84 FERTILITY AND FERTILIZER HINTS 



phate, Florida soft rock superphosphate, South Carolina land rock 

 superphosphate, South Carolina river rock superphosphate, Ten- 

 nessee brown rock superphosphate, Tennessee blue rock super- 

 phosphate, Tennessee white rock superphosphate, etc. Of course 

 all of these superphosphates will not contain the same amounts 

 of soluble phosphoric acid, as the mode of manufacture and con- 

 tent of phosphoric acid in the raw products determine this. A 

 superphosphate made from bone-black containing 30 per cent, of 

 phosphoric acid will be richer in soluble phosphoric acid than 

 one made from South Carolina land rock running 23 per cent, of 

 phosphoric acid. Bone-black and bone-ash because of their 

 higher phosphoric acid contents make richer superphosphates than 

 those manufactured from most of the mineral phosphates. 



Some Names Applied to Superphosphates. — Acid phosphate, dis- 

 solved bone, dissolved bone-black and dissolved bone-ash are 

 names that are used indiscriminately by the trade. A manufac- 

 turer may call a product made from rock phosphate, "dissolved 

 bone," and sell it under this name. Dissolved bone, strictly 

 speaking, is dissolved bone superphosphate, or a superphosphate 

 made from raw or steamed bones. Dissolved bone-black is a 

 superphosphate manufactured from bone-black. Dissolved bone- 

 ash is a superphosphate made from; bone-ash. The superphos- 

 phates made from rock phosphates are usually called acid phos- 

 phates by the trade, although this latter term is applied to any 

 superphosphate and is perhaps a more common name in the United 

 States than superphosphate. For superphosphates made from 

 ground rock phosphate, acid phosphate is perhaps a more correct 

 name as it is the phosphate acted upon by acid. 



Available Phosphoric Acid. — There seems to be a great deal of 

 confusion among farmers over what constitutes available phos- 

 phoric acid and this is not to be wondered at when one con- 

 siders the number of terms applied to reverted and insoluble 

 phosphoric acid. Reverted phosphoric acid is soluble in the weak 

 acids of the soil. The chemist uses a solution called ammonium 

 citrate or citrate, which has a similar action to the weak soil 

 acids, in dissolving out this form of phosphoric acid. For this 

 reason the term citrate soluble is often applied to reverted phos- 



