522 PHYSIOLOGICAL CHEMISTRY 



Procedure. To 25 c.c. of urine in a 200 c.c. Erlenmeyer flask add 15-20 

 grams of finely pulverized potassium oxalate, a few drops of phenolphthalein, 

 and titrate to a faint but permanent pink color with N/io NaOH. (The urine 

 mixture just after neutralization in the urinary acidity determination (see page 

 499) may be used.) Then add 10 c.c. of neutral formalin solution (see amino- 

 acid nitrogen), mix well and titrate with N/io sodium hydroxide to a permanent 

 pink color. 



Calculation. One c.c. of N/io sodium hydroxide is equivalent to 1.7 

 mg. of ammonia. Multiply the number of cubic centimeters of N/io alkali 

 used by 1.7 and by 4 to get the number of milligrams of ammonia + amino- 

 acid nitrogen (expressed as ammonia) in 100 c.c. of the urine examined. 



4. Permutit Method. 1 Principle. The urine is shaken with 

 particles of an " exchange silicate," which remove the ammonia from 

 solution. The ammonia is set free from the silicate by treating with 

 alkali solution. This is then Nesslerized and compared with a standard 

 ammonia solution treated in the same way. 



Procedure. Introduce about 2 gm. of permutit powder into a 200 c.c. volu- 

 metric flask. Add about 5 c.c. of water (no more), and with an Ostwald pipette 

 introduce i or 2 c.c. of urine, or with a 5 c.c. pipette introduce 5 c.c. of previously 

 diluted urine (corresponding to i or 2 c.c. of the original urine). With urines 

 very low in ammonia it may be necessary to use more urine (5 c.c.), but, in so 

 far as it is practicable, it is better not to use more than 2 c.c. and to employ 

 weaker standard (0.5 mg. of ammonia nitrogen) for the color comparison. 

 Rinse down the added urine by means of a little water (i to 5 c.c.), and shake 

 gently but continuously for 5 minutes. Rinse the powder to the bottom of the 

 flask by the addition of water (25 to 40 c.c.) and decant. Add water once more 

 and decant. (In the case of urines rich in bile it is advisable to wash once or 

 twice more.) Add a little water to the powder, introduce 2 c.c. of 10 per cent 

 sodium hydroxide, shake for a few moments and set aside, while preparing the 

 standard ammonium sulphate solution as follows : 



Transfer 10 c.c. of the standard ammonium sulphate solution (see p. 511) 

 containing i mg. of nitrogen to another 200 c.c. volumetric flask and add 2 c.c. 

 of 10 per cent sodium hydroxide (to balance the alkali added to the permutit 

 mixture in the other flask). Dilute to about 150 c.c. and mix. Transfer 20 c.c. 

 of Nessler's solution (see p. 517) to a measuring cylinder. Now give the volu- 

 metric flask a vigorous whirl so as to set the solution spinning within the flask 

 and add at once the whole of the Nessler solution in the cylinder. With another 

 whirling movement complete the mixing of the contents of the flask. If the 

 process of Nesslerization has been successful a deep red but crystal clear solu- 

 tion is obtained. If it is not perfectly clear throw it away and prepare a fresh 

 standard. Then dilute the contents of the flask containing the permutit and the 

 urinary ammonia to about 150 c.c., whirl the mixture and add the Nessler reagent 

 (20 c.c.) exactly as in the case of the standard solution. Dilute the contents 

 of both flasks to volume (200 c.c.) and compare in a colorimeter with the stand- 

 ard set at 20 mm. 



1 Folin and Bell: Jour. BioL Chem., 29, 329, 1917. 



