582 The Secondary Spectrum of Hydrogen. 



To carry out the experiment the apparatus shown in the 

 diagram was constructed. 





i 



tf/DROGEN 



A, vacuum tube ; B, bulb containing- charcoal; C v C 2 , drying-tubes 

 containing phosphoric oxide. The hydrogen was prepared from 

 sulphuric acid and pure zinc. 



The apparatus was exhausted and filled with Irydrogen 

 from the generator attached. This was repeated until the 

 lines due to oxygen and nitrogen could no longer be seen 

 in the spectrum of the gas. The charcoal had been heated 

 previous to sealing on to the apparatus to drive off all moisture, 

 and whilst the exhaustion was in progress it was again 

 heated to expel any gases which might be condensed in its 

 pores. The heating was not prolonged sufficiently to drive 

 off all the carbon dioxide present in the charcoal. The 

 amount o£ this gas was small, and would not interfere with 

 the absorbing properties of the charcoal when cooled by 

 liquid air. When a suitable vacuum had heen obtained 

 giving a spectrum of maximum brightness, the bulb B was 

 immersed in liquid air. On observing the spectrum the 

 intensity of the lines was seen to decrease, and the appearance 

 of the discharge in the tube indicated a decrease in pressure 

 of the gas. The relative intensities of the two spectra, 

 however, remained unchanged up to the total disappearance 

 of the whole spectrum, when a discharge would no longer 

 take place through the gas owing to the high vacuum. A 

 little more hydrogen was allowed to enter, and the spectrum 

 reappeared with its original brightness, but after a time the 

 same decrease in intensity as before was observed, though 

 the condensation did not proceed sufficiently to stop the 

 discharge. 



Two attempts were made, the first using only a small bulb 



