NESSLERIZATION 281 
nitrogen in water trace the changes through which the organic matter 
is made to pass by tne bacteria. The free and albuminoid ammonias 
indicate the organic matter while the nitrites and nitrates indicate the 
amount of oxidation which has taken place. 
Nesslerization. This may be done directly or after distillation de- 
pending upon the amount which is present in the sample. The following 
solutions are required: 
1. Standard Ammonium Chloride Solution. Dissolve 3.82 gms. of 
ammonium chloride in 1 liter of ammonium free water. Dilute 10 c.c. 
of this to I liter with ammonia free water. One c.c. of this latter solu- 
tion equals 0.00001 gm. N. 
2. Nessler Solution. Dissolve 50 gms. of potassium iodide in a little 
cold water. To this is added a saturated solution of mercuric chloride 
until a slight precipitate persists permanently. Add 400 c.c. of a 50 
per cent solution of potassium hydroxide. This should be a clear solu- 
tion made by allowing it to settle. Dilute to a liter and, after allowing 
it to settle, decant. This should give the required color with ammonia 
within five minutes and should not give a precipitate with small amounts 
in two hours. 
Folin and Dennis’ Modified Nessler Reagent. Double iodide solu- 
tion is made by dissolving 75 gms. of potassium iodide in 500 ¢.c. of 
warm water, adding 100 gms. of mercuric iodide and stirring. The 
solution will be complete in a few minutes but possibly not quite clear 
on account of impurities. Dilute with 400 to 500 c.c. of water and make 
the filtrate up to a liter. 
To 300 c.c. of the double iodide solution add 200 c.c. of 10 per cent 
sodium hydroxide, 500 c.c. of water, and mix. Fifteen c.c. of this mod- 
ified Nessler reagent rapidly added from a measuring cylinder will 
yield crystal clear mixtures with as large amounts of ammonia nitrogen 
as are usually involved (0.7 to 1.6 mg. ammonia nitrogen). 
This has the advantage over the standard Nessler reagent that it 
may be used very soon after preparation and will not give a precipitate. 
For ‘standards ”’ a series of Nessler tubes is prepared by adding 
increasing amounts of the standard ammonium chloride solution and 
diluting with ammonia free water to the 50 c.c. mark. Standard 
methods recommends the following standards, 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 standards 
should be Nesslerized by adding 1 c.c. of Nessler solution to the tubes 
and allowing them to stand for 10-20 minutes. The sample whether 
Nesslerized directly or after distillation is treated the same way and 
compared with the standards. If the amount of ammonia is known to 
