5 



PHYSIOLOGICAL CHEMISTRY 



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

 height (Fig. 163, p. 499), 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. 

 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 im- 

 proved absorption tube (Fig. 164), which is very effec- 

 tive 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 am- 

 monia in the air a similar absorption apparatus to the one 

 just described is attached to the other side of the aerom- 

 eter cylinder, thus insuring 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. 



FIG. 164. 

 IMPROVED ABSORP- 

 TION TUBE. 



Steele 2 has suggested a modification for use on 

 urines containing triple phosphate sediments. In 

 FOLIN this modification 0.5-1.0 gram of NaOH and 

 about 15 grams of NaCl are substituted for the 

 Na 2 C0 3 of the Folin method. The use of sodium 

 hydroxide and chloride instead of carbonate has also been recom- 

 mended by other workers 3 as a general procedure, inasmuch as triple 

 phosphate crystals are almost always formed on adding sodium car- 

 bonate 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 sul- 

 phuric 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 



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. 



