Manganefe. 35* 



afterwards becomes colourlefs, unlefs they 

 contain a large proportion of iron. But the 

 dephlogifticated nitrous acid does not at on 

 them except fugar be added, and then this 

 acid, as well as the concentrated vitriolic, 

 operates a colourlefs folution, which with mild 

 alkalis, gives a white precipitate of the fame 

 nature as the firft variety ; they contain more 

 iron and lefs fixed air than the former va- 

 rieties. 



14. Per Igor d Stone belongs to this variety, 

 it is of a dark grey colour like bafaltes or trapp, 

 may be fcraped with a knife, yet is difficultly 

 broken ; when calcined it becomes of a red- 

 difh brown colour and harder, but not mag- 

 netic. Its fpecific gravity is confiderable, it 

 does not mehperfe, but with borax it affords 

 an amethyftine glafs ; nitrous acid fcarcely 

 ats on it without the addition of fugar, 

 this ftone feems alfo to contain argill, and 

 fome portion of iron, 



15. One of the moft remarkable ores of 

 manganefe is that called black r wad j it is of 

 a dark brown colour, partly in powder and 

 partly indurated, and brittle. If half a pound 

 of this be dried before a fire, and afterwards 

 fuffered to cool for about an hour, and then 

 two ounces of lintfeed oil be gradually poured 

 on it, mixing them loofely like ba,rni with 



flour. 



