was to be expected, as it is not the molecules, but the atoms or the 
particles composing the atoms which react chemically. 
It is now the question, when may the law of the active masses 
be applied to a system which is exposed to light energy or electrical 
energy? The answer to this question is, in my opinion, as follows: 
When the quantity of transmitted energy is so great that during 
the passage of the current of energy no decrease of the energy which 
is active here, is to be observed, though energy is absorbed by the 
system, then the system is to be considered as in all respects homo¬ 
geneous just as in the case mentioned just now of the current of 
heat-energy, and the law of active masses must be of application. 
If, however, the current of energy is less intense, the decrease of 
energy will be clearly to be demonstrated, the state will differ from 
layer to layer, and so the system will be non-homogeneous. 
So in this case the law of active masses will not be applicable. 
It is clear that when the current of energy is too feeble, the 
equilibrium will be susceptible to a change of the intensity of the 
current of energy, and so that it is possible to decide in a simple 
way whether a system at a certain moment may be considered as 
a homogeneous system or not. 
Here we must observe that it must be borne in mind that all 
kinds of complications may appear; thus it appears among others 
from Davies’ investigationsthat some component or other may 
exert influence on the current of energy, which e. g. may give rise 
t0 P ecu Har light phenomena in the case of dark electrical dischargings. 
H is not surprising that in such a case it seems that the law of 
^tive masses does not hold, for the current of energy has been 
subjected to a change, and what the investigation has revealed is 
simply this that a change in the properties of the Current of energy 
K of great influence on the situation of the equilibrium. 
Since light energy and electrical energy are of a much more com- 
P icated nature than heat energy, phenomena may occur iq this new 
omain which were never met with in the thermic region. 
n conclusion we may point out that when equilibria are studied 
a * suc ^ high temperatures that the vessel in which the system is 
placed, has become a source of light, we shall get a final state 
W * c h ^presents a photo-chemical equilibrium 7 at this high temperature; 
m a few cases this circumstance will have to be reckoned with. 
Amsterdam, October 1909. Anorg. Chemical Laboratory 
of the University. 
) Zeitschr. f. physik. Chem. 64, 657 (1908) 
(November 25 , 1909 ). 
