CHAPTER L. COPPER, MERCURY, AND SILVER.

COPPER.

Examine native copper, chalcopyrite, malachite, azurite, copper
acetate, copper nitrate, copper sulphate.

278. Occurrence.--Copper occurs both native and in many
compounds, being diffused in rocks and, in minute quantities, in
soils, waters, plants, and animals. Spain, Chili, and the United
States are the chief Cu producing countries. The extensive mines
of Michigan yield the native ore. The Calumet and Heela mine
alone produces 4,000,000 pounds per month. The most abundant
compound of Cu is chalcopyrite, or copper pyrites, CuFeS2.
Malachite, which is green, and azurite, which is blue, are
carbonates, the former being used for ornamental purposes.

Cu is, next to Ag, the best conductor of electricity and heat
among the elements; it is very ductile, malleable, and tenacious.

Cu has two valences, 1 and 2. Symbolize and name its chlorides,
iodides, sulphides, and oxides. Cupric compounds, as a rule, are
more stable than cuprous.

279. Uses.--Thousands of tons of Cu find use in domestic
utensils, ocean vessels, electric wires, batteries, and plating.
Name the chief alloys of Cu and their uses. See page 136. How may
CuS be obtained? See Experiment 7. Cu2O, cuprous oxide, is used
to color glass red. CUSO4 is employed in calico-printing,
electric batteries, etc. It is called blue vitriol.

Paris green, used for killing potato-beetles, is composed chiefly
of copper arsenite. Write the symbol for this compound. All
soluble salts of Cu are poisonous; hence care should be taken not
to bring any acid in contact with copper vessels of domestic use.
With acetic acid, what would be formed?

MERCURY AND ITS COMPOUNDS.

Examine cinnabar, vermilion, mercury, red oxide, mercurous and
mercuric chloride.

280. Cinnabar, HgS, is practically the only source of mercury--
quicksilver. Austria, Spain, and California contain nearly all
the mines. In these mines the metal also occurs native to a small
extent. It is the only commonly occurring metal that is liquid at
ordinary temperatures; it solidifies at about -40 degrees. What
other common liquid element? See page 12. Hg is reduced from the
ore by Fe, Hg being distilled over and collected in water. Heat
regularly expands the metal.

281. Uses.--For uses see Reduction of Ag and Au, pages 165 and
170; amalgams, page 137; laboratory work, page 68. It is also
employed for thermometers and barometers, and as the source of
the red pigment vermilion, which is artificial HgS.

Compare the vapor density and the atomic weight of Hg, and
explain. See page 12. Hg is either a monad or a dyad. Symbolize
its ous and ic oxides and chlorides. Which of the following are
is salts, and which are ous, and why? HgNO3, Hg(NO3)2, HgCl,
HgCl2? Calomel, HgCl or Hg2Cl2, used in medicine, and corrosive
sublimate, HgCl2, are illustrations of the ous and ic salts. The
former is insoluble, the latter soluble. All soluble compounds of
Hg are virulent poisons, for which the antidote is the white of
egg, albumen. With it they coagulate or form an insoluble mass.

SILVER AND ITS COMPOUNDS.

282. Occurrence and Reduction.--Silver is found uncombined, and
combined, as Ag2S, argenite, and AgCl, horn silver. It occurs
usually with galena, PbS. It is abundant in the Western States,
Mexico, and Peru. Silver is separated from galena by melting the
two metals. As they slowly cool, Pb crystallizes, and is removed
by asieve, while Ag is left in the liquid mass. The principle is
much like crystallizing NaCl from solution and leaving behind the
salts of Mg, etc., in the mother liquor. When, by repeating the
process, most of the Pb is eliminated, the rest is oxidized by
heating in the air. Pb + O = PbO. Ag does not oxidize, and is
left in the metallic state.

Another mode of reduction is to change the silver salt to its
chloride, and then remove the Cl with Fe. Roasting with NaCl
makes the first change, 2 NaCl + Ag2S = Na2S + 2 AgCl, and with
Fe the second, 2 AgCl + Fe = FeCl2 + 2 Ag. Ag is separated from
the other products by adding Hg, with which it forms an amalgam.
By distilling this, Hg passes over and Ag remains. This is the
amalgamating process.

283. Salts of Silver are much employed in organic chemistry, and
AgCl, AgBr, and AgNO3 are used in photography. AgNO3 is a
soluble, colorless crystal, and is the basis of the silver salts.
It blackens when in contact with organic matter. Stains on a
photographer's hands are due to this substance, and the use of
AgNO3 in indelible inks depends on the same property. This may be
due to a reduction of AgNO3 to Ag4O. Stains can be removed from
the skin or from linen by a solution of Kl, or of CuCl2 followed
by sodium hyposulphite. Lunar caustic is made by fusing AgNO3
crystals, and is used for cauterizing (burning) the flesh. Much
AgCN finds use in electroplating.

Experiment 128.--Put 5 cc. AgNO3 solution in each of three t.t.
To the first add 3 cc. HCl, to the second 3cc.NaCl solution, and
to the third 3 cc. KBr solution. Write the reaction for each
case, and notice that the first two give the same ppt., as in
fact any soluble chloride would. Filter the second and third, on
separate filter papers, and expose half the residue to direct
sunlight, observing the change of color by occasionally stirring.
Solar rays reduce AgCl and AgBr, it is thought, to Ag2Cl and
Ag2Br. Try to dissolve the other half in Na2S2O3, sodium
thiosulphate solution. This experiment illustrates the main facts
of photography.