METHODS FOR QUANTITATIVE DETERMINATIONS. 431 



It is customary to speak in water analysis of free ammonia and albuminoid 

 ammonia. By free ammonia is meant the ammonia present as ammonium 

 hydroxide, or more generally as an ammonium salt, chiefly carbonate. Albu- 

 minoid ammonia refers to the ammonia obtainable from nitrogenous matter 

 by oxidation with alkaline permanganate solution. 



The process for the determination of both kinds of ammonia is carried out 

 as follows: 500 c.c. of the water are placed in a flask of about one liter 

 capacity and 5 c.c. of a saturated solution of sodium carbonate are added. The 

 flask is connected with a suitable condenser whose outlet is so connected with a 

 receiver that no loss of ammonia can occur. Heat is then applied to the flask 

 until 300 c.c. have distilled over. To this distillate, containing all the " free 

 ammonia," is added enough pure water to restore the original volume of 500 

 c.c., and the distillate is s^t aside for Nesslerizing. 



To the liquid remaining in the distilling flask are now added 50 c.c. of an 

 alkaline permanganate solution (made by dissolving 8 gm. of KMnO 4 and 200 

 gm. KOH in water to make 1 liter), and distillation is resumed until 200 c.c. 

 have passed over, which distillate is also diluted to the original volume of 

 water used i. e., to 500 c.c. 



Both distillates, containing the free and the albuminoid ammonia respect- 

 ively, are now ready to be tested for ammonia by a method depending on 

 the intensity of color imparted to them by Nessler's reagent. This reagent 

 gives with highly diluted ammonia a color varying from pale straw-yellow to 

 brown. In order to have a standard for comparison of the colors, an empirical 

 solution of ammonium chloride is made, containing of this salt 3.137 gm. in 1 

 liter, corresponding to 1 mg. of NH 3 in each c.c. Just before use, 5 c.c. of this 

 solution are diluted with pure water to 100 c.c., of which 1 c.c. now contains 

 0.05 mg. NH 3 . 



To make the test there are required five small cylinders of colorless glass, 

 of about 30 m.m. diameter and about 100 m.m high, each having a mark at 50 

 c.c., and being numbered from 1 to 5. Into four of these cylinders are measured 

 0.5, 1, 1.5, and 2 c.c., respectively, of the standard ammonium chloride solu- 

 tion, and all are then filled with water up to the 50 c.c. mark. This makes the 

 contents of the four cylinders correspond to water containing 0.5, 1, 1.5, and 2 

 mg. of NH 3 per liter. 



Cylinder No. 5 is next filled with 50 c.c. of the water specimen prepared for 

 the ammonia determination, and to each of the five cylinders, standing on white 

 paper, is added 1 c.c. of ^essler's reagent (see index), which is well mixed with 

 the water. A comparison of the yellow color produced in the sample with that 

 of the cylinders 1 to 4, containing known quantities, will afford an estimate of 

 the quantity of ammonia in the water examined. 



Should the color of the specimen be deeper than that of cylinder No. 4, or 

 lighter than that of No. 1, then the experiment has to be repeated, the water 

 or the standard solution being diluted in definite proportions until similarity 

 of color is reached. The calculation is based on the dilution made. 



Of course, both distillates have to be treated in this manner. Great care 

 must be taken to make sure that the water, reagents, and apparatus used in 

 the operation are absolutely free from ammonia. When only free ammonia is 

 to be determined the distillation can be dispensed with. If the water should 

 contain any considerable quantity of calcium salts, these must be precipitated 



