xv, i Witt: Portland Cement Raw Mixture H3 



sample may be directly calculated from the known content of the 

 standard by proportion. A table for making these calculations 

 covering the usual range of results for both the standard and 

 the sample may be easily prepared. Errors, such as those due 

 to absorption of carbon dioxide in the hydrochloric acid, lack of 

 accuracy in either thermometer or barometer, and the like, are 

 thus automatically corrected. Everything considered, the labor 

 required by this procedure is no greater than that required by 

 the other, and the results are more satisfactory. When the 

 sample contains considerably more silicate than the standard 

 there will be an error in the result, the reason for which is ex- 

 plained in this paper. It has been proposed to correct this by 

 preparing a series of standards ranging from the lowest to 

 the highest calcium content likely to be found in a sample, and 

 then, for a given determination, using the standard nearest 

 that sample in composition. This would be an improvement, 

 but it is doubtful if the increased labor would be justified. 



In the acid-alkali titration method, the sample is placed in a 

 300-cubic centimeter Erlenmeyer flask, fitted with a rubber 

 stopper bearing a vertical glass tube as a condenser. A measured 

 amount of 0.4 N hydrochloric acid is added, and brought just 

 to a boil over a Bunsen burner. The solution is cooled, diluted 

 to from 100 to 150 cubic centimeters, and titrated with standard 

 sodium hydroxide of the same concentration, using methyl orange 

 as the indicator. Of the several concentrations of acid tried, 

 0.4 N was the lowest that would dissolve nearly all the sample 

 without the application of heat. However, that solution was 

 not quite complete without warming. Methyl orange is pre- 

 ferred to phenolphthalein, although the end point is more dif- 

 ficult to see. It is not necessary to remove the carbonates in 

 preparing the standard sodium hydroxide solution (as should be 

 done if phenolphthalein is to be used), and it is not necessary 

 to boil the acid after the sample is dissolved, to remove the 

 carbon dioxide. 



The method for determining acid-insoluble matter is the same 

 as the one given by Meade, except that hydrochloric acid having 

 a density of 1.125 is used. The sample is treated w T ith this 

 acid, and the mixture is boiled several minutes. The insoluble 

 matter is then collected, washed, ignited, and weighed. 



The raw mixture with which this paper is concerned is made 

 from three materials; namely, a hard limestone, and two sili- 

 ceous materials that are designated silicate 1 and silicate 2. 

 The analyses of these materials are shown in Table I. 



166316 8 



