AND CHLORINE UNDER THE INFLUENCE OF LIGHT. 
77 
present. The oxidation of the chlorine is effected hy the water vaponr present in the 
mixture. 
They suppose, for example, an action of the following type 
Cl, + H 3 O = HCIO + HCl, HCIO + H 3 = R,0 + HCl. 
The presence of moisture was found by these observers, as well as by many others, 
to increase the rate of the action. The question arises, do hydrogen and chlorine 
combine at all under the influence of light when no water vapour is present ? Baker"^ 
found that complete combination did not take place after exjDosure to bright sunshine 
for two days. According to Pringsheim, action does occur slowly in the most 
carefully dried gases. 
The catalytic action of water vapour is of great importance in other actions besides 
the one under consideration. There have been several theories proposed for the 
explanation of this action, but none of them are very satisfactory. Dixon supposes 
that the molecules of water undergo decomposition; for example, in the oxidation of 
carbon monoxide he assumes two stages 
CO + R,0 = CO.^ + and 2R, + 63 = 2 H 3 O. 
Pringsheim’s theory is that, in addition to this tyj)e of action, we have the 
preliminary dissociation into atoms, which then act with the water molecules 
2 H + 2C1 + R,0 = CI 3 O + 2 H 3 , 
and finally 
CloO + 2 H 3 = 2HC1 + H 3 O. 
This explanation has been criticisedf from the point of view of Berthelot’s 
principle of maximum work. This criticism does seem to be applicable to Pringsheim’s 
scheme when we are dealing with free atoms of hydrogen and chlorine; Imt the 
principle does not necessarily hold when the rates of action between molecules come 
into consideration. If the action 
2 CO +03 = 2 CO 3 
takes place slowly compared with the actions 
CO + H 2 O = CO 3 + H 3 and 2 H 2 +03 = 2 H 3 O, 
the course of the oxidation of carbon monoxide to carbon dioxide may be as Dixon 
suggests. And the view in this case is more probable, as it appears from Dixon’s 
experiments that if the action 
2 CO + 03 = 2 CO 3 
can occur at all it occurs extremely slowly, 
* ‘Phil. Trans.,’ A, 1894. 
t ‘Brit, Ass. Rep.,’ 1894. 
