rV] WATERS 37 



NITROGEN IN THE FORM OF NITRITE.— OFFICIAL. 



12 REAGENTS. 



(a) Concentrated hydrochloric acid. — Sp. gr. 1.2. 



(b) Sulphanilic acid solution. — Dissolve 1 gram of sulphanilic acid in 100 cc. of 

 hot water. 



(C) Alpha-naphthylamin hydrochlorid solution. — Boil 0.5 gram of the salt with 

 100 cc. of water for 10 minutes at constant volume. 



(d) Standard nitrite solution. — Dissolve 1.1 gram of silver nitrite in nitrite-free 

 water, precipitate the silver with sodium chlorid solution and dilute to 1 liter, mix 

 and allow to settle. Dilute 100 cc. to 1 liter and then 10 cc. of this solution to 1 

 liter, using in each case nitrite-free water. Each cc. of the last solution is equivalent 

 to 0.0001 mg. of nitrogen as nitrite. 



1 3 DETERMINATION. 



Place 100 cc. of the water in a 100 cc. Nessler tube and treat with 1 or 2 drops of 

 concentrated hydrochloric acid. Add 1 cc. of the sulphanilic acid, 1 cc. of the alpha- 

 naphthylamin hydrochlorid, and thoroughly mix. Set aside for 30 minuteswith other 

 Nessler tubes containing known amounts of the standard nitrite made up to 100 cc. 

 with nitrite-free water, and treated with hydrochloric acid, sulphanilic acid, and 

 alpha-naphthylamin hydrochlorid in the manner just described. Determine the 

 amount of nitrite by comparing the depth of pink color in the known and unknown 

 solutions. Record as nitrogen in the form of nitrite. 



NITROGEN IN THE FORM OF NITRATE. 



Phenoldisulphonic Acid Method. — Official. 

 (For water of low chlorin content.) 



14 REAGENTS. 



(a) Phenoldisulphonic acid solution. — Dissolve 25 grams of pure white phenol in 

 150 cc. of concentrated sulphuric acid, add 75 cc. of fuming sulphuric acid (13-15% 

 SOs) and heat at 100°C. for 2 hours. 



(b) Standard nitrate solution. — Dissolve 0.722 gram of pure potassium nitrate in 

 1 liter of nitrate-free water. Evaporate 50 cc. of this solution to dryness in a porce- 

 lain dish; treatwith2cc.of the phenoldisulphonic acid solution, rubbing with a glass 

 rod to insure intimate contact. Dilute to 500 cc. ; 1 cc. is equivalent to 0.01 mg. of ni- 

 trogen as nitrate. This solution is permanent. Standards for comparison are pre- 

 pared by adding ammonium hydroxid to measured volumes of it in 100 cc. Nessler 

 tubes. 



(C) Standard silver sulphate solution. — Dissolve 4.3969 grams of silver sulphate, 

 free from nitrate, in 1 liter of water; 1 cc. is equivalent to 1 mg. of chlorin. 

 (d) Ammonium hydroxid. — Sp. gr. 0.90. 



15 DETERMINATION. 



Take 100 cc. of the sample, or an amount that will contain 0.05 mg. or less of 

 nitrogen as nitrate, and add standard silver sulphate, precipitating all but about 

 0.5 mg. of the chlorin. Heat to boiling, allow to settle, or add a little alumina cream, 

 filter, and wash with small amounts of hot water. Evaporate the filtrate to drynes* 

 in a porcelain dish on the water bath; when cool, treat with 2 cc. of the pheuoldieul- 

 phonic acid solution as in 14 (b). Dilute with water and add slowly ammonium hy- 



