MINERALOGY. 65 
iron to remove the chlorine from the chloride, and to separate the silver in 
the metallic state. The residuum is then, as before remarked, to be agitated 
for a long time with mercury and iron in vessels, during which operation 
the amalgam is formed. After straining this amalgam, to separate the 
uncombined mercury, the residuum is placed in iron vessels and distilled. 
The mercury passes over in a sublimation, and the silver is left pure. 
3. Sulphuret of Copper and Copper Pyrites. 
The expressions, glance and pyrites, generally indicate combinations of 
sulphur. The copper pyrites forms an important ore from which to obtain 
the pure metal. It is a combination of simple sulphuret of copper with 
simple sulphuret of iron, and contains from thirty-two to thirty-four per 
cent. of copper. It is extensively distributed in veins and beds in primitive 
and transition rocks, being generally accompanied by galena. Copper 
pyrites has a brassy-yellow color, rather deeper than that of sulphuret of 
iron, and generally occurs in coarse masses, whose cavities present crystals 
belonging to the dimetric system, and exhibiting the faces of an acute 
( pl. 33, fig. 37), or an oblong (fig. 48), square octahedron. When roasted 
in the air its sulphur is converted into sulphurous acid, while the iron and 
copper oxydize, and combining with the sulphuric acid, form a soluble salt 
obtained by leaching the roasted mass. This salt is much used in the arts, 
being known as blue vitriol, containing green vitriol. This same double 
salt forms in mines by the gradual oxydation of copper pyrites, a 
considerable amount of which is dissolved in the waters of such mines. 
The salt is obtained from this solution, either by evaporation or by 
precipitating metallic copper by means of iron. The principal portion of 
the pyrites procured in mines is, after roasting, reduced to metallic copper. 
It is first melted with its flint matrix, by which means the oxydized iron is 
principally combined with the quartz, and converted into a slag, under 
which lies the copper combined with sulphur. This, after repeated 
roasting, is again melted with quartz sand and charcoal, and still more freed 
frem iron, until finally an impure, sulphurous, and little ductile copper is 
found under the slag, mixed with the accompanying metals, lead, iron, 
arsenic, antimony, zinc, &c. This impure copper is_ purified by 
long-continued fusion in the melting furnace, in which the foreign 
admixtures are partly oxydized, partly driven off. The metal still requires 
additional preparation by being melted with charcoal before it will become 
perfectly malleable. 
4. Iron Pyrites. 
This is a sulphuret of iron which occurs extensively distributed, and in 
large quantity. It is found either crystallized or amorphous, in various 
rocks, clay slate, greenstone, hornblende, syenite, &c.; also in independent 
beds of considerable size, or in veins accompanying other ores. The 
erystallizations of pyrites are among the most perfect which occur in nature. 
Pi. 33, fig. 2, exhibits some single crystals from Chamouny: a is a cube 
distorted to a rectangular parallelopipedon ; b is a pentagonal dodecahedron, 
whose pure crystalline shape would be that of fig. 57. Fig. 15 exhibits an 
agglomeration of cubes of pyrites lying between crystals of calcareous. spar ; 
495 
