ally because the single step is too
inefÜcient to produce the desired re-
sult. For example, in various ura-
nium-enrichment processes the
separation of the desired isotope is
only poorly achieved in a single
stage; to achieve better separation
the process has to be repeated a
number of times, in a series, with
the enriched fraction of one stage
being fed to the succeeding stage for
further enrichment. Another exam-
ple of cascade process is that operat-
ing in a *cascade liqueÜer.case hardening The hardening of
the surface layer of steel, used for
tools and certain mechanical compo-
nents. The commonest method is to
carburize the surface layer by heat-
ing the metal in a hydrocarbon or by
dipping the red hot metal into
molten sodium cyanide. Diffusion of
nitrogen into the surface layer to
form nitrides is also used.caseinOne of a group of phos-
phate-containing proteins (phospho-
proteins) found in milk. Caseins are
easily digested by the enzymes of
young mammals and represent a
major source of phosphorus.CAS registry A database of chemi-
cal compounds, certain mixtures,
and biological sequences maintained
by the Chemical Abstracts Service of
the American Chemical Society. In
the registry every entry has a unique
CAS registry number (CASRN). This
has three parts: up to six digits, fol-
lowed by two digits, followed by one
digit. For example, the CAS number
of water is 7732-18-5. TheÜnal digit
is a check number. CAS registry
numbers are used for searching
chemical databases. The size of the
registry is immense, with over 32
million substances and 59 million se-
quences. It identiÜes every chemical
that has been described in the litera-ture since 1957 and around 50 000
new numbers are added each week.
A- Further information from the CAS site
- A free service forÜnding CAS numbers
from CambridgeSoft
cassiteriteA yellow, brown, or
black form of tin(IV) oxide, SnO 2 ,
that forms tetragonal, often twinned,
crystals; the principal ore of tin. It oc-
curs in hydrothermal veins and meta-
somatic deposits associated with acid
igneous rocks and in alluvial (placer)
deposits. The chief producers are
Malaysia, Indonesia, Democratic Re-
public of Congo, and Nigeria.cast iron A group of iron alloys
containing 1.8 to 4.5% of carbon. It is
usually cast into speciÜc shapes ready
for machining, heat treatment, or as-
sembly. It is sometimes produced di-
rect from the *blast furnace or it
may be made from remelted *pig
iron.Castner–Kellner cellAn elec-
trolytic cell used industrially for the
production of *sodium hydroxide.
The usually iron cell isÜlled with
brine (sodium chloride solution) and
employs liquid mercury as the cath-
ode. The sodium liberated there
forms an amalgam with the mercury,
which is run off and reacted with
water to give sodium hydroxide (and
hydrogen); the mercury is then re-
used. Chlorine gas produced at the
anode is another valuable by-product.castor oilA pale-coloured oil ex-
tracted from the castor-oil plant. It
contains a mixture of glycerides
of fatty acids, the predominant
acid being ricinoleic acid,
C 17 H 32 (OH)COOH. It is used as a
*drying oil in paints and varnishes
and medically as a laxative.catabolismThe metabolic break-
down of large molecules in living or-case hardening 106c