444 AGRICULTURAL ANALYSIS 



The flask is covered during the reduction to prevent loss by 

 spraying. It must be noted that it is essential that the iron be 

 finely divided ; it is mixed with the powdered zinc in equal parts. 



The total nitrogen can be determined in guanos and nitrate 

 mixtures by the following simple alteration in procedure: One 

 gram of the substance is dissolved in water, five cubic centimeters 

 of glacial acetic acid, and from two to three grams of the mixed 

 metallic powder added, and the whole gently heated for 10 or 15 

 minutes. After the contents of the flask have cooled, 25 cubic 

 centimeters of sulfuric acid are cautiously added in small portions, 

 undue frothing being restrained by the addition of a fragment 

 of paraffin wax. The acetic acid is driven off by heating, and the 

 remaining contents of the flask boiled until the organic matter is 

 completely decomposed as in the kjeldahl process. About two 

 hours boiling is required. Neutralization and distillation are ac- 

 complished as in the ordinary manner. The method is also ap- 

 plicable to the determination of nitrates in drinking water, provid- 

 ed nitrites and ammonia be absent. 



383. Method of Ulsch. In practice the method of Ulsch has 

 come into general use. 66 



For the determination of nitrogen in nitrates by this method 

 half a gram of saltpeter or four-tenths gram of sodium nitrate 

 is dissolved in 25 cubic centimeters of water, in a flask with a 

 content of about 600 cubic centimeters. Five grams of iron re- 

 duced by hydrogen, and 10 cubic centimeters of sulfuric acid 

 diluted with two volumes of water are then added to the flask. 

 To avoid mechanical losses during the evolution of hydrogen, a 

 pear-shaped glass stopper is hung in the neck of the flask. After 

 the first violent evolution of hydrogen has passed, the flask is 

 slowly heated until, in about four minutes, it is brought to a gentle 

 boil. The boiling is continued for about six minutes when the 

 reduction is complete. About 50 cubic centimeters of water are 

 added, an excess of soda-lye and a few particles of zinc ; then the 

 ammonia is distilled and collected in standard acid in the usual 

 way. 



The method of Ulsch can also be applied, according to Fricke, 

 86 Chemisches Central-Blatt, 1890, 2 : 926. 



