Nu. 6. DEPARTMENT OF AGRICULTURE. 829 



acid, 0.5 to 2 per cent, sulphate acid, 35 to 42 per cent, lime and a 

 little magnesia, soda, silica, iron and other elements. The finding 

 of the fossil bones, teeth, etc., spoken of has led to the term ''South 

 Carolina bone," being incorrectly applied to these mineral phos- 

 phates. 



DISSOLVED SOUTH CAROLINA ROCK. 



Rock which has been treated with sulphuric acid to render the 

 phosphoric acid soluble or available is termed Dissolved South Caro- 

 lina rock. This constitutes by far the greater bulk of the materials 

 now used in this country for making phosphate manures. An 

 immense trade has grown up in this class of phosphates during the 

 last thirtv-five vears. The most common name by which this class 

 is known is ''Acid Phosphate," but it is also found on the market 

 as Dissolved S. C. Rock, Dissolved S. C. Bone and Bone Phos- 

 phate Rock. While the rock which w'as first used for making this 

 class of fertilizers was first found in South Carolina, yet much of 

 it now conies from Florida and Tennessee. The dissolved phos- 

 phates of this class contain a large portion of their phosphoric acid 

 in the available condition, but not quite as much in the soluble 

 form as in dissolved bone black. 



DOUBLE SUPER-PHOSPHATE. 



This, as its name indicates, is a concentrated form of soluble 

 phosphoric acid. It is made by dissolving mineral phosphates in 

 phosphoric acid instead of sulphuric acid. The process of manu- 

 facture consists of treating a low grade of phosphate rock, or those 

 too poor in phosphoric acid to make a high grade or standard 

 super-phosphate, with an excess of dilute sulphuric acid. This sets 

 free the phosphoric acid, which, together with the excess of sul- 

 phuric acid, is removed and separated from the insoluble materials 

 by filtration and washing. The acid solutions thus obtained are con- 

 centrated and then used for dissolving the better class of phosphate 

 rock. Because the acids used for dissolving the phosphates con- 

 tain phosphoric acid, the product yielded contains more than double 

 the amount of phosphoric acid in the ordinary product. 



Double super-phosphate is manufactured to some extent in this 

 country, but mostly in Europe. Its use in this country is not as 

 great now as it was a few years ago. This source of phosphoric acid, 

 contains a minimum of impurities and a maximum of phosphoric acid 

 in the soluble form. 



SUPER-PHOSPHATE. 



This was the name originally given to a fertilizer which had been 

 treated with acid to render the phosphoric acid soluble, but in after 



