APPENDIX F 

 DETERMINATION OF AMMONIA 



For most bacteriological work witli soils the ammonia is best de- 

 termined after distillation with magnesium oxide. The analytical 

 material is placed in a Kjeldahl or other flask suitable for distilling. 

 Magnesium oxide is added to liberate the ammonia, and some shav- 

 ings of paraffin to prevent frothing. The distilling flask is connected 

 with a suitable condenser, the lower end of which dips into a meas- 

 ured amount of deei-normal acid in an Erlenmeyer flask. 



Distillation is continued for a period varying with the amount of 

 ammonia present, usually until 50 ce. or more of distillate has been col- 

 lected. A few drops of methylrot or of cochineal are added, and the dis- 

 tillate is titrated with deci-normal alkali. The difference between the 

 amount of alkali required to bring the solution to neutrality and the 

 amount of acid taken represents the amount of ammonia distilled over. 

 This difference multiplied by .0017 gives the grams of NH^ obtained. 



If the amount of ammonia is small, it is better to use the well- 

 known Nessler reaction, as used in water analysis. The solutions 

 for analysis must, however, be clear and colorless. Nessler's reagent 

 is an alkaline solution of mercuric potassium iodide. The alkali of 

 the reagent liberates the ammonia from its salts ; if the concentration 

 of the latter is considerable, a precipitate is formed, but if dilute, 

 the compound remains in solution, giving a yellow color. The inten- 

 sity of the color thus produced is proportional to the amount of 

 ammonia present and is compared with that of a dilute standard 

 ammonium chloride solution similarly treated. The substituted am- 

 monias give a similar precipitate and color with this reagent, and 

 in some lines of work it might be necessary to take this fact into 

 consideration. 



REAGENTS REQUIRED ' 



1. Ammonia-free water. This may be prepared by redistilling the 

 water of the laboratory after acidifying slightly with sulphuric acid. 

 For colorimetric purposes it may be quickly prepared by adding 



1 Adapted from Schreiner and Failyer, Bulletin No. 31, Bureau of Soils, U.S. 

 Dept. Agr., 1906. 



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