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which would require 88.2 per cent of the oxygen required for 
complete oxidation to sulfurous acid. They say, however, “When 
a solution of sulfurous acid is poured into an excess of permanga- 
nate only sulfuric acid is found.” 
Pinnow 3 carried out several series of titrations of sulfite with 
permanganate in parallel with titrations by the iodine method. 
The oxidation to sulfuric acid was never found to be complete. 
Temperature, concentration and acidity had little influence. His 
results vary from 90.9 per cent in acid to 97.2 in alkaline solution. 
He ialso' assigned the discrepancy to the formation of varying 
amounts of dithionate. 
Possibly encouraged by the statement quoted from Dymond 
and Hughes two papers have appeared which propose the deter- 
mination of sulfurous acid by oxidation with an excess of 
permanganate. Milbauer 4 added a very dilute solution of the 
sulfurous acid to ten times the requisite permanganate to oxidize 
it to sulfuric acid according to theory and determined the excess 
with oxalic acid. Even though the oxidation were complete it 
would be difficult to determine the fact by difference in his 
method owing to the large magnification of the unavoidable error 
in determining such a great excess of permanganate. Sweeney, 
Autcault and Withrow 5 added sulfur dioxide or sulfite to an 
excess of permang*anate and determined the excess color imetri- 
cally. They insist on an excess of permanganate at all times. 
This permanganate was standardized with specially purified so- 
dium sulfite. However, a later communication 6 from the same 
laboratory showed the impossibility of preparing in weighable 
condition pure sodium sulfite and called in question all deter- 
minations of sulfite basis on sodium sulfite as a standard. 
Though the preponderance of evidence seemed to be against the 
complete oxidation of sulfurous acid in acid solution by a moderate 
excess of permanganate, the question seemed to merit a more 
rigorous test than had apparently been applied to it, and the 
electrometric method, as one of us 7 had applied it in the deter- 
mination of nitrous acid, seemed to meet the requirements. 
The starting point was a solution of sodium sulfite placed in 
an atmosphere of hydrogen by use of an apparatus practically 
the same as that used by Thornton and Chapman. 8 After stand- 
3 Pinnow, Zeit. Anal. Chem., 43, 91 (1904). 
4 Milbauer, Zeit. Anal. Chem., 47, 17. 
5 Sweeney, Autcault and Withrow, J. Ind. and Eng. Chem., 9, 949 (1917). 
'6 Shenefield, Vilbrandt and Withrow, Chem. and Met. Eng., 25, 953 (1921). 
7 Hendrixson, Jour. Amer. Chem. Soc., 43, 1309. 
8 Thornton and Chapman, Jour. Amer. Chem. Soc., 43, 91. 
