DAL Cc. W. R. POWELL. 
permanganate. This investigation was carried out in order 
to throw some light on this point as well as to decide the 
order of the reaction, and to ascertain to what extent the 
concentration of the acid influenced the velocity of 
reaction. | 
Method.—The reaction proceeds in acid, neutral or alka- 
line solution, the rate being slowest in a neutral solution, 
and increasing with the addition of either acid or alkali. 
If the solution is not sufficiently acid, however, a dark pre- 
cipitate is thrown down Consisting in all probability mainly 
of manganese peroxide. This is no doubt the substance 
referred to by Maumené, who stated that in this reaction 
the permanganate was reduced to sesquioxide or a mixture 
of MnO, and MnO, or a combination of both. The stage 
to which the reaction had advanced at different times was 
determined by running a measured volume of the reaction 
mixture into an excess of ferrous ammonium sulphate and 
then determining the excess by titration against dilute 
potassium permanganate solution. This method being 
adopted, the formation of manganese peroxide in the reac- 
tion mixture was undesirable as manganese peroxide and 
sulphuric acid (which was the acid used to acidify the 
solution) liberate oxygen which would interfere with the 
titration of the ferrous ammonium sulphate. For this 
reason the greater number of the determinations were 
made in solutions sufficiently acid to prevent the precipita- 
tion of manganese peroxide. 
In the actual experiments 5 ccs. of the reaction mixture 
were run into 5 ccs. of 0°5 per cent. solution of ferrous 
ammonium sulphate made acid with about 4 ccs. of 5 normal 
sulphuric acid. This immediately checked the reaction at 
atime noted on a stop watch. The excess of ferrous 
ammonium sulphate was then determined by titration 
against potassium permanganate (about. 0°0031 normal), * 
