Disappearance of das in the Electric Discharge. f) ( ,)7 



of carbon monoxide or nitrogen could be made by special 



efforts at purification; atmospheric and chemical nitrogen 

 agreed perfectly. The argon used contained about 5 per cent. 

 of nitrogen : pure argon has not been examined. 



The effect of mercury vapour, which was absent from all 

 the gases of fig. 4, is especially remarkable. \( the lamp is 



Fig. 4. 



v 9 

 volt 



: / / 















1 y^^^^ ] 





7 / 













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3 J ' * 



















/ * 







r?\° >^ 

























&y 































>*l _s 













<u / 

 Oil 







-0 























/ c 





*ys 





















*7 /r 









nO / y 



':& 

















/ / ■& 







eiy/if 









^o""^ 



x 





/ / ^ 







^y X ^° 



















III / 







/yS C 



r 







x^ 













// / 



// V 









^^ > 



3°° 















w 











p 



essure & 



glow p 



tentia! 









1 























O 100 200 



l^p(MM"') 



p = oo 0-OImm 0-005 



500 

 0-002 



1000 



o-ooi 



completely evacuated of all permanent gases while mercury 

 vapour is allowed to remain, the glow potential is found to 

 be 32*5 volts. The pressure of this vapour is known to be 

 about 0'002 mm.; so that the glow potential of mercury is 

 very much lower than that of the other gases at the same 

 pressure — a difference to be expected from its greater 

 molecular weight. If, now, one of the permanent gases is 

 admitted, there is no change in the glow potential ; so long- 

 as mercury vapour has access to the lamp, the glow potential 

 is always 32*5 volts, whatever the nature of pressure of the 

 gas with which it is mixed. Such a result might be antici- 

 pated. Since the glow potential decreases with an increase 

 of pressure, it is not to be expected that the addition of any 



