DETERMINATION OF AMMONIA 383 



as well as absolutely, determined. Such a case would be presented 

 for instance, in that of a fertilizer containing dried blood, sodium 

 nitrate, and ammonium sulfate. It is evident here that the total 

 nitrogen could be determined by the volumetric method by com- 

 bustion with copper oxid, or by the moist combustion process 

 adapted to nitric nitrogen, but the method of determining the 

 percentage of each constituent has not yet been described. 



We have to deal here with a case entirely similar to that of 

 phosphoric acid in a superphosphate. There is no doubt what- 

 ever of the uneven assimilability of the different forms of nitro- 

 gen. A nitrate, for instance, is already in condition for assimi- 

 lation by plants. An ammoniacal salt is only partly changed to 

 a state suited to plant nutrition, while organic nitrogen is forced 

 to undergo a complete transformation before it becomes available 

 to supply the needs of the growing plant. It is important, there- 

 fore, equally to the analyst, the merchant and the agronomist, 

 to know definitely the forms of combination in which the nitrogen 

 exists and the relative proportion of the different combinations. 



334. Nitrogen as Ammonia. The most frequent form in 

 which nitrogen as ammonia is used for fertilizing is as sulfate. 

 The method of determination to be described is, however, equally 

 applicable to all ammonia salts. When no other form of nitrog- 

 enous compound is present the ammonia can be easily and di- 

 rectly determined by distillation with soda- or potash-lye, as de- 

 scribed in the final part of the moist combustion process. 



335. Determination of Ammonia. To one gram of the am- 

 monia salt add from 200 to 300 cubic centimeters of water and 

 30 grams of the soda-lye used in the moist combustion process ; 

 distil, collect the ammonia, and titrate the excess of sulfuric acid 

 exactly as there described. 



Fresenius recommends that the ammonia expelled by distilla- 

 tion be taken up by a standard solution of sulfuric (hydrochloric, 

 oxalic) acid, the excess of which is titrated with a standard solu- 

 tion of soda or other alkali, using litmus as an indicator. 28 If the 

 distillate, on examination, be found to contain thiocyanate, soda- 

 M Chemical Quantitative Analysis, Cohn's Translation, from the 

 Revised 6th German Edition, 1904, 1 : 254. 



