_Reagents._—1. Sodium or potassium hydroxide solution. Dissolve 250
grams of the hydroxide in 1.25 liters of distilled water. Add several
strips of aluminium foil and allow the evolution of hydrogen to continue
over night. Concentrate the solution to 1 liter by boiling.
2. Aluminium foil. Use strips of pure aluminium about 10 cm. long, 6 mm.
wide, and 0.33 mm. thick and weighing about 0.5 gram.
_Procedure._—To 100 cc. of the sample in a 300 cc. casserole add 2 cc.
of the hydroxide solution and concentrate by boiling to about 20 cc.
Pour the contents of the casserole into a test tube about 16 cm. long
and 3 cm. in diameter, or of approximately 100 cc. capacity. Rinse the
casserole several times with nitrogen-free water and add the rinse water
to the liquid already in the tube, thus making the contents of the tube
approximately 75 cc. Add a strip of aluminium foil. Close the tube by
means of a rubber stopper through which passes a bent glass tube about 5
mm. in diameter. Put the shorter arm of the tube flush with the lower
side of the rubber stopper and let the longer arm extend below the
surface of distilled water in another test tube. This apparatus serves
as a trap through which the evolved hydrogen escapes freely. The small
amount of ammonia escaping into the trap may be neglected. Allow the
action to proceed for a minimum period of four hours or over night. Pour
the contents of the tube into a distilling flask, dilute with 250 cc. of
ammonia-free water, distill, collect the distillate in Nessler tubes,
and Nesslerize. If the nitrate content is high collect the distillate in
a 200 cc. flask and Nesslerize an aliquot part. If the supernatant
liquid in the reduction tube is clear and colorless the solution may be
diluted to a definite volume and an aliquot part Nesslerized without
distillation.