CHEMISTRY OF FERTILIZERS 7 



(C) Nitrogen equal or equivalent to ammonia 

 is a form of expression which simply means that 

 the nitrogen is stated not as nitrogen but as 

 ammonia. 



It would be better on every account if all 

 guarantees stated simply nitrogen and never men- 

 tioned ammonia at all. As a matter of fact, 

 compounds of ammonia are quite uncommon in 

 commercial fertilizers, because nitrogen in this 

 form is the most expensive and, therefore, least 

 used. Strictly speaking, the term ammonia should 

 never be used except when sulphate of ammonia or 

 some similar compound is present in the fertilizer. 



(A) Phosphoric Acid, as used in connection 

 with fertilizers, is a compound containing phos- 

 phorous and oxygen, which in fertilizers is found 

 never by itself, but in combination with lime. 

 Phosphoric acid stands for a certain amount of 

 phosphate of lime. We may say roughly that 

 one part of phosphoric acid is equivalent to about 

 two parts of phosphate of lime, but it is exactly 

 2.1831 and the percentage of phosphoric acid mul- 

 tiplied by this number will give the percentage of 

 "bone phosphate of lime/' But we know that 

 phosphoric acid exists in several different forms. 



(B) Soluble phosphoric acid represents the 

 amount of phosphate of lime that dissolves easily 

 in water; it is formed by treating with sulphuric 

 acid some form of insoluble lime phosphate: 

 The phosphate thus formed is. readily soluble in 

 water. 



