( 357 ) 
Recently this supposition was not only confirmed, but it has 
appeared to Coehn ') that even at the ordinary temperature this 
equilibrium is so clear and so easy to demonstrate that m future 
the dissociation of HCl-gas by light can be an experiment regularly 
made at university lectures. 
Moreover of late some other equilibria have been studied in thi 
direction, so that the number of photo- and electrochemical reactions 
begins greatly to increase. 
Owing to the support of a few friends of science, also the Am¬ 
sterdam laboratory has been able for some time to reconnoitre the 
new territory of photo- and electrochemical equilibria, and now it 
can already be stated that the search in this domain has not been 
in vain. 
Before however proceeding to the results of the investigations, 
which were carried out in conjunction with Dr. Aten, I will make 
some preliminary general remarks,'from which it will appear, how 
in my opinion the photo- and electrochemical equilibria may be 
considered. 
For this purpose 1 shall take the following example. Suppose a 
high column of an aqueous solution of some electrolyte; if we now 
lead a hot current of air through this solution, and that in so large 
a quantity per second that the loss of heat of the current of air 
during its passage through the solution is very small compared with 
its total amount of heat, the temperature of the air that leaves the 
solution will not be appreciably lower than the temperature ot 
the air which enters the solution, and if we now disregard the 
influence of gravity, we may assume that the liquid column is a 
homogeneous system with everywhere the same temperature an t e 
same concentration, so that we may apply the law of the active 
masses to such a system. 
If we now expose the column of liquid to dark electrical dischargings 
or to light, and that in the direction of the longitudinal axis, we 
do the same thing as just now in so far that we send a current of 
energy through the column of liquid. 
How this current of energy works, need not be discussed here; 
the result, however, must be that the potentials of the reacting 
substances are increased, which at constant temperature must exclu¬ 
sively be the consequence of an increase of the internal energy of 
the molecules. 
Not only the external, but also the internal energy of the molecules 
Ber. 42, 8183 (1909). 
