24 BULLETIN 144, U. S. DEPAKTMENT OF AGKICULTUKE. 



Table VII. — Average cost per ton {2,000 pounds) of acid phosphate manufactured in a 

 den-system plant located at seaport and running at full capacity of 500 tons per week. 



Phosphate rock (1,133 pounds), at $5.09 per ton $2. 576 



Sulphuric acid (1,080 pounds), at $4.75 per ton 2. 565 



Direct labor 264 



Five-eighths superintendent's salary 091 



Power, oil, and waste 232 



Insurance on $60,000, at 1.55 per cent 035 



Taxes on $75,000, at 1.25 per cent 036 



Depreciation on $60,000, at 10 per cent 231 



Interest on $75,000, at 6 per cent 173 



Total cost per ton 6. 203 



The figures given in Table VII were compiled from data obtained 



through personal inspection of the principal fertilizer factories of 



the South and East. The costs do not include overhead charges, 



which vary greatly according to the size and number of the plants 



run by a company. 



DISPOSAL OF PRODUCT. 



Acid phosphate is sold on the basis of its so-called available phos- 

 phoric-acid content, and is worth, f. o. b. the factory from 40 to 56 

 cents per unit, 1 depending on the location of the plant and grade of 

 the product. 



The availability of phosphoric acid is determined by its solubility 

 in a solution of ammonium citrate. There seems to be no scientific 

 basis for the assumption that the amount of phosphoric acid thus 

 dissolved is equivalent to the quantity which is readily available to 

 crops. It is, however, a convention accepted by the fertilizer trade 

 as well as by many agronomists and agricultural chemists. 



The phosphates of South Carolina (27 per cent P 2 5 ) and those of 

 northern Africa (26 to 30 per cent P 2 5 ) yield as a rule acid phosphate 

 containing 14 per cent available phosphoric acid. 



Florida land-pebble phosphate gives an acid phosphate containing 

 16 per cent of available phosphoric acid, and the highest grade rock 

 from Florida, Tennessee, and certain islands in the Pacific Ocean 

 (containing from 35 to 38 per cent P 2 5 ) yield a product containing 

 from 18 to 21 per cent of available phosphoric acid. 



Acid phosphate is usually put up in 200-pound sacks and shipped 

 in closed box cars. The sacks are treated with a solution of silicate 

 of soda, paraffin, or some other substance to prevent the acid phos- 

 phate from acting upon them. 



The latest official figures on the output of acid phosphate are those 

 for 1909, which show a total production of 3,062,834 tons. It is 

 needless to say that the production has increased enormously since 

 these figures were compiled . 



1 The unit is 1 per cent of a ton, or 20 pounds. One ton of 16 per cent acid phosphate contains 320 

 pounds P2O5. 



