WATER ANALYSIS 47 



NITRITES AND NITRATES IN WATER. 



Ammonia present in water, derived either from the 

 decomposition of organic matter or by synthesis from urea, 

 tends in its passage through the soil to become oxidized, 

 first into nitrites, then into nitrates. Nitrates, however, 

 may be present in water which has dissolved it out of strata 

 through which it has passed. Sometimes these nitrates 

 become reduced, first to nitrites, then to ammonia, and this 

 has been specially observed as due to iron salts in the ferrous 

 state. In the London basin, the deep-well waters from the 

 " greensands " strata have been noted as yielding ammonia 

 thus derived. Waters polluted with vegetable matter yield 

 little nitrites and nitrates relatively, as plant life removes 

 these, and vegetable matter contains little nitrogen. 



Nitrites. 



Qualitative Tests. 



i. Starch Iodine Test. Take 50 c.c. of sample water in a 

 Nessler glass and 50 c.c. distilled water in another. To 

 each add a few drops of KI solution and a few drops of 

 freshly-made starch solution. Now add a few drops of 

 dilute sulphuric acid to each tube. The presence of 

 nitrites is indicated by an immediate blue colour. 



2. Naphthylamine Test. Take two Nessler glasses as above 

 and acidulate with acetic acid. Add to each a few drops of 

 naphthylamine solution in sulphanilic acid. With nitrites 

 a beautiful pink colour develops in two to three minutes. 



Quantitative Tests. 



Griess's Test. Solutions required : 



a. Metaphenylene-diamine solution, 5 grm. per litre, 

 slightly acidulated with sulphuric acid, decolorized by 

 boiling with pure animal charcoal. 



b. Sulphuric acid, one part of strong acid to two parts 

 of aq. dest. 



c. Standard nitrite solution. This is made from silver 

 nitrite because it is the most stable salt. AgNO 2 +KCl = 

 AgCl + KNO 2 . 154 parts of silver nitrite, when treated 

 with KG, give rise to 85 parts of KNO 2 , or 46 parts of 

 nitrous acid as represented by N0 2 , or 308 parts are 

 equivalent to 76 parts of N 2 3 . Hence, if 308 /y6 = 4-06 



