MANGANESE CHROMIUM-COBALT-NICKEL. 305 



the precipitate of calcium sulphate to settle, and evaporating the filtrate to 

 dryness. It is a pink crystalline powder, permanent in the air, and soluble in 

 6.6 parts of water. Its chief use is as a constituent of compound syrup of 



hypophosphites. 



Potassium permanganate, Potassii permanganas, KMnO 4 = 

 156.98. 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 a -f 3K 8 CO 8 + 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 Mn0 4 + 2H 2 SO 4 = MnO 2 + 2K 2 SO 4 + 2KMnO 4 + 2H 2 O. 



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 -f xO 5 . 



x represents here any substance capable of combining with oxygen 

 while in solution. 



Experiment 35. Heat in an iron 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. 



Permanganic acid, HMn0 4 , can now be obtained in solution by electrol- 

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