1 is prepared.
The difference between 100 c.c. of it and 100 c.c. of No. 1 is
ascertained, according to the method of Volhard, by means of solution
No. 3.
The contents of E, E, together with the rinsings from the tubes, are
poured into a capacious flask. 100 c.c. of the manganous sulphate and
a few drops of nitric acid are then added, and the whole boiled.
Finally, the excess of manganous sulphate is determined, in the manner
described by Volhard, by means of solution No. 3. Subtracting from the
total amount of permanganate thus used the quantity required to
equalize the 100 c.c. of solution No. 1 and the 100 c.c. of the
manganous sulphate, we shall have the quantity of permanganate reduced
by the nitric oxide.
It must, however, be remembered that the value of solution No. 3 is
now to be calculated on the basis of the equation KMnO_{2} + NO =
KNO_{3} + MnO_{2}. One molecule of permanganate equals one molecule of
nitric oxide when manganous sulphate is used, since no part of the
permanganate employed in this method is reduced below the superoxide
condition. In other words, solution No. 3 now represents only
three-fifths as much nitric acid as it does when oxalic acid is used.
The results obtained by this method were moderately satisfactory, but
not quite so exact as those obtained when oxalic acid was used.
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