MANGANESE. 367 



Thus it appears, that protoxide of manganese 

 and protoxide of iron have the same atomic 

 weight. If protoxide of manganese be a com- 

 pound of one atom manganese and one atom 

 oxygen, (as there is the strongest reason for be- 

 lieving) then an atom of manganese weighs 3*5, 

 or the same as an atom of iron. 



4. Manganese occurs most commonly in the Native 



. 1 . . , . black oxide. 



state or a black coloured oxide, which has been 

 long employed to deprive glass of its colour, and 

 is at present consumed in great quantities by 

 the bleachers and the preparers of the bleaching 

 powder. This black oxide is most commonly 

 impure ; but it occurs occasionally crystallized 

 in small needles, which have the form of rhom- 

 bic prisms, and the lustre and colour of iron, 

 though rather darker. I have met with speci- 

 mens of this kind perfectly pure. When 11 

 grains of this pure oxide are kept for some time 

 in a low red heat in a platinum crucible, they 

 lose exactly one grain of their weight, which 

 consists of pure oxygen gas. By this exposure 

 to heat, the metallic lustre disappears, and the 

 mass assumes a brownish black colour. The 

 powder thus formed is a peculiar oxide of man- 

 ganese; for it dissolves without effervescence 

 in sulphuric and in muriatic acid, and forms 

 dark red coloured solutions. This sulphate and 

 muriate do not crystallize ; indeed, when the 

 muriate is heated, chlorine gas is evolved, and 



