Properties of some Minerals and their varieties, 261 
Mispickel Fe(SAs), + England. 
€ . — Freiberg 
“ (Weisserz) (FeAg)(SAs), — Freiber 
ite 
Dana (CoFe)(SAs), + Yianosie 
. = — Norway. 
Although tables A and B embrace a considerable number of 
minerals, they afford only a few general conclusions. 
(a.) In the compounds of the negative metals Bi, Co, Ni, Pb, 
the character of the metal outweighs that of the S. 
(6.) The addition of antimony has the result of weakening 
this negative character; that of tellurium strengthens it. 
(c.) In combination with iron the arsenides are negative, but 
the majority of the sulphides positive. 
more accurate understanding of the relations between 
chemical nature and thermo-electricity can be obtained only 
from those minerals which are sometimes +, sometimes —. 
_ In order to give the proof of this, it is necessary to introduce 
into the following tables, besides our observations on the thermo- 
* Tait has shown recently that iron changes its thermo-electrical sign at a red 
heat; and this same is es of nickel at a somewhat lower temperature. a 
is inclined to ascribe this phenomenon to a change in the arrangement of t 
Molecules. Our investigations, however, are based upon the character _ iy ot 
ee eee 
substance ing into an allotropic condition in . 
The molecular arrangement is, therefore, to be assumed as unchanged in these 
experiments. : 
+ Analyses and specific gravity determinations, taken from other authors, are 
Printed in italics. os 
