quantity (the polarizability) and a
macroscopic quantity (the dielectric
constant); it was derived using
macroscopic electrostatics by the Italian physicist Ottaviano Fabrizio
Mossotti (1791–1863) in 1850 and independently by Rudolf *Clausius in
1879. It works best for gases and is
only approximately true for liquids
or solids, particularly if the dielectric
constant is large. Compare lorentz–
lorenz equation.
Claus process A process for obtaining sulphur from hydrogen sulphide
(from natural gas or crude oil). It involves two stages. First, part of the
hydrogen sulphide is oxidized to sulphur dioxide:
2H 2 S + 3O 2 → 2SO 2 + 2H 2 O
Subsequently, the sulphur dioxide reacts with hydrogen sulphide to produce sulphur:
SO 2 + 2H 2 S → 3S + 2H 2 O
The second stage occurs at 300°C and
needs an iron or aluminium oxide
catalyst.
clay A Üne-grained deposit consisting chieÛy of *clay minerals. It is
characteristically plastic and virtually
impermeable when wet and cracks
when it dries out. In geology the size
of the constituent particles is usually
taken to be less than 1/256 mm. In
soil science clay is regarded as a soil
with particles less than 0.002 mm in
size.
clay minerals Very small particles,
chieÛy hydrous silicates of aluminium, sometimes with magnesium and/or iron substituting for all
or part of the aluminium, that are
the major constituents of clay materials. The particles are essentially
crystalline (either platy or Übrous)
with a layered structure, but may be
amorphous or metalloidal. The clay
minerals are responsible for the plastic properties of clay; the particles
have the property of being able to
hold water. The chief groups of clay
minerals are:
kaolinite, Al 4 Si 4 O 10 (OH) 8 , the chief
constituent of *kaolin;
halloysite, Al 4 Si 4 (OH) 8 O 10 .4H 2 O;
illite, KAl 4 (Si,Al) 8 O 18 .2H 2 O;
montmorillonite, (Na,Ca) 0.33 (Al,Mg) 2 -
Si 4 O 10 (OH) 2 .nH 2 O, formed chieÛy
through alteration of volcanic ash;
and
vermiculite, (Mg,Fe,Al) 3 (Al,Si) 4 -
O 10 (OH) 2 .4H 2 O, used as an insulating material and potting soil.
cleavage The splitting of a crystal
along planes of atoms in the lattice.
Clemmensen reduction A
method of reducing a *carbonyl
group (C=O) to CH 2 , using zinc amalgam and concentrated hydrochloric
acid. It is used as a method of ascending a homologous series. The reaction is named after Erik Clemmensen
(1876–1941).
clinal See torsion angle.
clock reaction See b–z reaction;
oscillating reaction.
closed chain See chain; ring.
close packing The packing of
spheres so as to occupy the minimum amount of space. In a single
plane, each sphere is surrounded by
six close neighbours in a hexagonal
arrangement. The spheres in the second plane Üt into depressions in the
Ürst layer, and so on. Each sphere has
12 other touching spheres. There are
two types of close packing. In hexagonal close packing the spheres in the
third layer are directly over those in
the Ürst, etc., and the arrangement of
planes is ABAB…. In cubic close packing the spheres in the third layer occupy a different set of depressions
than those in the Ürst. The arrange129
close packing
c
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macroscopic quantity (the dielectric
constant); it was derived using
macroscopic electrostatics by the Italian physicist Ottaviano Fabrizio
Mossotti (1791–1863) in 1850 and independently by Rudolf *Clausius in
1879. It works best for gases and is
only approximately true for liquids
or solids, particularly if the dielectric
constant is large. Compare lorentz–
lorenz equation.
Claus process A process for obtaining sulphur from hydrogen sulphide
(from natural gas or crude oil). It involves two stages. First, part of the
hydrogen sulphide is oxidized to sulphur dioxide:
2H 2 S + 3O 2 → 2SO 2 + 2H 2 O
Subsequently, the sulphur dioxide reacts with hydrogen sulphide to produce sulphur:
SO 2 + 2H 2 S → 3S + 2H 2 O
The second stage occurs at 300°C and
needs an iron or aluminium oxide
catalyst.
clay A Üne-grained deposit consisting chieÛy of *clay minerals. It is
characteristically plastic and virtually
impermeable when wet and cracks
when it dries out. In geology the size
of the constituent particles is usually
taken to be less than 1/256 mm. In
soil science clay is regarded as a soil
with particles less than 0.002 mm in
size.
clay minerals Very small particles,
chieÛy hydrous silicates of aluminium, sometimes with magnesium and/or iron substituting for all
or part of the aluminium, that are
the major constituents of clay materials. The particles are essentially
crystalline (either platy or Übrous)
with a layered structure, but may be
amorphous or metalloidal. The clay
minerals are responsible for the plastic properties of clay; the particles
have the property of being able to
hold water. The chief groups of clay
minerals are:
kaolinite, Al 4 Si 4 O 10 (OH) 8 , the chief
constituent of *kaolin;
halloysite, Al 4 Si 4 (OH) 8 O 10 .4H 2 O;
illite, KAl 4 (Si,Al) 8 O 18 .2H 2 O;
montmorillonite, (Na,Ca) 0.33 (Al,Mg) 2 -
Si 4 O 10 (OH) 2 .nH 2 O, formed chieÛy
through alteration of volcanic ash;
and
vermiculite, (Mg,Fe,Al) 3 (Al,Si) 4 -
O 10 (OH) 2 .4H 2 O, used as an insulating material and potting soil.
cleavage The splitting of a crystal
along planes of atoms in the lattice.
Clemmensen reduction A
method of reducing a *carbonyl
group (C=O) to CH 2 , using zinc amalgam and concentrated hydrochloric
acid. It is used as a method of ascending a homologous series. The reaction is named after Erik Clemmensen
(1876–1941).
clinal See torsion angle.
clock reaction See b–z reaction;
oscillating reaction.
closed chain See chain; ring.
close packing The packing of
spheres so as to occupy the minimum amount of space. In a single
plane, each sphere is surrounded by
six close neighbours in a hexagonal
arrangement. The spheres in the second plane Üt into depressions in the
Ürst layer, and so on. Each sphere has
12 other touching spheres. There are
two types of close packing. In hexagonal close packing the spheres in the
third layer are directly over those in
the Ürst, etc., and the arrangement of
planes is ABAB…. In cubic close packing the spheres in the third layer occupy a different set of depressions
than those in the Ürst. The arrange129
close packing
c
www.AzShimi.ir www.AzShimi.com