QUANTITATIVE METHODS OF ANALYSIS 143 



with ammonia-free water, namely, o.o, o.i, 0.3, 0.5, 0.7, 

 i.o, 1.4? 1-7? 2.0, 2.5, 3.0, 3.5, 4.0, 4.5, 5.0, and 6.0. 



2. These will contain o.ox mg. of ammonia nitrogen for 

 each cubic centimeter of the standard solution used. 



3. Nesslerize the standards and also the distillates by 

 adding approximately 2 c.c. of Nessler's reagent to each 

 tube. 



4. Do not stir the contents of the tubes. 



5. After Nesslerizing, allow the tubes to stand for ten 

 minutes. 



6. Compare the color produced in these tubes with that 

 in the standards by looking vertically downward through 

 them at a white surface placed at an angle in front of a 

 window, so as to reflect the light upward. 



(4) Nitrates (Colorimetric) : 



1. Evaporate in a porcelain dish on a water-bath a 

 convenient quantity of unknown nitrate solution, depending 

 upon the amount of nitrate present, to dryness. 



2. When evaporated, add 2 c.c. of phenoldisulphonic acid 

 and stir with the rounded end of a glass rod for about ten 

 minutes so as to loosen the residue. 



Note. — ^Equations for the action of phenoldisulphonic acid on a nitrate: 



H2SO4 + 2KNO3 = 2HNOs + K2SO4 



C6H3(OH)(S03H)2 + HNO3 = C6H2(OH)(S03)2(N02) + H2O 



C6H3(OH)(S03H)2(N02) + 3NH4OH - 



C6H2(ONH4)(S020NH4)2N02 + 3H2O 



3. Dilute with water and add ammonia solution (strong 

 ammonium hydroxid diluted with an equal volume of water) 

 until alkahne ; a yellow color is formed. This is then diluted 

 to a known volume and compared with the standard. 



For example, take 500 c.c. of water to 100 grams of soil, 



