Simon test A *presumptive test for
methamphetamines. The Simon
reagent consists of 1 gram of sodium
nitroprusside (Na 2 Fe(CN) 5 NO) and 2
ml of acetaldehyde (ethanal) in 50 ml
of water. A 2% solution of sodium
carbonate is then added. MDA gives a
turquoise colour; MDMA gives an ini-
tial turquoise, which changes to dark
blue.
SIMSSee secondary-ion mass spec-
trometry.
single bondSee chemical bond.
singlet An atomic state in which
two spin angular momenta of elec-
trons cancel each other, resulting in
zero net spin. A singlet state usually
has a higher energy than a triplet
state because of the effect of correla-
tions of spin on the Coulomb interac-
tions between electrons (as in
Hund’s rules). This can lead to sub-
stantial energy differences between
triplet and singlet states.
sintered glass Porous glass made
by sintering powdered glass, used for
Ültration of precipitates in gravimet-
ric analysis.
sinteringThe process of heating
and compacting a powdered material
at a temperature below its melting
point in order to weld the particles
together into a single rigid shape.
Materials commonly sintered include
metals and alloys, glass, and ceramic
oxides. Sintered magnetic materials,
cooled in a magneticÜeld, make es-
pecially retentive permanent mag-
nets.
S-isomerSee absolute configura-
tion.
SI unitsSystème International
d’Unités: the international system of
units now recommended for all sci-
entiÜc purposes. A coherent and ra-
tionalized system of units derived
from the *m.k.s. units, SI units have
now replaced *c.g.s. units and *Impe-
rial units. The system has seven base
unitsand two dimensionless units
(formerly called supplementary
units), all other units being derived
from these nine units. There are 18
derived units with special names.
Each unit has an agreed symbol (a
capital letter or an initial capital let-
ter if it is named after a scientist,
otherwise the symbol consists of one
or two lower-case letters). Decimal
multiples of the units are indicated
by a set of preÜxes; whenever possi-
ble a preÜx representing 10 raised to
a power that is a multiple of three
should be used. See Appendix.skeletal electrons See wade’s
rules.
skewSee torsion angle.slagMaterial produced during the
*smelting or reÜning of metals by re-
action of theÛux with impurities
(e.g. calcium silicate formed by reac-
tion of calcium oxideÛux with sili-
con dioxide impurities). The liquid
slag can be separated from the liquid
metal because itÛoats on the surface.
See also basic slag.slaked limeSee calcium hydrox-
ide.SLNSee sybyl line notation.SLUMOSecond-lowest unoccupied
molecular orbital. See subjacent or-
bitals.
slurryA paste consisting of a sus-
pension of a solid in a liquid.
SMARTS See smiles.smecticSee liquid crystal.smeltingThe process of separating
a metal from its ore by heating the
ore to a high temperature in a suit-
able furnace in the presence of a re-
ducing agent, such as carbon, and a
Ûuxing agent, such as limestone. Iron485 smelting
s