1904.] produced by the Action of Light. 377 



Tm "RT 



because the osmotic pressures are pi = __/, p 2 = -" and p\-p^ = 





, - T,,). Therefore 



(i), 



i.e., the E.M.F. of thermogalvanic cells must be directly proportional to the 

 difference of temperature of the two electrodes, a law which is analogous to 

 the thermo-E.M.F. produced when two metals are in contact, instead 

 of a metal and solution. (The assumption, however, is made that p or 

 heat of ionisation can be taken between T, and T /y to remain constant.) 



The laws for thermogalvanic cells can be deduced in another way 

 from the solution pressures of the electrodes and the osmotic pressures 

 of the solution. We take the system (Ag, N0 3 Ag sol.)T, (N0 3 Ag sol., 

 Ag)T,, 



We have 



Ei = 0-860Ti loge ?*'- . 10- 4 volt ; E 2 = 0-860T,, log e ^ . 10~ 4 volt ; 

 Pi. PT H 



E 3 = E'(T-TJ; 



and 



XE = EI 2 + E 3 



= 0-860 T loge - T,, \og e ] 10- 4 volt + E' (T, - T,,) 

 PI, P?J 



where PT,, PT,, are the solution pressures of the silver electrodes at T, 

 and T /y . Similarly we get for cells reversible in respect of the anion 



2E = 0-860 ( T^oge g*- - T t log e g*\ 10~ 4 volt + E/ (T, - TJ .'. . (II). 

 \ "T,, "T,/ 



Since pt t , pt /t are directly proportional to the absolute temperature, 

 we have for systems reversible in respect of the cation 



p T/ = apT,, pr H = ^T //} 

 and 



2E = 0-860 (T^ogePr, - T,, log e P T// ) 10~ 4 volt 



+ r O-860 (T /y loge apT tl - T, log, apT t ) 10' 4 volt + E' (T, - T,,) . . . (I'), 

 and for systems reversible in respect of the anion, 

 2E = 0-860 (T,, log e PT - X log e P T| ) 10~ 4 volt 



+ 0-860 (T, loge ap T, - T,, log e ap TJ 10~ 4 volt + E x ' (T, - TJ. . . (IF)- 

 Equation (IF) differs from the equation of Nernst by the term E 3 

 which I put = E/ (T, - TJ, but while Nernst assumes that EI and E 3 

 remain unknown, and tries to eliminate them (i.e. their content), by the 

 use of two different concentrations, we shall try to determine the value 

 and content of these equations so as to get to the fundamental equation 

 concerning the thermogalvanic system for any one concentration. 



