STORES.] 
DATA FOR PYRITE AND MARCASITE 
IV. DATA FOR PYRITE. 
25 
The following table gives duplicate determinations of y>, made upon 
well-crystallized samples of pyrite free from visible impurities, but 
otherwise selected at random. 
Determinations of p made upon samples of pyrite. 
No. 
Locality. 
Density. 
P- 
Mean value 
of p. 
1 
Unknown ..... 
j 60. 1 
1 59. 9 
60.0 
2 
Custer County , Colo ........ 
5.018 
J 00.4 
1 59. 7 
60.0 
3 
Roxbury, Conn 
5.023 
J 61.2 
1 60. 9 
f 60. 2 
61.0 
4 
Lead ville, Colo 
60. 2 
60.4 
60. 3 
5 
Old Jordan mine, Utah . 
5.041 
f 60. 5 
| 61.1 
60.8 
Mean value of p, 60.4. 
No. 1. A large cube, with slight tarnisb and splendent conchoidal fracture. 
Traces of silica, copper, and arsenic. 
No. 2. Octahedron, with fracture on peripheral part conchoidal. on the interior 
somewhat uneven or granular. Slight trace of copper. 
No. 3. Combination of cube and octahedron, with conchoidal fracture. Traces 
o! copper end arsenic. 
No. 4. Cubes. Traces of silica and copper. 
No. 5. Cubes, splendent conchoidal fracture. Trace of copper. 
OXIDATION COEFFICIENT OF PYRITE. 
From the above figures it appears that the oxidation coefficient of 
pyrite is not likely to vary more than 0.6 per cent on duplicate deter- 
minations, and that it may vary about 1 per cent in typical speci- 
mens, which do not contain more than traces of impurities that can 
influence the result. Whether this difference is due to the chemical 
action of the impurity on the solvent, to its electrochemical action on 
the pyrite, or to slight physical differences in the pyrite itself, can 
not be decided at present. The oxidation coefficient of pure pyrite 
may be assumed to be 60.4. Figures higher than 61 or lower than 60 
may be taken to indicate greater contaminations, which can usually 
be detected by anal} r sis, and the influence of some of which is pointed 
out below. 
V. DATA FOR MARCASITE. 
The following table gives the values of p (mostly in duplicate) for 
various samples of marcasite, which were selected as being free from 
