of the Oxides of Manganese. 165 



Analysis of Manganite or the Prismatoidal Manganese-ore. 



This ore, even when selected with the greatest care, yields 

 to distilled water traces of the muriates and sulphates of lime and 

 soda. It dissolves without residue in muriatic acid, and is free 

 from siliceous earth, lime, baryta, and every other impurity. 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 per- 

 oxide by absorbing oxygen from the air. After exposure to the 

 air for six months, during which it was frequently moistened 

 with distilled water, it underwent no change of weight. Cold 

 sulphuric acid acts very feebly on this oxide. M. GMELIN * o 

 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 employ- 

 ing a considerable quantity of the oxide, and agitating the mix- 

 ture frequently, the acid does acquire a red tint in the course of 

 two or three days. In this respect manganite agrees with the 

 peroxide ; but differs from all the other species, which commu- 

 nicate 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 13.15 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, 



* 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 Oryktognosie. 



