1813.] a Chemical Knowledge of Manganese. 177 



a low temperature makes it necessary, after the reduction of the 

 metal, to break the crucible while still warm, in order as soon 

 as possible to put an end to the action of the charcoal on the 

 metal. This interesting experiment I made, without expecting 

 it, with the loss of the whole of the regulus which I had reduced. 

 I performed the process in the porcelain furnace at Berlin; and 

 because it was necessary to continue the heat of the furnace, I 

 left my crucible in it for two days after the fire was withdrawn. 



The metal takes oxygen from the dark brown oxide, and 

 changes it into liffht brown. 



W ■ 1 



It may be fused with borax without any of it dissolving in the 

 salt. If this experiment is performed in a charcoal crucible, the 

 manganese shows a quite different nature. It requires a much 

 less degree of heat than when the metal and salt are fused alone, 

 and the glass of borax appears to dissolve a very small portion 

 of the metal. 



Manganese, when fused with borax, acquires quite the exter- 

 nal appearance of tellurium; the colour, the lustre, and the fine 

 granular distinct concretions. These last show a truly regular 

 crystalline structure. 



Manganese, fused simply with charcoal, leaves behind it, 

 when it is dissolved in acids, a portion of charcoal which had 

 been in combination with the metal, as is the case in cast-iron. 

 If the oxide, before its reduction to the metallic state, con- 

 tained iron, in that case the residuum of charcoal becomes more 

 conspicuous. When the manganese is pure it scarcely amounts 

 to 0-01. 



Mangawse, fused with borax, undergoes an alteration, when 

 exposed to the air, with still greater facility; and when dissolved 

 in acids, it leaves no charcoal behind it. 



IV. Action of Carlonic Acid on Manganese. 



(A.) On the metal. — Carbonic acid exhibits very interesting 

 results on the oxidation of manganese. The same thin o- un- 

 doubtedly would happen with all acids, if their action upon 

 the regenerated oxide could be retarded by means of any me- 

 dium. It is ascertained that all metals before their solution in 

 acids must be converted into oxides, without which they cannot 

 form metallic salts. Now in very few cases does this oxide be- 

 come manifest to our senses. The rapid or instantaneous ac- 

 tion of the acid upon the oxide makes that impossible, and we 

 fonclude only from the gases disengaged (which being either hy- 

 drogen or imperfect acids, are bodies that have lost oxyo-en,) 

 that an oxidation of the metal has taken place. 



I will show hereafter that some vegetable acids, which do not 

 -• t so rapidly upon the regenerated oxide, constitute an excep- 



Vol. II. N° III. M 



