tion of wine casks. It is a general an-
tiseptic and bleaching agent. See also
aldehydes.
sodium hydroxide (caustic soda)
A white transluscent deliquescent
solid, NaOH, soluble in water and
ethanol but insoluble in ether; r.d.
2.13; m.p. 318°C; b.p. 1390°C. Hy-
drates containing 7, 5, 4, 3.5, 3, 2,
and 1 molecule of water are known.
Sodium hydroxide was formerly
made by the treatment of sodium
carbonate with lime but its main
source today is from the electrolysis
of brine using mercury cells or any of
a variety of diaphragm cells. The
principal product demanded from
these cells is chlorine (for use in plas-
tics) and sodium hydroxide is almost
reduced to the status of a by-product.
It is strongly alkaline andÜnds many
applications in the chemical indus-
try, particularly in the production of
soaps and paper. It is also used to ad-
sorb acidic gases, such as carbon
dioxide and sulphur dioxide, and is
used in the treatment of efÛuent for
the removal of heavy metals (as hy-
droxides) and of acidity. Sodium hy-
droxide solutions are extremely
corrosive to body tissue and are par-
ticularly hazardous to the eyes.
sodium iodideA white crystalline
solid, NaI, very soluble in water and
soluble in both ethanol and ethanoic
acid. It is known in both the anhy-
drous form (cubic; r.d. 3.67; m.p.
661 °C; b.p. 1304°C) and as the dihy-
drate (monoclinic; r.d. 2.45). It is pre-
pared by the reaction of hydrogen
iodide with sodium carbonate or
sodium hydroxide in solution. Like
potassium iodide, sodium iodide in
aqueous solution dissolves iodine to
form a brown solution containing
the I 3 – ion. ItÜnds applications in
photography and is also used in med-
icine as an expectorant and in the ad-
ministration of radioactive iodine for
studies of thyroid function and for
treatment of diseases of the thyroid.sodium methanoate (sodium for-
mate)A colourless deliquescent
solid, HCOONa, soluble in water and
slightly soluble in ethanol; mono-
clinic; r.d. 1.92; m.p. 253°C; decom-
poses on further heating. The
monohydrate is also known. The
compound may be produced by the
reaction of carbon monoxide with
solid sodium hydroxide at 200°C and
10 atmospheres pressure; in the labo-
ratory it can be conveniently pre-
pared by the reaction of methanoic
acid and sodium hydroxide. Its uses
are in the production of oxalic acid
(ethanedioic acid) and methanoic
acid and in the laboratory it is a con-
venient source of carbon monoxide.
sodium monoxideA whitish-grey
deliquescent solid, Na 2 O; r.d. 2.27;
sublimes at 1275°C. It is manufac-
tured by oxidation of the metal in a
limited supply of oxygen and puriÜed
by sublimation. Reaction with water
produces sodium hydroxide. Its com-
mercial applications are similar to
those of sodium hydroxide.sodium nitrate (Chile saltpetre) A
white solid, NaNO 3 , soluble in water
and in ethanol; trigonal; r.d. 2.261;
m.p. 306°C; decomposes at 380°C. A
rhombohedral form is also known. It
is obtained from deposits of caliche
or may be prepared by the reaction
of nitric acid with sodium hydroxide
or sodium carbonate. It was previ-
ously used for the manufacture of
nitric acid by heating with concen-
trated sulphuric acid. Its main use is
in nitrate fertilizers.sodium nitriteA yellow hygro-
scopic crystalline compound, NaNO 2 ,
soluble in water, slightly soluble in
ether and in ethanol; rhombohedral;
r.d. 2.17; m.p. 271°C; decomposes
above 320°C. It is formed by the ther-491 sodium nitrite
s