It is
also necessary, for the same reason, to avoid too rapid heating during
the decomposition of the nitrate.
When all of the nitric oxide has been forced into the solution of
permanganate, the determination is made in the manner already
described.
To test the method, nine determinations were made with quantities of
pure nitrate of potassium varying from 100 to 200 milligrammes. The
maximum difference between the volumes of permanganate actually used
and those calculated was 0.05 c.c., while the main difference was
0.036 c.c. The measurements of the permanganate were made from a
burette which had been carefully calibrated. We also made a number of
determinations, using a solution of manganous sulphate in the place of
the oxalic acid. The advantage of this method lies in the fact that it
is not necessary to dissolve the oxide which is precipitated upon the
glass within the tubes, E, E, since, in the presence of an excess of
permanganate, the reduction by nitric oxide extends only to the
formation of MnO_{2}; also in the fact that the solution of manganous
sulphate is more stable than that of oxalic acid. A solution of the
sulphate having been once carefully standardized, can be used for a
long time to determine the value of permanganate solutions.
The details of the method are as follows: A solution of manganous
sulphate slightly stronger than No.
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