36 METHODS OF ANALYSIS [Chap. 



250 cc. to dryness in a weighed platinum dish. Heat to constant weight at 105**C. 

 In the case of highly mineralized waters it is advisable to weigh again after drying 

 at 180°C. 

 g SUSPENDED MATTER.— OFFICIAL. 



(1) The difference between the values for total solids and dissolved solids rep- 

 resents the suspended matter; or, (2) Determine the suspended matter directly by 

 filtering a suitable quantity of the water through a tared Gooch crucible, suitably 

 prepared, and weighing after drying at 105°C. 



9 IGNITED RESIDUE.— OFFICIAL. 



Ignite the residue from 6 at a low red heat until the ash is white or nearly so. 

 Note any odor or change in color produced during ignition. Record the weight 

 of the ignited residue and calculate the loss on ignition. 



FREE AND ALBUMINOID AMMONIA.— OFFICIAL. 



10 REAGENTS. 



(a) Saturated solution of sodium carbonate. 



(b) Ammonia-free water. 



(C) Standard ammoriium chlorid solution. — One cc. is equivalent to 0.01 mg. of 

 nitrogen in the form of ammonia (NH3). 



(d) Nessler reagent. — Dissolve 50 grams of potassium iodid in aminimum quantity 

 of cold water. Add a saturated solution of mercuric chlorid until a slight perma- 

 nent precipitate is formed. Add 400 cc. of 50% solution of potassium hydroxid (or 

 an equivalent quantity of sodium hydroxid), dilute to 1 liter, allow to settle, and 

 decant. 



(e) Alkaline potassium permanganate solution. — Dissolve 200 grams of potassium 

 hydroxid and 8 grams of potassium permanganate in water and dilute to 1 liter. 



11 



DETERMINATION. 



Connect a flask of about 1500 cc. capacity with an upright bulb condenser by 

 means of a rather large glass tube and a soft rubber stopper or a recently extracted 

 cork stopper. Place in the flask 5 cc. of the saturated solution of sodium carbonate 

 and 500 cc. of ammonia-free water. Distil into 50 cc. Nessler tubes until no further 

 traces of ammonia are indicated on the addition of 2 cc. of the Nessler reagent to 

 50 cc. of the distillate. Continue the distillation until the volume of the solution 

 in the flask has been reduced to about 200 cc. Cool slightly, add 500 cc. of the water 

 under examination, and distil, at the rate of 1 tubeful in 15 minutes, into 50 cc. 

 Nessler tubes until ammonia ceases to be given off' (4 or 5 tubes are usually sufficient). 

 Add 2 cc. of the Nessler reagent to each tube and let stand 10 minutes. Freshly 

 prepare in a similar manner other tubes containing known amounts of the standard 

 ammonium chlorid, made up to 50 cc. with ammonia-free water, and compare the 

 nesslerized distillates with these. Report as milligrams per liter of nitrogen in the 

 form of free ammonia (NHj). Cool the flask and add 50 cc. of the alkaline perman- 

 ganate recently boiled. Distil, at the rate of 1 tubeful in 15 minutes, into 50 cc. 

 Nessler tubes until ammonia ceases to come off. Nesslerize and compare as in the 

 determination of free ammonia. Report as milligrams per liter of nitrogen in the 

 form of albuminoid ammonia (NHj). 



