of Hydrogen and Chlorine under the influence of Light. 403 



We obtain 



T B 



20° -0097 



30 -0084 



40 -0073 



50 -0057 



60 -0048 



The temperature effect shews, therefore, little agreement with 

 the theory applicable to reversible actions. 



The author (loc. cit.) has developed to some extent a theory 

 of the action, regarding it as an irreversible action taking place 

 by means of intermediate compounds, or at any rate aggregates 

 of molecules, the first step being the formation of groups involving 

 chlorine and water molecules. On this theory we should expect 

 that the rate of action when this reaches its steady value should 

 be proportional to the product of the concentrations of the chlorine 

 and water molecules. Or if the combination takes place through 

 aggregates of water molecules acting as regions in which the 

 Hydrogen and Chlorine can combine, then the final rate should 

 be proportional to the concentration of the water aggregates. 



Consider the consequences of assuming that an action takes 

 place first between the chlorine and water molecules, the rate 

 of action should then at a given temperature be proportional to 



x (a — x) 



where x is the concentration of water molecules and s the 



2 



concentration of chlorine molecules, which under the conditions 

 of the experiment remains constant. Now x is proportional to p, 

 the vapour pressure of the water at that temperature, and so the 

 rate of action may be put equal to 



kp (c -p). 



c in this expression is the pressure at which the experiment 

 is conducted, and may be put = 76"0, measuring pressure in cen- 

 timetres of mercury. If we calculate the factors p(c—p) we 

 obtain the following table : 



