QUANTITATIVE METHODS OF ANALYSIS 147 



thirds of the original volume recovered as distillate will 

 contain all the ammonia. 



14. The distillate is now titrated with standard alkali, 

 and from the cubic centimeters of standard acid neutralized 

 by the distillate the weight of nitrogen liberated as am- 

 monia is calculated. 



15. This should be reported as percentage of nitrogen 

 on the dry basis. 



(7) Total Nitrogen with Nitrates Present: 



Same as for (6); in addition: 

 Salicylic acid. 

 Sodium thiosulphate. 



1. Add to the substance to be analyzed in a Kjeldahl 

 flask 35 to 40 c.c. of sulphuric acid with salicylic acid 

 (i gram in 30 c.c. of sulphuric acid); shake until thoroughly 

 mixed and allow to stand five or ten minutes, with frequent 

 shaking. 



2. Now add 5 grams of crystallized sodium thiosulphate 

 and heat the solution gently for five minutes, then bring to 

 boiling for five minutes; cool; add 0.5 gram of copper 

 sulphate and boil. This reduces the danger of foaming. 



3. Heat very gently until foaming ceases, then heat 

 strongly until colorless. Continue boiling for thirty 

 minutes after the substance is colorless. The entire 

 process requires five to six hours. 



4. Cool and add about 200 c.c. of distilled water. 



5. Cool again, and add a few pieces of granulated zinc or 

 pumice powder to keep the contents of the flask from bump- 

 ing during distillation. 



6. Next add 100 c.c. or more of strong soda solution 

 sufficient to make the reaction strongly alkaline, pouring it 

 down the sides of the flask so that it does not mix at once 

 with the acid. 



