Chemistry Reference
In-Depth Information
century B.C.E., described mercury, and Theophrastus, his disciple, gave
details on a method used at that time for extracting the metal from its ore:
rubbing native cinnabar with vinegar in a copper mortar with a copper pestle
yielded the liquid metal (Hill 1774), an apparently very early example of a
mechanical chemistry reaction.
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MERCURY SMELTING
Smelting
cinnabar
a mercury ore (composed of mercury sulfide) is a rela-
tively simple, two-stage heating process: first roasting of the ore and then
reducing and boiling the metal. Heating the ore at a relatively low tem-
perature, in an atmosphere rich in oxygen, roasts the mercury sulfide,
which is converted to mercuric oxide:
HgS
+
O
→
HgO
+
SO
↑
2
2
cinnabar
mercuric sulfide
mercuric oxide
(
)
Further heating results in decomposition of the oxide formed and the
release of mercury vapor:
heat
2
HgO
2
Hg
O
→↑ +
↑
2
The mercury vapor evolved was, in the past, directed toward cooled earth-
enware pipes over the furnace, where it condensed into liquid metal.
From there it was then collected in special containers, together with con-
siderable amounts of soot. The crude metal thus obtained was refined by
further distillation.
Amalgams.
When gold or silver is mixed with mercury, it forms alloys
known as
amalgams
, which are soft when freshly prepared but harden after
some time. If an amalgam is heated to about 360°C, the boiling temperature
of mercury, the mercury in the amalgam evaporates, leaving behind the gold
or silver with which it was amalgamated. The property of gold and silver to
amalgamate was known in antiquity, and it was, and still is, used to extract
gold and silver from some of their ores. When extracting gold from aurifer-
ous sands, for example, the sand was brought into close contact with mercury
so that the gold combined with the mercury and formed an amalgam that can
