36 METHODS FOR THE ANALYSIS OF URINE 



is also required. The ferric chloride can scarcely be considered 

 indispensable; but it hastens the digestion, and the iron hydroxide 

 promotes even boiling during the subsequent distillation. 



TOTAL NITROGEN 



Folin-Farmer Microchemical Method * 



Principle. This method belongs with the so-called micro- 

 chemical methods inasmuch as it is adapted to the determination 

 of amounts of nitrogen in the neighborhood of 1 mg. while in the 

 ordinary Kjeldahl procedure 30 to 100 mg. of nitrogen are gen- 

 erally manipulated. One c.c. of diluted urine is decomposed with 

 sulphuric acid as in the Kjeldahl method, the ammonia formed 

 is set free by the addition of alkali and carried over into an acid 

 solution by means of a current of air. The ammonia solution is 

 then treated with the Nessler-Winkler reagent and the color pro- 

 duced compared with that of a standard solution of an ammonium 

 salt treated in the same way. 



Procedure. Introduce 5 c.c. of urine into a 50 c.c. volumetric 

 flask if the specific gravity of the urine is over 1018, or into a 

 25 c.c. flask if the specific gravity is less than 1018. Fill the 

 flask to the mark with distilled water and invert it several times 

 in order to guarantee thorough mixing. Transfer 1 c.c. of the 

 diluted urine to a large (20 to 25 mm. X 200 mm.) Jena-glass 

 test-tube. Add to this 1 c.c. of concentrated sulphuric acid, 

 1 gm. of potassium sulphate, 1 drop of 5 per cent copper sulphate 

 solution and a small, clean, quartz pebble or glass bead. (The 

 pebble or bead is added to prevent bumping.) Boil the mixture 

 over a micro-burner for about six minutes, i.e., about two minutes 

 after the mixture has become colorless. Allow to cool until 

 the digestion mixture begins to become viscous. This ordinarily, 

 takes about three minutes, but in any event the mixture must not 

 be permitted to solidify. Add about 6 c.c. of water (a few drops 

 at a time, at first, then more rapidly) to prevent solidification. 

 To this acid solution add an excess of sodium hydroxide (3 c.c. 

 of a saturated solution is sufficient) and aspirate the liberated 

 ammonia by means of a rapid air current into a volumetric flask 

 (100 c.c.) containing about 20 c.c. of ammonia-free water and 2 c.c. 

 1 Folin and Farmer: Jour. Biol Chem., 1912, 11, 493. 



