150 



BASIC SLAG 



rest of the process is conducted as in the original Bessemer or " acid " 

 process. This improvement was of great importance, especially to 

 iron masters in districts where the iron ore contained large quantities 

 of phosphates. 



The following table gives the data in the case of the Thomas-Gil- 

 christ or Basic-Bessemer process, the pig-iron used being so rich in 

 phosphorus as to be quite unfit for use by the ordinary Bessemer 

 process : 



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

 dised and removed, then the carbon, and not until practically all the 

 carbon is removed does the removal of the phosphorus begin. 



The slag obtained by the basic process therefore receives its phos- 

 phate 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 con- 

 siderable quantity of phosphoric acid was regarded as simply a bye- 

 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, l 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 



1 Maercker, Bied. Zentr., 1882, 490; Jour. Chem. Soc., 1882, Abstracts, 1229. 



