PHYSIOLOGICAL CHEMISTRY 



which may be obtained in this country (see page 297). For merely 

 approximate determinations the color comparisons may be made 

 directly with a series of colored standards of varying strengths made 

 up in exactly similar test-tubes or small flasks. Myers 1 has suggested 

 a satisfactory form of test-tube instrument (see Fig. 162). 



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 ioi8. 2 Fill the flask to the mark 

 with distilled water and invert it several times in 

 order to guarantee thorough mixing. Transfer i c.c. 3 

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

 Jena-glass test-tube. Add to this i c.c. of concen- 

 trated sulphuric acid, i gram of potassium sulphate, 

 i 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 4 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 hi 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 5 into a volumetric flask (100 c.c.) contain- 

 ing about 20 c.c. of ammonia-free water and 2 c.c. 

 of N/io hydrochloric acid (see Figs. 163 and 164, 

 page 511). The air current should be only moder- 

 ately rapid for the first two minutes but at the end 

 of this two-minute period the current should be run 

 at its maximum speed for an interval of eight minutes. 



Disconnect the flask, dilute the contents to about 60 c.c. with ammonia- 

 free water and dilute similarly i mg. of nitrogen hi the form of ammonium sul- 



^Myers: Jour. Lab. and Clin. Med. i, 178, 1916. 



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

 1.5 mg. of nitrogen. 



3 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. 



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



6 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 

 not large enough to permit of the use of a two-hole rubber stopper when suction is used, 

 the ammonia should be collected in one of the Jena test-tubes previously described which 

 contains 2 c.c. of N/io hydrochloric acid and about 5 c.c. of ammonia-free water. The am- 

 monium salt is then transferred to the volumetric flask with 40-50 c.c. of water and Nes- 

 slerized as described. 



FIG. 162. Myers Test- 

 tube Colorimeter. From 

 Myers, "Practical Chemical 

 Analysis of Blood," St. 

 Louis, 1921. 



