On Galvanic Cells produced ~by the Action of Light. 369 



to be denied that many chemical reactions (Jo take place instantaneously 

 on the boundary of two phases, and a considerable number of interesting 

 cases have been investigated by Brunner,* which evidently conform to 

 this rule. It does not, however, seem probable that a useful purpose 

 would be served in considering this rule to hold universally. 



I have examined consequences drawn from it with regard to 

 irreversible electrolytic reductions, and do not find them to agree with 

 facts.f Many other cases might also be brought forward that would 

 be very difficult to reconcile with this theory, e.g., the great difference 

 of velocity shown by metals in dissolving in different acids, \ catalysis 

 by substances such as nitrogen peroxide during the solution of copper 

 in nitric acid, and others. 



In conclusion, the author desires to say that he has had the 

 advantage of discussing the matter treated in this paper with 

 Dr. Senter and Professor Poynting, for which he acknowledges his 

 indebtedness. 



" On Galvanic Cells produced by the Action of Light. Pre- 

 liminary Communication.'^ By M. WILDERMAN, Ph.D., B.Sc. 

 (Oxon). Communicated by Dr. LUDWIG MONO, F.E.S. 

 Keceived November 8, Read November 24, 1904. 



(From the Davy-Faraday Laboratory of the Royal Institution.) 

 In my paper " On Chemical Statics and Dynamics " (' Phil. Trans./ 

 A, vol. 199, 1902, p. 337), and especially Zeit. Physik. Chemie,' vol. 42, 

 1902, pp. 316335, I deduced, from thermodynamics, the laws 

 experimentally found by me for velocity of chemical reaction, and for 

 chemical equilibrium under the action of light, from the fundamental 

 conception that the chemical potential of substance in light and in 

 the dark is different, becoming greater in light. The foundation for 

 this conception was that two metallic plates immersed in a liquid and 

 connected to a circuit form a " galvanic " combination, when one plate 

 is exposed to light while the other is kept in the dark; and, according 

 to Gibbs' equation, v"-v' = a0*a'-/O no g alvanic cel1 could be 

 formed, unless the chemical potentials at the two electrodes were 

 different in light and in the dark. 



The experiments of Becquerel and Minchin left students 



* ' Ztschft. Phys. Chem.,' vol. 47, p. 56 (1904). 



f Faraday Society, October 25, 1904. 



t Ostwald, ' Grundlinien d. anorganischen Chemie,' p. 249. 



Thi? paper contaias a preliminary account of the author'* further researches 

 on "Chemical Statics and Dynamics of Reversible and Irreversible Systems und 

 the Action of Light." 



