in a vacuum, would produce a force
between the conductors of 2 × 10
–7
N m
–1
. This deÜnition replaced the
earlier international ampere deÜned
as the current required to deposit
0.001 118 00 gram of silver from a solution of silver nitrate in one second.
The unit is named after the French
physicist André Marie Ampère (1775–
1836).
ampere-hour A practical unit of
electric charge equal to the charge
Ûowing in one hour through a conductor passing one ampere. It is
equal to 3600 coulombs.
ampere-turn The SI unit of magnetomotive force equal to the magnetomotive force produced when a
current of one ampere Ûows through
one turn of a magnetizing coil.
amperometric titration A
method of determining the chemical
composition of a solution by measuring the current passing through a
cell containing the solution; the potential is held constant during the
titration for both the indicator and
reference electrodes, with changes in
the current being measured. The current Ûowing through the cell is measured as a function of the amount of
substance being titrated.
amphetamine A drug, 1-phenyl-2aminopropane (or a derivative of this
compound), that stimulates the central nervous system by causing the
release of the transmitters noradrenaline and dopamine from nerve endings. It inhibits sleep, suppresses the
appetite, and has variable effects on
mood; prolonged use can lead to addiction.
amphetamines A group of synthetic stimulants, with structures
based in phenyl amines. Amphetamine itself has the formula
C 6 H 5 CH 2 CH(NH 2 )CH 3 .
Methamphetamine has a methyl
group on the amino group, i.e.
C 6 H 5 CH 2 CH(NHCH 3 )CH 3 .
The hydrochloride of methamphetamine can be crystallized giving a particularly powerful form known as
‘ice’ or crystal meth. Other examples
of amphetamines are *ecstasy and
*mescaline. In the UK, amphetamines are class B controlled substances (or class A if prepared for
injection).
amphiboles A large group of rockforming metasilicate minerals. They
have a structure of silicate tetrahedra
linked to form double endless chains,
in contrast to the single chains of the
*pyroxenes, to which they are
closely related. They are present in
many igneous and metamorphic
rocks. The amphiboles show a wide
range of compositional variation but
conform to the general formula:
X 2–3 Y 5 Z 8 O 22 (OH) 2 , where X = Ca, Na,
K, Mg, or Fe
2+ ; Y = Mg, Fe
2+ , Fe
3+ , Al,
Ti, or Mn; and Z = Si or Al. The hydroxyl ions may be replaced by F, Cl,
or O. Most amphiboles are monoclinic, including:
cummingtonite, (Mg,Fe
2+ ) 7 (Si 8 O 22 )(OH) 2 ; tremolite, Ca 2 Mg 5 (Si 8 O 22 )(OH,F) 2 ; actinolite, Ca 2 (Mg,Fe
2+ ) 5 -
(Si 8 O 22 )(OH,F) 2 ; *hornblende,
NaCa 2 (Mg,Fe
2+ ,Fe
3+
,Al) 5 ((Si,Al) 8 O 22 )(OH,F) 2 ; edenite, NaCa 2 (Mg,Fe
2+ ) 5 -
(Si 7 AlO 22 )(OH,F) 2 ; and riebeckite,
Na 2 ,Fe 3
2+ (Si 8 O 22 )(OH,F) 2 . Anthophyllite, (Mg,Fe
2+
) 7 (Si 8 O 22 )(OH,F) 2 , and
gedrite, (Mg,Fe
2+ ) 6 Al(Si,Al) 8 O 22 )(OH,F) 2 , are orthorhombic amphiboles.
amphibolic pathway A biochemical pathway that serves both anabolic
and catabolic processes. An important example of an amphibolic pathway is the *Krebs cycle, which
involves both the catabolism of carbohydrates and fatty acids and the
ampere-hour
34
a
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between the conductors of 2 × 10
–7
N m
–1
. This deÜnition replaced the
earlier international ampere deÜned
as the current required to deposit
0.001 118 00 gram of silver from a solution of silver nitrate in one second.
The unit is named after the French
physicist André Marie Ampère (1775–
1836).
ampere-hour A practical unit of
electric charge equal to the charge
Ûowing in one hour through a conductor passing one ampere. It is
equal to 3600 coulombs.
ampere-turn The SI unit of magnetomotive force equal to the magnetomotive force produced when a
current of one ampere Ûows through
one turn of a magnetizing coil.
amperometric titration A
method of determining the chemical
composition of a solution by measuring the current passing through a
cell containing the solution; the potential is held constant during the
titration for both the indicator and
reference electrodes, with changes in
the current being measured. The current Ûowing through the cell is measured as a function of the amount of
substance being titrated.
amphetamine A drug, 1-phenyl-2aminopropane (or a derivative of this
compound), that stimulates the central nervous system by causing the
release of the transmitters noradrenaline and dopamine from nerve endings. It inhibits sleep, suppresses the
appetite, and has variable effects on
mood; prolonged use can lead to addiction.
amphetamines A group of synthetic stimulants, with structures
based in phenyl amines. Amphetamine itself has the formula
C 6 H 5 CH 2 CH(NH 2 )CH 3 .
Methamphetamine has a methyl
group on the amino group, i.e.
C 6 H 5 CH 2 CH(NHCH 3 )CH 3 .
The hydrochloride of methamphetamine can be crystallized giving a particularly powerful form known as
‘ice’ or crystal meth. Other examples
of amphetamines are *ecstasy and
*mescaline. In the UK, amphetamines are class B controlled substances (or class A if prepared for
injection).
amphiboles A large group of rockforming metasilicate minerals. They
have a structure of silicate tetrahedra
linked to form double endless chains,
in contrast to the single chains of the
*pyroxenes, to which they are
closely related. They are present in
many igneous and metamorphic
rocks. The amphiboles show a wide
range of compositional variation but
conform to the general formula:
X 2–3 Y 5 Z 8 O 22 (OH) 2 , where X = Ca, Na,
K, Mg, or Fe
2+ ; Y = Mg, Fe
2+ , Fe
3+ , Al,
Ti, or Mn; and Z = Si or Al. The hydroxyl ions may be replaced by F, Cl,
or O. Most amphiboles are monoclinic, including:
cummingtonite, (Mg,Fe
2+ ) 7 (Si 8 O 22 )(OH) 2 ; tremolite, Ca 2 Mg 5 (Si 8 O 22 )(OH,F) 2 ; actinolite, Ca 2 (Mg,Fe
2+ ) 5 -
(Si 8 O 22 )(OH,F) 2 ; *hornblende,
NaCa 2 (Mg,Fe
2+ ,Fe
3+
,Al) 5 ((Si,Al) 8 O 22 )(OH,F) 2 ; edenite, NaCa 2 (Mg,Fe
2+ ) 5 -
(Si 7 AlO 22 )(OH,F) 2 ; and riebeckite,
Na 2 ,Fe 3
2+ (Si 8 O 22 )(OH,F) 2 . Anthophyllite, (Mg,Fe
2+
) 7 (Si 8 O 22 )(OH,F) 2 , and
gedrite, (Mg,Fe
2+ ) 6 Al(Si,Al) 8 O 22 )(OH,F) 2 , are orthorhombic amphiboles.
amphibolic pathway A biochemical pathway that serves both anabolic
and catabolic processes. An important example of an amphibolic pathway is the *Krebs cycle, which
involves both the catabolism of carbohydrates and fatty acids and the
ampere-hour
34
a
www.AzShimi.ir www.AzShimi.com