PHYSIOLOGICAL CHEMISTRY. 



hydroxide and distil about 40 minutes into an excess of standard 

 acid. Complete the process as described under the Kjeldahl method 

 (p. 381 ). Subtract the original ammonia content of the urine from 

 the total ammonia content (ammonia -j- urea) as determined by the 

 Kjeldahl method. 



V. Ammonia. 



i. Folin's Method. Place 25 c.c. of urine in an aerometer cylin- 

 der, 30-40 cm. in height (Fig. 122, below), add about one gram of 

 dry sodium carbonate and introduce some crude petroleum to pre- 

 vent 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. wide-mouthed flask which is 

 intended to absorb the ammonia and for this purpose should con- 

 tain 20 c.c. of Y\J- sulphuric acid, 200 c.c. of distilled water and a few 

 drops of an indicator ("alizarin red"). To insure the complete 

 absorption of the ammonia the absorption flask is provided with a 



FIG. 122. 



FOLIN'S AMMONIA APPARATUS. 



Folin improved absorption tube (Fig. 123, p. 381) which is very 

 effective in causing the air passing from the cylinder to come into 

 intimate contact with the acid in the absorption flask. In order to 

 exclude any error due to the presence of ammonia in the air a similar 



