METHODS OF ANALYSIS. 21 



or five jars are usually necessary. These jars are nesslerized and the 

 depth of color compared with that in other jars containing known 

 amounts of a standard ammonium chlorid solution (0.01 mg of NH 3 in 

 each cubic centimeter), made up to 50 cc with ammonia-free water and 

 nesslerized in the same manner. 



TOTAL AMMONIA. 



The same apparatus is used as that mentioned in the preceding para- 

 graph. In it are placed 200 cc of distilled water and 50 cc of alkaline 

 permanganate solution (prepared by dissolving 200 grams of potassium 

 hydroxid and 8 grams of potassium permanganate in 1,250 cc of water 

 and boiling the whole down to about 1 liter). The water is distilled 

 off in 50 cc Nessler jars until ammonia ceases to come over. Five hun- 

 dred grams of the water under examination are now added and the dis- 

 tillation continued until ammonia ceases to come off. Six jars are in 

 most cases sufficient. These jars are nesslerized and compared with 

 nesslerized jars of known strength just as in the determination of free 

 ammonia. From the total ammonia thus found subtract the free 

 ammonia and the result is the albuminoid ammonia in 500 cc of water. 



Many precautionaiy details of the two above methods are not given, 

 but can be found by consulting any good work on water analysis. 



OXYGEN-CONSUMING CAPACITY. 



In making this determination two solutions were prepared: (1) A 

 standard solution of potassium permanganate containing 0.3952 gram 

 to the liter, each cubic centimeter of which has 1 mg of ox}^gen 

 available for oxidation; and (2) a standard solution of oxalic acid con- 

 taining 0.7875 gram of crystallized oxalic acid to the liter. The value 

 of the oxalic acid in terms of the permanganate is determined by boil- 

 ing 10 cc of oxalic acid solution and 200 cc of distilled water with 10 cc 

 of sulphuric acid (1 to 3) and titrating the fluid while boiling with 

 the standard permanganate solution to the appearance of a pink 

 color. In the actual determination 200 grams of the water in a porce- 

 lain dish are treated with 10 cc of sulphuric acid (1 to 3) and the whole 

 brought to the boiling point. Standard permanganate is run in until the 

 water is quite red and the boiling continued for ten minutes, adding 

 permanganate every now and then to keep the pink color about the 

 same. The boiling is now stopped, 10 cc of oxalic acid run in, which 

 destroys the color, and the solution titrated with the standard perman- 

 ganate to the appearance of a pink color. From the total number of 

 cubic centimeters of permanganate used subtract the number of cubic 

 centimeters equal to 10 cc of oxalic acid. The result gives the number 

 of cubic centimeters of permanganate required for 200 grams* of water. 



