URINE 337 



tent. The pyrophosphate-phosphoric acid mixture, the prepara- 

 tion of which is described above, gives a faint color with rosalic 

 acid. Five c.c. when titrated with tenth normal alkali and 

 phenolphthalein should give a faint but distinct color with 

 about 18 c.c. of the alkali. 



Transfer with an Ostwald pipette 1 c.c. of diluted urea solu- 

 tion or urine (dilution sometimes 5 or 20, but usually 10 c.c. 

 diluted to 100 c.c.) to a clean test tube; add 1 or at the most 

 2 drops of buffer mixture and 1 c.c. of urease solution. Digest 

 in a beaker of warm tap water (40 to 55 C.) for 5 minutes 

 or at room temperatures for 15 minutes. At the end of the 

 digestion period rinse the contents of the test tube into a 200 

 c.c. volumetric flask and dilute to a volume of about 150 c.c. 



Transfer 1 mg. of N in the form of ammonium sulphate to 

 another 200 c.c. volumetric flask; to this standard add 1 c.c. 

 of urease solution and dilute to about 150 c.c. Then add with 

 shaking (with a cylinder) 20 c.c. of Nessler solution to each. 

 Dilute to volume and make the color comparison, never omitting 

 to first read the standard against itself. 



The height of the standard (usually 20 mm.) divided by the 

 height of the unknown, gives the nitrogen, in mg., present in 

 the fraction of a c.c. of undiluted urine present in the 1 c.c. 

 of diluted urine taken for the analysis. 



Unless the colorimetric reading is between 14 mm. and 30 mm. 

 the determination should be repeated with 1 c.c. of urine so 

 diluted as to give readings coming within those limits. Calcu- 

 late the total urea-N and subtract the preformed ammonia-N. 



38. Uric Acid. 



Folin-S chaffer Method. Phosphates and some organic ma- 

 terial are first precipitated and filtered off. The uric acid is 

 then precipitated as ammonium urate, and titrated with N/10 

 potassium permanganate. 



To 200 c.c. of urine in a beaker, add 50 c.c. of Folin-Schaf- 

 fer reagent (50% ammonium sulphate, 0.5% uranium acetate 

 and 0.5% acetic acid). Allow to stand for % hour and filter 

 through a dry filter. Measure out 125 c.c. of the filtrate (cor- 



