AND CHLORINE UNDER THE INFLUENCE OF LIGHT. 
Ub 
hydrogen makes the action take place more readily, leads us to conclude that the 
first stage of the action is the formation of an additive compound from the chlorine 
and water vaj)Our. Chlorine does form a hydrate with water, and the departure of 
chlorine from Henry’s lav^^, and other anomalous behaviour in solution, shows that it 
does tend to form additive molecules with water. We have seen that there is direct 
evidence for the existence of some new substance when light is allowed to fall on 
damp chlorine, but as yet we cannot say what this compound actually is. It is 
possible that a compound analogous to hydrogen peroxide is formed by simple 
addition of one molecule of water to one of chlorine. 
The constitution of this compound would be represented by the following formula, 
adopting to some extent Nee’s view of the action of an halogen in forming an additive 
compound. Such a compound might exist, but it would probably be extremely 
unstable, and would, if left to itself, break down into water and chlorine again, or 
into the molecules HCl and HCIO. The fact that damp chlorine, under the influence 
of light, does yield these two compounds, supports to some extent this view. 
However, in the absence of direct evidence for the constitution of this compound, we 
shall simjoly assume that an additive molecule (HgO),,^ is formed. 
Illumination of the hydrogen alone, before mixing with chlorine, does not affect the 
rate of combination, so that there appears to be no direct additive compound of water 
and hydrogen formed. But on the present theory we suppose that the next stage in 
the action is the formation of a still more complex molecule, by the addition of one 
or more hydrogen molecules to the complex water-chlorine molecule. A molecule 
(H, 0 ),, (Cb),, (H,).3 is thus formed. In this molecule the hydrogen and chlorine 
atoms can come into action with each other. A pair, consisting of a hydrogen atom 
and a chlorine atom, may nearly saturate each other, and, thus forming a system with 
little effect on the whole molecule, may split off from the complex molecule as a 
molecule of hydrochloric acid. The hydrochloric acid then finally j^roduced is the 
result of the breakdown of the complex hydrogen-water-chlorine molecule. The rate 
of formation of hydrochloric acid is proportional to the concentration of the complex 
molecules (HaO),,^ (Cla)^, (H2)„3. The rate of formation of these is proportional to 
the concentration of the water-chlorine molecules and power of the concentration 
of the hydrogen molecules. And the rate of formation of the water-chlorine molecules 
is proportional to the power of the concentration of the water molecules, and the 
power of the concentration of the chlorine molecules. 
As at present we do not know the composition of the intermediate compounds, we 
shall work out the case when the complex molecule is as simple as it can be, that is 
when n^ = 71 ^ = n^= 1. 
