16 Prof. Pliicker on the Spectra in Rarefied Gases 



hausted. The spectrum was evidently the result of the supei'po- 

 sitiun of the two spectra for hydrogen and nitrogen ; the ammoniacal 

 gas was immediately decomjtosed into its constituents, and it had 

 not been possible to obtain the spectrum of the chemically combined 

 gases. 



107. The determination and delineation of the oxygen spectrum 

 appeared now to be of chief importance. But here I encountered 

 new and unexpected difficulties, so that as yet I have not been 

 able to obtain a complete idea of this spectrum. I shall there- 

 fore confine myself here to the mere mention of two narrow bril- 

 liant bands, of which the one forms the boundary of the spectrum, 

 the other extends even into the orange. The space between the 

 two bands is of a dark brown. The red boundary of the oxygen 

 spectrum extends somewhat beyond that of the hydrogen spec- 

 trum ; and accordingly the dazzling-bright bordering bands do 

 not coincide. 



The above-mentioned difficulty in determining definitely the 

 spectrum for oxygen, consists in the gradual disappearance of the 

 free gas, which combines with the platinum of the negative elec- 

 trode. That such combination actually occurs, is not only 

 evinced by the alteration of the spectrum, but is shown at once 

 by the fact that the finely- divided oxide of platinum as it is 

 formed is deposited of a yellow colour upon the neighbouring 

 internal glass surface, showing by reflected light the colours of 

 Newton's rings in a very beautiful manner. If the tube contains 

 traces of hydrogen or nitrogen, pure metallic platinum is trans- 

 ferred to the glass surface. 



108. The colom- of the electric light-current in the narrow 

 tube was at first red ; it passed through a flesh-colour to green, 

 and then through blue to reddish violet. 



It would be of especial interest, by a careful examination of 

 the oxygen spectrum, to determine in what sequence the sepa- 

 rate prismatic colours disappear during the gradual extinguishing 

 of the electric light-current caused by the gradual abstraction of 

 oxygen gas, and the consequent withdrawal of the ponderable 

 matter essential for the conduction of the electricity. The above 

 scale of colours, through which the light passes in the narrow 

 tube, appears to justify the conclusion that at first the least re- 

 frangible rays are removed ; certainly the two bright-red bands 

 of the spectrum are first seen to become paler and perhaps 

 wholly to disappear. In order, however, that the phsenomenon 

 may be examined with perfect accuracy, it is necessary for espe- 

 cial precautions to be taken that the oxygen may be absolutely 

 pure. 



109. For if even the most minute traces of another gas be 

 mixed with the oxygen, the foreign gas will take a continually 



