Trowbridge — Spectra of Gases. 



423 



A Geissler tube, fig. 1, with an internal diameter of one 

 inch j was provided with an inner capillary, one end of which 

 was blown to the walls of the larger tube ; the other end was 

 free inside this larger tube. An electric discharge passed 

 between two ring electrodes A and B, which were placed in 

 the larger tube. The discharge, 

 therefore, started, so to speak, in 

 the larger tube, passed through the 

 narrow channel of the capillary 

 and emerged to the cathode. The 

 tube was filled with pure hydrogen 

 which was dried by phosphoric 

 pentoxide. Under the effect of 



powerful condenser discharges, the four-line spectrum was 

 much enfeebled in the capillary ; the red color, characteristic 

 of condenser discharges in hydrogen, gave place to a brilliant 

 white light, and when the capillary was viewed end on, a con- 

 tinuous spectrum was seen. When, however, the discharge 

 issued from the capillary a brilliant red aureole was seen 

 around the end of the capillary. This aureole gave a much 

 enhanced four-line spectrum. The temperature inside the 

 capillary was sufficient to volatilize the walls of the capillary, 

 and, therefore, was competent to decompose the water-vapor 

 into oxygen and hydrogen. Just outside the end of the capil- 

 lary, the temperature fell to the point of recombination of these 

 gases to water-vapor. 



In another experiment the Geissler tube G, fig. 2, was placed 

 between two manometer gauges, and was exhausted to such a 

 degree that the electric discharge failed to pass. One end of 

 the Geissler tube, that nearest to the pump, was shut off by 



means of a stopcock B ; and dry oxygen was admitted to the 

 pump until the manometer gauge connected with the pump 

 indicated two centimeters pressure. The stopcock was then 

 opened so as to admit the gas to the Geissler tube. The corre- 

 sponding manometer gauge at the opposite end of the Geissler 

 failed to register the requisite equalization of pressure, there 

 having arisen an oxidization of the mercury meniscus by 

 means of which the capillary constant between it and the glass 



