I1YPERMANGANIC ACID. 5^7 



It also follows that the per centage of chlorine, which the 

 same specimen of manganese would afford,, is obtained by mul- 

 tiplying the number of grains of sulphate of iron peroxidised by 



0.2588. 



Manganic add ; Mn O 3 ; 645.9 or 51.72. When peroxide of 

 manganese is strongly ignited with hydrate or carbonate of 

 potash in excess, manganic acid is formed, under the influence of 

 the alkali, together with a lower oxide of manganese. Ignition 

 in open vessels or with an admixture of nitrate of potash, in- 

 creases the production of the acid, by the absorption of oxygen 

 which then occurs. The product has long been known as 

 mineral chameleon., from the property of its solution, which is 

 green at first, to pass rapidly through several shades of colour. 

 But a more convenient process for preparing manganate of potash 

 is that recommended by Dr. Gregory. He mixes intimately 4 

 parts of peroxide of manganese in fine powder with 3| parts of 

 chlorate of potash, and adds them to 5 parts of hydrate of 

 potash dissolved in a small quantity of water. The mixture is 

 evaporated to dryness, powdered, and afterwards ignited in a 

 platinum crucible, but not fused, at a low red heat. Digested 

 in a small quantity of cold water, this affords a deep green solu- 

 tion of the alkaline manganate, which may be obtained in crys- 

 tals of the same colour by evaporating the solution over sul- 

 phuric acid in the air-pump. The manganates were discovered 

 by Mitscheiiich to be isomorphous with the sulphates and chro- 

 mates. It has not yet been found possible to isolate manganic 

 acid. Its salts in solution readily undergo decomposition, 

 unless an excess of alkali be present ; and are also destroyed by 

 contact of organic matter such as paper. 



Hy permanganic acid., Mn 2 O 7 ; 1391.8, or 111.44. When the 

 green solution of manganate of potash, prepared as above di- 

 rected, is diluted with boiling water, hydrated peroxide of man- 

 ganese subsides, and the liquid becomes of a beautiful pink or 

 violet colour. The manganic acid is resolved into peroxide of 

 manganese and hypermanganic acid : 



3Mn O 3 == Mn O 2 and Mn 2 O 7 . 



The hypermanganate of potash should be rapidly concentrated, 



