gencarbonate, which can then be cal-
cined to K 2 CO 3. Potassium carbonate
is soluble in water (insoluble in alco-
hol) with signiÜcant hydrolysis to
produce basic solutions. Industrial
uses include glasses and glazes, the
manufacture of soft soaps, and in
dyeing and woolÜnishing. It is used
in the laboratory as a drying agent.
potassium chlorateA colourless
crystalline compound, KClO 3 , which
is soluble in water and moderately
soluble in ethanol; monoclinic; r.d.
2.32; m.p. 356°C; decomposes above
400 °C giving off oxygen. The indus-
trial route to potassium chlorate in-
volves the fractional crystallization of
a solution of potassium chloride and
sodium chlorate but it may also be
prepared by electrolysis of hot con-
centrated solutions of potassium
chloride. It is a powerful oxidizing
agentÜnding applications in weed-
killers and disinfectants and, because
of its ability to produce oxygen, it is
used in explosives, pyrotechnics, and
matches.
potassium chloride A white crys-
talline solid, KCl, which is soluble in
water and very slightly soluble in
ethanol; cubic; r.d. 1.98; m.p. 772°C;
sublimes at 1500°C. Potassium chlo-
ride occurs naturally as the mineral
sylvite(KCl) and as carnallite
(KCl.MgCl 2 .6H 2 O); it is produced in-
dustrially by fractional crystallization
of these deposits or of solutions from
lake brines. It has the interesting
property of being more soluble than
sodium chloride in hot water but less
soluble in cold. It is used as a fertil-
izer, in photography, and as a source
of other potassium salts, such as the
chlorate and the hydroxide. It has
low toxicity.
potassium chromate A bright yel-
low crystalline solid, K 2 CrO 4 , soluble
in water and insoluble in alcohol;
rhombic; r.d. 2.73; m.p. 968.3°C; de-
composes without boiling. It is pro-
duced industrially by roasting pow-
dered chromite ore with potassium
hydroxide and limestone and leach-
ing the resulting cinder with hot
potassium sulphate solution. Potas-
sium chromate is used in leather
Ünishing, as a textile mordant, and in
enamels and pigments. In the labora-
tory it is used as an analytical
reagent and as an indicator. Like
other chromium(III) compounds it is
toxic when ingested or inhaled.
potassium chromium sulphate
(chrome alum) A violet or ruby-red
crystalline solid, K 2 SO 4 .Cr 2 (SO 4 ) 3.
24H 2 O, that is soluble in water and
insoluble in ethanol; cubic or octahe-
dral; r.d. 1.826; m.p. 89°C; loses
10H 2 O at 100°C, 12H 2 O at 400°C. Six
water molecules surround each of
the chromium(III) ions and the re-
maining ones are hydrogen bonded
to the sulphate ions. Like all alums,
the compound may be prepared by
mixing equimolar quantities of the
constituent sulphates. See alums.
potassium cyanide (cyanide)A
white crystalline or granular deli-
quescent solid, KCN, soluble in water
and in ethanol and having a faint
characteristic odour of almonds (due
to hydrolysis forming hydrogen
cyanide at the surface); cubic; r.d.
1.52; m.p. 634°C. It is prepared indus-
trially by the absorption of hydrogen
cyanide in potassium hydroxide. The
compound is used in the extraction
of silver and gold, in some metal-
Ünishing processes and electroplat-
ing, as an insecticide and fumigant
(source of HCN), and in the prepara-
tion of cyanogen derivatives. In the
laboratory it is used in analysis, as a
reducing agent, and as a stabilizing
*ligand for low oxidation states. The
salt itself is highly toxic and aqueous
solutions of potassium cyanide are
strongly hydrolysed to give rise to433 potassium cyanide
p