﻿certain Gases in Geissler's Tubes. 409 



tance were allowed in quick succession to pass through the tube. 

 By these discharges the resistance in the tube appeared even to 

 be permanently diminished ; for shortly afterwards the simple 

 induction-current of the small RuhmkorfT, passed through, again 

 produced the red light of hydrogen, which, however, again 

 changed into the white one with a continuous spectrum when 

 the current had passed for about a quarter of an hour through 

 the tube. 



3. After it had thus been established that the light of ignited 

 hydrogen, according to its different temperatures, which depend 

 on the mode of discharge, might be different, it was to be ex- 

 pected that there would be a similar difference when, with the 

 same discharge, the density of the gas in the tube varied. To 

 test this conclusion I made some experiments in conjunction 

 with Dr. Bettendorff, which not only confirmed it, but also gave 

 a new spectrum quite different from the preceding ones. 



The arrangement of the apparatus was as follows : — In front 

 of the slit of the spectrometer a spectrum-tube was fixed, which 

 near each electrode was provided with a small lateral tube that 

 could be closed by means of a Geissler's stopcock. The upper 

 of these lateral tubes was connected with the horizontal arm of a 

 Sprengel's pump* constructed by Dr. Bettendorff; the lower 

 one was connected with an apparatus for decomposing water, a 

 tube filled with anhydrous phosphoric acid and a bulb-apparatus 

 containing concentrated sulphuric acid being interposed. Over 

 the platinum electrodes of the apparatus for decomposing water 

 tolerably wide glass tubes provided with stopcocks were placed, 

 which at the same time served as gasometers. In preparing the 

 hydrogen, the oxygen was allowed to issue from the tube over the 

 positive electrode, so as not to contaminate the hydrogen with 

 oxygen dissolved in the water f. 



After the tube and the pump had been dried by heating and 

 the continued passage of air, the spectrum-tube was exhausted 

 and then filled with hydrogen from the decomposition-apparatus, 

 again exhausted and filled, and this repeated until, at a pres- 

 sure of from 8 to 10 millims., only the characteristic lines of the 

 hydrogen-spectrum could be seen on the passage of the current. 

 The tube was then again filled with hydrogen, and the light 

 produced by a RuhmkorfFs coil investigated while the tube was 



* Journal of the Chemical Society, S. 2. vol. iii. p. 9. 



t The necessity for this precaution was indicated by the observation that 

 the spectrum of the hydrogen-tube exhibited oxygen-lines when the oxygen 

 was collected and thus the acidulated water saturated with oxygen was 

 allowed to press out of the tube surrounding the anode and mix with the 

 other liquid. The absorbed oxygen which then, diffused throughout the 

 entire apparatus, escaped over the cathode was quite enough to produce in 

 the spectrum the most distinct oxygen-lines. 



