690 Research Staff of the G. E. C, London, on the 



Under the discharge the gas disappeared like other gases,. 

 but at a very much slower rate. The rate of disappearance 

 increased very suddenly when the pressure fell below 

 *005 mm., but even at these low pressures was not more than 

 one-fifth of the rate at which nitrogen would disappear^ 

 (In nitrogen there was a similar rapid increase in the rate of 

 disappearance at about '012 mm.) At the same time, rapid 

 blackening of the bulb occurred. In both nitrogen and argon 

 there is the intimate connexion between cathode spluttering 

 and absorption of gas which Vegard * has noted in the 

 discharge without an incandescent cathode. 



An interesting fact may be mentioned, though it has 

 probably no direct bearing on the matter "under discussion. 

 The blackening which occured with argon was not, like that 

 with nitrogen, distributed almost uniformly over the lamp. 

 Round the central portion of the lamp where the electrons 

 projected from the cathode would be expected to hit the 

 walls, there was absolutely clear glass with no sign of 

 blackening; on this clear glass were the sharp shadows of 

 the anode wire and the wire supporting the filament; and 

 elsewhere the division between the blackened portions and 

 the clear glass was absolutely sharp. The black material is 

 not deposited on the portion of the walls struck by electrons 

 projected at right angles to the cathode surface. Traces of 

 a similarly unequal blackening were seen in nitrogen, but 

 they were only traces of a distribution that is perfectly 

 definite with argon. 



When the lamp in which argon had disappeared was 

 heated, more gas was evolved (non-condensible in liquid air) 

 than had been absorbed. It appeared probable that all the 

 absorbed argon was contained in the evolved gas, together 

 with hydrogen, doubtless derived from the glass, although,, 

 as always, the glass had been baked until no more gas was- 

 evolved before the experiment started. 



17. The discliar ge in mercury vapour. — If the vessel is 

 baked just below the softening point of the glass until no 

 more gas is evolved, and completely exhaus^d of all gases 

 other than mercury vapour, and if the discharge is then 

 passed through this vapour in the cool lamp, the pressure in 

 the lamp increases rapidly. The gas evolved is hydrogen, 

 perhaps mixed with a little water. As long as there is 

 liquid mercury present from which a continual supply of 

 vapour can be drawn, the evolution continues without 



* L. Vegard, Ann, d. Phijs. I. p. 769 (1916). 



