98 Dr. Turner's Chemical Examination 



is free from siliceous earth, lime, baryta, and every other im- 

 purity. It is the purest native oxide of manganese which has 

 fallen under my notice. Its powder has a uniform brown tint, 

 and I have been unable to observe in it any tendency to pass 

 into the peroxide by absorbing oxygen from the air. After 

 exposure to the air for six months, during which it was fre- 

 quently moistened with distilled water, it underwent no change 

 of weight. Cold sulphuric acid acts very feebly on this oxide. 

 M. Gmelin* of Heidelberg states that it is not dissolved at all 

 by this acid in the cold, and I was at first of the same opinion : 

 but by employing a considerable quantity of the oxide, and 

 agitating the mixture frequently, the acid does acquire a red 

 tint in the course of two or three days. In this respect man- 

 ganite agrees with the peroxide ; but differs from all the other 

 species, which communicate a red colour to cold sulphuric 

 acid with much greater facility. 



When manganite is heated to redness it gives out 10*10 per 

 cent of water ; and the total loss from exposure to a white heat 

 is 1 3* 1 5 per cent. Deducting from the last number the amount 

 of water, 3*05 remain as the loss in oxygen. The result of 

 this analysis is therefore, 



Red oxide 86-85 



Oxygen 3*05 



Water 10-10 



100-00 

 According to this analysis, manganite contains an oxide of 

 manganese, 89*9 parts of which yield 3-05 of oxygen, on being 

 converted into the red oxide. An equal quantity of pure deut- 

 oxide, in undergoing a similar change, should lose 2*997 of 

 oxygen. 



Exposed to a strong red heat and a current of hydrogen 

 gas, 100 parts of manganite lost 19*09 parts in one experi- 

 ment, and 19*07 in another. The mean is 19*08, and sub- 

 tracting 10*10 as water, 8*98 remain as oxygen. According 

 to this analysis the manganite is composed of 



Protoxide 80*92 



Oxygen 8*98 



Water 10-10 



100-00 

 Now as 80-92 : 8'98 : : 36 : 3-995. 



* I regret that I have been unable to obtain a sight of that volume of 

 the Zeitschrift der Mineralogie, which contains M. Gmelin's paper on the 

 composition of the oxides of manganese. My knowledge of his labours is 

 solely derived from M. Leonhard's Handbuch der Orykiognosie. 



From 



