URINE 501 



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 centimeters of 

 N/io sulphuric acid neutralized by the NH 3 of the urine, we have the following 

 proportion : 



y' : 100 : : y' Xo.ooiy :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 acidosis it may be very greatly increased, being excreted in com- 

 bination with hydro-oxybutyric and other acids. Values of 5 grams 

 have been noted. It is at the same time increased relative to total 

 nitrogen and urea. In pronounced liver disorders the same thing is 

 noted, as ammonia is not so completely transformed into urea before 

 excretion. 



2 . Micro -chemical Method of Folin and MacCallum. l Principle . 

 This method is a combination of the aeration procedure for ammonia 

 with its colorimetric determination by means of Nessler-Winkler solu- 

 tion. It gives satisfactory results, but is probably not as accurate as 

 the regular Folin procedure where the amount of substance for analysis 

 is not limited. 



Procedure. By means of Ostwald pipettes introduce 1-5 c.c. of urine 2 

 into a Jena test-tube (20-25 mm. by 200 mm.) and add to the urine a few drops 

 of a solution containing 10 per cent of potassium carbonate and 15 per cent of 

 potassium oxalate. To prevent foaming add a few drops of kerosene or heavy, 

 crude machine oil. Pass a strong air current (see page 487) through the mixture 

 until the ammonia has been entirely removed. 3 Collect the ammonia in a 100 

 c.c. volumetric flask containing about 20 c.c. of ammonia-free water and 2 c.c. 

 of N/io acid. 



Nesslerize as described in the method for total nitrogen, page 488, and com- 

 pare with i mg. of nitrogen obtained from a standard ammonium sulphate solu- 

 tion and similarly Nesslerized. 



It has been noted that a trace of something capable of giving a color with 

 the Nessler-Winkler solution continues to come long after all the ammonia 

 has been removed from the urine. The nature of this substance has not yet 

 been determined. In actual determinations by this method, the influence of 

 this unknown substance, because of the small volume of urine used, is entirely 

 negligible. 



1 Folin and MacCallum: Jour. BioL Chem., n, 523, 1912. 



2 The volume of urine taken should contain 0.75-1.5 mg. of ammonia nitrogen. With 

 normal urines 2 c.c. will generally yield the desired amount. With very dilute urines 5 c.c. 

 may be required, while with diabetic urines rich in ammonium salts i c.c. may be ejxeessive,. 

 thus requiring dilution. 



3 Ordinarily a period of ten minutes is sufficiently long. 



