364 
IOWA ACADEMY OF SCIENCE Vor. XXIX, 1922 
variable, depending upon small differences in conditions that can- 
not be easily discovered or controlled. Only a few representative 
determinations are selected for each series. The value of the per- 
manganate was found by Na 2 C 2 0 4 to be N/20 x 1.033. 
The iodine method may not be perfect, but it is the best we have 
and is doubtless accurate enough for present purposes. Three 
determinations in parallel by the iodine method gave 0.00352 sul- 
furous acid in 1 cc. of the sulfite solution, which means that the 
permanganate gave only 93 per cent of its value. 
SERIES (2) 
TITRATION OF SULFUROUS ACID WITH SLIGHT EXCESS OF 
PERMANGANATE 
KMnOi reduc. cc. 
Excess KMnCE cc. 
Na 2 S0 3 cc. 
H2SO3 to 1 cc. 
1 . 
36.39 
4.10 
24.95 
0.00309 
2. 
37.10 
2.84 
25.00 
0.00314 
3. 
53.20 
3.39 
36.20 
0.00311 
Average 
0.003113 
The iodine method gave at the same date 0.003476, or the per- 
manganate method gave 89.6 per cent of the sulfurous acid 
present. 
Two titrations as shown in series (3) were made by running the 
sulfite solution into acidified permanganate to the end point, with 
the result that the percentage of oxidation was found not material- 
ly different. 
SERIES (3) 
TITRATION OF SULFUROUS ACID WITH PERMANGANATE TO 
THE END POINT 
KMnCE reduced cc. 
Na 2 S0 3 used cc. 
H 2 SOs to 1 cc. 
1 . 
44.72 
30.50 
0.0031 1 
2. 
63.18 
42.60 
0.00314 
Average 
0.003125 
The iodine method gave on the same day 0.00340, which is 
equivalent to 91.9 per cent of the sulfurous acid present. 
The conclusion from our results and the records of the work 
of others on this subject, is that the development of an accurate 
method for the determination of sulfurous acid with permanganate 
is impracticable, perhaps impossible. 
Department oe Chemistry, 
Grinnell College. 
