OF ARTS AND SCIENCES. 223 



nese in an atmosphere of nitrogen, if the temperature be sufficiently 

 low. On the contrary, we have made several experiments which tend 

 to the conclusion that this is perfectly possible under certain conditions. 

 A mixture of caustic potash and natural black oxide of manganese was 

 placed in a glass tube, which was then filled with nitrogen and sealed. 

 Thus hermetically closed, the tube was heated in a wax-bath to 180° 

 for three hours ; at the end of the experiment, we found that portions 

 of the mass in the tube had been changed into green manganate of pot- 

 ash, though the greater part seemed to be unaltered. Again, a mixture 

 of potash and the black oxide, artificially prepared, was gently heated 

 in a combustion-tube in a current of nitrogen to a temperature barely 

 high enough to fuse the mass, and the manganate of potash was formed, 

 small in amount, but perfectly unmistakable. In repeating this last ex- 

 periment, however, we failed quite as often as we succeeded, for it is dif- 

 ficult to heat the mixture hot enough to insure the formation of the man- 

 ganate without also heating it hot enough to destroy it. Moreover, no 

 experiments, intended to exhibit the formation of manganate of potash 

 in nitrogen from potash and the black oxide, can be conclusive, so long 

 as the experimenter is unable to answer any one who may please to al- 

 lege that the nitrogen used contained a trace of oxygen. Unless some 

 method of preparing the nitrogen is used which will enable the chemist 

 to assert that the gas is free from oxygen and from all other impurities 

 which might affect the reaction, such experiments will establish nothing. 

 The only conclusive method of testing the question whether manganate 

 of potash can be formed from the black oxide and potash alone, is that 

 so well applied by Beketoff, who proved that the manganate can be 

 produced from these materials in an atmosphere of oxygen at a low 

 temperature without the slightest absorption of that gas. His experi- 

 ments were obviously performed with such care that we have thought 

 it superfluous to repeat them. 



We have been at such pains to review and explain the experiments 

 of Chevillot and Edwards, in order to put the decomposition of the 

 substance called peroxide of manganese into manganic oxide and man- 

 ganic acid in its true light, as an uncontradicted fact, resting upon the 

 highest authority. If we add to this decomposition of the black oxide 

 of manganese by potash the other fact, that it is a perfectly neutral or 

 indifferent body, possessing none of the properties either of an acid or 

 of a base, we have evidence, not sufficient perhaps absolutely to prove 

 that its true rational formula is Mn^Os MnOa, but quite enough to show 



