86 FERTILITY AND FERTILIZER HINTS 



material from which the superphosphate is made influences the 

 value of the soluble phosphoric acid. Many farmers would rather 

 purchase soluble phosphoric acid as superphosphates manufac- 

 tured from bones than soluble phosphoric acid from mineral sup- 

 erphosphates. There is not any difference in the soluble phos- 

 phoric acid of superphosphates no matter what raw material is 

 used in making it. Of course a dissolved bone superphosphate 

 will perchance give better results than a raw rock superphos- 

 phate of equal soluble phosphoric acid composition as the dis- 

 solved bone superphosphate will contain in addition to the phos- 

 phoric acid, a certain amount of nitrogen, so if we judge the 

 value of soluble phosphoric acid in this way we are assuming 

 an unequal and unfair task. 



Some Farmers Favor Bone Superphosphates. — Many farmers 

 seem to be predjudiced against the mineral superphosphates and 

 always demand superphosphates made from bone. Often the 

 price is much higher for the bone superphosphates on account 

 of the greater price bones bring when sold for bone-black, manu- 

 facturing interests, etc. These farmers could generally purchase 

 their phosphoric acid more cheaply from mineral superphosphates. 

 Of course when dissolved bone and mineral superphosphate of 

 equal available phosphoric acid content, are offered for the same 

 price, it is more economical to select the dissolved bone ; but it 

 is seldom that one can get such a bargain as the dealers in fer- 

 tilizers always charge for the ammonia content. Generally phos- 

 phoric acid can be purchased cheaper from mineral superphos- 

 phates than from dissolved bone superphosphates. 



Double Superphosphate. — This is sometimes called double phos- 

 phate. This double superphosphate is manufactured as follows: 

 Phosphates are treated with an excess of sulphuric acid (chamber- 

 acid) and the phosphoric acid is dissolved out as free phosphoric 

 acid. The fluids, sulphuric acid and phosphoric acid are fil- 

 tered or separated from the insoluble matter and concentrated. 

 This concentrated solution is then used in dissolving high grade 

 phosphates and the resulting product is called double superphos- 

 phate because the phosphoric acid content is more than double 



