40 
CONTRIBUTIONS TO CHEMISTRY AND MINERALOGY. [bull. 167. 
Table II. 
[Varying amounts of standardNo. 2 (1 c. c. =0.2 rag. Cr 2 3 ) diluted till of the same concentration as 
standard No. 1.1 
No. 
Standard. 
Chromic 
oxide 
found per 
100 c. c. 
Chromic 
Chromic 
oxide 
found. 
Cubic cen- 
timeters. 
Water 
added. 
Contents 
as chromic 
oxide. 
oxide 
present in 
100 c. c. 
Error. 
18 
19 
20 
21 
22 
5 
10 
15 
20 
30 
c. c. 
5.2 
9.95 
15.8 
20.6 
29.5 
Mqs. 
1 
2 
3 
4 
5 
jslgs. 
9.80 
10.02 
9.74 
10.00 
10.08 
Mys. 
10 
10 
10 
10 
10 
Mg. 
—0.2 
+ .02 
— .26 
.00 
+ .08 
Per cent. 
98.0 
100.2 
97.4 
100.0 
100.8 
Mean perceDtage found, 99. 3; grand mean, 100. 36. 
The first table and the grand mean show an apparent personal 
tendency toward slightly high results, though it is possible that this 
is due to a slight difference in the internal dimensions of the two 
glasses, the same one always having been used for the standard solu- 
tion. If this is so, a long series of tests with glasses reversed should 
give a general mean slightly below 100. 
Testing the Method on Ores and Bocks. 
In order to prove the value of the method in rock analysis, varying 
amounts of the standard solution were evaporated in a large crucible 
with 5 grams of an iron ore carrying phosphorus and vanadium, and 
fused with 20 grams of sodium carbonate and 3 grams sodium nitrate. 
The aqueous extract, after reduction of manganese by methyl or ethyl 
alcohol, was nearly neutralized by nitric acid and evaporated to secure 
approximate separation of silica and alumina. As a precautionary 
measure, since a little chromium is usually carried down, the precipi- 
tate was ignited, silica was remove;! by hydrofluoric and sulphuric 
acids, the residue was fused with sodium carbonate, and alumina again 
separated as before. To the combined filtrate was added mercurous 
nitrate, and the slightly washed copious precipitate of phosphate, chro- 
mate, vanadate, and carbonate of mercury was ignited with the paper 
in a platinum crucible, which can be done without much fear of loss or 
of injury to the crucible. The residue was then fused with a little 
sodium carbonate, extracted with water, filtered into a graduated flask 
and made up to 50 or 100 cubic centimeters, according to the intensity 
of the color, and compared with the standard. A similar operation 
was carried out with a silicate rock. Table III shows the results. 
