pable of *luminescence (including
phosphorescence). Phosphors that re-
lease their energy after a short delay
of between 10–10and 10–4second are
sometimes called scintillators.
phosphor bronze An alloy of cop-
per containing 4% to 10% of tin and
0.05% to 1% of phosphorus as a deoxi-
dizing agent. It is used particularly
for marine purposes and where it is
exposed to heavy wear, as in gear
wheels. See also bronze.
phosphorescence See lumines-
cence.
phosphoric(V) acid (orthophos-
phoric acid)A white rhombic solid,
H 3 PO 4 ; r.d. 1.834; m.p. 42.35°C; loses
water at 213°C; very soluble in water
and soluble in ethanol. Phosphoric(V)
acid is very deliquescent and is gen-
erally supplied as a concentrated
aqueous solution. It is the most com-
mercially important derivative of
phosphorus, accounting for over 90%
of the phosphate rock mined. It is
manufactured by two methods; the
wet process, in which the product
contains some of the impurities origi-
nally present in the rock and applica-
tions are largely in the fertilizer
industry, and the thermal process,
which produces a much purer prod-
uct suitable for the foodstuffs and de-
tergent industries. In the wet process
the phosphate rock, Ca 3 (PO 4 ) 2 , is
treated with sulphuric acid and the
calcium sulphate removed either as
gypsum or the hemihydrate. In the
thermal process, molten phosphorus
is sprayed and burned in a mixture
of air and steam. Phosphoric(V) acid
is a weak tribasic acid, which is best
visualized as (HO) 3 PO. Its full system-
atic name is tetraoxo-phosphoric(V)
acid. It gives rise to three series of
salts containing phosphate(V) ions
based on the anions [(HO) 2 PO 2 ]–,
[(HO)PO 3 ]2–, and PO 4 3–. These salts are
acidic, neutral, and alkaline in char-acter respectively and phosphate ions
often feature in buffer systems.
There is also a wide range of higher
acids and acid anions in which there
is some P–O–P chain formation. The
simplest of these is pyrophosphoric
acid(technically heptaoxodiphos-
phoric(V) acid), H 4 P 2 O 7 , produced by
heating phosphoric(V) acid (solid) and
phosphorus(III) chloride oxide.
Metaphosphoric acid is a glassy poly-
meric solid (HPO 2 )x.phosphorous acid See phosphonic
acid.phosphorusSymbol P. A non-
metallic element belonging to
*group 15 (formerly VB) of the peri-
odic table; a.n. 15; r.a.m. 30.9738; r.d.
1.82 (white), 2.34 (red); m.p. 44.1°C
(α-white); b.p. 280°C (α-white). It oc-
curs in various phosphate rocks,
from which it is extracted by heating
with carbon (coke) and silicon(IV)
oxide in an electric furnace (1500°C).
Calcium silicate and carbon monox-
ide are also produced. Phosphorus
has a number of allotropic forms.
The α-white form consists of P 4 tetra-
hedra (there is also a β-white form
stable below –77°C). If α-white phos-
phorus is dissolved in lead and
heated at 500°C a violet form is ob-
tained. Red phosphorus, which is a
combination of violet and white
phosphorus, is obtained by heating
α-white phosphorus at 250°C with air
excluded. There is also a black al-
lotrope, which has a graphite-like
structure, made by heating white
phosphorus at 300°C with a mercury
catalyst. The element is highly reac-
tive. It forms metal *phosphides and
covalently bonded phosphorus(III)
and phosphorus(V) compounds. Phos-
phorus is an *essential element for
living organisms. It is an important
constituent of tissues (especially
bones and teeth) and of cells, being
required for the formation of nucleicphosphor bronze 412p