HO Philippine Journal of Science m» 



out. The iron and the aluminium are removed by precipitating 

 twice with ammonium hydroxide. The determination is com- 

 pleted as follows : 27 



To the combined filtrate from the AUOa -j- Fe : 3 precipitate a few drops 

 of NH4OH are added, and the solution brought to boiling. To the boiling 

 solution 20 cc of a saturated solution of ammonium oxalate is added, and 

 the boiling continued until the precipitated CaCsO* assumes a well-defined 

 granular form. It is then allowed to stand for 20 minutes, or until the 

 precipitate has settled, and then filtered and washed. The precipitate and 

 filter are placed wet in a platinum crucible, and the paper is burned off 

 over a small flame of a Bunsen burner. It is then ignited, redissolved 

 in HC1, and the solution made up to 100 cc with water. Ammonia is added 

 in slight excess, and the liquid is boiled. If a small amount of A1 2 3 sep- 

 arates this is filtered out, weighed, and the amount added to that found 

 in the first determination, when greater accuracy is desired. The lime is 

 then reprecipitated by ammonium oxalate, allowed to stand until settled, 

 filtered and washed,' 8 weighed as oxide after ignition and blasted in a 

 covered crucible to constant weight, or determined with dilute standard 

 permanganate. 2 " 



Although the procedure given the preference in the official 

 method (igniting the precipitate and weighing the oxide) is 

 subject to several sources of error, such as the solubility of the 

 oxalate in water,- the possible contamination of the precipitate/' 1 

 the absorption of moisture during weighing, and the like, it is 

 generally conceded to be the most accurate method known at 

 present. Its principal disadvantage in commercial work is the 

 time required. According to the original report, it takes almost 

 seven hours to run a sample of raw mixture to the completion 

 of the calcium determination, and the time required to obtain the 

 result can be only slightly shortened by omitting the completion 

 of the silica, iron, and aluminium determinations. Only a few 

 minutes for each sample may be saved by substituting the titra- 

 tion method, if all the separations are made as specified. 



In connection with the titration method, however, several 

 modifications have been developed which shorten the time, though 



" From Method suggested for the analysis of limestones, raw mixtures, 

 and Portland cement by the committee on uniformity in technical analysis 

 with the advice of W. F. Hillebrand, Cir. U. S. Bur. Standards 33 (1912) 15. 

 For the original report of this committee, see Journ. Soc. Chem. Ind. 21 

 (1902) 12-30. 



2 " The volume of wash water should not be too large; vide Hillebrand. 

 United States Geological Survey, Bull. 422, p. 119. [Footnote in original.] 



18 The accuracy of this method admits of criticism, but its convenience 

 and rapidity demand its insertion. [Footnote in original.] 



"• See also Peters, C. A., loc. cit. 



"Taubner, H., Chem. Zeitg. 26 (1902) 246. 



