304 
it becomes very difficult to determine the temperature coefficient 
accurately. It appears therefore that the reaction is auto-catalytic. 
Maruews and his colleagues (Jour. Phys. chem. 1913, 17, 211; 
Jour. Amer. chem. Soc. 1917, 39, 635) found that ultraviolet light 
markedly accelerates this reaction, and also established the fact that 
this is not a case of auto-oxidation. For this reaction, they could 
not find a positive catalyst; copper sulphate, which is known to be 
a powerful catalyst under ordinary conditions exerted no appreciable 
effect in ultra-violet light. On the other hand the negative catalysts 
like hydroquinone, phenol etc. exerted a retarding effect in presence 
of ultra-violet light. So it appears that there are very few positive 
catalysts, but very many negative ones for this reaction when carried 
out in light or darkness. 
The explanation of the negative catalytic effect of organic sub- 
stances in general on this reaction is this: 
The reaction consists in the oxidation of SO, radical into SO,, 
and the sulphite ion is the active agent. It is well known that several 
organic substances form complexes with sulphurous acid and sulph- 
ites; these complexes are stable so far as oxidation is concerned 
and hence the organie substances act as negative catalysts by dimin- 
ishing the concentration of sulphite ion by combining with it. 
In foregoing papers I have proved that the phenomenon of nega- 
tive catalysis is very common, whilst there are very few positive 
catalysts. According to Lutuer’s view a negative catalyst must have 
a positive catalyst as its counterpart, but this is not probable since 
there are so few positive catalysts and so many negative ones. 
Hence it appears that LurHer’s view which emphasises that nega- 
tive catalysis cannot take place in a reaction which is entirely free 
from positive catalysts, is not substantiated by experimental evidence. 
Summary. 
a. Cane sugar, lactose, glucose, camphor, and menthol are nega- 
tive catalysts, whilst naphthalene, and anthracene are without action 
on the oxidation of sodium sulphite. 
b. The weak organic acids and their sodium salts exert practic- 
ally the same effect. Benzoic, oxalic, salicylic acids and their sodium 
salts exert greater negative effect than the weak acids and their 
salts. It is very peculiar that the acid and its salt should exert the 
same effect. 
c. The temperature coefficient of the reaction is about 2 and it 
