76 COTTON CULTURE 



ble and reverted forms of phosphoric acid, because both 

 forms are available for the use of plants. 



(e) Soluble and Available Phosphoric Acid is an expres- 

 sion which means the same as available. 



(/) Insoluble Phosphoric Acid represents the form of 

 phosphoric acid in raw phosphate of lime, and which is of 

 least value for agricultural purposes. 



(g) Total Phosphoric Acid represents all of the phos- 

 phoric acid compounds without regard to the forms in 

 which they exist. The total phosphoric acid is, therefore, 

 the sum of the soluble, reverted, and insoluble forms; or, 

 to state it in another way, the sum of the available and 

 insoluble forms. 



(h) Phosphoric Acid equal (or equivalent) to Bone Phos- 

 phate of Lime is an expression which usually means 

 nothing more or less than insoluble phosphoric acid. 



NITROGEN (AMMONIA) 



(a) Nitrogen is a gas and, in this form, cannot be used 

 in fertilizers. Therefore, whenever we speak of nitrogen 

 in fertilizers we do not mean that nitrogen exists in them 

 as simple nitrogen. The nitrogen in fertilizers is always 

 combined with other elements, and may be present in one 

 or more different forms: (ist) in the form of nitrates, as 

 nitrate of soda; (26.) in the form of ammonia compounds, 

 as sulfate of ammonia; and (3d) in the form of organic 

 matter, animal or vegetable, as dried blood, meat, tobacco 

 stems, etc. Chemical analysis according to official methods 



