392 CEMENTS, LIMES, AND PLASTERS. 



retically possible. The aim of the manufacturer, therefore, is to get 

 a cement whose Cementation Index is on the safe side (i.e., over 1.0), 

 but not too much so. 



Use of the formula in proportioning mixtures. The use cf a similar 

 formula in calculating mixtures to be made from untried materials has 

 been well described by Prof. Newberry. The discussion here presented 

 differs from his only in the fact that the magnesia and iron are allowed 

 for, a correction which now seems necessary. 



Following this rule, the various steps in the proportioning of a cement 

 mixture are given below in sufficient detail to be readily followed. 



OPERATION 1. Multiply the percentage of silica in the clayey ma- 

 terial by 2.8, the percentage of alumina by 1.1, and the percentage 

 of iron oxide by 0.7; add the products; subtract from the sum thus 

 obtained the percentage of lime oxide in the clayey material plus 1.4 

 times the percentage of magnesia and call the result n. 



OPERATION 2. Multiply the percentage of silica in the calcareous 

 material by 2.8, the percentage of alumina by 1.1, and the percentage 

 of iron oxide by 0.7; add the products and subtract the sum from the 

 percentage of lime oxide plus 1.4 times the percentage of magnesia 

 in the calcareous material, calling the result m. 



OPERATION 3. Divide n by m. The quotient will be the number of 

 parts of calcareous material required for one part of clayey material. 



Example. Assuming that materials of the following composition are in 

 use the operation would be as follows: 



Clay. Limestone. 



Silica (SiO 2 ) 62.2 2.4 



Alumina (A1 2 O 3 ) 16 -! 2 - 



Iron oxide (Fe 2 O 3 ) 4 - 2 - 3 



Lime (CaO) 1.6 50.2 



Magnesia (MgO) 1.2 1.5 



Sulphur trioxide (SO 3 ) 1.7 0.6 



Alkalies (K 2 O,Na 2 O) 0.8 0.4 



Water, carbon dioxide, etc 12 .2 42 .6 



Operation (1). Clay. 



Silica X2. 8 = 62. 2X2. 8 = 174. 16 



Alumina XL 1 = 16. 1X1.1= 17.71 

 Iron oxide X0.7= 4.2x0.7= 2.94 



194.81 



Lime Xl.0= 1.6X1.0= 1.6 



Magnesia Xl.4= 1.2X1.4= 1.68 



3.28 

 194. 81 -3. 28 = 191. 53 = w. 



