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 has 

 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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