Dictionary of Chemistry [6th Ed.]

state may have been reached either
as a result of a randomÛuctuation or
an external force (such as an electric
or magneticÜeld) and that the evolu-
tion towards equilibrium is the same
in both cases (for a sufÜciently
smallÛuctuation). TheÛuctuation–
dissipation theorem enables *trans-
port coefÜcients to be calculated in
terms of response to externalÜelds.

ÛuidizationA technique used in
some industrial processes in which
solid particles suspended in a stream
of gas are treated as if they were in
the liquid state. Fluidization is useful
for transporting powders, such as
coal dust. Fluidized beds, in which
solid particles are suspended in an
upward stream, are extensively used
in the chemical industry, particularly
in catalytic reactions where the pow-
dered catalyst has a high surface
area. They are also used in furnaces,
being formed by burning coal in a
hot turbulent bed of sand or ash
through which air is passed. The bed
behaves like aÛuid, enabling the
combustion temperature to be re-
duced so that the production of
polluting oxides of nitrogen is dimin-
ished. By adding limestone to the
bed with the fuel, the emission of
sulphur dioxide is reduced.
High-pressureÛuidized beds are
also used in power-station furnaces
in a combined cycle in which the
products of combustion from the
Ûuidized bed are used to drive a gas
turbine, while a steam-tube boiler in
theÛuid bed raises steam to drive a
steam turbine. This system both in-
creases the efÜciency of the combus-
tion process and reduces pollution.

ÛunitrazepamA *benzodiazepine
used medically in some countries as
a powerful hypnotic, sedative, and
muscle relaxant. It was marketed in
the US under the tradename Rohyp-
nol. Flunitrazepam has become noto-

rious as a so-called ‘date rape’ drug. It

is quickly eliminated from the body,

difÜcult to detect, and causes amne-

sia, so that victims cannot remember

events that occur when under the

inÛuence of the drug.

229 fluorine

f

N

2 NH N

3 CH

O

F

Flunitrazepam

Ûuorescein A yellowish-red dye

that produces yellow solutions with a

greenÛuorescence. It is used in trac-

ing waterÛow and as an *adsorption

indicator.

Ûuorescence See luminescence.

ÛuoridationThe process of adding

very small amounts ofÛuorine salts

(e.g. sodiumÛuoride, NaF) to drink-

ing water to prevent tooth decay. The

Ûuoride becomes incorporated into

theÛuoroapatite (see apatite) of the

growing teeth and reduces the inci-

dence of dental caries.

ÛuorideSee halide.

ÛuorinationA chemical reaction

in which aÛuorine atom is intro-

duced into a molecule. See halogena-

tion.

ÛuorineSymbol F. A poisonous

pale yellow gaseous element belong-

ing to group 17 (formerly VIIB) of the

periodic table (the *halogens); a.n. 9;

r.a.m. 18.9984; d. 1.7 g dm–3; m.p.

–219.62°C; b.p. –188.1°C. The main

mineral sources are *Ûuorite (CaF 2 )