1824.] the Oxydum Manganoso-Mangunicum. 269 



gramme. Exposed to a stronger heat in a platinum crucibl e 

 over a charcoal fire, the weight was reduced to 1*100 gramme. 

 Thus 100 parts of protoxide by this treatment increase 10 parts 

 in weight ; and according to the preceding statement of the 

 constitution of the protoxide, this black oxide is composed of 



Manganese 71 100-00 



Oxygen 29 40-84 



100 140-84 



(2.) 1-192 gramme of protoxide of manganese, prepared as 

 before described, left, when burnt in the open fire, 1-383 gramme 

 of brown oxide. According to this experiment 100 parts of 

 protoxide took up 7-043 oxygen, and the constituents of brown 

 oxide are : 



Metal 100-00 



Oxygen 37-45 



137-45 



The 1*383 gramme of brown oxide was boiled to dryness with 

 nitric acid, and exposed to a strong red heat in a platinum 

 vessel. The matter had acquired a shining black colour, and 

 weighed 1 398 gramme. The increase of weight this time was 

 so inconsiderable that it seems probable that some disoxygena- 

 tion had taken place. It may be presumed, therefore, that the 

 black oxide when exposed to a violent heat may be completely 

 reduced to the state of brown oxide. The heat was continued 

 for nearly an hour, and was as great as could be applied. The 

 powder now resumed its former brown colour, and very nearly 

 its original weight. The excess amounted only to two mille- 

 grammes. 



To ascertain whether the black oxide can be prepared by 

 means of a smaller determinate degree of heat so as to give 

 constant results, the oxide of manganese already heated to red- 

 ness was again treated with nitric acid, and heated over a spirit- 

 lamp five different times, and the increase of weight was noted 

 each time. The following little table shows the result. 



100 parts of protoxide had taken up 



1 st time 14-4 parts of oxyeen. 



2d 13-93 



3d 10-52 



4th 10-37 



5th 10-13 



The smaller augmentation of weight in the last three experi- 

 ments was owing to a further evolution of nitrous gas. The expe- 

 riments show that the true increase of weight lies between 10-52 

 and 10-13. We may, therefore, consider the increase of weight 



