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chemical change and in order that ScHÖNBRIN’s law be applicable, it 
follows immediately that the oxidation of sodium sulphite, which is 
fairly rapid, becomes a slow change and the velocity of this oxida- 
tion becomes equal to that of the oxidation of sodium arsenite, 
because the same amount of oxygen will be taken up by the reducing 
agents in the same time. As a matter of fact from my experiments 
I have observed that in presence of sodium arsenite or potassium 
oxalate the velocity of the oxidation of sodium sulphite becomes 
very small. We assume that a molecule of oxygen splits up in this 
reaction into two atoms and each atom oxidises one of the reducing 
agents. Now as a solution of sodium sulphite is much more readily 
oxidised than a solution of sodium arsenite it becomes difficult to 
understand why the other oxygen atom instead of attacking the 
readily oxidisable nnacted sodium sulphite attacks the much more 
diffieultly oxidisable sodium arsenite. Or if we assume that at first 
a peroxide of the type of BopLANDErR’s benzoyl peroxide (Ahrens’ 
Sam. 8, 470 1899) is formed as a combination of the sodium sulphite 
with a molecule of oxygen, we are still encountered with the same 
difficulty. In this case we shall have to assume that this peroxide 
instead of attacking the readily oxidisable and unattacked sodium 
sulphite, will attack the less readily oxidisable sodium arsenite by 
preference. It seems to me therefore that the only course left to us 
is to find out the explanation in the view of the formation of a 
complex of sulphite and arsenite or of sulphite and oxalate and that 
this complex is oxidised as a whole. It is well known that complex 
oxalates and sulphites do exist. OsrwaLp thinks that in order to 
explain positive catalysis by the hypothesis of intermediate compound 
formation it is necessary to show that the intermediate reactions 
actually take place more readily than the direct reaction under the 
given conditions, because if a reaction goes more slowly via the 
intermediate product than the direct path, it will take the latter 
and the possibility of intermediate products can have no influence 
on the process. “Hence”, adds Osrwarp, ‘I see no possibility of 
explaining retarding catalytic influences by the intermediate products” 
(Nature, 1902, 65 522). 
I have observed in a previous paper (Proc. Akad. Wet. Amsterdam 
-1920) that in the oxidation of sulphites and sulphurous acid the 
sulphite ion is the active agent. If we can decrease the sulphite ion 
we can decrease the chemical change, and a solution of sulphurous 
acid which is a weak acid containing few sulphite ions is oxidised 
less readily than a solution of sodium sulphite of the same concen- 
tration. On the addition of an arsenite to a sulphite a complex which 
