164 HEALTHY URINE. 



From which again the quantity in 24 hours is easily 

 obtained. 



NOTE. The nitrogen evolved in the above process is not all derived from urea 

 in urine, but comes also from uric acid and creatinine. This is practically 

 balanced by a loss of N from the urea, which remains in the alkaline solution in 

 the form of nitrate, and partly as an unknown organic compound which gives off 

 ammonia when distilled with alkali. 



Estimation of the total Nitrogen in Urine by Kjeldahl's 

 process. There are three steps in the process : 



A. Incineration. Namely, decomposition of the nitrogenous 

 material by means of strong sulphuric acid, whereby ammonium 

 sulphate is formed. This contains all the nitrogen. 



B. Distillation. The ammonia is liberated by the addition of 

 an excess of caustic soda, and is distilled over into a measured 

 quantity of standard acid, a part of which it will neutralise. 



C. Titration. The unneutralised portion is measured with 

 standard alkali, and thereby the quantity which has been 

 neutralised by the ammonia becomes known. From this the 

 quantity of nitrogen is readily calculated. 



Reagents required : 



1. Sulphuric acid, strong pure, 15 g - 



2. Potassium sulphate, dry, 10 g - 



3. Sulphate of copper, dry, 0*5 g> 



4. Caustic soda solution, 25 p - c -, boiled with zinc shavings 

 to free it from nitrates. 



1ST 1ST 



5. - NaOH solution. Dilute stock - solution with 



9 volumes of distilled water. 



. 



6. Y7rH 2 SO 4 . Dilute stock solution with 9 volumes 



of distilled water. 



7. Methyl orange. 1 : 1000 solution. 



8. Powdered talc. Half a teaspoonful. 



