•752 



the anode a certain volume of iron has been replaced bj' the solution, 



whereas at the cathode tlie solution has been replaced by iron. The 



lat 

 v^olume of iron — . — • — will correspond to the quantity of elec- 



d kg 8 



tricit}' e, when a denotes the atomic weight, Ji\ the valency of the 

 atom, (/ the density of the iron. If we assume that at the anode 

 no magnetic tield is present, the substitution of iron solution for 

 iron will not bring about any modification in the magnetic part of 

 the free energy. At the cathode, however, this substitution will give 

 rise to a change in the expression (9),, which, when n^ represents 

 the permeability of the iron solution, j/ that of the iron, amounts to: 



a. e r rB rn n 



<r.(A.^)=_--[J-.5_J-.8j. . . . (13) 







when B means the absolute value of 33 and B this value at the 

 cathode. When we speak of "at the cathode" or "at the anode", 

 we mean by this that we must take the value of the considered 

 quantity at a plane that is at a very small distance from the 

 cathode resp. anode, this to evade the difticulties which the phe- 

 nomena taking place in the boundaiy layer might cause; we 

 shall examine this question more closely further on. On account of 

 the smallness of the considered volume we may assume that the 

 value of B is the same everywhere inside the volume. If we put 

 (Ltp = 1 -j- 47r Xj, in which jc,,, the susceptibility per unity of volume, 

 is to be considered as a small quantity, we get about : 



_ "b 



'B' , - rB 1 



__(1 .4^x„ -j-dBl . . (14) 



when Xp represents the susceptibility at the cathode. If we assume 



1 

 fi to be very great for iron, so that — is to be neglected with respect 



_^ 



to unity, and if we replace B by H, the absolute value of the inten- 

 sity of the tield in air at the cathode, we get : 



a. e H' - 



ö^{AmW)=-— ^(l-4;rx„) .... (15) 



Instead of (13), using the relation: 



bU J = 4:rt /, 



in which / is the absolute value of the magnetisation we may 

 further write : 



a. e 

 d.k„ .6 



