_Procedure for water._—Boil 500 cc. of the sample in a round-bottomed
flask to remove ammonia nitrogen. This usually causes the loss of 200
cc. of the sample, which may be collected for the determination of
ammonia nitrogen. Add 5 cc. of nitrogen-free concentrated sulfuric acid
and a small piece of ignited pumice. Mix by shaking and place over a
flame under a hood. Digest until copious fumes of sulfuric acid are
given off and the liquid finally becomes colorless or pale straw color.
Remove from the flame, and add potassium permanganate crystals in small
portions until a heavy green precipitate persists in the liquid. Cool.
Dilute to about 300 cc. with ammonia-free water. Make alkaline with 10
per cent ammonia-free sodium hydroxide. Distill the ammonia, collect the
distillate in Nessler tubes, Nesslerize, and compare with standards as
described (pp. 16–18).
_First procedure for sewage_[76].—Distill the ammonia nitrogen directly
from 100 cc. or less of the sample, diluted to 500 cc. with
nitrogen-free water. Collect the distillate and determine the ammonia
nitrogen in it. Add 5 cc. of nitrogen-free sulfuric acid and 1 cc. of 10
per cent nitrogen-free copper sulfate, and digest the liquid for half an
hour after it has become colorless or pale straw color. Add 0.5 gram of
potassium permanganate crystals to the hot acid solution, and dilute to
500 cc. with ammonia-free water. Dilute 10 cc. or more of this liquid,
in a Kjeldahl distilling flask, to about 300 cc. with ammonia-free
water. Make alkaline with 10 per cent sodium hydroxide, distill, and
Nesslerize. With some samples direct Nesslerization may be used. (See p.
19.)
In this determination care must be taken to digest thoroughly, to add
potassium permanganate to the point of precipitation, to sample
carefully after dilution, and to add enough sodium hydroxide to insure
the separation of the ammonia from the precipitated manganese hydroxide.
Potassium permanganate should not be added during digestion because it
causes loss of nitrogen.
_Second procedure for sewage._—Omit the separation of ammonia nitrogen
and determine the ammonia nitrogen and organic nitrogen together.
Determine the ammonia nitrogen in a separate sample by direct
Nesslerization as described on page 19. The organic nitrogen is equal to
the difference.