THE ANALYSIS OF PORTLAND CEMENT RAW MIXTURE 
By J. C. Witt 
Chemist, Bureau of Science, Manila 
TWO TEXT FIGURES 
Analyses of a cement raw mixture by several methods failed 
to give conformatory results. Each of these methods was 
studied with the object of increasing the accuracy, lessening the 
time required, and discovering the sources of error. Little ha§ 
been written on the analysis of raw mixtures, and still less con- 
cerning the sources of error, especially when indirect methods 
for determining the calcium carbonate content are followed. 
Though the mixture here discussed doubtless presents more 
analytical difficulties than the average, work with it has pointed 
out several factors that affect the results obtained with this 
class of materials. 
When a cement plant is past the experimental stage and is in 
regular operation, complete analyses of the raw materials or of 
the raw mixture are, as a rule, required only occasionally. The 
proportioning of the mixture is usually based on the percentage 
of calcium carbonate, which is the most important constituent. 
This determination must be made repeatedly ; its frequency at a 
given plant depending on a number of factors, such as the char- 
acter of the raw materials, the arrangement of the machinery, 
and the like. As with other manufacturing processes, it is 
desirable to find a method of analysis that will give results with- 
in the required limits of accuracy, in the shortest time. The 
methods available may be divided into two classes; namely, 
those in which the calcium itself is determined and those in 
which some other constituent is determined. They include the 
following: 
1. By determining calcium and calculating to calcium carbonate. 
By precipitation with ammonium oxalate. 
Drying or ignition of precipitate and weighing. 
Solution of precipitate in acid and titration. 
Precipitation without complete removal of silica. 
Precipitation in presence of an organic acid. 
Other methods for the determination of calcium. 
1 Received for publication May 26, 1919. 
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