1904.] produced ~by the Action of Light. 373 



period, directly proportional to the current, and gives the true measure 

 of the amount of silver salts decomposed by light. The equation for 

 the deduction period is also 



i.e., is directly proportional to the remoteness of the system from the 

 point of equilibrium in the dark, TT Q - TT, and to TT - TT O ', which gives the 

 amount of variation produced by the removal of the light in the 

 system already, up to the time T plus a constant K'. 



(4) The physico-mathematical theory of " constant cells reversible in 

 respect of the cation" (e.g., Ag plate in light, AgN0 3 solution in light, 

 AgNOs solution in dark, Ag plate in dark) is the following. The result 

 of the process under the action of light consists : 



+ 



(1) In one gramme-atom of the cation (Ag) of a higher chemical potential 

 passing from the electrode (Ag) in light into the solution of the salt of the 

 electrode in light. 



(2) From the solution in light the gramme-atom of the cation passes to the 

 solution in dark, transforming there into cations of a lower chemical potential, 

 passing a deduction period. 



(3) Finally from the solution in dark the gramme-atom of the lower chemical 

 potential separates upon the electrode (Ag) in dark. 



Let the solution pressure of the plate be in dark P^, the osmotic 

 pressure of the cations ( + Ag) in the solution in dark pa- Then, since 

 the chemical potential of a substance is different (greater) in light than 

 in dark, the solution pressure of the same plate in light will be PI, and 

 the osmotic pressure of the cations of the same concentration in light 

 will be pi. If now we calculate the work done by such a system, when, 

 under the action of light, 1 gramme-atom of Ag passes from the plate 

 in light to the plate in dark, we get 



for (1) E! = 0-860T log* -' . lO" 4 volt ; 



for (2) E 2 = 0-860T^ log/-' . 10~ 4 volt (very nearly) ; 



p d 



for (3) E 3 = 0-860T log, d . KT 4 volt ; 



Pd 



and 



2E = E! + E 2 - E 3 = 0-860T (log e ^ - -^ log, # ) 10- volt .. (I) 



\ _L d U + V Pd/ 



gives the value of the E.M.F. of such combinations under the action of 

 light. This equation shows : 



(1) The E.M.F. of such a combination must be independent of concentration, 

 i.e., 2E-2E' = 0. 



This was found experimentally to be the case. 



(2) Experiments were made which showed that both the value 



