QUALITATIVE AND QUANTITATIVE ANALYSIS 65 



take 10 cubic centimeters for a standard. Evaporate to dryness 

 in a porcelain dish on a water bath and treat as described on p. 

 64. Make up volume to 100 cubic centimeters. This standard 

 is equal to 0,1 milligram of nitrogen as nitrate. 



Determination of Nitrates by the Reduction Method 



Prepare an aqueous extract of the soil, peat or decomposing 

 organic matter which is to be analyzed. Extract 50 or 100 

 grams of the material three to six times with water and filter 

 through a folded paper, so as to collect 250 cubic centimeters of 

 solution. This solution is collected into a 500-cubic centimeter 

 Kjeldahl flask. 



Add 5 cubic centimeters of a 50 per cent solution of sodium 

 hydroxide and distill over an open flame, until about 100 to 150 

 cubic centimeters have been driven over. 



Replace the water driven off in heating. 



When cool, add 2 grams of finely divided Devarda's alloy 

 (about 60-mesh) and connect flask again with distilling apparatus. 



Boil carefully for 30 to 60 minutes and collect the distillate in 

 a definite volume of standard acid solution. 



Titrate the solution with standard alkali and calculate the 

 nitrate-nitrogen distilled over as ammonia. 



By this method one can determine both ammonia and nitrate 

 in soil, in peat, in manure, or in other organic composts. For 

 this purpose the original extract is made with 4 per cent KCl 

 solution instead of water. The first distillate will give the 

 ammonia present (collected in standard acid solution) and the 

 second distillate the nitrate. 



QUANTITATIVE METHODS FOR DETERMINATION OF TOTAL 



NITROGEN 



Sulphuric acid A''/14 



Sodium hydroxide ^ A^/14 



Sulphuric acid (concentrated) 



Potassium or sodium sulphate 



Mercuric oxide or metallic mercury 



Copper sulphate 



Pumice powder or zinc powder free of nitrogen 



Sodium hydroxide (40 per cent) 



Place a 10-gram sample of soil in a dry Kjeldahl flask of 800- 

 cubic centimeters capacity. 



