of the Oxides of Manganese. 153 



The protoxide of manganese is described by FORCHHAMMER as 

 being of a beautiful light-green, and by ARFWEDSON as of a pis- 

 tachio-green colour. I have seen specimens with a tint very 

 near the pistachio-green, but these always contained an admix- 

 ture of red oxide. The colour of the pure protoxide is very near 

 the mountain-green. 



With respect to the action of air, my observations differ from 

 those of FOKCHHAMMER who found that recently prepared prot- 

 oxide attracted oxygen from the atmosphere before he could 

 weigh it. The protoxide procured in my experiments is far 

 more permanent. I exposed fifteen grains of recently prepared 

 protoxide to the free action of the air during the space of nine- 

 teen days, when it was found to have undergone no change ei- 

 ther in appearance or weight. If, therefore, it does attract oxy- 

 gen at all from the air, the operation must proceed very tardily. 

 It absorbs oxygen very slowly even at a temperature of 400 F. ; 

 for 7.269 grains of the protoxide, after an hour's exposure to that 

 degree of heat, did not gain in weight more than 0.021 of a grain. 

 At a temperature of 600 F. it absorbs oxygen much more rapid- 

 ly ; and at a low red heat it loses its green tint, and becomes al- 

 most black in an instant, I have repeated this process frequent- 

 ly, but in no case did the protoxide take fire, as occurred in the 

 experiments of FORCHHAMMER and ARFWEDSON. I entirely 

 agree with M. ARFWEDSON, however, in the statement, that the 

 protoxide is converted, by simultaneous exposure to heat and air, 

 into the red oxide. This is the uniform result at whatever tem- 

 perature the oxidation is effected. 



I have already mentioned my opinion, that, of the oxides of 

 manganese, the protoxide is the only one which forms definite 

 compounds with acids. It unites readily with this class of bo- 

 dies, without effervescence, producing with them the same salt 

 which is formed when the same acids act on the carbonate of 

 manganese. When it comes in contact with concentrated sul- 



VOL. XI. PART I. U 



