Dictionary of Chemistry [6th Ed.]

is the number of degrees of freedom
of the particles. This new concept led
to Bose–Einstein statistics, and for
particles obeying the Pauli exclusion
principle, to Fermi–Dirac statistics.

steam distillationA method of
distilling liquids that are immiscible
with water by bubbling steam
through them. It depends on the fact
that the vapour pressure (and hence
the boiling point) of a mixture of two
immiscible liquids is lower than the
vapour pressure of either pure liquid.

steam point The temperature at
which the maximum vapour pres-
sure of water is equal to the standard
atmospheric pressure (101 325 Pa).
On the Celsius scale it has the value
100 °C.

stearate(octadecanoate)A salt or
ester of stearic acid.

stearic acid (octadecanoic acid)
A solid saturated fatty acid,
CH 3 (CH 2 ) 16 COOH; r.d. 0.94; m.p.
71.5–72°C; b.p. 360°C (with decompo-
sition). It occurs widely (as glyc-
erides) in animal and vegetable fats.

steel Any of a number of alloys con-
sisting predominantly of iron with
varying proportions of carbon (up
to 1.7%) and, in some cases, small
quantities of other elements (alloy
steels), such as manganese, silicon,
chromium, molybdenum, and nickel.
Steels containing over 11–12% of
chromium are known as *stainless
steels.
Carbon steels exist in three stable
crystalline phases: ferritehas a body-
centred cubic crystal, austenitehas a
face-centred cubic crystal, and ce-
mentitehas an orthorhombic crystal.
Pearliteis a mixture of ferrite and ce-
mentite arranged in parallel plates.
The phase diagram shows how the
phases form at different tempera-
tures and compositions.
Steels are manufactured by the

*basic-oxygen process (L–D process),

which has largely replaced the

*Bessemer process and the *open-

hearth process, or in electrical fur-

naces.

503 stereoisomerism

s

960

920

880

840

800

760

720

680

640

600

temperature (°C)

0 0.2 0.4 0.6 0.8 1.0 1.2 1.4 1.6

austeniteausteniteaustenite

austenite +austenite +austenite +

cementitecementitecementite

cementite +cementite +cementite +

pearlitepearlitepearlite

ferrite +ferrite +ferrite +

pearlitepearlitepearlite

ferrite +ferrite +ferrite +

austeniteausteniteaustenite

carbon (%)

Steel

stepA single stage in a chemical re-

action. For example, the addition of

hydrogen chloride to ethene involves

three steps:

HCl →H++ Cl–

H++ C 2 H 4 →CH 3 CH 2 +

CH 3 CH 2 ++ Cl–→CH 3 CH 2 Cl

steradianSymbol sr. The dimen-

sionless (supplementary) *SI unit of

solid angle equal to the solid angle

that encloses a surface on a sphere

equal to the square of the radius of

the sphere.

stere A unit of volume equal to

1m^3. It is not now used for scientiÜc

purposes.

stereochemistry The branch of

chemistry concerned with the struc-

ture of molecules and the way the

arrangement of atoms and groups af-

fects the chemical properties.

stereoisomerism See isomerism.