62 CROP GROWING AND CROP FEEDING 



part of the farm economy, the renewing of the phosphates in the soil becomes 

 a very important matter. There has long been an impression among farmers 

 that phosphoric acid from animal bones is more valuable than phosphoric 

 acid from rock phosphates or other sources. But this is not the case. A 

 superphosphate made from bones will contain some nitrogen, and hence, will 

 have that additional value; but its phosphoric acid is not a whit different 

 from the phosphoric acid from other sources. The only point of importance 

 to the farmer is the percentage of the phosphoric acid which is soluble in 

 water, and is hence immediately available for plant feeding. In the natural 

 state, the phosphoric acid of bones, rock or furnace slag is insoluble. Then if 

 the rock is finely pulverized, and the bone (if finely pulverized), the bone will 

 be the more quickly available of the two, because of the readiness with which 

 it decays in the soil ; and the fact that the raw bone carries with it a consider- 

 able percentage of nitrogen, while the phosphatic acid rock has none of this. 

 But when treated with sulphuric acid and made soluble, the acid of the rock 

 is just the same as the acid of the bones treated in the same way. But the 

 prejudice in favor of the bones is such that it is a common practice among 

 the manufacturers of fertilizers to call their articles bone phosphate, when, 

 in fact, no bones have ever been used in its manufacture. 



The great source of the phosphates used in this country is the phosphatic 

 rock mined from the land or dredged from the river beds in South Carolina. 

 Large quantities are also mined in Florida, which are classified as "soft/' 

 "rock/ 7 "pebble" and "bowlder" phosphates. There are also "apatites" from 

 Canada, and a very fine quality of phosphatic rock from Tennessee, and re- 

 cently a deposit has been found in the Juniata valley in Pennsylvania. 



When treated with sulphuric acid to render them soluble these are known 

 as acid phosphate, and this forms almost the entire source of the phosphoric 

 acid used in the making of fertilizers, though some are still made from the 

 refuse bone charcoal which has been used in the refining of sugar. A minor 

 source, as we have said, is the slag from the manufacture of steel by the 

 basic process. This is known as "basic slag," "Thomas slag" and "odorless 

 phosphate." The quantity produced in this country of this last, is yet too 

 small to have any great effect on the market. Much of the tankage from the 

 Western slaughter houses has large percentages of bone associated with the 

 nitrogenous matters, and this, too, is frequently treated with acid to render 

 it soluble. Untreated tankage is more valuable for its nitrogen than its phos- 

 phoric acid. Bones are also some times steamed, by which means a large 

 part of the nitrogen is extracted, which has the effect of increasing the 

 percentage of phosphoric acid in the product. Steamed bone may contain as 

 much as 28 per cent, of phosphoric acid and very little, if any, nitrogen. It 



