678 



CEMENTS, LIMES, AND PLASTERS. 



Per Cent. 

 Silica (SiO 2 ) 25.8 to 27.0 



Alumina (A1 2 O 3 ) 17.3 ' 



Iron oxide (FeO) 1.5' 



Manganese oxide (MnO) 0.0' 



Lime (CaO) 51 . 4 ' 



Magnesia (MgO) 0.4' 



Sulphur (S) 1.3 ' 



19.3 

 1.7 

 0.1 



51.5 

 2.5 

 1.8 



As the slag issues from the furnaces it is run into an inclined iron 

 trough in which cold water is flowing. In addition to granulating the 

 slag, a considerable portion of the sulphur is removed in this way. The 

 granulated slag is run into tanks, from which it is carried to the mixing 

 floor, as required, by conveyors. Here the slag is dumped into mixers, 

 together with thoroughly slaked lime in a pasty condition. The lime 

 is obtained by the calcination of a limestone of the following range in 

 composition : 



Per Cent. 



Silica (SiO 2 ) 0.2 to 0.6 



Alumina (A1 8 O 8 ) 1 n 2 " ft 8 



T I/T-I/-VN r (J .4 U.O 



Iron oxide (Fe 2 O 3 ) J 



Lime carbonate (CaCO 3 ) 97.0 " 98.4 



Magnesium carbonate (MgC0 3 ) 0.9" 1.9 



The mixture is then molded into shape under pressure in a brick- 

 machine with a capacity of 1000 bricks per hour. These bricks are 

 taken to the drying house, where they remain about eight days, at the 

 end of which time they are sufficiently hard to stand transportation. 

 In the size usually made, the dry bricks weigh about 4.75 kgs. each, 

 and will stand a pressure of 18 kgs. per square centimeter. In color they 

 vary from nearly white to grayish. Cement and mortar adhere to 

 them as well as to clay bricks. 



Occasionally bricks are made at this plant from slags of the follow- 

 ing average composition, derived from the smelting of a manganiferous 

 ore different from that commonly used at these furnaces: 



Per Cent. 



Silica (SiO 2 -) 33.00 



Alumina (A1 2 O 3 ) 18.67 



Iron oxide (FeO) 1 .00 



Manganese oxide (MnO) 4 .25 



Lime (CaO) 40.00 



Magnesia (MgO) 2.33 



Sulphur (S) 1.33 



Bricks made from this slag are dark colored, owing to the compara- 

 tively large percentage of manganese present. More lime must be used, 



