290 PHYSIOLOGICAL CHEMISTRY 



In accurate work, a blank determination should be made to 

 estimate the amount of nitrogen in the reagents used. 



4. Ammonia. 



(a) Folin Air Current Method. The most satisfactory 

 method for determining ammonia in urine is that of Folin. 

 This consists in measuring a given volume of urine into a tall 

 cylinder (B) fitted with a two hole rubber stopper. Through 

 one hole passes a glass tube reaching to the bottom of the 

 cylinder for the admission of compressed air. Through the 

 second hole a glass tube leads into a receiving flask (C) pro- 

 vided with a Folin absorption tube. In this flask is placed a 

 measured volume of N/10 acid, and enough distilled water to 

 cover the holes in the Folin absorption tube. The ammonia is 

 liberated from the urine by adding solid sodium carbonate. 



Into the receiving flask measure 20 c.c. N/10 acid and add 

 two drops of alizarine red. Add enough distilled water to 

 well cover the bell of the Folin absorption tube. Into the tall 

 cylinder measure 25 c.c. of urine. Cover with a thin layer of 

 kerosene to prevent foaming. Make sure that all connections 

 are tight and everything in readiness to start the air current. 

 The compressed air should be run through 10% H 2 S0 4 to 

 remove possible ammonia. Add about 1 gm. of anhydrous 

 sodium carbonate to the urine and stopper the cylinder at once. 

 Pass a fairly rapid stream of air through the apparatus, being 

 careful not to blow the contents of the cylinder into the acid 

 bottle. A loose plug of cotton may be introduced in the path 

 of the air passing from urine to acid by including a calcium 

 chloride tube in the circuit. This will prevent the blowing 

 over of any particles of carbonate. Run the air current for 

 iy 2 hours. Disconnect the acid container, rinse and remove the 

 Folin absorption tube, and titrate the remaining acid with N/10 

 alkali. 



Subtract the volume of alkali used in titration from the 

 original volume of N/10 acid. The result is the amount of N/10 

 acid neutralized by the ammonia. One cubic centimeter of N/10 



