,644 CEMENTS, LIMES, AND PLASTERS. 



ver, that one reason for carrying a high alumina-silica ratio does not 

 apply at Chicago, as there rapidity of set is gained by the use of the 

 Whiting process. Taking these two plants as representative of the 

 best European and American practice, the average of the analyses 

 given shows the ratios actually used to be: Choindez, Switzerland, 



-1,1, =0,0; and Chicle, HI., - -!., 



These results may be compared with the theoretical ratios advised 

 by Tetmajer, Prost, and Mahon, and discussed on a previous page of 

 the present Chapter. 



Selection of slags. The erection of a slag-cement plant in connection 

 with any given furnace is not justified, unless a sufficient amount of 

 the slags usually produced will fall within slag-cement requirements, 

 as these requirements have been outlined above in the section on chem- 

 ical composition of the slag. In a large plant it will usually be easy 

 to secure a constant supply of slag of proper composition without inter- 

 fering with the proper running of the furnaces. In a small plant, how- 

 ever, or in one running on a number of different ores, such a supply 

 may be difficult to obtain. These points, of course, should be settled 

 in advance of the erection of the cement-plant. 



In the case of any given furnace running on ores and fluxes, which 

 are fairly steady in composition and proportions, the selection of the 

 slag used for cement-making may be largely based on its color, checked 

 if necessary by rapid determinations of lime. The darker-colored slags 

 are generally richest in lime, except when the depth of color is due to 

 the presence of iron; the lighter-colored slags are usually higher in 

 silica and alumina. Candlot states further * in this connection that 

 the slag issuing at the commencement and toward the end of a discharge 

 should be rejected because of the air-chilling which attends its slow 

 movement. 



Granulating the Slag: Methods and Effects. 



Assuming that a slag of proper composition has been selected, the 

 first step in the actual manufacture of slag cement will be the " granu- 

 lation " of the molten slag. Granulation is the effect produced by 

 bringing molten slag into contact with a sufficient amount of cold water. 

 The physical effect of this proceeding is to cause the slag to break up 

 into porous particles ("slag sand")- Granulation has also certain 

 chemical effects, highly important from an economic point of view, 

 which will be discussed later. 



* Ciments et chaux hydrauliques. 



