( 7) 



We know the potential dilierence at 18° and with normal con- 

 centration of the ions, i. e. when solutions of 1 gr. aeq. per liter of 

 water are used. These potential differences are called electrode 

 potentials, and will be denoted here by Ao. 



If we express the concentration in the most rational measure, viz. 

 in the number of gr. molecules dissolved substance divided by the 

 total number of gr. molecules, we may write for the concentration 

 of 1 gr. eq. per liter 



1 

 55,5 r + 1 



in which v represents the valency of the metal. In this it has been 

 further assumed, that the dissociation is total, and the association of 

 the water molecules has not been taken into account. 



If we now write the equation for the electrode potential of an 

 arbitrary metal, we get: 



RT K 



^« = In 



vs 1 



55,5r + l 



or 



RT 

 A„= In A'(55,5r + 1) 



If we use ordinary logarithms for the calculation, we get: 



RT 



-log Kihh.hv -\- 1) 

 ~" V8 X 0,4343 ^ ^ ' ^ ^ 



If we now express R in electrical measure, then 



0,000198 

 t,^ — _: Tlog ^(55,5 v -f 1) 



V 



and for / = 18 or r=291° 



0,0578 

 • A„=z^— %A'(55,5r + l) 



V 



If we now calculate the quantity log K by means of this equation 

 from the observed values of A^, we get the following. (See table p. 8). 



In the succession in which the metals are written down here, (he 

 value of A„ decreases and with it the value of loy K. 



For the metals down to Fe {Fe included) log K is greater than 

 zero, so K greater than 1. 



Now we know that C for a solution is always smaller than 1 ; 

 hence K will always be larger than C for the metals mentioned, 

 and as K denotes the concentration of saturation of the metal-ions, 



