facture of certain paints, ceramics,
and paper. The naturally occurring
forms are used in the manufacture of
sulphuric acid.
CalgonTradename for a water-
softening agent. See hardness of
water.
caliche A mixture of salts found in
deposits between gravel beds in the
Atacama and Tarapaca regions of
Chile. They vary from 4 m to 15 cm
thick and were formed by periodic
leaching of soluble salts during wet
geological epochs, followed by drying
out of inland seas in dry periods.
They are economically important as a
source of nitrates. A typical composi-
tion is NaNO 3 17.6%, NaCl 16.1%,
Na 2 SO 4 6.5%, CaSO 4 5.5%, MgSO 4
3.0%, KNO 3 1.3%, Na 2 B 4 O 7 0.94%,
KClO 3 0.23%, NaIO 3 0.11%, sand and
gravel to 100%.
californium Symbol Cf. A radio-
active metallic transuranic element
belonging to the actinoids; a.n. 98;
mass number of the most stable iso-
tope 251 (half-life about 700 years).
Nine isotopes are known; cali-
fornium–252 is an intense neutron
source, which makes it useful in neu-
tron activation analysis and poten-
tially useful as a radiation source in
medicine. The element wasÜrst pro-
duced by Glenn Seaborg (1912–99)
and associates in 1950.
A
- Information from the WebElements site
calixarenes Compounds that have
molecules with a cuplike structure
(the name comes from the Greek
calix, cup). The simplest, has four
phenol molecules joined by four
–CH 2 – groups into a ring (forming
the base of the ‘cup’). The four phe-
nol hexagons point in the same di-
rection to form a cavity that can bind
substrate molecules. Interest has
been shown in the potential ability
of calixarene molecules to mimic en-
zyme action.calmodulinA protein, consisting
of 148 amino-acid residues, that acts
as a receptor for calcium ions in
many calcium-regulated processes in
both animal and plant cells. Calmo-
dulin mediates reactions catalysed by
many enzymes.calomelSee mercury(i) chloride.calomel half cell (calomel elec-
trode) A type of half cell in which
the electrode is mercury coated with
calomel (HgCl) and the electrolyte is
a solution of potassium chloride and
saturated calomel. The standard elec-
trode potential is –0.2415 volt (25°C).
In the calomel half cell the reactions
are
HgCl(s) ˆHg+(aq) + Cl–(aq)Hg+(aq) + e ˆHg(s)
The overall reaction is
HgCl(s) + e ˆHg(s) + Cl–(aq)
This is equivalent to a Cl 2 (g)|Cl–(aq)
half cell.calorieThe quantity of heat re-
quired to raise the temperature of 1
gram of water by 1°C (1 K). The calo-
rie, a c.g.s. unit, is now largely re-
placed by the *joule, an *SI unit. 1
calorie = 4.186 8 joules.Calorie(kilogram calorie; kilocalo-
rie)1000 calories. This unit is still in
limited use in estimating the energy
value of foods, but is obsolescent.caloriÜc valueThe heat per unit
mass produced by complete combus-
tion of a given substance. CaloriÜc
values are used to express the energy
values of fuels; usually these are ex-
pressed in megajoules per kilogram
(MJ kg–1). They are also used to meas-
ure the energy content of foodstuffs;
i.e. the energy produced when the
food is oxidized in the body. The
units here are kilojoules per gram95 calorific value
c