390 THE SCIENTIFIC PAPERS OF 



which latter, being thus set free from its combination with silicon, 

 continues the action of decarburization of the metallic bath. 

 Samples are again taken, until the steel-melter finds that, upon 

 breaking the sample, the peculiar silky fibre is obtained which is 

 indicative of a reduction of the carbon in the metal to O'l per 

 cent. The metal is now ready for final adjustment, according to 

 the strength or temper of the steel required. 



If it is intended to produce ordinary rail metal, from 7 to 8 cwt. 

 of spiegeleisen, containing 20 per cent, of manganese, previously 

 heated to redness, are charged in, the bath is stirred by means of 

 a rabble, and, after being allowed to rest for a few minutes, is 

 tapped either into a ladle or directly into ingot moulds, arranged 

 in groups, whilst the slag that followed the metal through the tap- 

 hole is collected in a pit or mould prepared for its reception. The 

 amount of slag produced depends chiefly upon the percentage of 

 silicon in the pig metal used, and also upon the degree of purity 

 of the ore employed in effecting the reduction, and amounts gene- 

 rally to 2 tons in an 8-ton charge. The yield of metal should be 

 within 1 or 2 per cent, of the total amount of pig metal and scrap 

 (if of a solid description) charged into the furnace, because, 

 although the pig metal would contain some 7 or 8 per cent, of 

 carbon and silicon, which have to be expelled, this loss of weight 

 is made up by the metallic iron given up by the ore. The lime 

 added near the end of the operation is useful in taking up some 

 of the other impurities, such as sulphur and phosphorus, from the 

 metal, although the amount so taken up is only small. 



After tapping, the steel-melter again inspects his furnace-bed, 

 repairing any slight defects that may have arisen, fills up the 

 tapping-hole, and introduces the next charge. 



The time each charge occupies is from seven to nine hours, 

 according to its character and to the heat of the furnace. When 

 pig metal and scrap alone are used, a charge can be worked in 

 from six to seven hours, and the proportion of pig metal employed 

 can be reduced to from 10 to 15 per cent, of the total charge, 

 whereas when no scrap at all is used, the amount of pig metal 

 charged must be equal to the total amount of steel to be produced, 

 and the reaction between the ore and pig metal extends the time 

 of each operation by about three hours. In this respect, then, the 

 scrap or Siemens-Martin process has an advantage over the ore 



