L^ 



Superphosphate 7 



There being several calcium compounds in 

 the rock phosphate which all appear finally 

 as hydrated calcium sulfate (gypsum) it is 

 not strange that the resulting superphos- 

 phate is composed of 60-70 per cent of 

 gypsum. From this it is easy to see why 

 superphosphate contains only 14 to 16 per 

 cent of phosphoric acid (P2O5). 



The deposits of rock phosphate at present 

 being extensivly workt are found in South 

 Carolina, Florida and Tennessee. The larg- 

 est and most newly discoverd deposits are 

 in Idaho, Utah and Wyoming. 



A good grade of ground rock carries 65 per 

 cent of tricalcium phosphate and the material 

 not infrequently runs over 80 per cent. In- 

 ferior rock containing a few per cent of 

 phosphoric acid and mixt with carbonate 

 of lime is abundant, but it is not economical 

 to ship this any great distance or treat it 

 with sulfuric acid. 



The use of '^ raw rock " vs. ^'dissolvd rock " 

 is a much discust question in agriculture. 

 Thru the East, on fight soils and for intensiv 

 cultivation, the dissolvd rock is used ex- 

 clusivly; for some of the heavy soils of the 

 West raw rock is recommended in connection 

 with decaying organic matter. According to 

 Professor Hopkins of Illinois the raw rock in 

 a heavy soil is converted to dissolvd rock 



