402 



It is tliereCor evident tlial the apparent suliibility product of 

 liydrogeii shows large deviations, from the value which would be 

 expected when the hydrogen is in inner equilibriuui. We will now 

 calculate what the value of Ihe solubility product of iiydrogen must 

 be in this case. 



In the above we have manifestly employed a value for Lh„ which 



2 X 13 25 



IS 10" ■ times too small. The value of L for the hydrogen 



11, 



which is being liberated, in the case under considerations, is therefore 



10 instead of 10 In oilier words this hydrogen has 



become so much more basic, that in respect to ils electromotive 

 behaveour il somewhat resembles zinc. 



If the OH-ion concenlralion in the surrounding li(piid layer is 

 lower than 10 ' then no precipilation of Mg(OH), will lake place. 

 If (OH'J=10^'", then L^^ = lO""" '"'■^" and electromotively the 

 hydrogen is beginning to resemble manganese. 



From Ihe above considerations it follows that an approximation 

 to the etpiilibrium potential of magnesium would only be possible 

 if the hydrogen could appear in a stronger stale of formation, for, 

 as already has been demonstrated, an increase in the solubility 

 product of magnesium will always be accompanied by an increase 

 in the solubility product for Ihe h^'drogeii which is being liberated. 

 This is not necessary Ihe case with less basic melals. It is clear 

 that the foregoing conclusions will also hold for aluminium and 

 we will now examine the conditions under which we can measure 

 the most active [lotentials of these melals. 



According to the theory of capillarity the change between two 

 liquid phases or between a liquid and a gaseous phase is really an 

 extremely sharp change in continuity. In Ihe above case however 

 we are dealing with random arrangements of particles in each phase. 

 When we come to consider a metal and an electrolyte one has a 

 definite structure and Ihe otlier has not. 



We are however sure, that in this case also in the bounding 

 layer there will be a very sharp transition, though with a discon- 

 tinuity, and that consequently the coexisting phases will only show 

 quantitative differences with respect to compositions. 



Now we make (he assumption, that the parts, present in the 

 metal bounding layer, in concentrations depending in the depth of 

 Ihe layer, in general will exerl influence in Ihe rapidity, with 

 which the inner equilibrium is establishing in Ihe bounding layer. 



Oxygen, nitric acid, nitrates, etc., are already known to exert a 

 rclarding influence on the establishment of internal equilibiiiim in 



