THE SUPERPHOSPHATES. 363 



ently adequate to supply our wants for years. South Carolina 

 phosphates may contain from 20 to 60 per cent, of bone 

 phosphate. Samples, containing from 54 to 56 per cent, of 

 bone phosphate, from five to ten per cent, of carbonates of 

 lime, besides several per cent, of oxide of iron and alumina, 

 on an average, have been sold at Charleston at $8.50 for 2,240 

 pounds. 



The same material, not ground, has been offered at New 

 York and Boston at from $11.50 to $12 per ton. The ex- 

 penses of grinding are stated to be, per ton, from $1.50 

 to $2. Navassa Island phosphate, which, in regard to its 

 chemical composition resembles somewhat the former, con- 

 tains from 65 to 70 per cent, of bone phosphate, and has 

 been sold of late at $16 per net ton of 2,000 pounds, after 

 being dried and ground. The manufacturer of superphos- 

 phates pays thus about from 2.5 to 3.0 cents per pound for 

 insoluble phosphoric acid obtained from these two mineral 

 phosphates, and asks the farmer to pay for it at the rate of 

 six cents per pound. 



Only a few of the mineral phosphates are well qualified for 

 an economical manufacture of a good superphosphate. Those 

 which contain either larger percentages of carbonates of lime 

 and iron, or of hydrates of oxides of iron and alumina, are 

 unfit for that purpose, for they require larger quantities of 

 sulphuric acid to produce the desired effect, and thus neces- 

 sitate an increase of the manufacturing expenses. 



A pure bone phosphate contains, for every 100 pounds of 

 phosphoric acid, about 120 pounds of lime. By adding 220 

 pounds of bone phosphate, 140 to 145 pounds of concentrated 

 sulphuric acid (=1.84 specific gravity), two-thirds of the 

 lime (80 pounds) combine with the latter, forming 196 pounds 

 of (anhydrated) sulphate of lime, and 100 pounds of phos- 

 phoric acid still combined with 40 pounds of lime ; this latter 

 combination is soluble in water, and known to chemists by 

 the name of monocalcic phosphate. To produce this com- 

 pound with the least waste of concentrated sulphuric acid, is 

 the object of the superphosphate manufacturer, — a task which 

 requires some familiarity with the chemistry involved, — other- 

 wise every change in the composition of the crude phosphates, 

 etc., turned to account, must result in the production of super- 



