444 



Introduction to the Study of Science 



nickel, chromium, and aluminum, may be introduced when 

 needed. It is also a point of economic significance that from a 

 given charge of iron the open-hearth yields a larger return than 

 the Bessemer converter. It is therefore not remarkable that 

 the annual output of open-hearth steel is rapidly increasing, 

 the 1913 production being about 21,600,000 tons, or more than 

 twice the tonnage of Bessemer steel. 



The chief features of the open-hearth furnace are shown in 

 Fig. 145. The basin into which the charge is put is rectangular 



in form and shallow in depth. 

 The dimensions of the sixty- 

 ton type, which is the usual 

 one for standard grades of 

 steel, are fifteen feet wide, 

 thirty to thirty-five feet long, 

 and twenty inches or less in 



depth. The hearth bottom 



,, , c i i i 



f the furnace, which IS Used 



to remove phosphorus and 



FIG. 145. Open-hearth furnace (Dia- 

 gram). The charge is introduced through 

 the door. The direction of the air and 

 fuel gas is frequently reversed, entering 



now through ports A and A', and leaving -, f . , . ., 



through ports B and B', and again pass- Slllf UT especially, IS made With 

 ing in the opposite direction ; this is the what is Called magnesite. 

 regenerative system of heating. -. .- . . . . , 



Magnesite is magnesium oxid 



prepared from magnesium carbonate by heating it to drive off the 

 carbon dioxid, just as quicklime is made from limestone. (See 

 page 417.) The ends, sides, and ceiling of the furnace are lined 

 with silica bricks, which are especially resistant to high tem- 

 peratures. The temperature of the furnace may reach 3000 F. 

 in the course of operation. The ports and chambers A A' and 

 B B' are made with silica brick. The bricks in the chambers are 

 arranged in such a way as to suggest the appearance of a 

 checker board. The chambers are therefore called checker 

 chambers or simply checkers. This arrangement is made to 

 provide a large surface over which the air and gas must pass in 

 entering, and the burned gases in leaving, the furnace. 



The fuels generally used are natural gas, which is the best for 



