URINE 519 



water. Extract and expel the air from urine and water. Then introduce i c.c. of 

 sodium hypobromite 1 solution. The mercury is lowered to the 50 c.c. mark and 

 apparatus is then shaken vigorously for about half a minute. The aqueous solution 

 is collected in the proper chamber below the lower stopcock, mercury is admitted to 

 the 50 c.c. chamber, and after adjusting the pressure, the volume of nitrogen is read. 

 This is reduced to standard conditions, and correction is made for air in the hypo- 

 bromite solution. Between 15 and 2oC. the correction is 0.006 c.c., and between 

 21 and 25C., it is 0.005 c - c - The corrected volume is then transformed into 

 grams of nitrogen, using gas reduction tables in Chapter IV. 



Ammonia 



. I. Folin's Method. Principle. The ammonia of the urine is set 

 free by the addition of an alkali and this ammonia is then carried over 

 by an air current into a flask containing a measured amount of standard 

 acid. The excess acid is then titrated. The necessity for distillation 

 is avoided. 



Procedure. Place 25 c.c. of urine in an aerometer cylinder, 30-40 cm. in 

 height (Fig. 167, below), add about i gram of dry sodium carbonate and introduce 

 some crude petroleum to prevent foaming. Insert into the neck of the cylinder a 

 rubber stopper provided with two perforations, into each of which passes a glass 

 tube, one of which reaches below the surface of the liquid. The shorter tube 

 (10 cm. in length) is connected with a calcium chloride tube filled with cotton, and 

 this tube is in turn joined to a glass tube extending to the bottom of a 500 c.c. 



FIG. 167. FOLIN AMMONIA APPARATUS. 



wide-mouthed flask which is intended to absorb the ammonia and for this pur- 

 pose should contain 20 c.c. of N/io sulphuric acid, 200 c.c. of ammonia-free 

 distilled water and a few drops of an indicator (alizarin red or Congo red). To 

 insure the complete absorption of the ammonia the absorption flask is provided 

 with a Folin improved absorption tube (Fig. 168), which is very effective in 



x Made by mixing equal volume of two solutions, one containing 12.5 gm. sodium 

 bromide and 12.5 gm. bromine per 100 c.c., and the other 28 gm. of NaOH per 100 c.c. 



