A STANDARD FOR THE DETERMINATION OF 



AMMONIA BY MEANS OF NESSLER 



SOLUTION 



ANTON R. ROSE and KATHERINE R. COLEMAN 

 {Research Laboratory, Fenton B. Turck, M.D., Director, New York City} 



The determination of nitrogen is one of the most frequent and 

 valuable Operations for the investigation of substances and processes 

 of animals and plants. The method of Kjeldahl has been a tool o£ 

 inestimable value to the biological chemist and it has had compara- 

 tively few hmitations in his hands. There are times, however, when 

 the available amount of material for analysis is so small that the 

 chemist resorts to the method grudgingly or must perforce omit it 

 entirely. This Hmitation has now been removed by the modifica- 

 tions of FoHn and his pupils, whereby the Operation can be con- 

 ducted on relatively minute quantities. 



For the measurement of the ammonia produced by the Kjeldahl- 

 Gunning digestion, Fohn^ uses the Nessler-Winkler Solution, so 

 familiär in sanitary laboratories. To match the colors produced 

 by the ammonia from the substance examined, and from the stand-« 

 ard ammonium sulfate, the Duboscq colorimeter is employed. The 

 method appealed to the workers in this laboratory, where the de-" 

 termination of the nitrogen distribution in small samples has been 

 an impending trouble. We trust that part of our experience with 

 it, which we now publish, may be of assistance to other beginners in 

 the application of this promising method. 



There are several procedures in making up the Nessler reagent. 

 The results of all these may be the same, but the one selected has 

 been adhered to throughout in order to obviate all chances of 

 further Variation. The reagent is prepared as follows: 62.5 gm. of 

 potassium iodid are dissolved in 250 c.c. of water, to which is added 

 a saturated sol. of mercuric chlorid, with stirring until a permanent 



ipolin and Farmer: Jour. Biol. Chem., 191 1, ix, p. 493; Folin: Ibid., pp. 

 507-525. 



407 



