1814.] Chemical Knouiedge of Manganese, 419 



and that 100 grains of this carbonate after being heated to redness 

 in a retort, leave 55*8 1 grains of green oxide. Hence it follows, 

 that 55'8 1 of green oxide contain 48*6 of metal, and consequently 

 7-24 of oxygen. Now 55-84 : 7-24 :: 100 : V2VU. Therefore 

 green oxide is composed of 



Metal 87-04 



Oxygen 12-9G 



100-00 



This estimate differs from the preceding only 0-007. We may 

 therefore consider 0-13 as the proportion of oxygen in 1-00 of green 

 oxide. 



B, Examination of the hrowii Oxide. 



I exposed the 92 grains of green oxide obtained by the decom- 

 position of water, for some days to the action of the air, until it 

 was completely changed to a dark brown powder. I then heated it 

 for an instant in a close vessel, and then weighed it. The weight 

 was increased 8 grains; so that 80 grains of metal, in order to be 

 changed into brown oxide absorb 20 grains of oxygen. Hence the 

 chesnut brown oxide of manganese is composed of 



Metal .' 80 



Oxygen 20 



100 



This oxide still continues to absorb oxygen from the atmospherej 

 but the absorption goes on so slowly, that after an interval of seve- 

 ral days the change of weight is hardly perceptible. 



I obtained the same result by exposing the pure metal for some 

 days to the open air, and then heating it in a small retort, in order 

 to drive off any moisture which it might have absorbed. 



C. Examination of the Hack Oxide. 



Though this oxide has been already examined by several cele- 

 brated chemists, yet the difference in their estimates of its compo- 

 sition is so great, that more experiments are obviously necessary to 

 determine the point. 



From tlie following experiment, which succeeded equally on 

 several repetitions, it seems clear that the proportion of oxygen, 

 supposed by several chemists to exist in this oxide, is excessive. 



1 dissolved lOO-J- grains of metallic manganese in nitric acid, 

 witli the exception of -^'- grain which remained undissolved, and was 

 separated by the filter. The solution was put into a small retort, 

 and cautiously distilled to dryness. I then Ijroke the retort, and 

 collected and weighed the black porous shining oxide wliich re- 

 mained Ijehind. Its weight was 140 grains. To see whether it 

 was pure oxide, a portion of it was digested in water, but no nitrate 

 of luarjgancse was dissolved. Another portion was heated to red- 



•2 1) 2 



