_Reagents._—1. Ammonia-free water.
2. Standard ammonium chloride solution. Dissolve 3.82 grams of ammonium
chloride in ammonia-free water and dilute to 1 liter; dilute 10 cc. of
this to 1 liter with ammonia-free water. One cc. equals 0.00001 gram of
nitrogen.
3. Nessler reagent.[8] Dissolve 50 grams of potassium iodide in a
minimum quantity of cold water. Add a saturated solution of mercuric
chloride until a slight precipitate persists permanently. Add 400 cc. of
50 per cent solution of potassium hydroxide, made by dissolving the
potassium hydroxide and allowing it to clarify by sedimentation before
using. Dilute to 1 liter, allow to settle, and decant. This solution
should give the required color with ammonia within five minutes after
addition and should not produce a precipitate with small amounts of
ammonia within two hours.
_Procedure._—Prepare a series of 16 Nessler tubes containing the
following amounts of the standard ammonium chloride solution, diluted to
50 cc. with ammonia-free water, namely: 0.0, 0.1, 0.3, 0.5, 0.7, 1.0,
1.4, 1.7, 2.0, 2.5, 3.0, 3.5, 4.0, 4.5, 5.0, and 6.0 cc. These solutions
will contain 0.00001 gram of nitrogen for each cubic centimeter of the
standard solution.
Nesslerize the standards and the distillates by adding approximately 1
cc. of Nessler reagent to each tube. Do not stir the contents of the
tubes. The temperature of the tubes should be practically the same as
that of the standards; otherwise the colors will not be directly
comparable.[45] Allow the tubes to stand at least 10 minutes after
Nesslerizing. Compare the color produced in the tubes with that in the
standards by looking vertically downward through them at a white or
mirrored surface placed at an angle in front of a window so as to
reflect the light upward.
If the color obtained by Nesslerizing the distillates is greater than
that of the darkest tube of the standards, mix the contents of the tube
thoroughly, pour out half of the liquid, and dilute the remainder to the
original volume with ammonia-free water; then make the color comparison
and multiply the result by two. If the color is still too dark after
pouring out half the liquid, repeat this process of division until a
reading can be made. The process of dilution may be shortened by mixing
together the distillates from one sample before making the comparison
and comparing an aliquot portion with the standards.
After the readings have been recorded add the results obtained by
Nesslerizing each portion of the entire distillate. If 500 cc. of the
sample is distilled this sum, expressed in cubic centimeters and
multiplied by 0.02, will give the number of parts per million of ammonia
nitrogen in the sample. If x cc. of sample is used multiply the sum of
the readings by 10/x.
If the ammonia is known to be high the distillate may be collected in
200 cc. flasks and an aliquot part Nesslerized.