6485 grams
Nitre taken 1.0000 "
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27.6485 "
Weight after ignition 27.1160 "
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Loss on ignition 0.5325 "
This is equal to 53.25 per cent. of nitrogen pentoxide.
VOLUMETRIC DETERMINATION.
This is based on the oxidising action of nitric acid, or of nitrates in
acid solutions on ferrous salts. The pentoxide (N_{2}O_{5}) of the
nitrate is reduced to nitric oxide (NO), so that 336 parts of iron
peroxidised represent 108 parts of nitric pentoxide as oxidising
agent.[112] The quantity of iron peroxidised is determined by taking a
known quantity of ferrous salt, oxidizing with a weighed sample of
nitrate, and then determining the residual ferrous iron by titration
with bichromate or permanganate of potassium solution. The difference
between the ferrous iron taken and that found, gives the amount oxidized
by the nitrate. The speed with which nitric oxide takes up oxygen from
the air, and thus becomes capable of oxidising more iron, renders some
precautions necessary; ferrous chloride should, therefore, be used,
since it is easier to expel nitric oxide (by boiling) from solutions of
a chloride than it is from those of a sulphate. The process is as
follows:--Dissolve 2 grams of thin soft iron wire in 50 c.
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