CLASSIFICATION OF METHODS 433 



age and irrigation waters. The method, however, can hardly sur- 

 vive as an important one in such work in competition with more 

 modern, speedy and equally accurate processes of analysis. 



DETERMINATION OF NITRIC NITROGEN BY REDUCTION 



TO AMMONIA 



371. Classification of Methods. When nitrogen is present 

 in a highly oxidized state, e. g., as nitric acid, it may be quickly 

 and accurately estimated by reduction to ammonia. This action 

 is effected, among other ways, by the reducing power of nascent 

 hydrogen, and this substance may be secured in the active state 

 by the action of an acid or alkali on a metal, or by means of an 

 electric current. The processes depending on the use of a finely 

 divided metal in the presence of an acid or alkali have come into 

 general use within a few years, and are now employed generally 

 instead of the more elaborate estimations depending on the com- 

 bustion method by the use of copper oxid or in the colorimetric 

 method with indigo. 



The typical reaction which takes place in all cases is repre- 

 sented by the following equation : 



2HNO 3 +8H 2 =2NH 3 +6H 2 O. 



The method will be considered under three heads; viz., i. 

 Reduction in an alkaline solution ; 2. Reduction in an acid solu- 

 tion ; 3. Reduction by means of an electric current. 



In the first class of processes the reduction and distillation 

 may go on together. In the second class the reduction is accom- 

 plished first and the distillation effected afterwards, with the 

 addition of an alkali. In the third class of operations the reduc- 

 tion is accomplished by means of an electric current and the 

 ammonia subsequently obtained by distillation, or determined by 

 nesslerizing. These processes may be applied to the nitrates or 

 nitrites as such, or as occurring in rain and drainage waters 

 and soil extracts. On account of the ease with which the analyses 

 are accomplished, the short time required and the accuracy of the 

 results, the reduction methods for nitrates have already com- 

 mended themselves to analysts, and are quite likely to supersede all 

 others for practical use where small yet wefghable quantities of 



