_Protoxide of Manganese_ exists as a green powder; as hydrate separated by caustic alkalies, it is white, but oxidizes very speedily upon exposure to the air. The protoxide is the base of the salts of manganese. These salts, which are soluble in water, are decomposed when heated in the presence of the air--except the sulphate (MnO, SO^{3}), but if the latter is exposed to ignition for awhile, it then ceases to be soluble in water, or at least only sparingly so. _Sesquioxide of Manganese_ (Mn^{2}O^{3}) Occurs very sparingly in nature as small black crystals (_Braunite_) which give, when ground, a brown powder. When prepared by chemical process, it is in the form of a black powder. The hydrate occurs sometimes in nature as black crystals (_manganite_). By digestion with acids, it is dissolved into salts of the protoxide. With hydrochloric acid, it yields chlorine. The _prot-sesquioxide of manganese_ (MnO + Mn^{2}O^{3}) occurs sometimes in black _crystals_ (_hausmannite_). Prepared artificially, it is in the form of a brown powder. _Peroxide of Manganese_ (MnO^{2}) occurs in considerable abundance as a soft black amorphous mass, or crystallized as pyrolusite, also reniform and fibrous. It is deprived of a part of its oxygen when exposed to ignition. It eliminates a considerable quantity of chlorine from hydrochloric acid, and is thereby converted into chloride of manganese (ClMn). Most of the manganese compounds which occur in nature yield water when heated in a glass tube closed at one end. The sesquioxide and peroxide give out oxygen when strongly heated, which can be readily detected by the increased glow which it causes, if a piece of lighted wood or paper is brought to the mouth of the tube. The residue left in the tube is a brown mass (MnO + Mn^{2}O^{3}). When exposed to ignition with free access of air, all manganese oxides are converted into (MnO + Mn^{2}O^{3}), but without fusion. Such, at least, is the statement of some of the German chemists, although it will admit perhaps of further investigation. Manganese oxides fuse with borax in the oxidation flame to a clear and intensely colored bead, of a violet hue while hot, but changing to red as it cools. If a considerable quantity of the oxide is added, the bead acquires a color so dark as to become opaque. If such be the case, we have to press it flat, by which its proper color will become manifest. In the reduction flame the bead is colorless. A very dark colored bead must be fused upon charcoal with the addition of some tin. The bead must be cooled very suddenly, for if it cools too slowly, it then has time to oxidize again. This may be effected by pushing it off the platinum wire, or the charcoal, and pressing it flat with the forceps.