combinations)A linear combination
of atomic orbitals (LCAO), which is a
‘building block’ of the LCAO orbitals
making up a *molecular orbital. The
SALC are constructed by group
theory appropriate for the symmetry
group of the molecule. SALC are used
in the construction of molecular or-
bitals.
salicylic acid (1-hydroxybenzoic
acid)A naturally occurring car-
boxylic acid, HOC 6 H 4 COOH, found in
certain plants; r.d. 1.44; m.p. 159°C;
sublimes at 211°C. It is used in the
foodstuffs and dyestuffs industries.
See also aspirin.
salineDescribing a chemical com-
pound that is a salt, or a solution
containing a salt.
salinometerAn instrument for
measuring the salinity of a solution.
There are two main types: one is a
type of hydrometer to measure den-
sity; the other is an apparatus for
measuring the electrical conductivity
of the solution.
sal sodaAnhydrous *sodium car-
bonate, Na 2 CO 3.
saltA compound formed by reac-
tion of an acid with a base, in which
the hydrogen of the acid has been re-
placed by metal or other positive
ions. Typically, salts are crystalline
ionic compounds such as Na+Cl–and
NH 4 +NO 3 –. Covalent metal com-
pounds, such as TiCl 4 , are also often
regarded as salts.
salt bridge An electrical connec-
tion made between two half cells. It
usually consists of a glass U-tube
Ülled with agar jelly containing a
salt, such as potassium chloride. A
strip ofÜlter paper soaked in the salt
solution can also be used.
salt cake Industrial *sodium sul-
phate.
salting inSee salting out.salting outThe effect in which the
solubility of a substance in a certain
solvent is reduced by the presence of
a second solute dissolved in the sol-
vent. For example, certain substances
dissolved in water can be precipi-
tated (or evolved as a gas) by addition
of an ionic salt. The substance is
more soluble in pure water than in
the salt solution. The opposite effect
involving an increase in solubility
may occur. This is known as salting
in.saltpetre See nitre.samariumSymbol Sm. A soft sil-
very metallic element belonging to
the *lanthanoids; a.n. 62; r.a.m.
150.35; r.d. 7.52 (20°C); m.p. 1077°C;
b.p. 1791°C. It occurs in monazite
and bastnatite. There are seven natu-
rally occurring isotopes, all of which
are stable except samarium–147,
which is weakly radioactive (half-life
2.5 × 1011 years). The metal is used
in special alloys for making nuclear-
reactor parts as it is a neutron ab-
sorber. Samarium oxide (Sm 2 O 3 ) is
used in small quantities in special op-
tical glasses. The largest use of the el-
ement is in the ferromagnetic alloy
SmCo 5 , which produces permanent
magnetsÜve times stronger than any
other material. The element was dis-
covered by François Lecoq de Bois-
baudran in 1879.
A- Information from the WebElements site
sandParticles of rock with diame-
ters in the range 0.06–2.00 mm. Most
sands are composed chieÛy of parti-
cles of quartz, which are derived
from the weathering of quartz-
bearing rocks.
Sandmeyer reaction A reaction of
diazonium salts used to prepare
chloro- or bromo-substituted aro-471 Sandmeyer reaction
s