3 required to decompose the excess of oxalic acid is determined.
If we subtract from the amount thus found the quantity of permanganate
required to equalize solutions Nos. 1 and 2 (previously ascertained),
we shall have the amount of permanganate actually reduced by the
nitric oxide, according to the reaction:
6KMnO_{4} + 10NO = 3K_{2}O + 6MnO + 5N_{2}O_{5};
in other words, on the basis that one molecule of potassium
permanganate will oxidize one and two-thirds molecules of nitric
oxide:
(KMnO_{4} = 1-2/3 NO).
The method of using the apparatus is simple. The nitrate is placed in
B, and the joints made tight, except that at _f_, which is left open.
A current of carbon dioxide is passed through the apparatus until all
of the air has been displaced. Connection is then made at _f_, and
soon afterward the current of carbon dioxide is shut off at _d_.
The flask, B, is now heated as long as may be necessary in order to
produce, on cooling, the diminished pressure required for the
introduction of the ferrous chloride and hydrochloric acid. Before
removing the flame, the joint at _f_ is closed to prevent the return
of the permanganate solution.
As soon as the flask, B, has become sufficiently cool, the ferrous
chloride and hydrochloric acid are introduced through the tube, _a_
(which has been full of water from the first), in the same manner and
quantities as in the well-known Tiemann-Schulze method.
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