EXPERIMENT STATION. 23 



EXPLANATION OF FEETILTZER-ANALTSIS AND VALUATION. 



Nitrogen is commercially the most valuable fertilizing element. 

 It occurs in various forms or states. Organic nitrogen is the 

 nitrogen of animal and vegetable matters generally, existing in 

 the albumen and fibrin of meat and blood, in the uric acid of bird 

 dung, in the urea and hippuric acid of urine, and in a number of 

 other substances. Some forms of organic nitrogen, as that of 

 blood and meat, are highly active as fertilizers ; others, as that of 

 hair and leather, are comparatively slow in their effect on vegeta- 

 tion unless these matters are reduced to a fine powder or chemi- 

 cally disintegrated. Ammonia and nitric acid are results of the 

 alteration of organic nitrogen in the soil and manure heap, and 

 are the most active forms of nitrogen. They occiir in commerce 

 . — the former in sulphate of ammonia, the latter in nitrate of 

 soda. 



Seventeen parts of ammonia, or 66 parts of pure sulphate of 

 ammonia, contain 14 parts of nitrogen. 



Eighty-five parts of pure nitrate of soda also contain 14 parts 

 of nitrogen. 



Soluble phosphoric acid implies phosphoric acid or phosphates 

 that are freely soluble in water. It is the characteristic ingredient 

 of superphosphates, in which it is produced by acting on " insolu- 

 ble " or " reverted " phosphates with oil of vitriol. It is not only 

 readily taken up by plants, but is distributed through the soil by 

 rains. Once well incorporated with soil, it shortly becomes 

 reverted phosphoric acid. 



Reverted {reduced or precipitated) phosphoric acid strictly 

 means phosphoric acid that was once freely soluble in water, but 

 from chemical change has become insoluble in that liquid. It is 

 freely taken up by a strong solution of ammonium citrate, which 

 is therefore used in analysis to determine its quantity.* " Reverted 

 phosphoric acid " implies phosphates that are readily assimilated 

 by crops, but generally have less value than soluble phosphoric 

 acid, because they do not distribute freely by rain. 



Insoluble phosphoric acid implies' various phosphates not freely 

 soluble in water or ammonium citrate. In some cases the phos- 



* To determine "reverted phosphoric acid," this Station continues to employ 

 the method first described by Presenius, Neubauer and Luck (known in this 

 country also as the Washington method, because adopted by the Convention of 

 Agricultural Chemists, held at Washington, in July, 1880), modified in a single 

 particular, viz: manufactured phosphates are not pulverized. 



