102 



ESSAY V. 



(d) Placed on a piece of charcoal, and heated with the 

 blowpipe, it at first resembles zeolite, fusing with some 

 effervescence and intumescence of the particles, which after- 

 wards coagulate into a light grey porous scoria, that is not 

 fusible of itself by means of the blowpipe. 



(e) It fuses easily with borax into a dark red or garnet- 

 coloured glass, and the fusion is accompanied with a brisk 

 effervescence ; but in order to be transparent it must be 

 diluted with a good deal of borax, and it then appears of a 

 beautiful red opposite the light. 



(/) When heated red hot in a test in an assay-furnace, it 

 turns black with small shining scales ; but in a stronger heat 

 the black colour passes away in part, and the powder becomes 

 brown. 



(g) The magnet does not attract any sensible quantity, 

 either before or after roasting. 



(h) This species of manganese in its crude state, and 

 reduced to a fine powder, does not make any effervescence 

 with strong aquafortis ; but in a gentle heat it is almost 

 entirely dissolved without imparting any colour to the 

 solution. 



(i) Fixed vegetable alkali precipitated a white powder 

 out of this solution, which, when washed and dried, effervesced 

 a little with acids, turned black upon being heated red hot ; 

 and, when treated by the blowpipe upon charcoal with glass 

 of borax, gave it a red colour. 



(k) The roasted powder (/) effervesced still less with 

 aquafortis ; a great part of it, however, by gentle boiling, 

 was dissolved, and yielded in like manner a white precipitate 

 on the addition of vegetable alkali. This precipitate, when 

 heated moderately red hot, grows as black as soot, and gives 

 a garnet colour to borax. The residuum which did not 

 dissolve in aquafortis was as black as before. 



