491 
Perrin has deduced the following eqiiation connecting the velocity 
coëfficiënt and the temperature: 
dT 
2 d log■^^k = Qv where ^ = velocity coëfficiënt, y = wave- 
length of the activating radiation and T= absolute temperature, 
From his calculations, it is seen that the wavelengths which are 
active in bringing forth the ordinary Chemical changes vary from 
2.56 to 0.8 microns. It is also seen that a reaction which is highly 
sensitive to the influence of temperature has a small value for its 
activating wavelength, that is, a reaction of this type would be most 
sensitive to violet and ultraviolet end of the spectrum. From Perrin’s 
calculations it is seen that the reaction between K,CjO^ and I, which 
has the high temperature coëfficiënt of 7.2 in the dark, has 0.8 
micron for the wavelength of its activating radiation. In other words, 
this reaction would be most sensitive to light near the red end of 
the spectrum. But it is experimentally shown that this reaction is 
not sensitive to the indigo part near the violet end of the spectrum. 
My own experiments on several photochemical reactions have shown 
that the blue and violet portions of the spectrum are most active 
so far as Chemical effects are concerned. Although the hypothesis 
of Perrin is still of a qualitative nature, it is a highly suggestive 
one and my experiments give this hypothesis a sort of general 
support. 
I have tried to prove experimentally that reactions, which are 
most sensitive to the influence of temperature, are also most sensi- 
tive to the influence of light. In a foregoing paper, I have advanced 
the hypothesis that temperature and light affect a Chemical change 
in a similar way. The experimental evidence brought forward in 
this article, as well as Perrin’s hypothesis that all Chemical changes 
are induced by radiations, give additional confirmation to my hypo- 
thesis regarding the identity of effects of temperature and light on 
Chemical reactions. 
Summary : 
a. Evidence has been brought forward in support of the view 
that reactions, having large temperature coefficients, are sensitive to 
light. Hence for a Chemical reaction, sensitiveness to the influence 
of temperature and sensitiveness to light radiations go hand in hand. 
b. The indigo part near the violet end of the spectrum is most 
active in the reaction between KjCjO^ and Ij ; blue and violet parts 
more active than the red in the following cases: 
32 
Verslagen der Afdeeling Natuurk. Dl. XXIX. A®. 1920/21. 
