85 
or, — if the electrolytic dissociation of these salts is taken into 
account, perhaps better by the relations : 
2 {Co(C,O,),}" = 2 {Co(C,0,),}" + C,0," + 2 CO,, 
and FCO. One Cortes GION. 
$ 2. The photochemical reaction mentioned was, for the first lime, 
studied systematically in 1917 by Vranek'), under conditions of 
experiment very widely differing from ours. This author studied 
extremely dilute solutions of the salt, with concentrations ranging 
from 0,01 to 0,0001 mol. per Liter, and experimented always 
with very small volumes of the solution, — conditions made necessary 
by the optical method followed by him in this investigation. 
Nevertheless, the measurements were carried out with much care and 
a precision as great as possible, yet the results obtained give the 
impression that the reaction is in reality much more complicated 
than the author himself seems to believe. For, on the one hand, he 
thinks it probable with respect to the numbers obtained, that the 
reaction is a bimolecular one, in agreement with the ionic equation 
suggested above; but his absorption-measurements do not give any 
numbers, which might be looked upon as true reaction-‘‘constants”’, 
and it can be easily seen, that they do not agree really either 
with a monomolecular or with a d:molecular process, so that it 
were better to speak in this case of an accelerated bimolecular, 
or of a retarded monomolecular reaction. By spectrophotometric 
observation, he was, moreover, able to demonstrate, that the eme- 
raldgreen solutions have two principal absorption-maxima, for 
— 4260 A.U., and for == 6050 A. U. respectively ; and he stated, 
that the reaction goes on in darkness as well, light-radiation 
therefore chiefly acting as an accelerator. The temperature-coefticient 
of the dark reaction appeared to be rather great (4,56), but that of 
the photocatalysis, on the contrary, very small; finally an appre- 
ciable BrcQurrer-effect through the total volume of liquid is mani- 
fested, as soon as it is exposed to the light, which fact could be 
demonstrated by means of measurements of the electromotive force 
produced in mixed solutions of cobalto- and cobalti-salt with respect 
to a normal calomel-electrode, if the solutions are brought from 
the dark into the neighbourhood of a source of light. Vranexk 
could state as disturbing factors: 1. the slight solubility of the 
cobalto-oxalate formed in the solution of potassiwm-ovalate; 2. the 
retarding action exerted on the photocatalytic process by the potas- 
situm-oxalate formed in the reaction, — which influence, however, 
1) J. Vranek, Zeits. f. Elektrochem., 23, 336, (1917). 
