THE MANUFACTURE OF ACID PHOSPHATE. 



21 



STORING THE ACID PHOSPHATE. 



In order that the acid phosphate produced may contain a maximum 

 quantity of soluble phosphoric acid when ready for shipment, it is 

 usually stored in well-ventilated buildings for at least two weeks. 

 During this time the quantity of the so-called available phos- 

 phoric acid should steadily increase. This is especially true of prop- 

 erly mixed acid phosphate made by the "open dump" method where 

 the heat is not sufficiently great to bring about rapid chemical 

 reactions. 



On the other hand, the storing of acid phosphate for protracted 

 periods in large piles often seriously impairs its mechanical condition 

 and sometimes its chemical composition. The pressure exerted on 

 the material in the lower part of the heap, coupled with its con- 

 traction as the mass cools, tends to pack it. When the formation of 

 gypsum is still in progress the superphosphate often becomes so 

 closely cemented that it is difficult to break up. Again, improperly 

 mixed acid phosphate or that high in compounds of iron and alumi- 

 num when closely packed is very apt to become gummy or to revert. 

 Porter 1 states that in making acid phosphate by the "open dump" 

 method the material should not be discharged on the pile until it is 

 stiff enough to "set up," 



The storing of acid phosphate in medium-sized piles, however, 

 should cause no trouble, provided it is not allowed to stand too long 

 and the climatic conditions are not unfavorable. Even when the 

 material improves by storing it is hardly economical to keep it over 

 a few months, as the interest on the money invested more than 

 counterbalances the added value of the product due to the increase 

 in available phosphoric acid. 



In Table V, the figures of which are taken from Fritsch, 2 the 

 changes taking place in stored acid phosphate made from three 

 different samples of Tennessee phosphate (A, B, and C) are shown. 



Table V. — Changes taking place in acid phosphate made from Tennessee rock on storing 



from 2\ to 4\ months. 





Composition. 



Sample. 



Directly after mixing. 



After storing for 2-J months. 



After storing for 4J months. 



P2O5. 



Fe 2 3 +Al 2 3 . 



P2O5. 



Al 2 3 +Fe 2 3 . 



P 2 3 . 



Al 2 3 +Fe 2 3 . 





Insol. 



Insol. 



Sol. 



Insol. 



Insol. 



Sol. 



Insol. 



Insol. 



Sol. 



A 



Per cent. 

 2.27 

 2.20 

 1.98 



Per cent. 



Per cent. 

 1.16 



1.34 

 1.57 



Percent. 

 2.35 

 2.33 

 2.32 



Per cent. 

 1.21 

 1.20 

 1.17 



Percent. 

 0.82 

 1.05 



Per cent. 

 2.30 

 2.23 



Per cent. 

 1.00 

 1.12 

 1.12 



Per cent. 

 1.31 



B 



1.05 

 1.01 



1.30 



C... 



1.31 



2.48 



1.38 



1 Jour. Ind. Eng. Chem., 3, 108 (1911). 



2 Manufacture of Chemical Manures, p. 137 (1911). 



