of the Oxides of Manganese. 103 



this deficiency of oxygen, I at first suspected that the baryta 

 might prevent the usual quantity of oxygen from being expelled 

 from the peroxide by heat. Accordingly I ascertained the 

 quantity of pure red oxide by the way ofprecipitation ; 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 regard it as a compound of baryta 

 and peroxide of manganese, accidentally containing an ad- 

 mixture of some other oxide in a lower stage of oxidation ; but 

 the fact noticed by Mr. Haidinger of psilomelane being fre- 

 quently and intimately associated with pyrolusite in the mi- 

 neral kingdom, appears to justify the inference, that the un- 

 cleavable manganese-ore consists essentially of some com- 

 pound, in proportions not yet ascertained, of baryta and the 

 deutoxide of manganese, and that pyrolusite is the accidental 

 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 in- 

 gredients, and in which an admixture of pyrolusite may be 

 detected by the eye. 



Analysis of the Manganese oxide noir Barytifere^om Ro- 

 maneche. — The observations of Mr. Haidinger leave no doubt 

 of this ore being a mixed mineral ; and according to my ana- 

 lysis it is very analogous to psilomelane. The specific gravity 

 of some of the purest fragments which I could select, is 4*365; 

 and the density of psilomelane, according to Mr. Haidinger, 

 is 4*14)5. 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 4*13 per cent of water. At a white heat it loses 1 1 *39 per 

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

 as the loss in oxygen. 



In order to ascertain the quantity of baryta, 32*13 grains 

 were dissolved in muriatic acid ; and after separating a small 

 portion of silica, which amounted to 0*953 per cent, I preci- 

 pitated the baryta by means of the sulphate of soda. The in- 

 soluble sulphate, after exposure to a red heat, weighed 8*113 

 grains, equivalent to 5*363 grains, or 16*69 per cent of pure 

 baryta. J 00 parts of the oxide are accordingly resolved into 



Red oxide 70*967 



Oxygen 7*260 



Baryta 16*690 



Silica 0*953 



Water 4*130 



100*000 



This 



