272 § 141. BEVEKAGES. 



slow current of carbonic acid tlirough it for a while, and 

 dry the residue for a considerable time at 150-180°. 



This determination of organic matter in water is con- 

 sidered by some good chemists as possessing no great value. 



h. Potassa* — The estimation of this in water used for 

 irrigation is sometimes important. For this purpose, 

 evaporate 2000-4000 c.c. of the water to dryness, elimi- 

 nate the silica in the usual way, and the alkalies as chlo- 

 rides in the filtrate from the silica (§ 93, G). 



c. Ammonia. — To determine this in rain-water, evapo- 

 rate 2000-3000 c.c. down to 200 c.c, after acidifying the 

 water very slightly with hydrochloric acid, add an excess 

 of freshly prepared sodic hydrate, or of baric hydrate, to 

 the residue, and distil the ammonia off in the usual man- 

 ner (§ 47, c). 



Detennine the ammonia in the distillate with the aid of 

 platinic chloride, or by the indirect process with the 

 Nessler solution. 



To insure greater accuracy, the whole operation should 

 be repeated without the water, and with the same amount 

 of sodic or bade hydrate and platinic chloride or Nessler's 

 solution ; if any ammonia is thus found, it is due to im- 

 purities in the reagents, and should be subtracted from 

 the amount obtained in the first experiment. 



If the water is a colored one, derived from some other 

 source, add calcic chloride, sodic carbonate, and a few 

 drops of potassic hydrate before distilling. 



d. Nitric Acid. — Evaporate 2000-4000 c.c. of the water, 

 after having added some sodic carbonate, filter out the 

 precipitate, if any is formed, wash it well, evaporate the 

 filtrate and washings to a small bulk, and determine the 

 acid by Schlossing's process (§ 62, «). 



e. Organic Matter.— Evaporate 100 c.c of the water 

 down to about 60 c.c, in a flask of 500 c.c capacity, in 

 order to decompose ammoniacal compounds by the calcic 



