MgCO 3 (s) + CO 2 (g) + H 2 O(l) →
Mg(HCO 3 ) 2 (aq)
On heating, this process is reversed.
Magnesium hydrogencarbonate is
one of the compounds responsible
for temporary *hardness in water.
magnesium hydroxide A white
solid compound, Mg(OH) 2 ; trigonal;
r.d. 2.36; decomposes at 350°C. Magnesium hydroxide occurs naturally as
the mineral brucite and can be prepared by reacting magnesium sulphate or chloride with sodium
hydroxide solution. It is used in the
reÜning of sugar and in the processing of uranium. Medicinally it is
important as an antacid (milk of
magnesia) and as a laxative.
magnesium oxide (magnesia) A
white compound, MgO; cubic; r.d.
3.58; m.p. 2800°C. It occurs naturally
as the mineral periclase and is prepared commercially by thermally decomposing the mineral *magnesite:
MgCO 3 (s) → MgO(s) + CO 2 (g)
It has a wide range of uses, including
reÛective coatings on optical instruments and aircraft windscreens and
in semiconductors. Its high melting
point makes it useful as a refractory
lining in metal and glass furnaces.
magnesium peroxide A white
solid, MgO 2 . It decomposes at 100°C
to release oxygen and also releases
oxygen on reaction with water:
2MgO 2 (s) + 2H 2 O → 2Mg(OH) 2 + O 2
The compound is prepared by reacting sodium peroxide with magnesium sulphate solution and is used as
a bleach for cotton and silk.
magnesium sulphate A white soluble compound, MgSO 4 , existing as
the anhydrous compound (rhombic;
r.d. 2.66; decomposes at 1124°C) and
in hydrated crystalline forms. The
monohydrate MgSO 4 .H 2 O (monoclinic; r.d. 2.45) occurs naturally as
the mineral kieserite. The commonest hydrate is the heptahydrate,
MgSO 4 .7H 2 O (rhombic; r.d. 1.68),
which is called Epsom salt(s), and occurs naturally as the mineral epsomite. This is a white powder with a
bitter saline taste, which loses 6H 2 O
at 150°C and 7H 2 O at 200°C. It is
used in sizing and ÜreprooÜng cotton
and silk, in tanning leather, and in
the manufacture of fertilizers, explosives, and matches. In medicine, it is
used as a laxative. It is also used in
veterinary medicine for treatment of
local inÛammations and infected
wounds.
magnetic moment The ratio between the maximum torque (T max )
exerted on a magnet, currentcarrying coil, or moving charge situated in a magnetic Üeld and the
strength of that Üeld. It is thus a
measure of the strength of a magnet
or current-carrying coil. In the Sommerfeld approach this quantity (also
called electromagnetic moment or
magnetic area moment) is the ratio
T max /B. In the Kennelly approach the
quantity (also called magnetic dipole
moment) is T max /H.
In the case of a magnet placed in a
magnetic Üeld of Üeld strength H, the
maximum torque T max occurs when
the axis of the magnet is perpendicular to the Üeld. In the case of a coil of
N turns and area A carrying a current
I, the magnetic moment can be
shown to be m = T/B = NIA or m = T/H
= µNIA. Magnetic moments are measured in A m
2 .
An orbital electron has an orbital
magnetic moment IA, where I is the
equivalent current as the electron
moves round its orbit. It is given by I
= qω/2π, where q is the electronic
charge and ω is its angular velocity.
The orbital magnetic moment is
therefore IA = qωA/2π, where A is the
orbital area. If the electron is spin337
magnetic moment
m
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Mg(HCO 3 ) 2 (aq)
On heating, this process is reversed.
Magnesium hydrogencarbonate is
one of the compounds responsible
for temporary *hardness in water.
magnesium hydroxide A white
solid compound, Mg(OH) 2 ; trigonal;
r.d. 2.36; decomposes at 350°C. Magnesium hydroxide occurs naturally as
the mineral brucite and can be prepared by reacting magnesium sulphate or chloride with sodium
hydroxide solution. It is used in the
reÜning of sugar and in the processing of uranium. Medicinally it is
important as an antacid (milk of
magnesia) and as a laxative.
magnesium oxide (magnesia) A
white compound, MgO; cubic; r.d.
3.58; m.p. 2800°C. It occurs naturally
as the mineral periclase and is prepared commercially by thermally decomposing the mineral *magnesite:
MgCO 3 (s) → MgO(s) + CO 2 (g)
It has a wide range of uses, including
reÛective coatings on optical instruments and aircraft windscreens and
in semiconductors. Its high melting
point makes it useful as a refractory
lining in metal and glass furnaces.
magnesium peroxide A white
solid, MgO 2 . It decomposes at 100°C
to release oxygen and also releases
oxygen on reaction with water:
2MgO 2 (s) + 2H 2 O → 2Mg(OH) 2 + O 2
The compound is prepared by reacting sodium peroxide with magnesium sulphate solution and is used as
a bleach for cotton and silk.
magnesium sulphate A white soluble compound, MgSO 4 , existing as
the anhydrous compound (rhombic;
r.d. 2.66; decomposes at 1124°C) and
in hydrated crystalline forms. The
monohydrate MgSO 4 .H 2 O (monoclinic; r.d. 2.45) occurs naturally as
the mineral kieserite. The commonest hydrate is the heptahydrate,
MgSO 4 .7H 2 O (rhombic; r.d. 1.68),
which is called Epsom salt(s), and occurs naturally as the mineral epsomite. This is a white powder with a
bitter saline taste, which loses 6H 2 O
at 150°C and 7H 2 O at 200°C. It is
used in sizing and ÜreprooÜng cotton
and silk, in tanning leather, and in
the manufacture of fertilizers, explosives, and matches. In medicine, it is
used as a laxative. It is also used in
veterinary medicine for treatment of
local inÛammations and infected
wounds.
magnetic moment The ratio between the maximum torque (T max )
exerted on a magnet, currentcarrying coil, or moving charge situated in a magnetic Üeld and the
strength of that Üeld. It is thus a
measure of the strength of a magnet
or current-carrying coil. In the Sommerfeld approach this quantity (also
called electromagnetic moment or
magnetic area moment) is the ratio
T max /B. In the Kennelly approach the
quantity (also called magnetic dipole
moment) is T max /H.
In the case of a magnet placed in a
magnetic Üeld of Üeld strength H, the
maximum torque T max occurs when
the axis of the magnet is perpendicular to the Üeld. In the case of a coil of
N turns and area A carrying a current
I, the magnetic moment can be
shown to be m = T/B = NIA or m = T/H
= µNIA. Magnetic moments are measured in A m
2 .
An orbital electron has an orbital
magnetic moment IA, where I is the
equivalent current as the electron
moves round its orbit. It is given by I
= qω/2π, where q is the electronic
charge and ω is its angular velocity.
The orbital magnetic moment is
therefore IA = qωA/2π, where A is the
orbital area. If the electron is spin337
magnetic moment
m
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