224 Dr. S. W. J. Smith on the Weston Cell 



a similar effect accompanies the transference of dm 2 of 

 cadmium. 



In consequence, if we suppose the electric potential of the 

 amalgam to be V and of the electrolyte to be \ r ", it will be 

 seen that the reversible energy variation may now be 

 written 



de + de" = 6(dr i + dr{ l )-p(dv + do") ^i^-p^dn^ 



+ (fi 2 -f* 2 l, )dm i + (V-V l %k 1 dm 1 + k 2 dm 2 ) 



in which / ~de \ , / tt , &] 



\OWi.l/>i«m 2 /'3 



with similar expressions for the other quantities, fx z referring 

 to the surface layer and ^" to the interior of the electrolyte. 

 For equilibrium, as before, 



(,*i-A*i") + *i(V-V") + ^Oi.-WO = 0, ] 



and (/^ — yUo'^ + ZofV — V'')+ 7 2 (/a 3 — yu,/') = 0. J 



*3 J 



In the same way, considering the solid amalgam and the 

 electrolyte, we must have 



(^'-A*i")+*i(V'-V")+|(M 3 '-^") =0 "] 



and |> 



(m 2 '-^ 2 ") + A- 2 (V'-V")+ jjfli/--V) = O.J 



Considering the equilibrium of the amalgams with each 

 other we assume 



fii = fii, fM 2 = fi 2 '. and V - V. 



Suppose now that we ignore possible differences at the 

 surfaces separating the electrolyte and the fluid and solid 

 amalgams respectively and put/u 3 = jZ-/ (see also § 13, below). 



Then it will be possible to find values of /x/', /z, 2 " and /j, d ", 

 which will be related in such a way as to satisfy the above 

 equations simultaneously and make 



V— V" = V— V". 



In other words it will be possible to find electrolytes 

 within which the two amalgams can exist side by side in 



