156 Dr TURNER'S Chemical Examination 



carbonic oxide gas, collecting around the heated manganese, 

 reduced it more or less nearly to the state of protoxide. On 

 avoiding this source of fallacy, the results were no longer dis- 

 cordant ; and I am now quite satisfied that the red oxide formed 

 at a white heat and with free exposure to atmospheric air, is 

 uniform in its composition. The accuracy of this inference is 

 established by the occurrence of the red oxide in nature, as will 

 appear in the sequel of the present communication. 



The red oxide, when formed at a white heat and rubbed in a 

 mortar to the same degree of fineness, is always of a brownish- 

 red colour when cold, and nearly black while warm. The pow- 

 der of the native red oxide has a reddish-brown tint, and the 

 colour of the red oxide prepared by exposing the precipitated 

 protoxide or the carbonate to a moderate red heat, has most 

 commonly an admixture of yellow, something like rhubarb, 

 though of a deeper hue ; but both of these acquire the red co- 

 lour when heated to whiteness. 



The red oxide manifests little tendency to pass into a higher 

 degree of oxidation by abstracting oxygen from the atmosphere, 

 even by the aid of heat. Thus a portion of the red oxide, pre- 

 served for an hour at a low red heat, and freely exposed to the 

 air at the same time, did not acquire any appreciable addition 

 to its weight. The protoxide of manganese precipitated from 

 the sulphate by an excess of pure potash, collected on a filter 

 and washed, fully exposed to the air in its moist state for twenty- 

 four hours, and then heated in an open vessel to a moderate red 

 heat, which was insufficient to decompose the deutoxide, lost 

 only 0.218 per cent by subsequent exposure to a white heat. 

 The quantity of deutoxide present, therefore, must have been 

 very minute. The anhydrous protoxide, as already mentioned, 

 always yields the pure red oxide when heated to redness in the 

 open air. The carbonate, also, in similar circumstances, is con- 



