WATER ANALYSIS 51 



Required : (i) Thin aluminium foil ; (2) 10 per cent 

 solution NaOH. 



PROCESS. Take 100 c.c. of the water sample and 100 c.c. 

 of the NaOH solution in a 300 c.c. boiling-flask. Add a 

 piece of aluminium foil about 1-5 inch square. Cover but 

 do not cork. Set aside for six hours at least. Then 

 connect the flask to a condenser and distil over the ammonia 

 into 50 c.c. Nessler glasses, collecting three lots. The 

 amount of ammonia is determined by comparison of the 

 coloration developed in these glasses by adding to each 

 2 c.c. Nessler's solution, and that developed in glasses 

 containing 50 c.c. ammonia- free distilled water, plus i c.c., 



2 c.c., and 3 c.c. respectively of standard NH 4 C1 (i c.c. 

 = o-oi mgr. NH 3 ), and similarly treated. The amount 

 estimated by this method includes ammonia present in 

 the sample, ammonia derived from nitrites, and ammonia 

 derived from nitrates. The two former are separately 

 estimated and deducted, and the remainder is the amount 

 derived from nitrates, and is readily converted back into 

 terms of NO 3 or of N. 



EXAMPLE. 100 c.c. gave ammonia equal to 40 c.c. of 

 standard AmCl = 40 x o-oi = 0-4 mgr. NH 3 . But the 

 water contained 0-006 mgr. of free and saline ammonia 

 per 100 c.c., and 0-042 mgr. N as nitrites per 100 c.c. = 

 0-042 x 17 -f- 14 = o - o5iNH 3 per 100 c.c. Hence, 0-4 - 

 (0-006 + 0-051) = 0-343 mgr. NH 3 due to nitrates = 0-282 

 mgr. N as nitrates per 100 c.c. or 100,000 mgr. 



Copper-Zinc Couple Method. This method is similar in 

 principle to the above. A bright piece of thin zinc foil, 



3 in. x 2 in., is cleansed with dilute sulphuric acid. It is 

 then rolled into a coil, so that it may fit into a 200 c.c. 

 wide-mouthed bottle. Now immerse the coil for three 

 minutes in a 3 per cent solution of copper sulphate. . The 

 zinc becomes coated with a black deposit of metallic 

 copper. Remove the coil carefully, wash in ammonia-free 

 distilled water, wash in sample water, and then immerse 

 in no c.c. of sample water contained in a wide-mouthed 

 bottle. Stopper tightly, place in a cool dark place for 

 twenty-four hours. The " Copper-zinc couple " acts 

 electrically on the sample, changing any nitrates present 



