ON MANGANESE 75 



be an excess of the acid, all the manganese is not pre- 

 cipitated by vegetable alkali, though it be added till the 

 acid is completely saturated; for the aerial acid, which is 

 extricated from the alkali, dissolves part of the manganese. 



SECTION XXXII. 



The peculiar kind of earth found in all the limpid 

 solutions of manganese, and mentioned in Sec. XVIIL (4), 

 remains to be more carefully examined. I shall here 

 speak of a few particulars in which it differs from others. 



(a) The small crystals which appear on the evaporation 

 of the solution of manganese in nitrous and muriatic acids, 

 Sec. iv. (c), Sec. vi. (d), consist of this earth combined with 

 those acids. They are easily soluble in water, and may 

 be freed from the adhering solution of manganese by 

 repeated evaporation and crystallisation. They are in- 

 soluble in spirit of wine, have an austere taste, and do 

 not attract moisture from the atmosphere. (b) Dissolved 

 in water, they are neither precipitated by fixed nor 

 volatile caustic alkalies, nor by lime-water; but, on addition 

 of the mild, fixed, and volatile alkalies, an earthy precipitation 

 takes place, (c) This precipitate, after being edulcorated 

 and dried, is white, and effervesces with all the acids. If 

 calcined, it grows a little bluish, and produces no effervescence 

 with acids, but is dissolved by them when heat is applied. 

 It is not soluble in water, but expels the volatile alkali 

 from sal ammoniac, (d) Exposed to the blowpipe, it is 

 at last changed into an opal-coloured glass, which is again 

 soluble in acids, (e) With fixed alkali it undergoes no 

 change. (/) Borax dissolves it with effervescence, and 

 thus forms a glass, which is colourless and transparent 

 as long as it continues hot, but opaque when cold, (g) The 



