266 A. Schrauf and EB. 8. Dana—Thermo-electrical 
eal characters had been tested. We give the result in a number 
of individual cases. 
_ + Exceptions. 
G=6°375 Octahedron 67072 - 
6°370 Oct. 5°93 6°411 Cube 
6°356 Oct. Tunaberg 6°046 6°415 Cube, Pyr. 
6°341 Pyr., Oct. 6°010 | Cube alone 
6°442 Cube Pyr. 5°927 { from Tunaberg 
6°387 Oct. Pyr. 5905 
6151 
6°160 
6°215 ) Pyritohedrons from 
6°263 a ecubs 
6°208 | Pyr. from 
6-265 thn 
aberg 
5984 Pyr. from Skutterud. 
These figures agree essentially—to 80 or 90 per cent—with our 
preceding conclusions, that the crystals rich in cobalt are nega- 
iv e a higher specific gravity. e may, however, 
with more certainty conclude that the octahedrons are negative 
and have G>6°30, while the cubes are positive and have 
G<6'1; the pyritohedrons vary in sign +, and have G>611. 
We found also two exceptions in the density, which we place 
beside the others without attempting an explanation by the 
suggestion of a possible admixture of nickel. 
G. Sulphides of Iron. 
The important work of G. Rose has directed especial atten- 
tion to this species. On page 258 we have already given some 
results, which we obtained under the supposition of some eS 
sential connection between form and electrical character. A 
few observations are here added which relate especially to the 
chemical composition. 
Sulphid of Tron, | Marcasite. Pyrite. 
=A _—e — 
FPlight® \G@=4°83\G=5-019 Elba G=4°°°6 b Seeak 
1 =5°020 Piedmont =4°941 { Devon 
| =5°195 polished =4'992 Cube 
erystals, Zephar+ | =4:998 Turinsk. | 
_ Among the very large number of crystals we were able to 
investizate, we found only a few which over the whole surface, 
as well as in the interior, were homogenous +.¢ This will ex- 
plain the small number of determinations of specific gravity. 
. * Flight, Ann. 
