693 



tn this case the chlorine would, therefore, indirectly bring about 

 an increase of (he disturbance of the internal equilibrium. What is 

 not improbable for iron, may also be true for nickel in the ex[)eri- 

 ment with bromine, when namely the nickel possesses ions of 

 different valence, but this cannot yet be stated with certainly. 



Besides this tigure accounts for the discontinuous course of the 

 potential, when passive iron immerged in an iron-salt solution, passes 

 into the active form. 



Iron which has passed into the passive state by anodic polarisation 

 or by attack with strong HNO3, is greatly enobled superficially, and 

 the potential possesses even a positive value. The concentration of 

 the surface of passive ii'on, therefore, corresponds to a point on the 

 line eb, and that below the line A = 0. 



When this passive iron is immerged iji a solution of ferro-sidphate, 

 transformations will take place, in consequence of which the unary 

 electromotive equilibrium is approached, and while the potential is 

 falling, the metal surface moves upward along be, till it has arrived 

 in e. Here a second metal phase must occur, viz. d, and as long 

 as the two metal phases occur side by side, the potential of the 

 metal remains constant. The phase e must be entirely converted to 

 d, and when this has taken place, the potential descends furthei-, 

 till the unary electromotive equilibrium has been reached, and the 

 metal phase has been superficially transformed into S. 



This is exactly the behaviour that has been observed by many 

 others and also by us. According to our measurements the three- 

 phase equilibrium cde must lie at -J- 0,20 V. with respect to Vio N. 

 calomel electrode. The place of the dotted line A = is therefore 

 not correct here; it must be thought between L.S' and cde. 



We too found that the transition passive-active is accelerated by 

 H-ions, and we are therefore obliged to assume that hydrogen is an 

 accelerator for the internal transformations in the metal, as are also 

 the ions of the halogens. On treatment with strong HNO3 ^^^'^ on 

 anodic polarisation the hydrogen is superficially removed, and this 

 greatly promotes the internal transfoi-mation, so that the strongly 

 metastable state which we call passive iron, is observed for some time. 



Through the diffusion of the hydrogen from within towards the 

 surface the passive iron, no longer sulijected to the action of strong 

 HNO3 or anodic polarisation, will soon again return to the active 

 form. 



Summarizing we come to the following conclusion. 



1. Faraday's oxide theory, which seemed already- sufficiently 

 refuted by others, cannot give an explanation of the origin of the 



