42 
NORTH GALLERY. 
[UPPER 
other ; but the transition is not an abrupt one. The alloys, or mix- 
tures of metals of one and the same group, were associated in the 
first division with the metallic elements that compose them. But 
where metals belonging to distinct chemical groups are combined, they 
cannot be classed with the free elements. Such are the combinations 
of Arsenic, Antimony, and Bismuth with metals of other groups, and 
they (the Arsenides, Antimonides, &c.) accordingly take their places as 
the first section of Division II. and will be found arranged in the latter 
half of Case 4. 
Section ii. Next in order to these are placed, as a second section of Division 
II., the compounds of metals with the "thionid elements;" and 
accordingly the Tellurides, Selenides, and Sulphides are displayed in 
Cases 5 to 9 inclusive. 
These are succeeded by a third section of this division, namely, by 
Case 5 (i.) Minerals to form which compounds belonging to each of the former 
sections are combined together. 
These three sections may be severally represented by their promi- 
nent members, the arsenides, the sulphides, and the arseno-sulphides. 
Case 7 (i.) The ^ rst °f tnese sections comprises the cuprous Arsenides, such 
as Domeykite, the tricuprous arsenide ; also, the antimonide of 
Silver or Discrasite, diargentous antimonide. Besides these there 
are included in this section several compounds of Iron, Cobalt, and 
Nickel. Nickeline, called also " Copper Nickel," from its colour, is a 
Cases 5 & 6. rhombohedral mineral, the nickelous monarsenide. Rammelsbergite 
Case 8 (i.) is the nickelous diarsenide and Smaltine, or " tin- white Cobalt," the 
cobaltous diarsenide, SafHorite being a variety of this last, containing 
Iron in place of a part of its Cobalt. These minerals are cubic in 
form, but some of the same substances which constitute them are 
also found in prismatic forms, affording examples of dimorphism. 
Thus the nickelous diarsenide, when thus occurring in crystals of 
the prismatic system, is the mineral Chloanthite, and Leucopyrite is a 
ferrous diarsenide. 
In this section is also included the cobaltous triarsenide, Skutteru- 
dite. 
The second section includes the various compounds of Sulphur, 
Selenium, or Tellurium — the Thionid elements — with the metals. 
Silver, a monad element, and Copper, a metal that in one group of its 
salts plays the part of a monad element, contribute to form a small 
group in this section of the type M 2 2. Thus Petzite is the Silver 
(diargentous) telluride, Naumannite the corresponding selenide of 
Silver, while Argentite i3 the sulphide of Silver. These are cubic in 
crystallization, but the sulphide of Silver is a dimorphous mineral pre- 
senting itself as Acanthite in forms belonging to the prismatic system. 
To this system belongs also Redruthite, a valuable ore of Copper, the 
"cuprous" (or dicupric) sulphide. Among the other important 
minerals in this section, a cubic series of mono-sulphides occurs which 
Beetfon i mc ^ Uf ^ es two commercially very important ores — Galena, the sulphide 
Caae 4 (ii.; °f Load, and Blende, the sulphide of Zinc. 
A Ithombohedral series includes Covelline, the cupric (monocupric) 
