BASIC SLAG. 



161 



It will be seen from the above table that the silicon is first 

 oxidised and removed, then the carbon, and not until practi- 

 cally all the carbon is removed does the removal of the 

 phosphorus begin. 



The slag obtained by the basic process therefore receives its 

 phosphate in the last few minutes of the process. This is 

 seen from the following figures : 



The process resulted in a still further cheapening of steel. 

 For some years the slag produced, though it was known 

 to contain a considerable quantity of phosphoric acid, was 

 regarded as simply a waste product of no use. It was thought 

 that the oxide of iron present in the slag would prevent the 

 phosphoric acid from being available to plants. Its use as a 

 manure for soils poor in lime was suggested about 1882, * as it 

 was found that a considerable proportion of the phosphoric 

 acid in the slag was in such a state of combination as allowed 

 of its easy solubility in ammonium citrate solution. This led 

 to numerous trials of the slag, and many of these proving 

 highly satisfactory its use rapidly extended and has now 

 assumed gigantic proportions. 



The composition of the slag necessarily varies somewhat, 

 but its main constituents are represented in the following 

 analysis of a specimenf: 



* Maercker, Bied. Centr. 1882, 490 ; Jour. Chem. Soc. 1882, abst. 1229. 

 t Stead and Ridsdale, Jour. Chem. Soc. 1887, Trans. 601. 



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