OF ARTS AND SCIENCES. 221 



potash, when caustic potash is fused in a retort with peroxide of man- 

 ganese without access of air. Upon such authority this statement must 

 have great weight, ahhough the omission of the details of the experi- 

 ments renders it impossible to form any opinion of the sufficiency of the 

 evidence upon which it rests. Fortunately the results of Mitscherlich 

 find full confirmation in the recent experiments of Beketoff".* This ob- 

 server has shown that, when a mixture of caustic potash and black oxide 

 of manganese is heated, in a closed tube filled with oxygen, to a tempera- 

 ture of 180°, an abundance of the green manganate of potash is formed 

 without the slightest absorption of oxygen. Unless these experimental 

 results can be disproved, it seems impossible to escape the conclusion 

 that the substance called peroxide of manganese contains manganic 

 acid, since it yields manganic acid while the ratio of its manganese to 

 its oxygen remains unchanged. 



In 1817 Chevillot and Edwards f published an account of some ex- 

 periments in which they endeavored to prove that the presence of air 

 or oxygen was absolutely necessary to the formation of chameleon from 

 caustic potash and black oxide of manganese. To demonstrate this, 

 they first heated the mixture of these two substances in a silver cruci- 

 ble, within a glass vessel which was filled with nitrogen, and found that 

 no manganate of potash was produced. The amount of heat applied is 

 not stated, but the nature of the apparatus indicates that a high temper- 

 ature was used. Secondly, they heated the same mixture of caustic 

 potash and black oxide of manganese in an atmosphere of oxygen, and 

 measured the considerable quantity of oxygen absoi'bed during tlie for- 

 mation of the manganate. These experiments seem at first sight abso- 

 lutely to contradict those of Mitscherlich and Beketoff"; but it is easy to 

 show that they have no such tendency, and that the conclusions which 

 Chevillot and Edwards drew from them were entirely erroneous, though 

 the experiments themselves were perfectly correct and faithfully re- 

 poi'ted. It is obvious that an absorption of oxygen is just as necessary 

 in order to convert the substance, whose formula would be written 

 MuaOa MnOg, completely into manganic acid, as it is for the entire conver- 

 sion of the so-called oxide MnOg into the same acid. The same amount 

 of oxygen must be absorbed in changing one gramme of the black ox- 

 ide of manganese into manganic acid, however the rational formula of 



* Bulletin de Soc. Chim. de Paiis, Seance 13 Mai, 1859, 1. 43. 

 t Ann. de Cli. et de Phys., [2.] IV. 290. 



