60 PUBLIC HEALTH CHEMISTRY 



Process. Take a Kjeldahl flask (a 200 c.c. flask with 

 a round bottom, and made of fire-resisting glass), pipette 

 into it 10 c.c. of sewage or 25 c.c. of the effluent. Add 

 1 c.c. of strong sulphuric acid, mix well, and evaporate 

 slowly over a small flame guarded with wire gauze. When 

 the fluid is reduced to very small bulk, add 5 grm. 

 potassium sulphate, and 20 c.c. strong sulphuric acid. 

 Heat over a small Bunsen flame, very slowly at first, until 

 all frothing ceases. Continue heating for about two 

 hours, or until the liquid is colourless and clear. Then 

 cool the flask and contents, and carefully transfer the 

 liquid to a 700 c.c. boiling-flask, washing the small flask out 

 repeatedly with ammonia-free distilled water, and adding 

 the washings to the large flask, making up the bulk to 

 about 200 c.c. Now add sufficient strong KOH solution 

 to neutralize the excess of acid, and some extra to make 

 alkaline. Add a few pieces of granulated zinc to prevent 

 bumping, connect with a Kjeldahl's safety bulb and con- 

 denser, and distil over the ammonia into N/i sulphuric 

 acid, the end of the tube from the special condenser dipping 

 under the surface of 20 c.c. of the N /i acid in an Erlenmeyer 

 flask. About 100 c.c. are distilled over, slowly. There- 

 after the acid is titrated with N/i NaOH, using methyl- 

 orange as indicator. The number of c.c. of soda required 

 deducted from the number of c.c. of normal acid used (20) 

 gives the number of c.c. of normal acid neutralized by 

 the ammonia distilled over. Each c.c. of normal acid is 

 chemically equivalent to 0-014 grm. of N. The organic 

 N is got by deducting from the result obtained the amount 

 previously found to be present as free and saline ammonia. 

 (When this process is applied to food stuffs, this correction 

 is not necessary.) 



The rationale of the process is that the organic matter 

 is broken up by the acid and sulphate, and the nitrogen 

 converted into ammonia, which is fixed by the excess of 

 acid as ammonium sulphate. On adding excess of KOH, 

 the ammonia is liberated, and is then distilled over. It is 

 received into N/i sulphuric acid, forming again ammonium 

 sulphate. The amount of acid left unneutralized is then 

 estimated, and by difference the amount combined with 

 the ammonia. 



