of the Oxides of Manganese. 35 



than when the former is employed. It is hence probable that 

 the red colour is really communicated by the red oxide. 



Peroxide of Manganese. — To procure a pure peroxide of 

 manganese, a solution of the protonitrate was evaporated to 

 dryness, and the heat continued until the whole of the salt was 

 converted into a uniform black mass. It was then reduced to 

 fine powder, carefully washed with distilled water, and dried 

 by exposure for several hours to a temperature of 600° F. 

 On heating a portion of this peroxide to redness in a glass 

 tube, a little moisture was expelled, which reddened litmus 

 paper powerfully. Consequently the peroxide still retained a 

 little nitric or nitrous acid, which I found it impossible to ex- 

 pel entirely, except by the employment of a temperature bor- 

 dering on a commencing red heat. The peroxide, after ex- 

 posure to that degree of heat, was quite free from acid, but 

 still retained a trace of moisture. On exposure to a white heat 

 it lost only 10*82 per cent of oxygen, whereas had the per- 

 oxide been pure, it should have yielded 12*122 per cent. It 

 appears therefore that the heat required to expel the last por- 

 tions of the nitric acid, decomposes some of the oxide itself; 

 and this circumstance induced me not to rely on the analysis 

 of the artificial peroxide of manganese. 



From my examination of the native peroxide of manganese, 

 I conclude with all other chemists who have of late years 

 studied the oxides of manganese, that it contains twice as much 

 oxygen as the protoxide. It is accordingly composed of 28 

 parts or one equivalent of manganese, and 16 parts or two 

 equivalents of oxygen; and in being converted by a white heat 

 into the red oxide, it should yield 12*122 per cent of oxygen 

 gas. 



Sulphuric acid acts very feebly on the peroxide of man- 

 ganese. At first I could observe no action at all ; but on em- 

 ploying a considerable quantity of the oxide, and agitating the 

 mixture frequently, the acid after an interval of two or three 

 days acquired an amethyst-red tint, a minute quantity of 

 oxygen gas being at the same time disengaged. The nature 

 of the change which is produced when sulphuric acid is heated 

 with the peroxide of manganese, has already been discussed. 



Muriatic acid, as is well known, acts upon the peroxide of 

 manganese at common temperatures, chlorine gas being dis- 

 engaged with effervescence. If heat and an excess of acid be 

 employed, a colourless muriate of the protoxide is procured ; 

 but in the cold, or if the oxide be in excess, in addition to the 

 protomuriate, a deep red coloured solution is formed, similar 

 to that already mentioned in the description of the red oxide. 

 [To be continued.] 



F 2 VIII. jEr- 



