110 
Philippine Journal of Science 
1919 
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 AhCh -f Fe : Oj precipitate a few drops 
of NH 4 OH 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 CaCiCh 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 0 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, 18 weighed as oxide after ignition and blasted in a 
covered crucible to constant weight, or determined with dilute standard 
permanganate. 29 
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 / 10 the possible contamination of the precipitate , 71 
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. 
28 The volume of wash water should not be too large; vide Hillebrand. 
United States Geological Survey, Bull. 122, p. 119. [Footnote in original.] 
29 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. 
SI Taubner, H., Chem. Zeitg. 26 (1902) 246. 
