176 RALPH S. LILLIE. 



any oxidizer which is capable of being reduced by FeCl 2 may be 

 substituted for chlorine ; and any substance which is capable of 

 being oxidized by the oxidizer may be substituted for the ferrous 

 salt. 1 The above substances serve merely to furnish the simplest 

 possible illustration. Oxidation at the anode, reduction at the 

 cathode, with accompanying flow of current between the two 

 regions, form the constant features of the phenomenon; ob- 

 viously the energy of the current is derived from the energy of 

 the oxidation. It will thus be readily understood that the 

 chemical changes at the electrodes may in some cases be much 

 more complex than those cited above for illustration; and that 

 under certain conditions they may result in decompositions and 

 syntheses of a far-reaching character. 



In the above diagram one half of the circuit, designated as 

 medium M, is regarded as consisting of a metallic conductor 

 which itself undergoes no chemical change; the other half, 

 medium E, is the electrolyte solution. Obviously a metallic 

 conductor which is not chemically indifferent but is capable of 

 combining chemically with the ions of the electrolyte-solution 

 will produce similar electrical effects. A metal of low solution- 

 tension like zinc or iro'n will contribute cations to the solution 

 at the anode; these will form chemical combinations according 

 to the nature of the substances present in the solution. Or the 

 reducing influence at the cathode will affect all reducible sub- 

 stances there present; if, e. g., the cathode is composed of a 

 conducting oxide like copper oxide, as in the Edison cell, this is 

 reduced to the metallic state. Evidently the more complex the 

 material of anode and cathode, and the more complex the con- 

 tiguous solution, the more numerous the chemical transforma- 

 tions that may occur. In all cases, however, Faraday's law 

 holds, and the energy freed in the resulting process is strictly 

 dependent upon the difference in the chemical potential of the 

 substances undergoing transformation at the two regions. 



The case does not appear to be altered in essential principle 

 when medium M is considered to be not a metal, but a second 



1 See the text-books of electrochemistry for examples of the various possible 

 combinations. An oxidizable organic substance, e. g., pyrogallol, a-naphthol, 

 sugar, may be the substance at the anode; a peroxide the oxidizer at the cathode. 

 These examples are adduced to suggest biological possibilities. 



