304 METALS AND THEIR COMBINATIONS. 



sulphate, MnSO 4 . The oxygen does not escape, but goes to the reducing com- 

 pound. Conversely, when oxygen is forcibly added to any of the lower oxides 

 in the presence of alkalies, the MnO 3 state of oxidation is attained, that is, 

 salts of manganic acid, or manganates, are produced, as K 2 MnO 4 , from which 

 the more stable permanganates are readily obtained (see below). 



While manganous salts are stable and do not absorb oxygen like ferrous 

 salts, manganous hydroxide and carbonate readily absorb oxygen and turn 

 dark, resembling in this respect iron. 



Manganous oxide is a greenish-gray powder obtainable by heating 

 the carbonate ; or as a nearly white hydroxide by precipitating a 

 manganous 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, MnO 2 , is by far the most important com- 

 pound of manganese found in nature, as it is largely used for gener- 

 ating chlorine and oxygen, as described in former chapters. 



Precipitated manganese dioxide, Mangani dioxidum praecipitatum, 

 MnO.j 86.36, is obtained by pouring a mixture of ammonia water and 

 hydrogen peroxide into a solution of manganese sulphate, when manganese 

 dioxide mixed with some oxide is precipitated as a heavy, black powder : 



MnS0 4 + 2NH 4 OH + H 2 O 2 = (NH 4 ) a SO 4 + 2H 2 O -f MnO 2 . 



Experiment 34. Mix 10 c.c. of 5 per cent, ammonia water with 10 c.c. of 

 1.5 per cent, hydrogen dioxide solution, and pour slowly while stirring into 

 20 c.c. of a 5 per cent, solution of manganous sulphate. Let the mixture 

 stand for one hour, stirring frequently. Then filter and wash thoroughly with 

 hot water, let drain, and dry. Heat some of the precipitate with hydrochloric 

 acid in a test-tube and explain the result. 



Manganese sulphate, Mangani sulphas, MnSO 4 .4H 2 O = 221.47, 

 maybe obtained by dissolving the oxide or dioxide in sulphuric acid ; 

 in the latter case oxygen is evolved : 



MnO 2 + H,SO 4 = MnSO 4 -f H 2 O -f 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 lixiviated with water, 

 and the filtered solution evaporated for Crystallization. 



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

 the sulphates of magnesium and zinc ; it is easily soluble in water. 



Manganese hypophosphite, Mangani hypophosphis, Mn(PH 2 2 ) 2 .H,0 



= 201.54, may be made by mixing a solution of 1 part of calcium hypo- 

 phosphite with a solution of 1.31 parts of manganous sulphate, allowing 



