QUALITATIVE AND QUANTITATIVE ANALYSIS 67 



The proper amount of standard acid should be measured 

 into flasks connected to the distillation shelf prior to adding 

 the alkali. 



Distill slowly. After the first 15 minutes the flame may be 

 raised, but never so high that the distillate collects in the con- 

 densing bulbs. Generally the first two-thirds of the original 

 volume recovered as distillate will contain all the ammonia. 



The distillate is now titrated with standard alkali, using 

 methyl-red or any other convenient indicator. From the cubic 

 centimeters of standard acid neutralized by the distillate the 

 weight of nitrogen liberated as ammonia is calculated. 



Methyl-red Indicator. — Dissolve 1 gram of methyl red in 50 

 cubic centimeters of 95 per cent alcohol and dilute to 100 cubic 

 centimeters with water. Filter if the solution is turbid. 



The percentage of nitrogen should be reported on the dry basis 

 of the soil. 



A. Quantitative Methods for Determination of Total 

 Nitrogen Including Nitrates 



Follow the same method as described under Quantitative 

 Methods for Total Nitrogen Determination, except for the use of 

 salicylic acid and sodium thiosulphate during digestion. 



Add to the substance to be analyzed in a Kjeldahl flask, 10 

 cubic centimeters of sulphuric acid with salicylic acid (1 gram in 

 30 cubic centimeters of sulphuric acid) ; shake until thoroughly 

 mixed and allow to stand 5 or 10 minutes, with frequent shaking. 



Now add 10 grams of sodium thiosulphate and heat the solu- 

 tion gently for 5 minutes, then bring to boiling for 5 minutes; 

 cool; add 0.5 gram of copper sulphate and mercuric oxide and 

 boil. This reduces the danger of foaming. Heat gently until 

 SO3 fumes begin to come off. Cool. Add 15 cubic centimeters of 

 the salicylic — sulphuric acid reagent, making in all 25 cubic centi- 

 meters of acid in each flask. 



Heat very gently until foaming ceases, then heat strongly until 

 colorless. Continue boiling for 2 hours after substance is color- 

 less. The entire process requires 5 to 6 hours. 



Follow the directions as given in Quantitative Methods for 

 Total Nitrogen Determination. 



