xv, i Witt: Portland Cement Raw Mixture HI 
they have some effect on the accuracy of the results. One such 
modification is to precipitate and reprecipitate the iron and alu- 
minium from hydrochloric acid solution without first removing 
the silica. The calcium in the filtrate is precipitated once as 
the oxalate, and the precipitate is titrated with permanganate. 32 
The method may be still further shortened by neutralizing 
the original hydrochloric acid solution with ammonia and adding 
some organic acid in which calcium oxalate is not appreciably 
soluble. The calcium may be precipitated as oxalate without 
the removal of iron and aluminium. The calcium oxalate is 
filtered out, and the determination is completed in the regular 
manner. Citric, 33 tartaric, 34 and oxalic 35 acid have been used. 
Of the methods noted above, several are used extensively for 
controlling the calcium carbonate content of raw mixtures in 
cement plants. These include some modification of the determi- 
nation of calcium by precipitation with ammonium oxalate and 
titration with permanganate, the determination of carbon dioxide 
wfith the calcimeter, the determination of total alkalinity by 
titration with standard acid and alkali, and the determination 
of acid-insoluble matter. The last named is used much less fre- 
quently than the others. The procedure in each case that I have 
found best suited to the raw mixture discussed in this paper is 
as follows : 
In determining the calcium, the usual method of igniting the 
raw mixture before adding hydrochloric acid at the beginning 
of an analysis is not sufficient. 3 ® Eesults are the same either 
with or without ignition, but almost 2 per cent too low. It is 
necessary to fuse with sodium carbonate. To avoid one filtra- 
tion, the whole sample is fused instead of simply the acid- 
insoluble residue. The melt is dissolved in hydrochloric acid and 
the iron and the aluminium are removed by twice precipitating 
with ammonia. The calcium in the filtrate is precipitated once 
with ammonium oxalate, and the precipitate is dissolved in dilute 
sulphuric acid and titrated with permanganate. The titration 
method has been found more satisfactory than ignition, for use 
"Enright, B., Journ. Am. Chem. Soc. 26 (1904) 1003. 
88 Passon, Max, Zeitschr. f. Ang. Chem. (1898) 776. 
“ Blum, L., Zeitschr. f. Anal. Chem. 39 (1900) 152. 
“Meade, R. K., Chem. Eng. 1 (1904) 21. 
“With reference to igniting the sample, W. F. Hillebrand, Journ. Soc. 
Chem. Ind. 21 (1902) 25, says: “Whether all cement mixtures can be thus 
rendered wholly soluble I am unable to say, but doubtless most of them 
can be, and if so, this method should always be resorted to in order to avoid 
the use of alkali carbonates.” 
