yellowing. Fluorescent brighteners
are compounds that absorb visible or
ultraviolet radiation andÛuoresce in
the blue region of the optical spec-
trum.Brillouin zoneA cell in a recipro-
cal lattice. TheÜrst Brillouin zone is
the cell of smallest volume enclosed
by those planes that are perpendicu-
lar bisectors of reciprocal lattice vec-
tors. Higher Brillouin zones also
exist. Brillouin zones are used in the
theory of energy levels in a periodic
potential, as in a crystal. They are
named after the French physicist
Léon Brillouin (1889–1969), who in-
troduced them into the theory of
crystals in 1930.Brinell hardness A scale for meas-
uring the hardness of metals intro-
duced around 1900 by the Swedish
metallurgist Johann Brinell (1849–
1925). A small chromium-steel ball is
pressed into the surface of the metal
by a load of known weight. The ratio
of the mass of the load in kilograms
to the area of the depression formed
in square millimetres is the Brinell
number.Brin process A process formerly
used for making oxygen by heating
barium oxide in air to form the per-
oxide and then heating the peroxide
at higher temperature (> 800 °C) to
produce oxygen
2BaO 2 →2BaO + O 2Britannia metalA silvery alloy
consisting of 80–90% tin, 5–15% anti-
mony, and sometimes small percent-
ages of copper, lead, and zinc. It is
used in bearings and some domestic
articles.British thermal unit (Btu)The Im-
perial unit of heat, being originally
the heat required to raise the tem-
perature of 1lb of water by 1°F. 1 Btu
is now deÜned as 1055.06 joules.bromate A salt or ester of a bromic
acid.bromic(I) acid (hypobromous acid)
A yellow liquid, HBrO. It is a weak
acid but a strong oxidizing agent.bromic(V) acid A colourless liquid,
HBrO 3 , made by adding sulphuric
acid to barium bromate. It is a strong
acid.bromide See halide.bromination A chemical reaction
in which a bromine atom is intro-
duced into a molecule. See also halo-
genation.bromine Symbol Br. A *halogen el-
ement; a.n. 35; r.a.m. 79.909; r.d.
3.13; m.p. –7.2°C; b.p. 58.78°C. It is a
red volatile liquid at room tempera-
ture, having a red-brown vapour.
Bromine is obtained from brines in
the USA (displacement with chlo-
rine); a small amount is obtained
from sea water in Anglesey. Large
quantities are used to make 1,2-di-
bromoethane as a petrol additive. It
is also used in the manufacture of
many other compounds. Chemically,
it is intermediate in reactivity be-
tween chlorine and iodine. It forms
compounds in which it has oxidation
states of 1, 3, 5, or 7. The liquid is
harmful to human tissue and the
vapour irritates the eyes and throat.
The element was discovered in 1826
by Antoine Balard.
A- Information from the WebElements site
bromoethane (ethyl bromide) A
colourlessÛammable liquid, C 2 H 5 Br;
r.d. 1.46; m.p. –119°C; b.p. 38.4°C. It
is a typical *haloalkane, which can
be prepared from ethene and hydro-
gen bromide. Bromoethane is used as
a refrigerant.bromoform See
tribromomethane; haloforms.Brillouin zone 84b