in a vacuum, would produce a force
between the conductors of 2 × 10 –7
Nm–1. This deÜnition replaced the
earlier international ampere deÜned
as the current required to deposit
0.001 118 00 gram of silver from a so-
lution 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 con-
ductor passing one ampere. It is
equal to 3600 coulombs.ampere-turn The SI unit of magne-
tomotive force equal to the magneto-
motive force produced when a
current of one ampereÛows through
one turn of a magnetizing coil.amperometric titration A
method of determining the chemical
composition of a solution by measur-
ing the current passing through a
cell containing the solution; the po-
tential is held constant during the
titration for both the indicator and
reference electrodes, with changes in
the current being measured. The cur-
rentÛowing through the cell is meas-
ured as a function of the amount of
substance being titrated.amphetamineA drug, 1-phenyl-2-
aminopropane (or a derivative of this
compound), that stimulates the cen-
tral nervous system by causing the
release of the transmitters noradren-
aline and dopamine from nerve end-
ings. It inhibits sleep, suppresses the
appetite, and has variable effects on
mood; prolonged use can lead to ad-
diction.amphetaminesA group of syn-
thetic stimulants, with structures
based in phenyl amines. Ampheta-
mine itself has the formula
C 6 H 5 CH 2 CH(NH 2 )CH 3.Methamphetaminehas a methyl
group on the amino group, i.e.
C 6 H 5 CH 2 CH(NHCH 3 )CH 3.
The hydrochloride of methampheta-
mine can be crystallized giving a par-
ticularly powerful form known as
‘ice’ or crystal meth. Other examples
of amphetamines are *ecstasy and
*mescaline. In the UK, ampheta-
mines are class B controlled sub-
stances (or class A if prepared for
injection).amphibolesA large group of rock-
forming 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:
X2–3Y 5 Z 8 O 22 (OH) 2 , where X = Ca, Na,
K, Mg, or Fe2+; Y = Mg, Fe2+, Fe3+, Al,
Ti, or Mn; and Z = Si or Al. The hy-
droxyl ions may be replaced by F, Cl,
or O. Most amphiboles are mono-
clinic, including:
cummingtonite, (Mg,Fe2+) 7 (Si 8 O 22 )-
(OH) 2 ; tremolite, Ca 2 Mg 5 (Si 8 O 22 )-
(OH,F) 2 ; actinolite, Ca 2 (Mg,Fe2+) 5 -
(Si 8 O 22 )(OH,F) 2 ; *hornblende,
NaCa 2 (Mg,Fe2+,Fe3+,Al) 5 ((Si,Al) 8 O 22 )-
(OH,F) 2 ; edenite, NaCa 2 (Mg,Fe2+) 5 -
(Si 7 AlO 22 )(OH,F) 2 ; and riebeckite,
Na 2 ,Fe 3 2+(Si 8 O 22 )(OH,F) 2. Anthophyl-
lite, (Mg,Fe2+) 7 (Si 8 O 22 )(OH,F) 2 , and
gedrite, (Mg,Fe2+) 6 Al(Si,Al) 8 O 22 )-
(OH,F) 2 , are orthorhombic amphi-
boles.amphibolic pathway A biochemi-
cal pathway that serves both anabolic
and catabolic processes. An impor-
tant example of an amphibolic path-
way is the *Krebs cycle, which
involves both the catabolism of car-
bohydrates and fatty acids and theampere-hour 34a