Licence: Public Domain Mark
Credit: Qualitative chemical analysis / by C. Remigius Fresenius. Source: Wellcome Collection.
Provider: This material has been provided by the Royal College of Physicians of Edinburgh. The original may be consulted at the Royal College of Physicians of Edinburgh.
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![§ 107.] PROTOXIDE OF MANGANESE. § 107. h. Manganous Oxide, or Protoxide of Manganese, MnO [MnO]. 1 Metallic manganese is whitish-gray, cluU, very hard, brittle, ^nd f^^ses^^th very gx-eat difficulty. It oxidizes rapidly m moist air, tnd i^ wX-with evolution of hydrogen, and crumbles to a dark gray powder It dissolves readily in acids, the solutions containing the corresnonding salt of the protoxide. ,-, i j. i 2 Protoxide of manganese is light green; the hydrated prot- oxide is white. The former smoulders to brown protosesquioxide when Wed in the air, the latter even at the ordinary temperature rapidly absorbs oxygen from the aii- and passes into brown hydrated protosesqui- o5de they%re both readily soluble in hydrochloric, nitric, and sul- phuric acids. All the higher oxides of manganese without exception dissolve to protochloride, with evolution of chlorine, when heated with hydrochloric acid; and to sulphate of protoxide, with evolution of oxygen, when heated with concentrated sulphuric acid. 3 The salts of protoxide of manganese are colourless or pale red-'some are soluble in water, the others in acids. The salts soluble in water are readily decomposed by a red heat, with the exception ot the sulphate. The solutions do not alter vegetable colours. 4 Sulphuretted hydrogen does not precipitate acid solutions; neutral solutions also it fails to precipitate, or precipitates them but very imperfectly. . i i i 5 Sulphide of ammonium throws down from neutral, and sul- phuretted hydrogen from alkaline solutions the whole of the metal as hydrated sulphide of manganese, MnS,HO [MnS.H.O], m the form of a licrht flesh-coloured* precipitate, which becomes dark-brown on exposure to air; this precipitate is insoluble in sulphide of ammonium and in alkalies, but readily soluble in hydrochloric, nitric, and acetic acids. The separation of the precipitate is materiaUy promoted by the addition of chloride of ammonium. From very dUute solutions, the pre- cipitate separates only after standing for some time m a warm place Oxalate of ammonia, tartrate of ammonia, and especially citrate ot ammonia retard the precipitation, the latter salt also keeps some of the manganese in solution. In the presence of ammonia and sulphide ot ammonium in large excess, the flesh-coloured hydrated precipitate occasionally passes into the green crystalline sulphide 3Mnb,2HO i:3MnS,2H,,0], even in the cold, the change being greatly facilitated by boiling, and being hindered more or less by the presence of chloride of ammonium; solutions containing much free ammonia should first be nearly neutralized with hydrochloric acid before adding the sulphide of ammonium. , . 6. Potassa, soda, and ammonia produce whitish precipitates of hydrate of protoxide of manganese, MnO,HO [MnH,0,,], which on exposure to the air speedily become brownish and finally of a deep blackish-brown, owing to the conversion of the hydrated protoxide of manganese into the hydrated protosesquioxide by the absorption of * If the quantity of the precipitate is only trifling, the colour appears yellowish white.](https://iiif.wellcomecollection.org/image/b21966953_0145.jp2/full/800%2C/0/default.jpg)
