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 -f- (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ysis are of course no longer applicable and any calculation of the 
Fig. 2. Analysis of rary mixture at various stages of its conversion into clinker. 
