176 METALS AND THEIR COMBINATIONS. 



By evaporation and crystallization potassium permanganate is ob- 

 tained in slender, prismatic crystals, of a dark- purple color, and a 

 somewhat metallic lustre. The solution in water has a deep purple, 

 or, when highly diluted, a pink color (Plate II. , 1). It is a power- 

 ful oxidizing agent, and an excellent disinfectant, both properties 

 being due to the facility with which a portion of the oxygen is given 

 off to any substance which has affinity for it. If the oxidation 

 takes place in the absence of an acid, a lower oxide of manganese is 

 formed, which separates as an insoluble substance. If an acid is 

 present, both the potassium and manganese combine with it, forming 

 salts, thus : 



2(KMnO 4 ) 4- 6HC1 + x = 2KC1 + 2MnCl 2 + 3H 2 O + xO 5 . 



x represents here any substance capable of combining with oxygen 

 while in solution. 



Experiment 28. Heat in a porcelain crucible a mixture of 2 grammes man- 

 ganese dioxide, 2 grammes potassium hydroxide, and 1 gramme potassium 

 chlorate, until the fused mass has turned dark-green. Dissolve the cooled 

 mass with water, filter the green solution of potassium manganate, and pass 

 carbon dioxide through it until it has assumed a purple color, showing that 

 the conversion into permanganate is complete. Notice that the acidified solu- 

 tion is readily decolorized by ferrous salts and other deoxidizing agents. 



Analytical reactions. 

 (Manganous sulphate, MnSO 4 , may be used.) 



1. Ammonium sulphide produces a yellowish-pink or flesh-colored 

 precipitate of hydrated manganous sulphide, MnS.H 2 O, soluble in 

 acetic and in mineral acids (Plate II. , 2) : 



MnSO 4 4- (NH 4 ) 2 S = (NH 4 ) 2 SO 4 + MnS. 



2. Ammonium (or sodium) hydroxide produces a white precipitate 

 of manganous hydroxide, which soon darkens by absorption of oxygen 

 (Plate II., 3) and dissolves in oxalic acid with a rose-red color : 



MnCl 2 + 2NH 4 OH = 2NH 4 C1 + Mn(OH) 2 . 



3. Sodium (or potassium) carbonate produces a nearly white pre- 

 cipitate of manganous carbonate : 



MnSO 4 + Na. 2 CO s B= Na 2 SO 4 + MnCO 3 . 



4. Any compound of manganese heated on platinum foil with a 

 mixture of sodium carbonate and nitrate forms a bluish-green mass, 

 giving a green solution in water, which turns red on addition of an 

 acid. (See explanation above.) 



