L. MECHANICS AND ENGINEERING. 525 



from the slag. It seems settled that only two methods are 

 available for this, either the formation, at ordinary tempera- 

 ture of fusion, of a very fluid slag, rich in iron, in an appara- 

 tus similar to a finery or puddling hearth, or the employment 

 of an unusually high temperature, at which even the slightly 

 carbureted iron, in a suitably fluid condition, would separate 

 from poor, very fluid slag. Such a temperature can only be 

 produced by a Siemens' furnace, as he seems to realize; 

 though whether he will also use a rotary apparatus in con- 

 nection with it for separating the slag remains to be seen. 

 In all recent processes, although various obstacles are en- 

 countered, the doubts of success turn mainly upon econom- 

 ical considerations, from the fact that in the Dank process, 

 as well as the old Sttickofen process, only one half of the iron 

 in pure, rich ore could be calculated on a fact that entirely 

 forbids the use of poor ores ; and it is only when cast iron is 

 produced that the loss of the slag can be reduced to a small 

 percentage. Under conditions present in the Bessemer oper- 

 ations alone is it possible to combine fluid bar-iron, contain- 

 ing little carbon, with slag containing a small percentage of 

 iron. But, in addition to the loss of half the iron of the ore 

 in rotary hearths, the consumption of fuel, amounting to two 

 to three times that required for puddling the same amount 

 of cast iron, renders their economical employment doubtful; 

 and with the reduction of the quality of the ore the cost in- 

 creases so rapidly that the use of ores of forty to fifty per 

 cent, is out of the question, especially if the impurities are 

 silica and alumina. After advising experiments in Austria, 

 Tunner suggests that in order to lessen the loss in the slag, 

 by the addition of a larger amount of carbon instead of soft 

 iron, cast iron and a poor slag might first be formed in a ro- 

 tary hearth, the latter be removed, and the iron puddled im- 

 mediately by Bank's process, as is in fact done in the Yates 

 plan and direct methods in common puddling furnaces. But 

 it seems that with this treatment the time required, and con- 

 sequent consumption of fuel, w^ould be so great that favora- 

 ble economical results could not be expected. Still it is more 

 promising than the first, where poorer ores must be used. 

 On the whole, the possibility of the direct manufacture of 

 soft iron, in the way discussed, depends on the relation be- 

 tween the reduction of iron slag and its immediate carburet- 



