QUANTITATIVE METHODS OF ANALYSIS 145 



2. Replace the water driven off in heating. 



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

 alloy (about 60 mesh) and connect the flask with the 

 distilling apparatus. 



4. The distillation should not be hurried. 



5. Allow the solution to boil for thirty to sixty minutes. 

 (6) Total Nitrogen Without Nitrates: 



Sulphuric acid N/14 



Sodium hydroxid N/14 



Sulphuric acid (concentrated). 



Potassium or sodium sulphate. 



Copper sulphate. 



Pumice powder. 



Sodium hydroxid (50 per cent.)- 



1. Place the substance to be analyzed in a Kjeldahl 

 flask (the amount for analysis will depend on the nitrogen 

 content); if soil is used, about 10 grams. 



2. Add 5 grams of powdered potassium sulphate or 

 sodium sulphate, 0.5 gram copper sulphate, 30 to 40 c.c. 

 of sulphuric acid, and mix thoroughly. It is important 

 that the substance be thoroughly moistened by the sulphuric 

 acid before heating. 



3. Place the flask on the digestion shelf under a hood and 

 heat slowly until frothing ceases. Avoid a very high 

 flame; do not allow the flame to touch the flask above the 

 part occupied by the liquid. If sugar is present, for ex- 

 ample, mannit agar culture, the acid mixture will foam 

 very badly. In order to prevent any loss it is well to heat 

 very slowly until all foaming has ceased. Sometimes this 

 requires one hour or more. 



4. Now raise the heat (avoid a very hot flame) until 

 the acid boils rapidly. 



5. Digest for thirty minutes after the acid mixture is 



10 



