110 PRACTICAL FARM CHEMISTRY. 



phoric acid, as in quick-maturing crops, a different 

 course must be adopted; and instead of using plain, 

 ground rock, we must apply phosphoric acid in the 

 soluble state. Thus we have it in '' dissolved South 

 Carolina rock." This is raw ground rock or floats, 

 treated with sulphuric acid in same manner as de- 

 scribed for fresh bone. 



Acid phosphate contains about fifteen per cent of 

 phosphoric acid, twelve of this soluble and three 

 insoluble. A ton of the plain, ground rock has 

 about 540 pounds of phosphoric acid (nearly all in- 

 soluble); the acid phosphate has only about 300 

 pounds, of which 240 pounds is soluble. The pound 

 of soluble phosphoric acid will cost us from five and 

 three-fourths to seven and one-half cents, which is 

 somewhat cheaper than in bone phosphate. 



We might also buy the raw ground rock, dissolve 

 it by treatment with sulphuric acid in the way men 

 tioned for bones. To do this we moisten 265 pounds 

 of the ground rock with about eighty pounds of 

 water in a tank or vat, then slowly and carefully 

 add the contents of a carboy (160 pounds) of sul- 

 phuric acid (oil of vitriol), sixty-six degrees in 

 strength, and stir thoroughly. The result will be 

 about 450 pounds of dissolved rock or acid phos 

 phate, containing about seventy pounds phosphoric 

 acid, mostly soluble, at a cost of $3.00 or $4.00. 



The latest reports from Florida assure us that the 



mines there found, and now opened, may also be 



considered inexhaustible, and perhaps 



^Kock.* ^^^^ easier worked than those in other 

 parts of the south. At the same time the 

 Florida phosphates are claimed to be of a higher 

 grade than the other, and to contain not only phos- 

 phoric acid, but also the nitrogen which was in the 



