520 



PHYSIOLOGICAL CHEMISTRY 



causing the air passing from the cylinder to come into ultimate 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 absorption apparatus to the one just 

 described is attached to the other side of the aerometer cylinder, thus insur- 

 ing the passage of ammonia-free air into the cylinder. With an ordinary filter 

 pump and good water pressure the last trace of ammonia should be removed 

 from the cylinder in about one and one-half hours. 1 The number of cubic 

 centimeters of the N/io sulphuric acid neutralized by the ammonia of the 

 urine may be determined by direct titration with N/io sodium hydroxide. 



Steele 2 has suggested a modification for use on urines containing 

 triple phosphate sediments. In this modification 0.5-1 .o gram of NaOH 

 and about 15 grams of NaCl are substituted for the Na2COs of the Folin 

 method. The use of sodium hydroxide and chloride instead of carbo- 

 nate has also been recommended by other workers 3 as a general pro- 

 cedure, inasmuch as triple phosphate crystals are almost always formed 

 on adding sodium carbonate and these are decomposed with some 

 difficulty by sodium carbonate but readily by the hydroxide. It 

 has not been shown that the use of sodium hydroxide in this manner 



brings about the decomposition of any other urinary 



nitrogen compounds. 



Calculation. Subtract the number of cubic centimeters 

 of N/io sodium hydroxide used in the titration from the 

 number of cubic centimeters of N/io sulphuric acid taken. 

 The remainder is the number of cubic centimeters of N/io 

 sulphuric acid neutralized by the NH 3 of the urine. One 

 c.c. of N/io sulphuric acid is equivalent to 0.0017 gram of 

 NH 3 . Therefore if y represents the volume of urine used 

 in the determination and y' the number of cubic centi- 

 meters of N/io sulphuric acid neutralized by the NH 3 of 

 the urine, we have the following proportion : 



y':ioo::y' X 0.0017 :x (percentage of NH 3 in the urine 

 examined). 



Calculate the quantity of NH 3 in the 24-hour urine 

 specimen. 



Interpretation. The average daily output of 

 ammonia in the urine is about 0.7 gram, amounting 

 to 2.5-4.5 per cent of the total nitrogen excretion. 

 It is increased by the ingestion of acids or acid-forming foods and 

 decreased by the ingestion of alkalis or base-forming foods. In acid- 



1 With any given filter pump a "check" test should be made with urine or, better, with a 

 solution of an ammonium salt of known strength to determine how long the air current must 

 be maintained to remove all the ammonia from 25 c.c. of the solution. 



2 Steele: Jour. Biol. Chem., 8, 365, 1910. 



3 Benedict and Osterberg: Biochem. Bull., 3, 41, 1913. 

 Shulansky and Gies: Biochem. Bull., 3, 45, 1913. 



FIG. 1 6 8. FOLIN 

 IMPROVED ABSORP- 

 TION TUBE, 



