of the Oaddes of Manganese. 173 



quantity of oxygen from being expelled from the peroxide by 

 heat. Accordingly I ascertained the quantity of pure red oxide 

 by the way of precipitation ; but its amount corresponded closely 

 with the number already stated. Psilomelane must therefore, 

 I conceive, be a mixed mineral. I was at first disposed to re- 

 gard it as a compound of baryta and peroxide of manganese, 

 accidentally containing an admixture of some other oxide in a 

 lower stage of oxidation ; but the fact noticed by Mr HAIDIN- 

 GER of Psilomelane being frequently and intimately associated 

 with Pyrolusite in the mineral kingdom, appears to justify the 

 inference, that the uncleavable manganese-ore consists essentially 

 of some compound, in proportions not yet ascertained, of baryta 

 and 'the deutoxide of manganese, and that Pyrolusite is the ac- 

 cidental ingredient. The propriety of this view is further shown 

 by an analysis of the following ore from Romaneche, a mineral 

 which is analogous to Psilomelane in the proportion of its ingre- 

 dients, and in which an admixture of Pyrolusite may be detected 

 by the eye. 



Analysis of the Maganese oxide noir Barytifere/mw Romaneche. 



The observations of Mr HAIDINGER leave no doubt of this 

 ore being a mixed mineral ; and according to my analysis it is 

 very analogous to Psilomelane. The specific gravity of some of 

 the purest fragments which I could select, is 4'365 ; and the den- 

 sity of Psilomelane, according to Mr HAIDITSTGER, is 4'145. The 

 colour of both minerals is similar. 



The black oxide of Romaneche yields a very faint odour of 

 chlorine with sulphuric acid. When heated to redness it gives 

 out 413 per cent of water. At a white heat it loses 11 '39 per 

 cent ; and after subtracting 4' 13 for water, there remain 7'26 as 

 the loss in oxygen. 



