142 SOIL BACTERIOLOGY 



4. Erlenmeyer flasks of good quality should be used to 

 collect the distillate. 



5. The apparatus for this work differs from the usual 

 Kjeldahl stand in that a jet of steam is passed directly 

 into the distilling flask. It is so arranged that the rubber 

 stopper for the Kjeldahl flask has two holes, one for the 

 condensing bulb and one for the steam tube. Steam is 

 allowed to bubble slowly through the solution in the bottom 

 of the Kjeldahl flasks. In order to hasten the analysis a 

 very low flame should be kept under the distilling flask. 

 The period of distillation will vary with the amount of 

 ammonia present. As a rule, one hour is long enough to 

 drive off all ammonia nitrogen. 



6. If methyl-red is used as an indicator, the distillate 

 should be boiled for a few minutes, cooled to 15 or 20 C., 

 about 5 drops of methyl-red added, and the solution titrated. 



7. The distillate is titrated with standard alkali, and 

 from the cubic centimeters of standard acid neutralized by 

 the distillate the weight of nitrogen liberated as ammonia 

 is calculated. 



(3) Ammonia (Nesslerization). Ammonia-free Water. 

 This is readily prepared by adding sodium hydroxid and 

 potassium permanganate to laboratory water and redistil- 

 ling. Discard the first portion of the distillate. After 

 about one-fourth of the water has been evaporated, the 

 subsequent distillate will be free of ammonia. . 



Standard Ammonium Chlorid Solution. Dissolve 3.82 

 grams of ammonium chlorid in 1000 c.c. of distilled water; 

 dilute 10 c.c. of this to 1000 c.c. with ammonia-free water. 

 One c.c. equals o.oi mg. of nitrogen. 



i. Prepare a series of sixteen Nessler's tubes which con- 

 tain the following number of cubic centimeters of the 

 standard ammonium chlorid solution, dilute to 50 c.c. 



