374 BOARD OF AGRICULTURE. 



economical application for the manufacture of superphos- 

 phates, — as far as the quantity of sulphuric acid required is 

 concerned, — suffers somewhat on account of the presence of 

 from 10 to 15 per cent, of alumina and sesquioxide of iron, 

 besides of from 2.5 to 5 per cent, of carbonate of lime. It 

 compares, however, favorably for that purpose with the Som- 

 brero, Maiden, Jarvis, South Carolina phosphates, and most 

 Apatites ; yet it is less valuable than the Baker Island phos- 

 phate of former days, and the Mejillones guano of Chili and 

 Bolivia of a more recent date. 



Most mineral phosphates contain the main portion of their 

 phosphoric acid in the form of bone-phosphate, or tricalcic 

 phosphate. One hundred parts of this compound, — consist- 

 ing of 54.19 per cent, of lime and 45.81 per cent, of phos- 

 phoric acid, — require 63 per cent, of sulphuric acid of 1.72 

 specific gravity, 60° Beaume, or 51.6 per cent, of anhydride 

 of sulphuric acid, to render its phosphoric acid (as monocalcic 

 phosphate) soluble in water. In multiplying, therefore, 

 merely the percentage of bone-phosphate contained in any of 

 them, by 0.63, we learn the amount of sulphuric acid (of 1.72 

 specific gravity) necessary to render its entire amount of 

 phosphoric acid soluble in water ; provided they contain no 

 other constituents, which are acted upon by the former. 

 Every one of the above-named phosphates contains, however, 

 more or less of either carbonate of lime and magnesia, or of 

 alumina and oxide of iron, or of both ; and as these substances, 

 without exception, combine sooner or later with sulphuric 

 acid, more or less of the bone-phosphate remains unchanged, 

 and a superphosphate with less soluble phosphoric acid than 

 counted on is obtained. 



To secure, in cases like these, the entire amount of phos- 

 phoric acid in a soluble form, requires thus a larger quantity of 

 sulphuric acid than the decomposition of the bone-phosphate 

 alone would consume, which in turn causes increased expense, 

 and thus a more costly phosphoric acid. For instance : as 

 carbonate of lime is readily changed into sulphate of lime, 

 one part of carbonate of lime combining for that purpose with 

 1.16 parts of sulphuric acid of the above-stated strength (1.72 

 specific gravity) , we know that any natural bone-phosphate, 

 which contains an admixture of 5 per cent, of carbonate of 



