18 Prof. Pliicker on the Spectra in Rarefied Gasses 



same as in the case of the binoxide of nitrogen tube, excepting 

 that the red band due to the oxygen was at first of still greater 

 brilliancy. 



113. A further experiment showed that nitrous oxide (NO) 

 also immediately splits up into its simple constituents. The 

 band due to the oxygen was less bright. 



114. The next gas examined was aqueous vapour. M. Geissler 

 prepared an excellent tube for this purpose with his accustomed 

 skill, in the following manner. Two large bulbs were blown 

 upon a tube, one of them being provided with a cock towards 

 the end of the tube ; the tube, having been filled with water, was 

 heated until the last trace of air was driven out and nothing but 

 aqueous vapour remained. The cock was then closed. The tube 

 was then heated over a spirit-lamp, while the bulb with the cock 

 was immersed in a freezing mixture. This bulb, to which the 

 cock was attached, was then fused off. The same operation was 

 repeated by plunging the second bulb in the freezing mixture, 

 and then fusing it off while the tube itself was heated. The 

 electric current in the narrow tube showed the most beautiful 

 deep red. The spectrum was that of pure hydrogen with its 

 three prominent bands, in comparison with the brightness of 

 which, the rest of the luminous divisions were so insignificant, 

 that here the shading off of colour and luminous intensity was 

 scarcely to be recognized. The aqueous vapour had separated 

 into its simple constituents; but unfortunately M. Geissler 

 had already passed the current through. The one constituent, 

 namely oxygen, had already been removed lay combining with 

 the negative platinum electrode. 



115. After the above- described experiments, it necessarily 

 seemed very doubtful whether the spectrum of carbonic acid 

 previously described really belonged to this acid in its undecom- 

 posed state. It was not possible for the acid to have been de- 

 composed into its simple constituents ; for in that case we must 

 have obtained the spectrum for oxygen gas, while the small 

 quantity of solid carbon must have been deposited (perhaps in 

 inappreciable quantity) on the interior of the glass tube. Hence 

 the only possible remaining alternative was either that the acid 

 had continued undecomposed, or had split up into oxygen and 

 carbonic oxide. The fact of a deposit of oxide of platinum 

 having been formed, was hostile to the first supposition (107). 

 All doubt was removed on determining the spectrum of carbonic 

 oxide. This spectrum was identical with that into which the 

 carbonic acid spectrum was soon transformed by the diminution 

 of the brightness of the extreme red. The spectrum of carbonic 

 oxide, obtained either directly or by the abstraction of fi-ee oxygen, 

 is not constant, although its alteration is very gradual. As oxide 



