MANGANESE-CHROMIUM COBALT-NICKEL. 303 



28. MANGANESE CHROMIUM COBALT MCKEL. 



Manganese, Mn = 54.6. The principal ore is the dioxide (black 

 oxide of manganese, pyrolusite), MnOj, which is always accompanied 

 by iron compounds. Other forms occurring in nature are braunite, 

 Mn f O 3 , hausmannite, Mn^O^, and manganese spar, MnCO 3 . In small 

 quantities it is a constituent of many minerals. 



Metallic manganese resembles iron in its physical and chemical 

 properties, and may be obtained by reducing the carbonate with 

 charcoal. Manganese is darker in color than iron, considerably 

 harder, and somewhat more easily oxidized. Alloys of iron and 

 manganese (20 to 80 per cent.), known as ferro-manganese, are used 

 in the arts. 



Oxides of manganese. Six oxides are known. MnO 3 and 

 Mn 2 O 7 have been obtained in the free state, but they are very unsta- 

 ble, and are known best through their compounds : 



Manganoos oxide (monoxide or protoxide), MnO. 



Manganous manganic oxide, MnOMn,0^ = Mn^O^ 



Manganic oxide (sesquioxide), MiijQj. 



Manganese dioxide (binoxide, peroxide, black oxide), MnO r 



Manganese trioxide, MnQ,. 



Manganese heptoxide, Mn,Oj. 



The chemical behavior of these oxides varies with the degree of oxidation, 

 or, in other words, with the valence of the manganese. MnO is strongly basic ; 

 Mn,Oj is weakly basic; MnOj has feebly acidic character; MnO s is more 

 strongly acidic, being the anhydride of manganic acid, HjMnO 4 , which is 

 known only in its salts ; Mn s O T is the anhydride of permanganic acid, which 

 is known in aqueous solution, and has strong acid character. 



The only stable salts of manganese are the manganou.* salts, derived from 

 manganons oxide, MnO, in which the valence of manganese is 2. When any 

 oxide of manganese (or compounds of those oxides which are unstable in the 

 free state) is heated with an acid, a manganous salt is obtained. In this action 

 the oxides higher than MnO give off oxygen, or oxidize the excess of acid (see 

 action of hydrochloric acid on MnOj). The decomposition of potassium per- 

 manganate, which has been used hitherto as an oxidizer, may now be explained. 

 In dilute sulphuric acid solution permanganic acid is liberated thus : 



2KMn0 4 + H,SO 4 = K,SO 4 + 2HMnO 4 . 



The acid is stable enough when nothing else is present that can be oxidized, 

 but if such a substance is added the permanganic acid breaks down to mangan- 

 ous oxide and oxygen : 



2HMnO 4 = H S O + MnA, 

 Mn,O, = 5O + 2MnO, 



2MnO + 2HjSO 4 = 2MnSO 4 + 2H,O. 



The manganous oxide is dissolved by the acid to form the colorless manganous 



