yellowing. Fluorescent brighteners
are compounds that absorb visible or
ultraviolet radiation and Ûuoresce in
the blue region of the optical spectrum.
Brillouin zone A cell in a reciprocal lattice. The Ürst Brillouin zone is
the cell of smallest volume enclosed
by those planes that are perpendicular bisectors of reciprocal lattice vectors. 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 introduced them into the theory of
crystals in 1930.
Brinell hardness A scale for measuring the hardness of metals introduced 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 peroxide and then heating the peroxide
at higher temperature (>800°C) to
produce oxygen
2BaO 2 → 2BaO + O 2
Britannia metal A silvery alloy
consisting of 80–90% tin, 5–15% antimony, and sometimes small percentages of copper, lead, and zinc. It is
used in bearings and some domestic
articles.
British thermal unit (Btu) The Imperial unit of heat, being originally
the heat required to raise the temperature 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 introduced into a molecule. See also halogenation.
bromine Symbol Br. A *halogen element; 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 temperature, having a red-brown vapour.
Bromine is obtained from brines in
the USA (displacement with chlorine); a small amount is obtained
from sea water in Anglesey. Large
quantities are used to make 1,2-dibromoethane as a petrol additive. It
is also used in the manufacture of
many other compounds. Chemically,
it is intermediate in reactivity between 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
colourless Ûammable 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 hydrogen bromide. Bromoethane is used as
a refrigerant.
bromoform See
tribromomethane; haloforms.
Brillouin zone
84
b
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are compounds that absorb visible or
ultraviolet radiation and Ûuoresce in
the blue region of the optical spectrum.
Brillouin zone A cell in a reciprocal lattice. The Ürst Brillouin zone is
the cell of smallest volume enclosed
by those planes that are perpendicular bisectors of reciprocal lattice vectors. 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 introduced them into the theory of
crystals in 1930.
Brinell hardness A scale for measuring the hardness of metals introduced 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 peroxide and then heating the peroxide
at higher temperature (>800°C) to
produce oxygen
2BaO 2 → 2BaO + O 2
Britannia metal A silvery alloy
consisting of 80–90% tin, 5–15% antimony, and sometimes small percentages of copper, lead, and zinc. It is
used in bearings and some domestic
articles.
British thermal unit (Btu) The Imperial unit of heat, being originally
the heat required to raise the temperature 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 introduced into a molecule. See also halogenation.
bromine Symbol Br. A *halogen element; 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 temperature, having a red-brown vapour.
Bromine is obtained from brines in
the USA (displacement with chlorine); a small amount is obtained
from sea water in Anglesey. Large
quantities are used to make 1,2-dibromoethane as a petrol additive. It
is also used in the manufacture of
many other compounds. Chemically,
it is intermediate in reactivity between 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
colourless Ûammable 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 hydrogen bromide. Bromoethane is used as
a refrigerant.
bromoform See
tribromomethane; haloforms.
Brillouin zone
84
b
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