OXIDATION OF SUCROSE BY POTASSIUM PERMANGANATE. 239 
sulphurous acid, stating that “‘Sulphurous acid, as is well 
known, when mixed with a large bulk of water which has 
been exposed to the air, is but slowly oxidised and the 
change proceeds still more slowly if the solution is freely 
acidified. If, however, a minute quantity of manganese 
sulphate is added the oxidation of the sulphurous acid is at 
once determined.’’ He then supposes that if the water 
can act to a small extent upon the manganese salt, as it 
~ acts upon a bismuth salt, that is, separate the base from 
the acid, then, no doubt, the hydrate of manganese thus 
displaced would absorb free oxygen and the sulphurous acid 
would at once again reduce the peroxide formed. Without 
insisting on this definite hypothesis, he thinks it is probable 
that this action of the manganese salt is in some way 
related to the fact that the protohydrate of this metal has 
the property of absorbing oxygen from water and parting 
with it again to sulphurous acid. 
Ina later paper in conjunction with Esson,* it was found 
that at ordinary temperature, in a dilute and feebly acid 
solution, permanganic acid acts very slowly on oxalic acid, 
but the presence of a manganous salt formed by the reduc- 
tion of the permanganic acid or previously added, caused a 
great acceleration. In this case the acceleration reached 
a Maximum when three molecules of manganese sulphate 
were present to one of potassium permanganate :— 
2KMnO,+3 MnSO,+2 H,O = K,S80,+2H.SO,+5Mn0O, 
These reactions although somewhat similar, are not 
identical with the reaction in question, namely the oxida- 
tion of sucrose by potassium permanganate. In the latter 
reaction decomposition can proceed rapidly in either acid, 
neutral or alkaline solution, and without any previous 
addition of manganese sulphate. Further, this salt, when 
added, increases the initial rate of reaction to an extent 
1 Proc. Roy. Soc., London, xtv, p. 470, 1865. 
