and seventy pounds of ash containing fifty-eight pounds of 

 phosphate of lime, made up of twenty-four pounds phosphoric 

 acid and thirty four pounds of lime, the remaining twelve pounds 

 consists of magnesia, carbonate of lime, etc. 



It was found by various experiments that the phosphoric 

 acid in the bone was the chief cause of the well-known effect of 

 bone fertilizers. The first great improvement in the use of bone 

 dates with the introduction of a bone mill, by which they were 

 reduced to meal. This was in 1814. The next step was the 

 process suggested by Liebig in 1839, by which bones were dis- 

 solved with sulphuric acid ; bones thus dissolved, or " cut," 

 with acid were called superphosphate, and differ from the raw 

 bone in having the greater part of the phosphate of lime soluble 

 in water, while very little of the lime phosphate in the raw bone 

 is thus dissolved out when treated with water 



The term superphosphate should only be applied to a fertil- 

 izer containing soluble phosphoric acid, and is not correctly 

 used when applied to the /r^^^ri?^ or commercial fertilizers. In 

 1843 "^ '^^™ source of phosphoric acid was discovered in Spain. 

 A vein of rock, about seven feet wide, was found there which 

 contained about thirty-four to fifty per cent, of phosphoric acid ; 

 in 1844 English farmers tried this new source of phosphoric acid 

 and found it a valuable substitute for bone. 



In the United States bone was first used about 1790. The 

 first bone mill was established in 1830, and superphosphate, or 

 dissolved bone, was first tried in 185 1. 



One of the most important geological discoveries in the 

 United States was that of the so-called South Carolina Rock. 

 This rock is found in masses varying from the size of the fist to 

 fragments weighing a hundred pounds or more, and forms a 

 closely packed layer, covering a considerable area near Charles- 

 ton, S. C, and in other of the coast states. It is intermingled with 

 shark's teeth and the bones ,of various animals, which have 

 changed to stone. The " Rock " contains from twenty-five to 

 thirty-two per cent of phosphoric acid. This rock was first 

 put on the market in 1868, six tons being the total output. In 

 1885 437,856 tons were mined, and in 1887, 480,558 tons. 



The phosphoric acid in these rock phosphates is insoluble, 

 but when ground and treated with sulphuric acid they become 

 converted into superphosphates, or soluble phosphates. 



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