SLAG CEMENT: LIME, MIXING AND GRINDING. 659 



covers the use of "caustic soda, potash, sodium chloride, or equiva- 

 lents or any substance of which the latter are ingredients", added either 

 as aqueous solutions or in a dry state at any stage of the process of 

 slag-cement manufacture. In the specifications accompanying the 

 application for this patent, the patentee states that, in the case of dry 

 caustic soda the amount added will vary from 0.125 to 3 per cent, 

 "depending chiefly upon the use for which the cement is intended". 

 The patent was subsequently conveyed to the Illinois Steel Company, 

 and the process covered by it is used by that company in the manu- 

 facture of its "Steel Portland " cement. A license has been issued to the 

 Brier Hill Iron and Coal Company, of Youngstown, Ohio, under which 

 license this company manufactures its "Brier Hill Portland " cement. 



The process, as practised in the slag-cement plant of the Illinois 

 Steel Company, Chicago, 111., is described as follows: The quicklime 

 used is obtained from the calcination of Marblehead or Bedford lime- 

 stone and carries less than 1 per cent MgO. On its arrival at the mill 

 it is unloaded into bins, beneath which are placed two screens of differ- 

 ent mesh, the coarser at the top. A quantity of lime is drawn upon 

 the upper screen, where it is slaked by means of the addition of water 

 containing a small percentage of caustic soda. As the lime is slaked 

 it falls through the coarse screen onto the finest screen, through which 

 it falls into a conveyor which carries it to a rotary drier. After heat- 

 ing, the resulting slaked and dried lime is carried by elevators to hoppers 

 above the tube mills, where it is mixed in proper proportions with the 

 granulated slag, which has been dried and powdered. 



General Practice. The general practice followed at a number of 

 American and European slag-cement plants will now be described. 



A very recent and typical installation is shown in Fig. 163, which 

 gives the plan and elevation of the slag-cement plant of the Stewart 

 Iron Co., at Sharon, Pa. It will be seen that the granulated slag is 

 passed through Ruggles-Coles driers, three of which are in use, and 

 is then elevated to a dry-slag bin on the second floor of the mill. The 

 lime is slaked in an adjoining room, and is also elevated to the second 

 floor. Here the two materials are fed in proper proportions to a screw 

 conveyor, which carries them to a Broughton mixer. The mix is then 

 conveyed to three West tube mills, which deliver the finished product. 

 The Maryland Cement Company,* at Sparrows Point, Md., obtains the 

 slag from the furnaces of the Maryland Steel Company. The slag is 

 dried in Ruggles-Coles driers, and after mixing with the slaked lime 



* Lewis, F. H. Cement Industry, p. 184. 



