MANGANESE This metal was not isolated till about the middle of the 18th century, the natural compounds containing it having been up to that time supposed to be ores of Iron. It is a con stituent of many minerals and, its black oxide, occurs frequently in abundance. The composition of its ores, and the localities whence they are derived, will be fuund described under MANGANESE, in NAT. HIST. Div.
Metallic mangeneee may be obtained, though with difficulty, by Igniting carbonate of manganese made up Into a paste with oil and sugar. For this purpose, a crucible should be lined with charcoal, the cover lifted on, and the whole exposed to the hest of a smith's forge fur a couple of hours. A button of metal is thus procured which may be purified by re-Igniting in a crucible with a little more of the carbonate.
Manganese is a grayish white metal of inferior lustre, is hard enough to scratch steel, is very brittle, easily split, feebly magnetic, has a granular texture, and a specific gravity of When pure, it speedily absorbs oxygen from the air, and is therefore most conveniently kept below the surface of naphtha. It appears to exist in two allo tropic modifications, and combines with carbon and with silicon when fused iu contact with those substances. In the finely divided state it slowly decomposes cold water ; hot water being rapidly attacked by it, with liberation of hydrogen. Most acids act upon it energetically.
The equivalent of manganese is Its specific gravity, 8'013.
Manganese and o.rygen unite in seven different proportions; two of the resulting compounds are, however, usually considered to be mix tures of the other oxides. They are :— • • • • ""•••. .....
I. Protaride of manganese (MnO). Manganous oxide. Obtained on heating carbonate of maneanese in a current of hydrogen. It is a green coloured powder, if prepared at a dull red heat, has such affinity for oxygen as to be spontaneously inflammable. It is a powerful base, and forms stable salts with the acids.
Hydrated proloxide is a white precipitate produced on adding an alkali to an aqueous solution of a menganous salt. In contact with
air it rapidly absorbs oxygen and becomes brown.
2. Sesquioxide of manganese is formed when the protoxide ie exposed to the air. It is a feeble base, isomorphous with alumina and sesquioxide of iron.
It occurs native as braunite. Its solution in dilute sulphuric acid is red, and on the addition of an alkaline sulphate, octohedml crystals are deposited, resembling alum, but haring in the place of A1,0. The potash salt contains 31n,0,, 24Aq.
Hydrated sesquioxide is produced by exposure of the hydrated pro toxide to the air. It also occurs native. [MANGANESE, Manganite, in NAT. HIST. Div.] 3. Binoxide of manganese (31n0,). Peroxide of manganese. This oxide occurs largely in nature, and is called pyrolusite by mineralogists, see NAT. Him.. Div. In commerce, it is generally simply termed manganese, and is largely used in the manufacture of chlorine com pounds, also to give a black colour to earthenware, and in GLASS MANUFACTURE (VOL iv., col. 391).
When heated, binoxide of manganese yields up one-third of its oxygen ; boiled with sulphuric acid it is converted into a salt of the protoxide, oxygen here also being eliminated.
The assay of binoxide of manganese is an important operation con nected with the manufacture of bleaching-powder. It depends upon the conversion of oxalic acid into carbonic acid, by tire action of the oxygen that is evolved when binoxide of manganese is heated with sulphuric acid. The apparatus in which it is performed is weighed before and after the evolution of the carbonic acid, and the loss sus tained, that is the weight of the carbonic acid, exactly indicates the weight of peroxide of manganese in the sample.
4. Red oxide of manganese (31n,0„ or 31n0 +3110,, or 231110+ MnO,) °Celan! native. [MANGANESE, //a718Malf/liCe, in NAT. If SST. DIV.] 5. l'arrieite or + See also MANGANESE, in NAT. HIST. Div.