Energy of Light and Chemical Energy. 225 



which is van't HofF's equation, /. e., the variation of the 

 logarithm of the constant of chemical equilibrium in homo- 

 geneous (gaseous) systems with the variation of temperature 

 must follow in the light the same law which it follows in the 

 ■dark. 



At a constant temperature equation 12 or DJ becomes 



i. e., the law of mass-action must hold good for equilibrium in 

 homogeneous systems, when the equilibrium is shifted* under the 

 action of light to a new point in the same manner as in the dark. 

 This is exactly what was found to be the case in the experi- 

 mental part of the paper '' On Chemical Dynamics and Statics 

 under the Influence of Light/' Phil. Trans, of the Royal 

 •Society, Oct. 1902. 



The above equation (O") can in homogeneous systems be 

 decomposed in the usual manner into two equations of two 

 -opposite velocities of reaction, 



(£)=c'(<r co- -©"=<=» 0y, 



which at equilibrium become equal, i. e., the velocity of a 

 chemical reaction when caused (or influenced) by the liglit-energy 

 introduced into the system follows in light the same law of 

 mass-action as it follows in the dark, when a reaction is brought 

 about by the intrinsic properties of matter always existent in 

 and inseparable from the same, and which we call chemical 

 ■affinity or chemical potential. This is just the principal 

 result of the experimental research communicated in the above- 

 mentioned paper. No law analogous to Faraday's for electro- 

 lysis was found to hold oood for light introduced into the 

 system. 



The experimental results obtained by the author thus led 

 him gradually to believe that the light-energy introduced 

 from an external source into the system does not act upon 

 the same in a manner similar to that of introduced electrical 

 energy ; that the above conceptions as to the mode of 

 working of the introduced light upon a system must give the 

 true state of things, the more so as they also furnish a 

 rational and detailed explanation of the phenomena obtained 

 with metallic plates when exposed to light, and of the phe- 

 nomena of induction and deduction, which otherwise seem to 

 be of a mysterious and complicated nature. 



From this result follows further the conclusion, drawn 

 already in the above-mentioned paper in connexion with 



Phil. Mag. S. 6. Vol. 5. No. 26. Feb. 1903. Q 



