Clean 400 ml, beakers (preferably unscratched)
and pyrex watch glasses with hydrochloric acid.
Weigh a 0.5 gram sample,
and add 10 ml. of water and 35 ml. of nitric acid.
Boil down on the hot
plate at fairly high heat with the watch glass in place to the sudden
appearance of red nitrogen dioxide fumes at a volume of about 1 ml. and
immediately remove the beaker from the hot plate.
Just prior to the
appearance of the nitrogen dioxide, the solution will start to foam.
beaker should be removed from the hot plate before the foaming has ceased.
If the solution is heated too long (to the point at which white fumes
Carry along a reagent
appear) the determination should be discarded.
blank prepared by adding 35 ml. of nitric acid to 10 ml, of water and
After removing the beakers from the hot
evaporating just to dryness.
plate, allow to cool, add 75 ml. of water, and boil down to about 35 ml.
with the watch glass in place.
Cool to room temperature (but not lower),
add 10 ml. of hydroxylamine hydrochloride solution (5 percent) and allow
Add 10 ml. of orthophenanthroline solution
tc stand for 15 minutes.
(0.2 percent) and 15 ml. of sodium citrate solution (20 percent). dilute
to 100 ml. in a volumetric flask, and allow to stand for 1 hour.
the transmittance at 510 millimicorns with a spectorphotometer that has
been set at 100 percent transmittance with the reagent blank.
the reading to mg. of iron by consulting the calibration curve.