KJELDAHL NITROGEN METHOD 241 



25 c.c. N/10 acid. To make the alkali exactly N/10 it should 

 be diluted in the ratio of 23.2 :25. 



Measure the total volume of your alkali in a large cylinder 

 (first returning any of the solution remaining in the burette) 

 and calculate the amount of water necessary to dilute it to 

 tenth normal alkali. Add this amount of water from a cylinder, 

 shake well and allow to stand for a few minutes. 



Kinse out the burette with the diluted alkali, and repeat the 

 titration against standard acid. 



If your alkali does not check with the standard acid, correct 

 it again by adding the calculated amount of water, or the cal- 

 culated amount of sodium hydrate if the solution has been 

 made too dilute. 



Preserve your tenth normal solution for future use. 



8. Kjeldahl Method for Nitrogen Determination. 



This method is of utmost importance and is widely used for 

 estimating total nitrogen. The various nitrogen compounds 

 are broken down by heating with concentrated sulphuric acid, 

 the nitrogen being converted into ammonia, and the carbon into 

 carbon dioxide. The ammonia is retained in the solution as 

 (NH 4 ) 2 S0 4 . It then is liberated by the addition of sodium 

 hydrate and distilled into a known volume of N/10 hydrochloric 

 or sulphuric acid. The excess of N/10 acid is then determined 

 by titration and the amount of ammonia calculated. 



In analyzing liquids it is customary to use 5 or 10 c.c., ac- 

 cording to the nitrogen content. If the material is a solid, 1 

 gram accurately weighed is the usual amount. 



With a pipette measure 5 c.c. urine into a 500 c.c. Kjeldahl 

 flask. Add 8-10 g. potassium sulphate which raises the boiling 

 point, 15 c.c. of concentrated H 2 S0 4 and 2 c.c. of 5% copper 

 sulphate which acts as a catalyser. 



Heat the flask in an inclined position over a small flame until 

 the contents become clear and pale green. There must be no 

 suggestion of yellow and no black specks of unoxidized carbon 

 anywhere in the liquid or on the inner surface of the flask. If 



