XV, 1 



Witt: Portland Cement Raw Mixture 



119 



In general, both the calcimeter and the acid-alkali titration 

 results are below the results obtained with potassium perman- 

 ganate. Due to errors of the apparatus and of the process, 

 however, the calcimeter results are frequently higher than the 

 acid-alkali titration results. Up to the present it has not been 

 found possible to obtain concordant results by any two of the 

 three principal methods investigated, nor to discover a correction 

 formula by which the results obtained by one of the indirect 

 methods could be calculated to those of the direct method. The- 

 oretically the true calcium carbonate content should be given 

 by the formula : 



Percentage of calcium carbonate = x -\- (100 — x) k, 



in which x is the percentage of calcium carbonate found by the 

 calcimeter and k is a constant depending on the amount of cal- 

 cium in the siliceous materials. However, it may be seen from 

 Table II that, due to irregularities in the composition of the 

 raw materials, the clay contamination of the limestone, and 

 certain phases of the manufacturing process, the constant, k, 

 cannot be calculated with sufficient accuracy to justify the use 

 of the formula. 



When cement raw mixture enters a kiln and is gradually con- 

 verted into clinker, results obtained by indirect methods of anal- 

 ysis are of course no longer applicable and any calculation of the 



Raw Mixture > Clin ken 





Fig- 2. Analysis of raw mixture at »arir>us stares of ita conversion into elinker. 



