The Oxidation of Cane Sugar. 219 



and Stingl, /oc. cit.) and the CO.^, foi- the filtrate is neutral to 

 litmus, and effervesces with dilute acids. 



If in pi'esence of free acid, this uncertainty does not exist, and 

 as the precipitated MnO.2 is insoluble in dilute sulphuric acid, we 

 may write as the final result of the oxidation of the sugar by acid 

 solutions of permanganate, 



Ci, H,, 0„ + 1 6 K Mn 0, + 8 H,S O, = 8 K„ S O4 + 1 6 MnO, + 1 2 C O, 



+ 19HA 



As, however, we get MnOo formed in presence of KMnO^ 

 especially when excess of the latter is used, it is necessary to take 

 account of any possible interaction between them. 



Literature of Secondary Reaction. 



Morse, Hopkins and Walker (^Ain. Chem. Journ., 18, p. 401) 

 have shewn that under similar conditions MnOo is capable of 

 reducing KMn04 with liberation of free oxygen. Thenard 

 noticed and commented on this reducing action in 1856. 



After pointing out that the stability or otherwise of different 

 samples of "permanganate solutions " is due to the absence or 

 presence of this manganese peroxide, they describe an experiment 

 in which half of the manganese in a measured quantity of 

 KMn04 is precipitated as MnOo by the calculated amount of 

 manganese sulphate and the flask containing the solution 

 immersed in boiling water. After some time the pink colour of 

 KMn04 will have disappeared altogether. The amount of 

 "active oxygen" remaining, shows that all the manganese is 

 present as MnO^ and measurement of the oxygen evolved 

 confirms this. 



They give this equation as representing the reaction. 

 2HMn04 + MnO„ = H2O + 3MnO, + 30. 



The oxide resulting from complete reduction of a neutral 

 solution of KMnO^ contains all the potassium of the original salt 

 and the supernatant liquid is therefore neutral and gives 

 practically no deposit on evaporation. 



Unless excess of KMnO^ be present, the precipitated oxide 

 loses oxygen even at ordinary temperatures, so that if it be first 

 dried, or the analysis be delayed for a few hours, then the pro- 

 portion of oxygen to manganese will be smaller than will satisfy 

 the formula MnOo. 



