Hydrogen and some of its Compounds. 373 



When we examine the photograph of the discharge repre- 

 sented on lig. 1 (PI. VI.), we see an interesting exhibition of 

 ionization and molinization. The hydrocarbon bands at wave- 

 length 4315 show a series gradually decreasing in length of 

 waves ; while another band, beginning at wave-length 3900, 

 due probably to water-vapour, shows a series increasing in 

 length of waves. It would seem that the carbon in one case 

 endeavoured to throw off the hydrogen from the hydrocarbon 

 molecule ; and in the other case the hydrogen became loaded 

 with oxygen molecules. This to and fro ionization and 

 molinization continues until the oxide of copper at the posi- 

 tive terminal has taken up a large share of the oxygen of the 

 water-vapour present. There is thus a critical point in the 

 tube at which a sudden increase of resistance takes place. 

 It is possible to exhaust glass tubes to such a degree by the 

 mere passage of a strong steady current, that x-rays begin 

 to manifest themselves. 



AVhen a similar tube, filled with hydrogen with great care, 

 and prepared by long heating at a temperature a little below 

 500° C, is submitted to electrical discharges, the water- 

 vapour bands become far less pronounced, and the hydro- 

 carbon band at wave-length 4315 entirely disappears ; while 

 the light of the tube greatly diminishes in brilliancy. The 

 hydrocarbon or cyanogen band at wave-length 3884 is 

 present in all the tubes I have employed, and with all gases I 

 have submitted to these strong discharges. Strong heating 

 does not cause it to disappear, and it seems to be due to car- 

 bonaceous matter introduced into the tubes, probably in 

 the process of blowing ; for I cannot trace it to impurities 

 coming from the pump. Professor Hartley, in a late com- 

 munication in ' Nature,' has called attention to the constant 

 presence of hydrocarbon spectra in Geissler-tubes. At a 

 later point in this paper I shall return to a further study of 

 these spectra due to the combination of hydrogen and nitrogen 

 with carbon. At present I desire to dwell upon the point I 

 wish to make : that all discharges in rarefied gases, contained 

 in glass vessels, are conditioned by the amount of water- 

 vapour present ; and that a steady current passes through a 

 gas at comparatively low pressure much in the same manner 

 that it does through an electrolyte. 



In an article on the production of the #-rays by a steady 

 battery-current*, I dwelt upon the phenomena presented in 

 highly rarefied tubes, which represent, to my mind, the dis- 

 sociation of water-vapour; and 1 will refer again at this 



* Phil. xMag. Julv 1900. 

 Phil. Mag. S. 6. Vol. 2. No. 10. Oct. 1901. 2 C 



