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possible only when the catalyst is liable to be oxidised. These cases 
are of great importance in connection with the controversial question 
of negative catalysis. 
In a previous paper (Jour. Chem. Soc. 1917, 111, 707) I have 
shown that tnanganous salts act as a povverful negative catalyst in 
the oxidations of fonnic and phosphorous acids by chromic acid and 
manganous salts can easily pass into the manganic state. Moreover 
it lias been shown by myself as well as other investigators that 
various organic substances notably hydroquinone, brucine etc. act 
as negative catalysts in the oxidation of sodium sulphite by oxygen 
and all these organic substances are thernselves readily oxidised. lt 
is well known that the oxidation of phosphorus by oxygen of the 
air is retarded by the vapours of various organic substances e.g. 
ether, alcohol, turpentine etc. and the oxidation of chloroform is 
retarded by the presence of a small quantity of alcohol. Now all 
these negative catalysts are good reducing agents and are thernselves 
readily oxidised. Hence in oxidation reactions the phenoinenon of 
negative catalysis takes place when the catalyst itself is liable to 
be readily oxidised. 
A study of the slower oxidations that take place at ordinary 
temperatures has not only shown that the process of oxidation is 
complicated by the presence of water, but the question has been 
raised that just so much oxygen takes part in the induced reaction 
as combines with the substance undergoing oxidation. 
Schönbein (Jour. prakt. Chem. J858, 75 , 99; 1864, 93 , 25; 105 , 
226, 1868) first noticed that when certain substances are undergoing 
oxidation S])ontaneously by atmospheric oxygen one part of the 
oxygen combines directly with the substance undergoing oxidation 
whilst another part of it is converted into ozone, hydrogen peroxide 
or simultaneously oxidises sorae other substance. Schönbein (loc. cit.) 
still further demonstrated that just so much oxygen is rendered 
active as is consumed by the substance which is being oxidised or 
in all slow oxidations the same arnount of oxygen is required as is 
consumed in the formation of hydrogen peroxide from water or is 
consumed in the induced oxidation. 
Later investigators like Jorissen (Zeit. phys. Chem. 1897 23, 667) 
Engler and Wild (Ber. 33, 1109, 1000) have verified the law of 
Schönbein in several cases. If we expose a mixture of sodium sulphite 
and sodium arsenite to atmospheric oxygen according to Schönbein 
(loc. cit.) one atom of oxygen should go to oxidise sodium sulphite 
while the other atom would oxidise a molecule of sodium arsenite 
in the same time. The oxidation of sodium arsenite is a very slow 
