at. no. 25, at. wt. 54.93, metal, row 5, col. 7B, val. 2-3-4-6-7, orbits 2-8-13-2

{Merck Index - © 1952 by Merck & Co., Inc.}

Manganese. Mn; at. wt. 54.93; at. no. 25; valence 2-3-4-6-7. First isolated by Galin in 1774. Occurs in the minerals pyrolusite, braunite, hausmannite, manganite, and in several others; occurs in minute quantities in water, plants, and animals. Prepn. of the metal: John, et al., cited by Mellor, A Comprehensive Treatise on Inorganic and Theoretical Chemistry, 12, 163 (1932).

Steel-gray, lustrous, hard, brittle metal. Exists in three allotropic forms: Alpha-form, cubic, stable below 742°; Beta-form, cubic, stable in the range 742-1191°; Gamma-form, or electrolytic manganese, tetragonal, stable above 1190°, claimed to be a hydride: Bradley, Thewlis, Proc. Roy. Soc. 115, 456 (1927). in. 12471: Moser, et al., Z. anorg. Chem. 210, 67 (1933); b. 2032° (extrapolated): Baur, Brunner, Helv. Chim. Acta 17, 958 (1934); d. 7.23. Superficially oxidized on exposure to air. Burns with an intense white light when heated in air. Decomposes water slowly in the cold, rapidly on heating; pure electrolytic manganese is not attacked by water at ordinary temperature; slightly attacked by steam. Dissolves readily in dil. mineral acids with evolution of hydrogen and formation of divalent manganous salts. Soluble in aqueous solutions of sodium or otassium bicarbonate. When heated in nitrogen above 2000° burns to form a nitride. It is converted by fluorine into the di- and the trifluoride, by chlorine into the dichloride. In form of powder reduces most metallic oxides on heating. On heating, reacts directly with carbon, phosphorus, antimony or arsenic.

Use: In the manufacture of steel; for rock crushers, railway points and crossings, wagon buffers; as a constituent of several alloys, e.g., ferromanganese, copper manganese, manganin.

Toxicity: Occurs by inhalation of dust or fumes. Symptoms: languor, sleepiness, weakness, emotional disturbances, spastic gait, paralysis.

Max. allowable concn. 6 mg./cu. m.

{Mineral Deficiencies in Plants}

The functions of manganese are regarded as being closely associated with those of iron and as being concerned with chlorophyll formation. Hence, when manganese is deficient, chlorosis is a common symptom. Manganese may decrease the solubility of iron by oxidation and hence an abundance of manganese within the plant may lead to iron deficiency and chlorosis; conversely manganese deficiency may be induced by an excessive iron supply.

Manganese is regarded as having the functions of a catalyst, its activities being specially concerned with oxidation and reduction reactions within the plant tissues. Iron and manganese together may well be the main oxidation reduction regulators in plants.

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