Stokes lines being called the S-branch
of the Raman spectrum.
Stokes radiation is named after the
British physicist Sir George Gabriel
Stokes (1819–1903).
stopped-Ûow techniqueA tech-
nique for investigating fast reactions
in solution. The reactant solutions
are rapidly mixed andÛow through a
tube. The composition or properties
of the mixture are monitored at
some point in the tube (e.g. by pho-
tometry). TheÛow is suddenly
stopped and the change of signal
with time is used to elucidate the ki-
netics of the process. The stopped-
Ûow technique is useful for reactions
occurring in the millisecond time
range.s.t.p.Standard temperature and
pressure, formerly known as N.T.P.
(normal temperature and pressure).
The standard conditions used as a
basis for calculations involving quan-
tities that vary with temperature and
pressure. These conditions are used
when comparing the properties of
gases. They are 273.15 K (or 0°C) and
101 325 Pa (or 760.0 mmHg).
straight chainSee chain.strange attractorSee attractor.
streaming potential A potential
difference that occurs when a liquid
under pressure is forced through a
narrow opening or diaphragm. It can
be measured between two electrodes
at each end of a capillary tube made
of the same material as the dia-
phragm.
strong acid An *acid that is com-
pletely dissociated in aqueous solu-
tion.
strontia See strontium oxide.strontianite A mineral form of
*strontium carbonate, SrCO 3.strontium Symbol Sr. A soft yel-lowish metallic element belonging to
group 2 (formerly IIA) of the periodic
table (see alkaline-earth metals);
a.n. 38; r.a.m. 87.62; r.d. 2.6; m.p.
769 °C; b.p. 1384°C. The element is
found in the minerals strontianite
(SrCO 3 ) and celestine (SrSO 4 ). It can
be obtained by roasting the ore to
give the oxide, followed by reduction
with aluminium (i.e. the *Gold-
schmidt process). The element,
which is highly reactive, is used in
certain alloys and as a vacuum getter.
The isotope strontium–90 is present
in radioactive fallout (half-life 28
years), and can be metabolized with
calcium so that it collects in bone.
Strontium was discovered by Martin
Klaproth (1743–1817) and Thomas
Hope (1766–1844) in 1798 and iso-
lated by Humphry Davy in 1808.
A- Information from the WebElements site
strontium bicarbonate See stron-
tium hydrogencarbonate.
strontium carbonate A white
solid, SrCO 3 ; orthorhombic; r.d. 3.7;
decomposes at 1340°C. It occurs nat-
urally as the mineral strontianite and
is prepared industrially by boiling ce-
lestine (strontium sulphate) with am-
monium carbonate. It can also be
prepared by passing carbon dioxide
over strontium oxide or hydroxide or
by passing the gas through a solution
of strontium salt. It is a phosphor,
used to coat the glass of cathode-ray
screens, and is also used in the reÜn-
ing of sugar, as a slagging agent in
certain metal furnaces, and to pro-
vide a redÛame inÜreworks.
strontium chloride A white com-
pound, SrCl 2. The anhydrous salt
(cubic; r.d. 3.05; m.p. 872°C; b.p.
1250 °C) can be prepared by passing
chlorine over heated strontium. It is
deliquescent and readily forms the
hexahydrate, SrCl 2 .6H 2 O (r.d. 2.67).
stopped-Ûow technique 506s