308 PRINCIPLES OF CHEMISTRY 



the exception of the fact that MnX 2 are rose coloured and are easily 

 oxidised in the presence of alkalis), we will- not dwell upon them, but 



oxalate, MnC 2 O 4 . This precipitate is insoluble in water, and is used for the preparation 

 of manganous oxide' itself because it decomposes like oxalic acid when ignited (in a tube 

 without access of air), with the formation of carbonic anhydride, carbonic oxide, and 

 manganous oxide. Manganous oxide thus" obtained is a green powder, which however 

 oxidises with such facility that it burns in air when brought into contact with an 

 incandescent substance, and passes into the red intermediate oxide Mn 3 4 . In solutions 

 of manganous salts, alkalis produce a precipitate of the hydroxide MnH 2 O 2 , which 

 rapidly absorbs oxygen in the presence of air and gives the brown intermediate oxide, 

 or, more correctly speaking, its hydrate. 



Manganous oxide, besides being obtained by the above-described method from man- 

 ganous oxalate, may also be obtained by igniting the higher oxides jn a stream of 

 hydrogen, and also from manganese carbonate. The manganous oxide ignited in the 

 presence of hydrogen acquires a great density, and is no longer so easily oxidised. It 

 may also be obtained in a crystalline form, if during the ignition of the carbonate or 

 higher oxide a trace of dry hydrochloric acid gas be passed into the current of hydrogen. 

 It Is thus obtained in the form of transparent emerald green crystals of the regular 

 system, and in this state is easily soluble in acids. 



Manganous oxide in oxidising gives the red oxide of manganese, Mn 3 O 4 . This is the 

 most stable of all the oxides of manganese ; it is not only stable at the ordinary but also 

 at a high temperature that is, it does not absorb or disengage oxygen spontaneously. 

 When ignited, all the higher oxides of manganese pass into it by losing oxygen, arid 

 manganous oxide by absorbing oxygen. This oxide does pot give any distinct salts, 

 but it dissolves in sulphuric acid, forming a dark red solution, which contains both 

 manganous and manganic (of the oxide, Mn 2 O 3 ) sulphates. The latter with potassium 

 sulphate gives a manganese alum, in which the alumina is replaced by its isomorphoua 

 oxide of manganese. But this alum, like the solution of the intermediate oxide in sul- 

 phuric acid, evolves oxygen and leaves a manganous 'salt when slightly heated. 



Manganese dioxide is still less basic than the oxide, and disengages oxygen or a 

 halogen in the presence of acids, forming manganous salts, like the oxide. However, if it 

 be suspended in ether, and hydrochloric acid gas passed into the mixture, which is kept 

 cool, the ether acquires a green colour, owing to the formation of tetra- chloride of 

 manganese, MnCl 4 , corresponding with the dioxide which passes into solution. It is 

 however very unstable, being exceedingly easily decomposed with the evolution of 

 chlorine. The corresponding fluoride, MnF 4 , obtained by Nickles is much more stable. 

 At all events, manganese dioxide does not exhibit any well-defined basic character, but 

 has rather an acid character, which is particularly shown in the compounds MnF 4 and 

 MnCl 4 just mentioned, and in the property of manganese dioxide of combining with 

 alkalis. If the higher grades of oxidation of manganese be deoxidised in the presence of 

 alkalis, they frequently give the dioxide combined with the alkali for example, in the 

 presence of potash a compound is formed which contains K 2 0,5MnO 2 , which shows the 

 weak acid character of this oxide. When ignited in the presence of sodium compounds 

 manganese dioxide frequently forms Na 2 O,SMnO a and Na 2 O,12Mn0 2 , and lime when 

 heated with MnO 2 gives from CaO,3MnO 2 to (CaO.) 2 ,MnO 2 (Rousseau) according to the 

 temperature. Besides which, perhaps, MnO.> is a saline compound, containing 

 MnOMnO 3 or (MnO) 5 Mn 2 O 7 , and there are reactions which support such a view (Spring, 

 Richards, Traube, and others) ; for instance it is known that manganous chloride and 

 potassium permanganate give the dioxide in the presence of alkalis. 



Manganese dioxide may be obtained from manganous salts by the action of oxidis- 

 ing agents. If manganous hydroxide or carbonate be shaken up in water through 

 which chlorine is passed, the hypochlorite of the metal is not formed, as is the case 

 with certain other oxides, but manganese dioxide is precipitated 2MnO 2 H 2 + Cl a 

 = MnCl 2 + MnO 2 ,H 3 O + H 2 O. Owing to this fact, hypochlorites in the presence of alkalis 

 and acetic acid when added to a solution of manganous salts give hydrated manganese 



