URINE 



487 



comparisons may be made directly with a series of colored standards of 

 varying strengths made up in exactly similar test-tubes or small flasks. 



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 loiS. 1 Fill the flask to the mark with distilled water and 

 invert it several times in order to guarantee thorough mixing. Transfer i c.c. 2 

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

 Add to this i c.c. of concentrated sulphuric acid, i gram of potassium sulphate, 

 i drop of 5 per cent copper sulphate solution and a small, clean, quartz pebble or 



FIG. 154. FIG. 155. 



FIGS. 154 AND 155. FORMS OF APPARATUS USED IN METHODS OF FOLIN AND ASSOCI- 

 ATES FOR DETERMINATION OF TOTAL NITROGEN, UREA AND AMMONIA. (From Jour. Biol. 

 Chem. vol. n, 1912.) 



glass bead. (The pebble or bead is added to prevent bumping.) Boil the mix- 

 ture over a micro-burner 3 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 4 



1 The purpose is to so dilute the urine that i c.c. of the diluted fluid shall contain 0.75- 

 i .5 mg. of nitrogen. 



2 This measurement should be made by means of a modified Ostwald pipette (see Ost- 

 wald-Luther: Physiko-Chemische Messungen, 2d. ed., p. 135). Such pipettes may be 

 obtained from Eimer and Amend, New York. 



3 A type of burner which has proven satisfactory is Eimer and Amend's No. 2587. 



4 Either a vacuum pump or compressed air or a force pump may be used. The com- 

 pressed air method is rather the more convenient inasmuch as the ammonia may be col- 

 lected directly in a volumetric flask. Inasmuch as the necks of such flasks (100 c.c.) are 



