ORGANIC MATTER AND AMMONIA 217 



fitted with a rubber stopper through which passes a 2 c.c. 

 pipette (Fig. 29). 



(b) Standard Ammonia Solution. — Two solutions are 

 generally prepared — (i) a stock solution, I c.c. of which 

 contains i mg. of ammonia, and (2) a solution for use 

 in the tests, i c.c. containing o-oi mg. of ammonia. 

 For the former of these 3- 1 5 grams of freshly sublimed, 

 pure ammonium chloride are dissolved in ammonia- 

 free water, and the solution made up to i litre at 

 15-5° C. The second is prepared by accurately measur- 

 ing out 10 C.C. of this solution and diluting to I litre 

 with ammonia-free water, care being taken that the 

 temperature during the measurements is 15.5° C. 



{c) Ammonia-free water for the tests can be prepared 

 from ordinary tap-water by first adding 10 c.c. of 10 per 

 cent, sodium carbonate solution to a litre of water and 

 then distilling from a flask connected with a Liebig's con- 

 denser. The distillate should be rejected until 50 c.c. 

 no longer give a yellow coloration with 2 c.c. of 

 Nessler reagent, after standing for a few minutes. A 

 portion of the remaining water is then distilled into a 

 clean bottle, but the distillation should not be carried 

 too far, as the latter fractions are liable to contain 

 ammonia. 



{d) Alkaline Potassium Permanganate Solution. — 

 This reagent is prepared by dissolving 8 grams of 

 crystallised potassium permanganate and 200 grams of 

 stick potash in 1-5 litres of water. The solution is 

 boiled vigorously in an open dish until about two-thirds 

 of its original volume, and is then allowed to cool and 

 transferred to a bottle. 



Estimation of Am monia. 

 212. Apparatus. — The distillation apparatus may be 

 fitted up as shown in Fig. 30. The distilling flask should 



