THE EXAMINATION OE WATER 657 



They are also the final products of completely oxidized organic 

 nitrogenous matter. 



Test (i). 



Fill a large test-tube with the sample. 



Add a few c.c. of diphenylamine solution. 



Pour concentrated H2SC)4 carefully down the side of the tube. 



A blue ring at tiie junction of the two licfuids = nitrates. 



Test (2) 



Repeat the above using a solution of brucine in H2SO4. 

 A red ring is formed ^\hicll turns yellow, then brown. 

 Both these tests are given ^\ilh nitrites also, hence nitrites should 

 be excluded or Test (3) applied, which does not react with nitrites. 



Test (3). 



Evaporate 50 c.c. of the water to dryness in a water bath. 



Add I c.c. of phenolsulphonic acid. 



]\Iix well Avith a glass rod. 



Heat on a water bath for one minute. 



Transfer the fluid to a 100 c.c. Nessler glass, washing the basin and 

 rod with water, adding same to the glass. 



Add 10 c.c. of concentrated ammonia. 



Stir and make up to 100 c.c. with distilled water and shake. 



A yellow coloration denotes nitrates. 



By this method the nitrates are converted into picric acid. 

 The ammonia forms ammonium picrate which has an intense yellow 

 colour. 



To Estimate. 



Method (i). 



Retain the above yellow fluid and match it. 



Take 5 c.c. of the standard KXO3 solution (i c.c. = o"oooi 



grm. N). 

 Evaporate to dryness and treat it exactly as the above solution. 

 There are now two cylinders of yellow fluid that are not of 

 similar tints. 



Suppose the Sample is the darker of the tzvo Solutions. 



Pour out some of the darker, say 15 c.c, and make up the 



85 c.c. to 100 c.c. with distilled water. 

 If now too dark pour out more, say 10 c.c, and make up the 



90 c.c. to 100 c.c with distilled water. 

 Suppose the tints now coincide we get : — 



looj^oo X 00005 X loo.ooo _ J. ^^^^ ^ ^^ j^ijj.^^fg . 100,000. 



85 X 90 X 50 ^' ^ ^ 



