308 Gooch and Danner — Points in the Interaction of 



the degree of decomposition of the permanganate being finally 

 determined, as in the experiments of Tables I and II, by add- 

 ing a small excess of oxalic acid to those mixtures contained 

 in Erlenmeyer flasks, heating to about 80° C, and titrating 

 with permanganate the residual oxalic acid. 



In the first five experiments little change of tint was noted 

 upon the addition of the oxalic acid to the cold solution, but 

 in the last two experiments the reddish olive color became at 

 once distinctly red — presumably because the higher sulphate 

 of manganese was attacked in the cold by the oxalic acid (as 

 Brauner has shown) and so the natural color of the permanga- 

 nate was permitted to assert itself. The extreme decomposi- 

 tion — that which took place in the last experiment, in which 

 TO per cent of the [1 : 1] acid was present — corresponds 

 nearly to the reduction of the entire amount of permanganate 

 present to the condition of oxidation of MnQ 2 which is known 

 to exist in combination with sulphuric acid in the form of a 

 higher manganic sulphate. It is to be noted that the separa- 

 tion of the insoluble higher oxide took place only when the 

 percentage of acid was low. 



It appears therefore, in brief, that when potassium per- 

 manganate and sulphuric acid are brought into solution 

 together under the conditions which we. have studied there is 

 developed a tendency toward reduction on the part of the 

 former which is the greater as the strength of the acid is 

 increased, as the temperature is raised, and as the duration of 

 action is extended. It appears further, at least when the acid 

 is not present in proportion greater than 50 per cent of the 

 [1 : 1] mixture, that in the early stages of the action the oxygen 

 lost to the permanganate is liberated, and that later on the 

 decomposition of the permanganate results in the precipitation 

 of manganese in the form of a higher oxide or in the reten- 

 tion of the manganese in solution in the form of a higher sul- 

 phate. It is natural to suppose that the first effect of the 

 mutual action of the acid .and the permanganate is to set free 

 permanganic acid, which, being unstable, breaks up with the 

 results described. 



The bearing of these observations and inferences upon the 

 question of the action of potassium permanganate during 

 oxidations carried on in the presence of sulphuric acid is obvi- 

 ous ; for, if the aqueous acid is able to liberate permanganic 

 acid in such proportions as to be spontaneously unstable, it is 

 reasonable to presume that any reducing substance present at 

 the time of such action may, by virtue of its attractive action 

 upon the oxygen of many more molecules of the permanganic 

 acid than would be necessary to supply the exact amount 

 needed for perfect oxidation, tend to increase the general 



