154 METALS AXJ) THEIR COMBINATIONS. 



Manganous oxide is a greenish-gray powder, obtainable by 

 heating the carbonate; or as a nearly white hydrate by pre- 

 cipitating a manganous salt by sodium hydrate. 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., = 86. This 

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

 largely msed for generating chlorine: 



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



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

 oxygen when heated to redness : 



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



Manganous sulphate, Mangani sulphas, MnS0 4 .4H 2 = 222, may 

 be obtained by dissolving the oxide or dioxide in sulphuric 

 acid; in the latter case oxygen is evolved : 



MnO 2 -f H 2 SO 4 = MnSO 4 + H 2 O -f O. 



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

 morphous with the sulphates of magnesium and zinc; it is 

 easily soluble in water. 



Potassium permanganate, Potassii permanganas, K 2 Mn 2 8 = 314 



(Permanganate of potassium). Whenever a compound (any oxide 

 or salt) of manganese is fused with alkaline carbonates (or 

 hydrates) and alkaline nitrates (or chlorates) the manganese is 

 converted into manganic acid, which combines with the alkali, 

 forming potassium (or sodium) manganate : 



3Mn0 2 -f 3K 2 CO 3 + KC10 3 = 3K 2 MnO 4 + 3C0 2 -f- KC1. 



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

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

 evaporation, green crystals of potassium manganate may be ob- 

 tained. 



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

 by water in large quantity) into a red solution of potassium 

 permanganate and a precipitate of dioxide of manganese : 



3K 2 Mn0 4 -f 2H 2 SO 4 = MnO 2 -f 2K 2 SO 4 + K 2 Mn,0 8 -f 2H 2 O. 



