URINE 521 



osis it may be very greatly increased, being excreted in combina- 

 tion with hydroxy butyric 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 FolinandMacCallum. 1 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 nun, 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 519) 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 510, 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. 



3. Formol Titration Method (Malfatti). 4 Principle. This method 

 is based on the reaction taking place when formalin solution is 

 added to a solution containing ammonium salts (see Amino-acid 

 Nitrogen, below). An acid reaction is produced in the mixture, 

 which is then titrated with standard alkali using phenolphthalein as 

 an indicator. Amino-acids give the same reaction so that the. result 

 of the titration represents ammonia + amino-acid nitrogen. This 

 method may be used for the rapid clinical estimation of these forms of 

 nitrogen as a substitute for an ammonia determination, but the results 

 do not represent ammonia as is sometimes stated. 



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



* 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 exces- 

 sive, thus requiring dilution. 



1 Ordinarily a period of ten minutes is sufficiently long 



4 Malfatti: Z. anal. Chem., 47, 273, 1908. 



