322 AGRICULTURAL ANALYSIS 



after the oxidation of the other constituents; viz., carbon and 

 hydrogen, originally present. 



In the second class of methods the nitrogen is converted into 

 ammonia, which is absorbed by an excess of standard acid, the 

 residue of which is .determined by subsequent titration with a 

 standard alkali. There are two distinct processes belonging to 

 this class, in one of which ammonia is directly produced by dry 

 combustion of an organic nitrogenous compound with an alkali, 

 and in the other ammonium sulfate is produced by moist com- 

 bustion with sulfuric acid, and the salt thus formed is subse- 

 quently distilled with an alkali and the free ammonia resulting 

 therefrom estimated as above described. Nitric nitrogen may 

 also be reduced to ammonia by nascent hydrogen either in an 

 acid or alkaline solution. 



In the third class of determinations is included the estimation of 

 nitric nitrogen by colorimetric methods. These processes have 

 little practical value in connection with the analyses of com- 

 mercial fertilizers, but find their chief use in the detection and 

 estimation of extremely minute quantities of nitrites and nitrates. 

 In the following paragraphs will be given the standard methods 

 for the determination of nitrogen in practical work with fertiliz- 

 ing materials and fertilizers, and also the methods for the esti- 

 mation of minute quantities of ammoniacal and nitric nitrogen. 



281. Determination of the State of Combination. Some of 

 the sample is mixed with a little powdered soda-lime. If am- 

 moniacal nitrogen be present free ammonia is evolved even in 

 the cold and may be detected either by its odor or by testing 

 the escaping gas with litmus or turmeric paper. A glass rod 

 moistened with strong hydrochloric acid will produce white 

 fumes of ammonium chlorid when brought near the escaping 

 ammonia. 



If the sample contain any notable amount of nitric acid it will 

 be revealed by treating an aqueous splution of it with a crystal 

 of ferrous suifate and strong sulfuric acid. The iron salt should 

 be placed in a test-tube with a few drops of the solution of the 

 fertilizer and the sulfuric acid poured down the sides of the tube 

 in such a way as to run under and not to mix with the other 



