MANGANESE CHROMIUM COBALTNICKEL. 175 



Manganous oxide is a greenish-gray powder, obtainable by heating 

 the carbonate ; or as a nearly white hydroxide by precipating a man- 

 ganous salt by sodium hydroxide. It is a strong base, saturating 

 acids completely, and forming salts which have generally a rose 

 color or a pale reddish tint. 



Manganese dioxide, Mangani oxidum nigrum, MnO 2 = 86.8. 

 This is by far the most important compound of manganese, as it is 

 largely used for generating chlorine : 



MnO 2 + 4HC1 = MnCl 2 -f 2H 2 O + 2C1. 



It is a heavy, grayish-black, crystalline mineral, liberating oxygen 

 when heated to redness : 



3MnO 2 = Mn 3 O 4 + 2O. 



The official article should contain at least 66 per cent, of MnO 2 . 



Manganous sulphate, Mangani sulphas, MnSO 4 .4H 2 O = 222.8, 

 may be obtained by dissolving the oxide or dioxide in sulphuric 

 acid ; in the latter case oxygen is evolved : 



Mn0 2 + H 2 S0 4 = MnS0 4 + H 2 O + O. 



As manganese dioxide generally contains iron oxide, the solution 

 contains sulphates of both metals. By evaporating to dryness and 

 strongly igniting, the iron salt is decomposed. The ignited mass is 

 now lixivated with water, and the filtered solution evaporated for 

 crystallization. 



It is an almost colorless, or pale rose-colored substance, isomor- 

 phous with the sulphates of magnesium and zinc ; it is easily soluble 

 in water. 



Potassium permanganate, Potassii 



157.8. Whenever a compound (any oxide or salt) of manganese is 

 fused with alkali carbonates (or hydroxides) and alkali nitrates (or 

 chlorates) the manganese is converted into manganic acid, which 

 combines with the alkali, forming potassium (or sodium) manganate: 

 3MnO 2 + 3K 2 CO 3 + KC1O 3 = 3K 2 MnO 4 + 3CO, + KC1. . 



The fused mass has a dark-green color, and when dissolved in 

 water gives a dark emerald -green solution, from which, by evapora- 

 tion, green crystals of potassium manganate may be obtained. 



The green solution is decomposed easily by any acid (or even by 

 water in large quantity) into a red solution of potassium perman- 

 ganate and a precipitate of manganese dioxide. 



3K 2 MnO 4 + 2H 2 SO 4 = MnO 2 + 2K 2 SO 4 -f 2KMnO 4 + 2H 2 O. 



