can be extracted by reduction of the
oxide using magnesium (Kroll
process) or aluminium (Gold-
schmidt process). Often the ore is
mixed with iron ore and reduced in
an electric furnace to produce ferro-
manganese for use in alloy steels.
The element is fairly electropositive;
it combines with oxygen, nitrogen,
and other nonmetals when heated
(but not with hydrogen). Salts of
manganese contain the element in
the +2 and +3 oxidation states. Man-
ganese(II) salts are the more stable. It
also forms compounds in higher oxi-
dation states, such as manganese(IV)
oxide and manganate(VI) and man-
ganate(VII) salts. The element was
discovered in 1774 by Karl *Scheele.
A
- Information from the WebElements site
manganese(IV) oxide (manganese
dioxide)A black oxide made by heat-
ing manganese(II) nitrate. The com-
pound also occurs naturally as
pyrolusite. It is a strong oxidizing
agent, used as a depolarizing agent in
voltaic cells.
manganic compoundsCom-
pounds of manganese in its +3 oxida-
tion state; e.g. manganic oxide is
manganese(III) oxide, Mn 2 O 3.
manganin A copper alloy contain-
ing 13–18% of manganese and 1–4%
of nickel. It has a high electrical re-
sistance, which is relatively insensi-
tive to temperature changes. It is
therefore suitable for use in resis-
tance wire.
manganous compounds Com-
pounds of manganese in its +2 oxida-
tion state; e.g. manganous oxide is
manganese(II) oxide, MnO.
mannanSee mannose.
Mannich reaction A reaction in
which a primary or secondary amine
reacts with methanal (formaldehyde)
and a carbonyl compound to produce
an amino-carbonyl compound. It
takes place in two stages. First the
amine reacts with methanol to form
a Schiff base:
R 2 N + H 2 CO →R 2 N+=CH 2.
This then reacts with the carbonyl
compound:
R 2 N+=CH 2 + R^1 R^2 CHCOR^3 →
R 2 N–CH 2 –C(R^1 R^2 )COR^3.
The reaction wasÜrst reported by
Carl Mannich in 1912.
mannitolA polyhydric alcohol,
CH 2 OH(CHOH) 4 CH 2 OH, derived from
mannose or fructose. It is the main
soluble sugar in fungi and an impor-
tant carbohydrate reserve in brown
algae. Mannitol is used as a sweet-
ener in certain foodstuffs and as a di-
uretic to relieveÛuid retention.mannoseA *monosaccharide,
C 6 H 12 O 6 , stereoisomeric with glu-
cose, that occurs naturally only in
polymerized forms called mannans.
These are found in plants, fungi, and
bacteria, serving as food energy
stores.
manometerA device for measur-
ing pressure differences, usually by
the difference in height of two liquid
columns. The simplest type is the U-
tube manometer, which consists of a
glass tube bent into the shape of a U.
If a pressure to be measured is fed to
one side of the U-tube and the other
is open to the atmosphere, the differ-
ence in level of the liquid in the two
limbs gives a measure of the un-
known pressure.many-body problem The prob-
lem that it is very difÜcult to obtain
exact solutions to systems involving
interactions between more than two
bodies – using either classical me-
chanics or quantum mechanics. To
understand the physics of many-body
systems it is necessary to make use of341 many-body problem
m