ment is ABCABC.... See also cubic
crystal.
A- An interactive version of cubic close-
packing - An interactive version of hexagonal
close packing
closo-structure See borane.club drugA drug typically used by
young people at clubs, parties, etc.
Examples are ecstasy, gammahydrox-
ybutyric acid (GHB), and metham-
phetamines.Clusius columnA device for sepa-
rating isotopes by thermal diffusion.
One form consists of a vertical col-
umn some 30 metres high with a
heated electric wire running along its
axis. The lighter isotopes in a gaseous
mixture of isotopes diffuse faster
than the heavier isotopes. Heated by
the axial wire, and assisted by nat-
ural convection, the lighter atoms
are carried to the top of the column,
where a fraction rich in lighter iso-
topes can be removed for further en-
richment.cluster compoundA compound
in which groups of metal atoms are
joined together by metal–metal
bonds. The formation of such com-
pounds is a feature of the chemistry
of certain elements, particularly
molybdenum and tungsten, but also
vanadium, tantalum, niobium, and
uranium. Isopoly compounds are
ones in which the cluster contains
atoms of the same element; het-
eropoly compounds contain a mix-
ture of different elements.
CMLSee chemical markup lan-
guage.coacervateAn aggregate of macro-
molecules, such as proteins, lipids,
and nucleic acids, that form a stable
*colloid unit with properties that re-
semble living matter. Many arecoated with a lipid membrane and
contain enzymes that are capable of
converting such substances as glu-
cose into more complex molecules,
such as starch. Coacervate droplets
arise spontaneously under appropri-
ate conditions and may have been
the prebiological systems from
which living organisms originated.coagulationThe process in which
colloidal particles come together irre-
versibly to form larger masses. Coag-
ulation can be brought about by
adding ions to change the ionic
strength of the solution and thus
destabilize the colloid (see floccula-
tion). Ions with a high charge are
particularly effective (e.g. alum, con-
taining Al3+, is used in styptics to co-
agulate blood). Another example of
ionic coagulation is in the formation
of river deltas, which occurs when
colloidal silt particles in rivers are co-
agulated by ions in sea water. Alum
and iron (III) sulphate are also used
for coagulation in sewage treatment.
Heating is another way of coagulat-
ing certain colloids (e.g. boiling an
egg coagulates the albumin).
coalA brown or black carbonaceous
deposit derived from the accumula-
tion and alteration of ancient vegeta-
tion, which originated largely in
swamps or other moist environ-
ments. As the vegetation decom-
posed it formed layers of peat, which
were subsequently buried (for exam-
ple, by marine sediments following a
rise in sea level or subsidence of the
land). Under the increased pressure
and resulting higher temperatures
the peat was transformed into coal.
Two types of coal are recognized:
humic(or woody) coals, derived from
plant remains; and sapropelic coals,
which are derived from algae, spores,
andÜnely divided plant material.
As the processes of coaliÜcation (i.e.
the transformation resulting fromcloso-structure 130c