Pentacalcium silico-phosphate 



BASIC SLAG, THOMAS SLAG 



O O 



/ \ / \ 



Ca P Ca 



\ /\\- / 



o o 

 o 



I 



o 



/ \l 



Ca Si 



229 



Ca 



O 



O 



O 



O 



O 



O 



Ca 



(c) Availability. — Basic slag is usually considered about 

 one-half as available as acid phosphate, although on acid 

 soils it is much more readily soluble and quick acting. It is 

 considered an excellent form of phosphate. In this country 

 its use is limited by few importations and relatively high 

 price. Iron ores in this country are too low in phosphorus 

 to produce a slag from steel that is valuable as a fertilizer. 

 In Europe, on the other hand, the slags are rich in phos- 

 phorus, the phosphoric acid content- running from 10 to 

 20 per cent. 



(d) Effect on the Soil. — Basic slag was formerly thought 

 to have considerable free lime, since it was basic in character 

 and was excellent on an acid soil. As a matter of fact it 

 contains only a few per cent, of free calcium oxide (1 to 6 

 per cent.). The decomposition of the basic slag in the soil, 

 however, results in the production of calcium carbonate. 

 The action of water and carbon dioxide produces di- or tri- 

 calcium phosphates and bicarbonate of calcium, in addition 

 to silicic acid or free silica. In this way basic slag acts as a 

 neutralizer of soil acidity, and an improver of soil texture. 

 There is not, however, enough calcium carbonate resulting 

 from an ordinary application of basic slag — say 500 or GOO 

 pounds — to entirely correct the acidity of an ordinarily 



