OFFICIAL KJEXDAHL METHOD 363 



60.5X0.002211=0.13377. 



0.20783 o. 1 3377=0.07406. 



o.o74o6Xioo=7.4o6=per cent, nitrogen in sample when one 

 gram is used for the combustion. 



316. The Official Kjeldahl Method. Not Applicable in the 

 Presence of Nitrates. In order to determine if the sample con- 

 tains nitric acid or nitrates, apply the following test: 7 



Mix five grams of the fertilizer with 25 cubic centimeters of 

 hot water and filter. To a portion of this solution add two vol- 

 umes of concentrated sulfuric acid, free from nitric acid and 

 oxids of nitrogen, and allow the mixture to cool. Add cautiously 

 a few drops of concentrated solution of ferrous sulfate, so that 

 the fluids do not mix. If nitrates are present the junction shows 

 at first a purple, afterwards a brown color, or if only a very 

 minute quantity be present, a reddish color. To another por- 

 tion of the solution add one cubic centimeter of dilute solution of 

 nitrate of soda (three grams to 300 cubic centimeters) and test 

 as before to determine whether sufficient sulfuric acid was added 

 in the first test. 



Preparation of Reagents. (i) Acids. (a) Standard hydro- 

 chloric acid, the absolute strength of which has been determined 

 by precipitating with silver nitrate, and weighing the silver chlo- 

 rid as follows : 8 



To any convenient quantity of the acid to be standardized, 

 add a solution of silver nitrate in slight excess, and two cubic cen- 

 timeters of pure nitric acid, of specific gravity 1.2. Heat to 

 boiling-point, and keep at this temperature for some minutes 

 without allowing violent ebullition, constantly stirring until 

 the precipitate assumes the granular form. Allow to cool 

 somewhat, and then filter the fluid through asbestos. Wash 

 the precipitate by decantation, with 200 cubic centimeters of very 

 hot water, to which have been added eight cubic centimeters 

 of nitric acid and two cubic centimeters of dilute solution of silver 

 nitrate containing one gram of the salt in 100 cubic centimeters 

 of water. The washing by decantation is performed by adding 



7 Division of Chemistry, Bulletin 49, 1897 : 19. 



8 Division of Chemistry, Bulletin 46, Revised Edition, 1899 : 14. 



