CH. XIII.] 



AMMONIA. 



331 



Into C measure 20 cc. of standard sulphuric acid (about o-i N.) 

 and a few drops of methyl red. 



Into B measure 25 cc. of urine, add 5 or 6 drops of caprylic 

 alcohol (to prevent foaming) and 2 grams, of anhydrous sodium 

 carbonate. Connect up the apparatus at once, and draw air through 

 for two hours. 



Disconnect the apparatus, wash the tube E with distilled water 

 into C, and titrate with CO 2 - free sodium hydroxide (about o-i N.). 



Calculation. Determine the percentage of nitrogen in the form of 

 ammonia as described for Kjeldahl's method, p. 323. The result thus obtained 

 is the mgms. of ammonia-nitrogen in 25 cc. 



To convert this to grams, of ammonia per cent. , multiply by 



4 x x = '4 86 (lg- 3-6864). 



To find the ammonia in terms of cc. of o-i N. acid per cent., multiply the 



10 

 mgms. of ammonia-nitrogen in 25 cc. by 4 x = 2-86 (log. '45 60 )- 



399. Van Slyke's method. 



Principle. 5 cc. of urine are made strongly alkaline with potassium 

 carbonate, which decomposes the ammonium salts. The ammonia liberated 

 is driven over by an air current into a measured amount of standard acid, 

 which is subsequently titrated with standard alkali. The treatment of urine 

 at room temperature with potassium carbonate does not lead to the formation 

 of ammonia from urea, etc., as does boiling with caustic soda. 



Apparatus. This is shewn in fig. 44.* A is a wash bottle containing 



To pump 



C-- 



F..-.\ 



Fig. 44. Apparatus for estimation ol ammonia and urea by Van Slyke's 



methods. 



* This can be obtained from Messrs. Baird and Tatlock (Ltd.), 14, Cross 

 Street, Hatton Garden, London, E.G. 



