160 MANURES. VII. 



This process quite revolutionised the iron industry, and steel 

 became so cheap that it almost replaced iron. The Bessemer 

 process, however, -could only be applied to pig-iron fairly free 

 from phosphorus, for the process does not remove any phos- 

 phorus, and if steel contains much of this element its proper- 

 ties are so altered that it becomes valueless. 



The following table shows the change in the composition of 

 the metal in the " Bessemer converter" (acid lining) : 



Original After Before addition Finished 



pig-iron. 9 minutes, of spiegeleisen. steel. 



It will be noticed that there is no reduction in the amount of 

 phosphorus, but rather an increase, while the sulphur, carbon, 

 and silicon are almost entirely removed. 



About 1878-79 a modification in the method of working 

 the Bessemer process was introduced by Thomas and Gil- 

 christ, by which pig-iron containing high percentages of 

 phosphorus could be successfully converted into steel of good 

 quality. Their improvement consisted in lining the converter 

 with lime or a mixture of lime and magnesia and the intro- 

 duction of freshly burnt lime into the converter. They found 

 that under these circumstances the phosphorus in the pig-iron 

 (existing in combination with iron as phosphide) was oxidised 

 by the air after the carbon had been completely removed, and 

 the phosphoric acid so formed united with the lime and mag- 

 nesia of the basic lining to form a slag which floated on the 

 molten iron. The 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 Thorn as- 

 Gilchrist 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 : 



