WATER ANALYSIS 49 



PROCESS. Take 100 c.c. of sample in a Nessler glass, and 

 in another the same quantity of aq. dest. and i c.c. standard 

 nitrite solution. To each add 2 c.c. of each of the above 

 solutions, a and b. Set aside for five minutes and then 

 compare tints. If not equal in tint, abstract some fluid 

 from the darker by pipette and make up the bulk with 

 aq. dest. If the colours still do not match, more fluid is 

 removed, and bulk made up as before. Suppose sample 

 is darker, and that 40 c.c. are removed, and bulk made up ; 

 and that again, 30 c.c. are removed, when finally tints 

 match. Then we get : 100 x 60/100 x 70/100 = 42 c.c. 

 of the original 100 c.c. match i c.c. of standard nitrite 

 solution, say i c.c. = o-oi mgr. N : then 42 c.c. of sample 

 contain o-oi mgr. N, and therefore 100 c.c. will contain 

 o-oi x 100 -=- 42 = 0-023 m g r - N, or 0-023 P a rt of N 

 as nitrite per 100,000 parts. 



The nitrites first act on the sulphanilic acid and form 

 a new compound which reacts with the naphthylamine 

 and forms the substance which gives the pink colour to 

 the liquid. 



A water containing nitrites is not safe for domestic use, 

 and should be rejected on that evidence alone, unless 

 unexceptionable in all other respects. 



Nitrates. 



QUALITATIVE TESTS. 



i. Brucine Test. Take 5 c.c. of sample and add 5 c.c. of 

 bmcine solution (i in 1000), then mix, and pour carefully 

 down the side of the test tube some pure, strong sulphuric 

 acid, free from nitrates, when a positive result is denoted 

 by the appearance of a pink ring at the junction of the 

 liquids on gentle shaking. The test is also performed by 

 evaporating 10 c.c. of sample to dryness in a clean porcelain 

 basin, then adding a crystal of brucine, and then allowing 

 one drop of pure sulphuric to run down the side of the 

 dish, over the solids ; when in the presence of nitrates 

 a pink is obtained. Detects 0-7 part per 100,000. 

 Unreliable in the presence of nitrites, which should be 

 first destroyed by addition of urea and sulphuric acid to 

 sample ; allow to stand aside for an hour, when test can 

 be applied as before. 



4 



