220 PROCEEDINGS OF THE AMERICAN ACADEMY 



III. The Black Oxide of Manganese (3 MnO^ = Mn^Oa MnOg). 



Another question now suggests itself, — Would analogy lead us to 

 suppose that there was an oxide of chromium containing two atoms of 

 oxygen ? Comparing chromium, as before, with the allied metals, alu- 

 minum, iron, and manganese, we meet with no such oxide of aluminum, 

 and we have Fremy's * direct statement that he could find no oxide of 

 the formula FeOj. Manganese, however, forms a compound with oxy- 

 gen, stable, insoluble, and natural, which has heretofore always been 

 spoken of as an oxide of manganese and been represented by the for- 

 mula MnOg. Is not the existence of this compound a strong argument 

 for the oxide CrO^? We propose to adduce the evidence which makes 

 it most probable that this so-called peroxide of manganese is in reality 

 a compound, sometimes definite but oftener indefinite, of manganic acid 

 and manganic oxide, and that its normal composition is to be rep- 

 resented by the formula MnjOs MnOs. 



We shall not expect to resolve this substance into manganic oxide 

 and manganic acid with the same facility with which we analyze the 

 chromate of chromic oxide. This latter body is less stable than either 

 chromic oxide or chromic acid, whereas manganic acid and oxide are 

 both exceedingly unstable substances, obtained with difficulty but easily 

 destroyed. On the other hand, there is no more stable compound of 

 manganese than that called the peroxide. It is not therefore decom- 

 posed, as the chromate of chromium is, by boiling water, boiling caustic 

 potash, or a boiling solution of chloride of ammonium. We prepared 

 artificial peroxide of manganese by passing a stream of chlorine through 

 water in which carbonate of protoxide of manganese was diffused, and 

 washing the precipitate, first with dilute nitric acid and then with water. 

 The artificial peroxide thus prepared resisted solutions of chloride of 

 sodium and of caustic potash, even when heated with these liquids in 

 closed tubes to a temperature of 180° by means of a wax bath. 



But, notwithstanding the stability of this black oxide of manganese, 

 it is not impossible to obtain from it manganic acid under circumstances 

 which seem to preclude the possibility of any oxidation of the substance 

 during the process by which the manganic acid is exhibited. Mitscher- 

 lich t observed and reported the formation of the green manganate of 



* Ann. de Ch. et de l*hys., [3.] XII. 381. 



t Abhandlunrjen der Akademie der Wiss. zu Berlin, 1831, p. 218. Ann. de Ch. 

 et de Phjs., [2.] XLIX. 114. Pogg. Ann., XXV. 287. 



