Dictionary of Chemistry [6th Ed.]

hydrogen. Sorbitol is used as a sweet-

ener (in diabetic foods) and in the

manufacture of vitamin C and vari-

ous cosmetics, foodstuffs, and medi-

cines.

sorption*Absorption of a gas by a

solid.

sorption pumpA type of vacuum

pump in which gas is removed from

a system by absorption on a solid

(e.g. activated charcoal or a zeolite) at

low temperature.

Soxhlet apparatusAn apparatus

for extracting components from a

solid (e.g. extracting natural products

from plant material). The material

used is placed in a thimble made of

thickÜlter paper and this is held in a

specially designed reÛex condenser

with a suitable solvent. The chamber

holding the thimbleÜlls with warm

solvent and this is led back to the

source via a side arm. The apparatus

can be operated for long periods,

with components concentrating in

the source vessel. It is named after

Franz Soxhlet, who devised it in

1879.

spSynperiplanar. See torsion

angle.

space group A group of symmetry

elements applying to a lattice. Com-

pare point group.

speciesA chemical entity, such as a

particular atom, ion, or molecule.

speciÜc 1.Denoting that an exten-

sive physical quantity so described is

expressed per unit mass. For exam-

ple, the speciÜc latent heat of a body

is its latent heat per unit mass. When

the extensive physical quantity is de-

noted by a capital letter (e.g. L for la-

tent heat), the speciÜc quantity is

denoted by the corresponding lower-

case letter (e.g. l for speciÜc latent

heat). 2.In some older physical

quantities the adjective ‘speciÜc’ was

added for other reasons (e.g. speciÜc

gravity, speciÜc resistance). These

names are now no longer used.

speciÜc activitySee activity.

speciÜc gravitySee relative den-

sity; specific.

speciÜc heat capacitySee heat

capacity.

spectrochemical series A series

of ligands arranged in the order in

which they cause splitting of the en-

ergy levels of d-orbitals in metal com-

plexes (see crystal-field theory).

The series for some common ligands

has the form:

CN–>NO 2 – >NH 3 >C 5 H 5 N>H 2 O>OH–>

F–>Cl–>Br–>I–

spectrograph See spectroscope.

spectrometer Any of various in-

struments for producing a spectrum

and measuring the wavelengths, en-

ergies, etc., involved. A simple type,

for visible radiation, is a spectroscope

equipped with a calibrated scale al-

lowing wavelengths to be read off or

calculated. In the X-ray to infrared re-

gion of the electromagnetic spec-

trum, the spectrum is produced by

dispersing the radiation with a prism

or diffraction grating (or crystal, in

the case of hard X-rays). Some form

of photoelectric detector is used, and

the spectrum can be obtained as a

graphical plot, which shows how the

intensity of the radiation varies with

wavelength. Such instruments are

also called spectrophotometers. Spec-

trometers also exist for investigating

the gamma-ray region and the mi-

crowave and radio-wave regions of

the spectrum (see electron paramag-

netic resonance; nuclear mag-

netic resonance). Instruments for

obtaining spectra of particle beams

are also called spectrometers (see

spectrum; photoelectron spec-

troscopy).

sorption 496

s