CALCULATION AND CONTROL OF THE MIX. 393 



Operation (2). Limestone. 



Silica X2.8 = 2.4 X2.8= 6.72 



Alumina Xl.l= 2.0X1.1= 2.20 



Iron oxide X0.7 = 0.3X0.7= 0.21 



9.13 



Lime Xl .0 = 50.2x1 .0= 50.2 



Magnesia Xl.4= 1.5X1.4= 2.10 



52.30 



52. 30-9. 13 = 43. 17=m. 

 Operation (3). 



~~~ .01^ =4.4,4 = parts of limestone to be used for each part of clay, by weight. 

 tn 4.5.17 



It must be recollected that the value given by the above formula 

 represents the highest amount of lime theoretically possible under 

 the best possible conditions of fine grinding and thorough burning. 

 Even in the best-run plants these conditions cannot be attained in 

 practice, and in a trial run either in a test kiln or in an actual plant 

 it is foolish to attempt to reach this limit. The limestone shown by 

 the formula should therefore be reduced in order to get safe results. 

 A reduction of 10 per cent will probably be satisfactory. In the ex- 

 ample given above this would work out as follows: 



4.44 = parts limestone (to 1 of clay) allowed by formula 



0.44 = 10% reduction for safety 



4.00 = parts limestone (to 1 of clay) to be actually used 



Calculating Mixtures in Current Work. 



After a plant has once gotten into good working order, and as long 

 as the same raw materials are in use, the calculation of the mix becomes 

 a much simpler affair. Two general methods are in use: 



At most plants the percentage of carbonates in the mix is made 

 the criterion. If good results have been attained with mixtures carry- 

 ing 78 to 80 per cent total carbonates (CaCOs + MgCOs), the aim of 

 the chemist is simply to keep the mix within these limits. The calcu- 

 lation in this case is simply a matter of arithmetic which does not re- 

 quire explanation. The other method is to keep a fixed ratio between 

 the total insoluble matter and the total carbonates. This ratio will 

 naturally be different at each plant, but will always be fairly constant 

 at any one plant. 



In a well-known and admirably managed marl-plant the marl is 

 analyzed after being pumped into tanks at the mills, and the clay on 



