44 
NORTH GALLERY. 
[UPPER 
In one — and that a somewhat ambiguous — class of these Salts, Iron, 
either as a ferric sulphide (Fe 2 S 3 ) or as ferrous bisulphide (Fe S 2 ), 
would seem to enter as a constituent of the "acid" ingredient. In 
this class we meet with two important copper ores, the largely worked 
Case 10. Chalco-pyrites or Copper-pyrites, and Bornite or Purple Copper-ore. 
Of both these minerals, there are crystallized specimens from Corn- 
wall ; and massive pieces from Tuscany are seen in the front of Case 7. 
The rare mineral, Sternbergite, consisting of Iron, Sulphur, and 
Silver, belongs also to this class; while Linnaeite, or " Cobalt-pyrites," 
is a sulphur-compound of Cobalt, exactly analogous to the oxygen-com- 
pounds termed the " magnetic oxides" of Iron or Manganese, (Co 3 S 4 , 
cobaltous epitrisulphide). 
Case 13. Tin-pyrites is a bibasic sulphostannate of Copper, containing Iron 
and Zinc, and is a salt of the stannic sulphide Sn S 2 , (sulphos tannic 
acid). 
The largest class of the sulphur salts is that consisting of sulph- 
arsenites, sulpho-bismuthites, and sulph-antimonites. Among these 
Case 1L Tetrahedrite (Fahlore or Grey Copper), is noticeable as a most im- 
portant ore of Copper. It is a sulph-antimonite of that metal, in which 
cuprous sulphide is frequently displaced by small amounts of argentic 
sulphide, and is also associated with sulphides of Iron and Zinc. In 
some of its varieties, as in Tennantite, the trisulphide of Antimony is 
entirely, and in others partially, displaced by an equivalent trisulphide 
of Arsenic. The argentiferous Tetrahedrite is a valuable ore of Silver. 
The specimens of Bournonite, a tri-basic sulph-antimonite of Copper 
and Lead, recently raised in Cornwall, are the finest that have been 
Case 11. found; and those from the Hartz, and from Traversella, are not un- 
worthy of juxtaposition with them. The so-called Bed Silvers, a group 
of isomorphous rhombohedral minerals, are the tri-basic sulphantimo- 
Case 12. nite and sulpharsenite of Silver, Pyrargyrite and Proustite ; sometimes 
in a comparatively isolated state, but more frequently blended together 
in various proportions. Beautiful as well for their forms as for their 
blood-red colours, that are deeper in intensity according as the anti- 
mony preponderates over arsenic, they constitute one of the more pre- 
cious of the ores of Silver. The specimens of Pyrargyrite and Proustite 
exhibited in Case 12, and in particular those of the latter mineral from 
Chili, are extremely fine. 
Among the rarer minerals, attention may be called to the fine 
Case 12. specimens of Frieslebenite, a mineral which is abundant enough to 
become an ore at Huendelencina, in Spain; also to Fireblende and 
Xanthocone, the latter containing a sulpharseniate of Silver, combined 
with the tri-basic sulpharsenite of that metal. 
Div. III. Compounds of the Halogen Elements. 
Cases 13, This next principal division of the Collection is also subdivided into 
14. the simpler compounds, and a more complex section of Salts. Among 
the former will rank Calomel, Salammoniac, Common Salt, and the 
