AND CHLOEINE UNDER THE INFLUENCE OF LIGHT. 
119 
same, we have a period of inertness, a period of acceleration, and, finally, the constant 
value for the velocity, as we have in the experimental curves. 
The main features of the induction period are therefore given by the formula we 
have obtained. If we make the more general assumption with regard to the 
intermediate compounds, we should considerably complicate the results, but it is 
easy to see that the inert period and acceleration period would be represented; but 
as at present we do not know what these compounds are, it is not worth while 
working out any more detailed results. We can at present only regard the 
expressions found above as giving the qualitative nature of the reaction, for we have 
omitted various possibilities of which account must be taken for a more exact theory. 
For example, we have neglected to take account of spontaneous decomposition of the 
intermediate products. We know that the water-chlorine molecule decomposes or 
is absorbed by the solution. We should have, therefore, in the equation for the rate 
of formation of this body another term, say Cx, so that the equation would become 
dxjdt = Cg — (cg C) X, 
where C is a constant, independent of the light intensity. 
If then the light intensity be very small, Cg would be small compared with C, and 
so X will increase exceedingly slowly, so that the apparently inert period may be 
prolonged to a very large extent. In any case, more terms in the equations of this 
type indicate prolongation of the period of induction, and especially the early part of 
this period. 
With regard to the action of impurities, we can explain the phenomena if we 
assume that an action can take place between the impurity and the intermediate 
compounds. In this w'ay a relatively small quantity of inq^urity would produce a 
large effect on the final rate of action, since the quantity of the intermediate products 
is always small. 
If now we again consider the equations on p. 116 for the action when the hydro¬ 
chloric acid is not absorbed, we notice that after the induction period is over, the 
action settles down to that represented approximately by the monomolecular equation 
dzjdt = Cg^. 
But here again the effect of spontaneous decomposition will be to change the 
character of the action. Assuming as before that the chlorine-water molecule 
spontaneously decomposes, we have, after the period of induction for the rate of 
formation of hydrochloric acid, 
dz _ CgCgl^^ 
dt ~ Cg (C + 
If C be large compared with then the action is approximately bi-molecular. 
These considerations show that for such an action as we are considering, we cannot 
