URINE 335 



mated. Of the various recent modifications of the urease 

 method this is perhaps the best suited for use in a large class 

 unless exceptional laboratory facilities are available. 



The apparatus required is identical with that described in the 

 Folin ammonia determination above. 



Measure about 50-60 c.c. of distilled water into the tall cylin- 

 der. Add 1 gin. of finely powdered soy bean (jack bean con- 

 tains a more active urease), 5 c.c. of urine from a pipette, and 

 kerosene or liquid paraffin to prevent foaming. Connect with a 

 receiving bottle containing 50 c.c. of tenth normal acid accu- 

 rately measured and two drops of alizarine red. Stand the 

 cylinder in vessels containing water at 35-40 C. The water 

 in the outside vessel should be kept at this temperature by the 

 addition of hot water as required. Run an air current through 

 the series to drive the liberated ammonia into the acid bottle 

 where it will be absorbed. As the air from the compressed air 

 tap may contain traces of ammonia it should be run through 

 10% sulphuric acid washing bottles before being run into the 

 urine cylinder. After about an hour, disconnect the cylinder 

 and add about a gram of anhydrous sodium carbonate to the 

 urine. Connect again and run the air current for another hour. 

 Titrate the excess of acid in the acid bottle with N/10 NaOH. 

 Subtracting this value from the total amount of acid used will 

 give the amount of acid neutralized by the liberated ammonia. 

 Calculate the weight of nitrogen liberated from the volume of 

 urine used and from this, the amount present in the total 24-hour 

 specimen. This value represents the amount of nitrogen pres- 

 ent as urea + ammonia. Subtract the value found above for 

 ammonia. The result will be the amount of nitrogen present 

 as urea. Calculate the per cent of the total nitrogen which is 

 present as urea. 



37b. Colorimetric Method for Determination of Urea in 

 Urine. (Folin: Jour. Biol. Chem., xxvi, 501, 1916; xxxviii, 

 111, 1919). 



Merck's blood charcoal was a necessary reagent in the deter- 



