120 Philippine Journal of Science 



calcium present must be based on the determination of the cal- 

 cium itself. The reason for this is shown in fig. 2, which is 

 based on the analysis of a number of samples of raw mixture 

 at various stages of conversion into clinker. Curve a shows total 

 calcium ; b, total alkalinity ; and c, carbon dioxide — all calculated 

 to percentage of calcium oxide. The raw mixture as it entered 

 the kiln contained almost 44 per cent calcium oxide as indicated 

 by the three methods of analysis, taking into account the errors, 

 which have been explained. 



The first part of all three curves rises, because during the first 

 period no chemical change in the constituents of the mixture is 

 taking place, and the percentage of calcium oxide is increasing 

 because of the loss in moisture, organic matter, and the like. 

 However, the change at once becomes pronounced, when the tem- 

 perature becomes sufficiently high to decompose the limestone. 

 Due to the loss in weight caused by the evolution of carbon 

 dioxide, the percentage of calcium oxide present continually in- 

 creases and the percentage of carbon dioxide decreases. The 

 curve representing the alkalinity, or the acid-consuming value, 

 of the mixture does not change so much as the other two. The 

 factors that tend to make the curve rise and those having the 

 reverse effect largely neutralize each other. 38 



SUMMARY 



In determining the calcium carbonate content of Portland ce- 

 ment raw mixture the methods available may be divided into two 

 classes; namely, those in which the calcium is determined and 

 those in which some other constituent is determined. Although 

 some methods of the first class have been greatly shortened by 

 several investigators, generally some method of the second class 

 is employed in control work because of simplicity and rapidity. 

 While all methods are subject to errors arising from the appa- 

 ratus and from the procedure employed, errors due to the nature 

 of the constituents of the raw mixture may greatly influence 

 the results. The causes of errors that may arise have been 

 studied. » 



" An investigation of certain phases of the subject is now in progress. 



