IOWA ACADEMY OF SCIENCE 
211 
LIMONITE 
a 
Residue , per cent 2.25 
Residue from filtrate, per cent 1.60 
Silica from first residue, per cent 
Silica from second residue, per cent, 
. 2.12 
1.40 
Total silica, per cent 3.52 
b 
3.68 
0.12 
3.52 
0.12 
3.64 
A SPECIMEN OF COMMERCIAL MANGANESE DIOXIDE 
Residue, per cent 12.76 
Residue from filtrate, per cent 1.32 
Silica from first residue, per cent. 7.56 
Silica from second residue, per cent 0.42 
Total silica, per cent 7.98 
A SPECIMEN OF PYROLUSITE 
Residue, per cent 
Residue from filtrate, per cent. 
a 
12.79 
1.60 
Silica from first residue, per cent 7.92 
Silica from second residue, per cent 0.28 
13.95 
0.12 
7.81 
0.12 
7.93 
b 
14.79 
0.19 
7.92 
0.19 
Total silica, per cent 8.20 
8.11 
In the case of the siderites and dolomites studied, the simpler 
method gives results fairly concordant with the more complicated 
method, and the former is therefore to be preferred. A second 
evaporation and stirring to a dry powder gave no residue and 
added nothing to the value of the results. Nitric acid as a solvent 
of the siderites gave smaller residues than hydrochloric acid. 
With the ores of iron other than siderite that were studied, as well 
as the specimens of manganese dioxide, the shorter method, simply 
dissolving in hydrochloric acid, gave generally as satisfactory re- 
sults as the longer method. 
Among the works consulted or referred to in this paper may be 
mentioned Bulletin 305 of the United States Geological Survey 
(Hillebrand) ; The Chemical Analysis of Rocks, Washington; Mil- 
ler-Kiliani Analytische Chemie; Treadwell-Hall Quantitative Anal- 
ysis; Talbot’s Quantitative Chemical Analysis; Fresenius’ Quan- 
titative Analysis; Cairn’s Quantitative Analysis; Clowes and Cole- 
man Quantitative Analysis; Crooke’s Select Methods; Morse, Ex- 
ercises in Quantitative Analysis. 
