690 



Iron. 



The metal iron yielded a remarkable result. The potential of a 

 rotating iron electrode immerged in 100 cm', of V^o NFeCP, could 

 he afected neither by addition of hromine up to saturation, nor by 

 addition of a solution of N.KBr. 



This remarkable result must be explained in the following way. 

 As we shall soon see, iron is strongly attacked by a solution of 

 FeClj, and when acted on in this way iron becomes nobler. Now 

 Br. also attacks iron pretty strongly, and this attack would undoubt- 

 edly also lead to an enobling of the iron surface. Evidently, how- 

 ever, the disturbance called forth on attack by Br, is slighter than 

 that caused by FeCig, on account of which the addition of Br could 

 of course have no influence in the just mentioned experiment. What 

 is further most convincingly proved here is this that the iron abso- 

 luteh/ cannot behave as bromine electrode in consequence of the attack. 



This is quite in accordance with what has now been found by 

 us, that namely an enobling of the potential of a metal-electrode 

 caused by addition of bromine, must be attributed to a disturbance 

 of the internal metal equilibrium, at least when the metal is attacked 

 by bromine. 



Chlorine acting more strongly on iron than bromine, it was 

 expected that when the former experiment was repeated with chlo- 

 rine instead of with bromine, a marked rise of the iron potential 

 would be found. As the following table shows, this was actually 

 the case. 



Fe-electrode in 100 cm^ of N.FeCls-solution. 



! Potential of the Fe-electrode with 

 Ubstrvations | respect to '/lo Norm. Calomel electrode 



Fe in Norm. FeCls-solution 

 In a current of chlorine. 



— 0,292 V 



> 0,108 V 



- 0,184 „ 



We may be sure that the iron which is strongly attacked by 

 chlorine, cannot have behaved here as chlorine electrode, and that 

 this experiment therefore proves that we have succeeded also for 

 iron in disturbing the internal equilibrium in the surface. 



Another phenomenon which is in perfect harmony with this view, 

 and which had already been observed by Finkelstein '), is the elec- 



1) Z. f. phys. Ghem. 39, 91 (1901). 



