. 146 (1864). 



Pliicker and Hittorf: 'Phil. Trans.' civ. p. 23 (1865). 



Brassak: 'Abh. Nat. Ges. Halle,' x. (1866). 



Wiillner : ' Pogg. Ann.' cxxxv. p. 515 (1868) ; cxxxvii. p. 350 (1869) ; 



cxliv. p. 481 (1872) ; cxlvii. p. 329 ; ' Wied. Ann.' viii. p. 263 



(1879). 

 Salet : 'Ann. Ch. Ph.' xxviii. p. 35 (1873). 

 Schuster : ' Phil. Trans.' clxx. p. 37 (1879) ; ' Wied. Ann.' vii. p. 670 



(1879). 



The spectrum of oxygen has been examined by Pliicker, Wiillner, 

 Salet, and more recently, by the author of this report, to whose paper the 



