an alkali. Ammonia and sodium hydroxide are common examples.
The original Arrhenius deÜnition of
a base has been extended by the
Lowry–Brønsted theory and by the
Lewis theory. See acid.
base dissociation constant See
dissociation.
base metal A common relatively
inexpensive metal, such as iron or
lead, that corrodes, oxidizes, or tarnishes on exposure to air, moisture,
or heat, as distinguished from precious metals, such as gold and silver.
base pairing Pairing of nucleotide
bases by hydrogen bonding. Base
pairing holds together the two
strands in the double helix structure
of *DNA. The purine adenine pairs
with the pyrimidine thymine and the
purine guanine pairs with the pyrimidine cytosine. See also chargaff’s
rule.
base unit A unit that is deÜned arbitrarily rather than being deÜned by
simple combinations of other units.
For example, the ampere is a base
unit in the SI system deÜned in terms
of the force produced between two
current-carrying conductors, whereas
the coulomb is a derived unit,
deÜned as the quantity of charge
transferred by one ampere in one
second.
basic 1. Describing a compound
that is a base. 2. Describing a solution containing an excess of hydroxide ions; alkaline.
basic dye See dyes.
basicity constant See dissociation.
basic-oxygen process (BOP
process) A high-speed method of
making high-grade steel. It originated
in the Linz–Donawitz (L–D) process.
Molten pig iron and scrap are
charged into a tilting furnace, similar
to the Bessemer furnace except that
it has no tuyeres. The charge is converted to steel by blowing highpressure oxygen onto the surface of
the metal through a water-cooled
lance. The excess heat produced enables up to 30% of scrap to be incorporated into the charge. The process
has largely replaced the Bessemer
and open-hearth processes.
basic salt A compound that can be
regarded as being formed by replacing some of the oxide or hydroxide
ions in a base by other negative ions.
Basic salts are thus mixed salt–oxides
(e.g. bismuth(III) chloride oxide,
BiOCl) or salt–hydroxides (e.g. lead(II)
chloride hydroxide, Pb(OH)Cl).
basic slag *Slag formed from a
basic Ûux (e.g. calcium oxide) in a
blast furnace. The basic Ûux is used
to remove acid impurities in the ore
and contains calcium silicate, phosphate, and sulphide. If the phosphorus content is high the slag can be
used as a fertilizer.
bathochromic shift A shift of a
spectral band to longer wavelengths
as a result of substitution in a molecule or a change in the conditions.
Compare hypsochromic shift.
battery A number of electric cells
joined together. The common car
battery, or *accumulator, usually
consists of six secondary cells connected in series to give a total e.m.f.
of 12 volts. A torch battery is usually
a dry version of the *Leclanché cell,
two of which are often connected in
series. Batteries may also have cells
connected in parallel, in which case
they have the same e.m.f. as a single
cell, but their capacity is increased,
i.e. they will provide more total
charge. The capacity of a battery is
usually speciÜed in ampere-hours,
59
battery
b
www.AzShimi.ir www.AzShimi.com
The original Arrhenius deÜnition of
a base has been extended by the
Lowry–Brønsted theory and by the
Lewis theory. See acid.
base dissociation constant See
dissociation.
base metal A common relatively
inexpensive metal, such as iron or
lead, that corrodes, oxidizes, or tarnishes on exposure to air, moisture,
or heat, as distinguished from precious metals, such as gold and silver.
base pairing Pairing of nucleotide
bases by hydrogen bonding. Base
pairing holds together the two
strands in the double helix structure
of *DNA. The purine adenine pairs
with the pyrimidine thymine and the
purine guanine pairs with the pyrimidine cytosine. See also chargaff’s
rule.
base unit A unit that is deÜned arbitrarily rather than being deÜned by
simple combinations of other units.
For example, the ampere is a base
unit in the SI system deÜned in terms
of the force produced between two
current-carrying conductors, whereas
the coulomb is a derived unit,
deÜned as the quantity of charge
transferred by one ampere in one
second.
basic 1. Describing a compound
that is a base. 2. Describing a solution containing an excess of hydroxide ions; alkaline.
basic dye See dyes.
basicity constant See dissociation.
basic-oxygen process (BOP
process) A high-speed method of
making high-grade steel. It originated
in the Linz–Donawitz (L–D) process.
Molten pig iron and scrap are
charged into a tilting furnace, similar
to the Bessemer furnace except that
it has no tuyeres. The charge is converted to steel by blowing highpressure oxygen onto the surface of
the metal through a water-cooled
lance. The excess heat produced enables up to 30% of scrap to be incorporated into the charge. The process
has largely replaced the Bessemer
and open-hearth processes.
basic salt A compound that can be
regarded as being formed by replacing some of the oxide or hydroxide
ions in a base by other negative ions.
Basic salts are thus mixed salt–oxides
(e.g. bismuth(III) chloride oxide,
BiOCl) or salt–hydroxides (e.g. lead(II)
chloride hydroxide, Pb(OH)Cl).
basic slag *Slag formed from a
basic Ûux (e.g. calcium oxide) in a
blast furnace. The basic Ûux is used
to remove acid impurities in the ore
and contains calcium silicate, phosphate, and sulphide. If the phosphorus content is high the slag can be
used as a fertilizer.
bathochromic shift A shift of a
spectral band to longer wavelengths
as a result of substitution in a molecule or a change in the conditions.
Compare hypsochromic shift.
battery A number of electric cells
joined together. The common car
battery, or *accumulator, usually
consists of six secondary cells connected in series to give a total e.m.f.
of 12 volts. A torch battery is usually
a dry version of the *Leclanché cell,
two of which are often connected in
series. Batteries may also have cells
connected in parallel, in which case
they have the same e.m.f. as a single
cell, but their capacity is increased,
i.e. they will provide more total
charge. The capacity of a battery is
usually speciÜed in ampere-hours,
59
battery
b
www.AzShimi.ir www.AzShimi.com