COMMERCIAL FERTILIZER MATERIALS 457 



ties. The water soluble and reverted phosphoric acid are both 

 rated as available. 



The phosphates of acid phosphate when added to the soil 

 quickly revert to an insoluble form: 



CaH 4 (P0 4 ) 2 + 2CaH 2 (C0 3 ) 2 = Ca 3 (P0 4 ) 2 +4C0 2 + 4H 2 

 Ca 2 H 2 (P0 4 ) 2 + CaH 2 (CO,) 2 = Ca 8 (POJ 2 + 2C0 2 + 2H 2 



Plenty of active calcium should be present when acid phos- 

 phate is used to insure this reaction instead of the formation 

 of the very insoluble ferric phosphate (FeP0 4 ) and aluminum 

 phosphate (A1P0 4 ). Acid phosphate does not seem to make 

 the soil acid. 1 In fact, it is considered by some investigators 

 to decrease the acidity by rendering aluminum and iron in- 

 soluble. 



257. Basic slag ( (CaO) 5 .P 2 5 .Si0 2 +).— Iron or steel con- 

 taining over 2 per cent, of phosphorus is too brittle to be 

 useful and, as a consequence, ores of this character were little 

 used until methods of removing this phosphoric acid were 

 discovered. The use of wood in smelting provided a basic ash, 

 thus removing phosphorus from the pig iron. With coal, how- 

 ever, the slag is acid and the phosphorus remains with the 

 ore. In the open-hearth method of smelting the furnaces are 

 lined with a specially prepared dolomitic limestone. Lime is 

 later added as the smelting proceeds. The calcium of the 

 slag unites with the phosphorus of the iron, thus reducing 

 the percentage of that element in the steel. The most prob- 

 able formula for the phosphorus compound in basic slag is 

 (€aO) 5 .P 2 5 .Si0 2 . Basic slag contains a large amount of 

 iron and calcium hydroxide. Below is a typical analysis : 



CaO 45.0 A1 2 3 1.7 



MgO 6.2 Si0 2 6.9 



FeO + Fe 2 3 17.6 P 2 5 18.1 



MnO 3.5 Other constituents. . . 1.0 



1 Conner, S. D., Acid Soils and the Effect of Acid Phosphate and 

 Other Fertilizers Upon Them; Jour. Ind. and Eng. Chem., Vol. 8, No. 

 1, pp. 35-40, 1916. 



