mal decomposition of sodium nitrate
and is used in the preparation of ni-
trous acid (reaction with cold dilute
hydrochloric acid). Sodium nitrite is
used in organic *diazotization and as
a corrosion inhibitor.
sodium nitroprusside test See
simon’s test.
sodium orthophosphateSee
trisodium phosphate(v).sodium peroxide A whitish solid
(yellow when hot), Na 2 O 2 , soluble in
ice-water and decomposed in warm
water or alcohol; r.d. 2.80; decom-
poses at 460°C. A crystalline octa-
hydrate (hexagonal) is obtained by
crystallization from ice-water. The
compound is formed by the combus-
tion of sodium metal in excess oxy-
gen. At normal temperatures it
reacts with water to give sodium
hydroxide and hydrogen peroxide.
It is a powerful oxidizing agent react-
ing with iodine vapour to give the
iodate and periodate, with carbon at
300 °C to give the carbonate, and
with nitrogen(II) oxide to give the
nitrate. It is used as a bleaching
agent in wool and yarn processing,
in the reÜning of oils and fats, and
in the production of wood pulp.
sodium sesquicarbonateA white
crystalline hydrated double salt,
Na 2 CO 3 .NaHCO 3 .2H 2 O, soluble in
water but less alkaline than sodium
carbonate; r.d. 2.12; decomposes on
heating. It may be prepared by crys-
tallizing equimolar quantities of the
constituent materials; it also occurs
naturally as trona and in Searles
Lake brines. It is widely used as a
detergent and soap builder and,
because of its mild alkaline proper-
ties, as a water-softening agent and
bath-salt base. See also sodium car-
bonate.
sodium sulphateA white crys-
talline compound, Na 2 SO 4 , usuallyknown as the anhydrous compound
(orthorhombic; r.d. 2.67; m.p. 888°C)
or the decahydrate (monoclinic; r.d.
1.46; which loses water at 100°C).
The decahydrate is known as
Glauber’s salt. A metastable heptahy-
drate (Na 2 SO 4 .7H 2 O) also exists. All
forms are soluble in water, dissolving
to give a neutral solution. The com-
pound occurs naturally as
mirabilite(Na 2 SO 4 .10H 2 O),
threnardite (Na 2 SO 4 ), and
glauberite(Na 2 SO 4 .CaSO 4 ).
Sodium sulphate may be produced
industrially by the reaction of mag-
nesium sulphate with sodium chlo-
ride in solution followed by
crystallization, or by the reaction of
concentrated sulphuric acid with
solid sodium chloride. The latter
method was used in the *Leblanc
process for the production of alkali
and has given the name salt cake to
impure industrial sodium sulphate.
Sodium sulphate is used in the man-
ufacture of glass and soft glazes and
in dyeing to promote an evenÜnish.
It alsoÜnds medicinal application as
a purgative and in commercial aperi-
ent salts.sodium sulphideA yellow-red
solid, Na 2 S, formed by the reduction
of sodium sulphate with carbon
(coke) at elevated temperatures. It is
a corrosive and readily oxidized ma-
terial of variable composition and
usually contains polysulphides of the
type Na 2 S 2 , Na 2 S 3 , and Na 2 S 4 , which
cause the variety of colours. It is
known in an anhydrous form (r.d.
1.85; m.p. 1180°C) and as a nonahy-
drate, Na 2 S.9H 2 O (r.d. 1.43; decom-
poses at 920°C). Other hydrates of
sodium sulphide have been reported.
The compound is deliquescent, solu-
ble in water with extensive hydroly-
sis, and slightly soluble in alcohol. It
is used in wood pulping, dyestuffs
manufacture, and metallurgy on ac-sodium nitroprusside test 492s