﻿542 Prof. It. W. Wood on Atomic Hydrogen 



The action of a condenser is to pass currents of enormous 

 magnitude but of very brief duration through the tube. 



With these very heavy currents (hundreds or even 

 thousands of amperes) we have a sufficient momentary 

 concentration of atomic hydrogen to bring out its charac- 

 teristic lines, even with the tube wall thoroughly freed 

 from water vapour — the condition which gives the secondary 

 spectrum only, owing to the powerful catalyzing action of 

 the walls. 



Merton's observation that the discharge became white 

 when the hydrogen tube was immersed in liquid air, is 

 at once explained by the greater catalyzing power possessed 

 by the wall at a low temperature. Langmuir found that 

 the atomic hydrogen produced by incandescent tungsten 

 would not pass through a tube cooled by liquid air, though 

 it passed to a considerable distance down a tube at room 

 temperature. This observation I have confirmed in the 

 study of the properties of atomic hydrogen, pumped from 

 a discharge tube operated by a heavy current, small 

 particles of thorium oxide being brought to incandescence 

 at a distance of 20 cm. from the discharge tube. Touching 

 the wall of the tube leading to the pump with a pad of 

 cotton wet with liquid air, at once extinguished the 

 specks of thoria in the tube beyond the cooled spot. A 

 fine tungsten wire, inserted in the tube leading to the 

 pump at a distance of 4 or 5 cm. from the discharge 

 tube, is brought to a red heat by the current of atomic 

 hydrogen pumped from the tube. Clean aluminium foil of 

 the thickness of writing-paper, when introduced into the 

 discharge tube, at first caused the appearance of the 

 secondary spectrum in its vicinity, but after several 

 minutes' operation the deep purple colour returned and 

 the secondary spectrum disappeared. If the hydrogen 

 current was now shut off and air admitted, and the tube 

 operated with air at about 0*5 mm. for a few minutes, 

 it was found that, on again operating it with hydrogen, 

 the aluminium had regained its catalyzing power, and the 

 white discharge appeared in its vicinity ; in a few minutes 

 this disappeared, however, as before. This makes it seem 

 probable that slightly oxidized aluminium will catalyze 

 the atomic hydrogen, but that the clean metal will not. 



The mystery of why the long tube gives a pure Balmer 

 spectrum at the centre now appears to be explained. The 

 more or less oxidized aluminium electrodes act as catalyzers 

 supplying molecular hydrogen continuously from the atomic 

 hydrogen formed by the discharge, and the concentration of 

 the atomic gas never reaches a high value at the ends of the 



