92 M. E. Wiedemann's Investigations on 



the negative electrode becomes bright, and the positive dis- 

 charge spreads out into a luminous tuft. At 160° the green 

 nitrogen-lines are distinctly seen, and the lines of mercury 

 become more feebly luminous. At 130° the mercury-lines 

 at the negative electrode are less bright than in the positive 

 luminous sphere. First at 100° do traces of the nitrogen- 

 lines appear in the luminous tuft and at the positive pole, and 

 come out more and more with a further lowering of the tem- 

 perature. 



The same phenomena were displayed at pressures of 30, 60, 

 and 100 millims. ; the nitrogen-lines then made their appear- 

 ance in the positive tuft at temperatures between 100° and 

 140°. Above 230°, everywhere only mercury-lines could be 

 seen. 



In another experiment some mercury was introduced into a 

 Greissler tube containing hydrogen. Before the heating, in 

 the capillary part the hydrogen-lines showed distinctly. On 

 heating, they disappeared, and did not reappear with the cool- 

 ing. Even when the current was interrupted for some time, 

 they showed themselves only for a moment after its closing. 

 It is probable that, at the first heating and cooling, some traces 

 of mercury were precipitated in the capillary tube. The glass 

 was then heated so strongly by the passage of the electric 

 spark that they were vaporized. Not till the tube was wholly 

 immersed in a mixture of ice and salt, and thereby the glass 

 made very cold, so that the layer of yellowish mercury (oxide?) 

 no longer furnished enough vapour, did the hydrogen-lines 

 reappear. 



In order to discover whether other metallic vapours have 

 the same properties as are exhibited by mercury vapour, some 

 sodium was enclosed with hydrogen or nitrogen. Here also, 

 at the heating, the nitrogen- and hydrogen-lines vanish ; 

 and this commenced earlier at the positive than at the negative 

 pole. At temperatures at which the glass began to soften, 

 there remained only the yellow, green, and blue double lines 

 of sodium visible. That in these experiments the fused sodium 

 did not chemically combine with the nitrogen present, and 

 that the disappearance of the nitrogen-lines was not conditioned 

 thereby, was made known by the fact that, differing from 

 Salet's experiments, the hydrogen- and nitrogen-lines again 

 made their appearance after the cooling. 



If a spectrum-tube filled with nitrogen and hydrogen be 

 suitably heated at one part far below redness, very slight traces 

 of sodium and other metals from the glass are vaporized there; 

 and there also the hydrogen- and nitrogen-lines almost com- 

 pletely disappear, together with the metallic lines that occur. 



