Cathode Fall in Helium and Argon 9 



potassium hydrate and phosphorus pentoxide in the bulbs B and C, 

 respectively. The system was evacuated and the clevite in A was 

 heated over a sand bath. The increase in pressure was measured 



J\^^ 



^ 



A 



5? 



a/icfiatqe 

 rube.' 



B 



N 



Fig. 3 



by the manometer. M. The gas thus generated, which is mainly 

 helium with hydrogen, oxygen, nitrogen and water vapor as im- 

 purities, was allowed to stand for at least twenty- four hours in the 

 drying bulbs B and C. 



Having removed the water vapor from the gas, it was allowed 

 to enter the purifying chamber D. This was a discharge tube 

 with an aluminium wire, E, as one electrode and an alloy of 

 metallic potassium, sodium, and mercury for the second electrode. 

 E'. E' was heated to about 300° C, at which temperature the 

 glass becomes sufficiently conducting so that potassium and sodium 

 were passed through the glass into the chamber by electrolysis. 

 The current was then reversed and a glow current maintained in 

 the tube using the alloy, E', as cathode.^" According to Mey,^^ 

 this treatment eliminates nitrogen, oxygen, and hydrogen, leaving 

 only argon as an impurity. The writer was able to remove all 

 traces of oxygen and hydrogen so that spectroscopic examination 

 failed to show any trace of either gas. Nitrogen, however, was 



12 Much trouble was encountered in the purification because the glass 

 deteriorated and cracked while the current was passing through it. Sev. 

 eral samples of helium were lost in. this way. 



13 K. Mey, Ann. d. Physik, (4) 11, p. 127, 1903. 



