capable of weighing masses of the
order 10–6to 10–9kg.
microcrystal test See crystal test.
microscopic Designating a size
scale comparable to the subatomic
particles, atoms, and molecules.
Microscopic objects and systems are
described by *quantum mechanics.
Compare macroscopic; mesoscopic.
microscopic reversibility The
principle that in a reversible reaction
the mechanism in one direction is
the exact reverse of the mechanism
in the other direction. See also de-
tailed balance.
microwaves Electromagnetic
waves with wavelengths in the range
10 –3to 0.03 m.
microwave spectroscopy A sen-
sitive technique for chemical analysis
and the determination of molecular
structure (bond lengths, bond angles,
and dipole moments), and also rela-
tive atomic masses. It is based on the
principle that microwave radiation
(see microwaves) causes changes in
the rotational energy levels of mol-
ecules and absorption consequently
occurs at characteristic frequencies.
In a microwave spectrometer a mi-
crowave source, usually a klystron
valve, produces a beam that is passed
through a gaseous sample. The beam
then impinges on the detector, usu-
ally a crystal detector, and the signal
(wavelength against intensity) is dis-
played, either as a printed plot or on
an oscilloscope. As microwaves are
absorbed by air the instrument is
evacuated.
migration1.The movement of a
group, atom, or double bond from
one part of a molecule to another.
2.The movement of ions under the
inÛuence of an electricÜeld.
milk of magnesiaSee magnesium
hydroxide.
milk sugarSee lactose.
Miller indicesA set of three num-
bers that characterize a face of a crys-
tal. The French mineralogist René
Just Haüy (1743–1822) proposed the
law of rational intercepts, which
states that there is always a set of
axes, known as crystal axes, that al-
lows a crystal face to be character-
ized in terms of intercepts of the face
with these axes. The reciprocals of
these intercepts are small rational
numbers. When the fractions are
cleared there is a set of three inte-
gers. These integers are known as the
Miller indices of the crystal face after
the British mineralogist William Hal-
lowes Miller (1810–80), who pointed
out that crystal faces could be charac-
terized by these indices.
If a plane is parallel to one of the
crystal axes then its intercept is at
inÜnity and hence its reciprocal is 0.
If a face cuts a crystal axis on the
negative side of the origin then the
intercept, and hence its reciprocal,
i.e. the Miller index for that axis, are
negative. This is indicated by a bar
over the Miller index. For example,
the Miller indices for the eight faces
of an octahedron are(III), (I_
II), (II
_
I),
(III
_
), (I
_
I
_
I), (II
_
I
_
), (I
_
II
_
) and (I_
I
_
I
_
).
milli-Symbol m. A preÜx used in
the metric system to denote one
thousandth. For example, 0.001 volt
= 1 millivolt (mV).Millon’s reagent A solution of
mercury(II) nitrate and nitrous acid
used to test for proteins. The sample
is added to the reagent and heated
for two minutes at 95°C; the forma-
tion of a red precipitate indicates the
presence of protein in the sample.
The reagent is named after French
chemist Auguste Millon (1812–67).mineralA naturally occurring sub-
stance that has a characteristic chem-
ical composition and, in general, a355 mineral
m