446 AGRICULTURAL ANALYSIS 



ammonia. Tests were made after boiling for 30 minutes and 

 traces of ammonia were still found ; after 40 minutes these traces 

 entirely disappeared. 



The method is a quick one. One man can easily do six deter- 

 minations at a time, and these six determinations can be made 

 in but a little over an hour. Magnesia gives results closely agree- 

 ing with theory and causes a very slight frothing, which can be 

 easily controlled. One gram of reduced iron is sufficient in all 

 ordinary complete fertilizers. 



Magnesia is preferred to caustic soda in the distillation be- 

 cause it produces less frothing and by reason of the danger of 

 some of the soda-lye being carried over mechanically and thus 

 tending to produce an error of a plus nature. In the use of mag- 

 nesia, assurance must be had that it is strongly in excess. Being 

 less active in its effects, a longer time for the distillation must 

 be taken than when soda-lye is used. The modified ulsch method 

 just described is recommended provisionally, and with the expec- 

 tation that each analyst will ascertain its true merits before allow- 

 ing it to displace longer approved processes. 



385. Kruger's Method for Nitric Acid. About 0.3 gram of 

 the nitrate dissolved in water is mixed with 20 cubic centimeters 

 of a hydrochloric acid solution of stannous chlorid holding 150- 

 grams of tin per liter. 69 One and a half grams of spongy tin 

 prepared by the action of zinc on stannous chlorid are added. 

 The flask containing the mixture is heated until the tin is dis- 

 solved, by which time the nitric acid is completely reduced. The 

 subsequent distillation and titration are accomplished as usual. 

 In the case of nitro and nitroso compounds, after the solution of 

 the tin, 20 cubic centimeters of sulfuric acid are added and 

 heated until sulfuric vapors escape. After cooling, the amido 

 substances formed are oxidized by potassium bichromate before 

 the distillation takes place. 



Kriiger also estimates the nitrogen in benzol, pyridin, and 



chinolin derivatives by dissolving them in sulfuric acid, using 



from 0.2 to 0.8 of a gram of the alkaloidal bodies, and, after 



cooling the solution, oxidizing by adding finely powdered potas- 



<* Berichte der deutschen chemischen Gesellschaft, 1894, 27 : 609, 1636. 



