632 Prof. Skinner on the Drop] of Potential 



Table VII. 



Drop of Potential at Cathode, comparing Steel and 



Aluminium. 



Area of Steel Electrode, 2*5 sq. cm. Area of Aluminium 



Electrode, 30 sq. cm. 



Cur- 



p=l'8 mm. 



jj=0'7 mm. 



p — Q-^D mm. 



2>=0-25 mm. 



lower. 



Further 

 reduced. 



























Steel. 



Al. 



Steel. 



Al. 



Steel. 



Al. 



Steel. 



Al. 



Al. 



Al. 



0-2 





















490 



0-4 















420 



390 



500 



600 



05 







275 



235 



360 



350 







530 





0-6 



... 













470 



425 



560 



670 



0-8 















505 



470 



625 



710 



1-0 



260 



250 



305 



265 



440 



400 



550 



495 



670 





lo 



280 



260 



340 



285 



495 



440 











20 







360 



300 



555 



480 











25 



295 



280 



















3-5 



310 



290 



















For, expressing the tangent of the angle of inclination of the 

 line for steel by c 1? that for aluminium by c 2) we find the 

 ratio Cijc 2 at the various pressures p : 



p- 





cjc.,. 



1*8 mm. 





1-23 



0-7 „ 





1-25 



0-45 „ 





1-46 



0-25 „ 





113 





Mean ... 



... 127 



Were the difference due to current- density alone, this ratio r 

 being the ratio of the area of the two electrodes, should have 

 been 



51° =1-2 

 2-5 



Considering again the limits of experimental accuracy, the- 

 indications are that, for the same gas, the rate of increase of 

 the cathode drop with the current-density is practically 

 independent of the kind of metal used as cathode. On the 

 other hand, it depends vitally on the quality of the gas. I 

 have observed that the greater the care taken in purifying 

 (especially drying) the gas, the more rapid the increase in. 

 drop with the current- density. 



