1814.] Chemical Knowledge of Manga?iese. 417 



in hot water, for some weeks, the water was gradually decomposed, 

 and the oxide formed united with the acid, and constituted a white 

 powder. The green oxide and carbonate of numganese unite with 

 tungstic acid neaiiy as slowly. Tungstate of manganese is most 

 easily obtained by decomposing a solution of manganese, by means 

 of tungstate of potash. The precipitate, thus obtained, is to be 

 collecied, washed, and dried. 



The tungstate of manganese has a white c v ur. It is tasteless, 

 insoluble in v/ater, and not ;iltered by exposur lO the air. Before 

 the blow pipe upon charcoal, it assumes first a yellow, and then a 

 brown colour j but does not melt. 



ACTION OF ARSENIC ACID. 



a. On the Metal. 



Arsenic acid dissolves the metal, and when the acid is nearly 

 saturated, arseniate of manganese precipitates in the form of a 



gelly. 



b. On the Oxide. 



Arsenic acid dissolves both the green oxide and the carbonate. 

 The solution always contains an excess of acid. If we nearly 

 saturate the acid, the solution immediately gelatinizes, and neutral 

 arseniate of manganese precipitates, which is insoluble in water. 

 If some drops of diluted sulphuric acid be dropt into the gelatinous 

 mass, a complete solution is again effected, and by evaporation 

 striated crystals are obtained, which appear to be a triple salt, com- 

 posed of sulphuric acid, arsenic acid, and oxide of manganese. 



ON THE OXIDATION OF MANGANESE. 



How difficult it is to determine the proportion of oxygen which 

 unites with a metal in its different degrees of oxidation, is obvious 

 from the different results obtained by the latest and best chemists in 

 their analyses. That this difficult determination must hold in all 

 metals, whose oxides on the one hand, while iinperfectly saturated. 

 with oxygen, absorb more of that principle by simple exposure to 

 the air, or on the other, containing a maximum of oxygen, give 

 out a portion of that substance when exposed io a high temperature, 

 must l)e obvious to every one who is in the least acquainted with 

 practical chemistry. These difficulties hold in a very high degree, 

 when we attempt to determine the composition of the oxides of 

 manganese. And though i)y varying and frequently repeating my 

 experiments, I succeeded in obtaining a constant result, yet 1 must 

 acknowledge, that nothing more seems to have been established by 

 me, than the limits of the different oxides. 



From my trials, it appears that there are three oxides of manga- 

 nese different from eacli other, in which the proportion o'i oxygen 

 may be determined; namely the o/yy-w, the A; Ott//, and the lluck. 

 Besides these oxides indeed, I tliought I < ' served the metal passing 

 into several others. Thus I thought the gicen, when deprived of 



Vol. 111. N° VI. 2 D 



