Value of Black Oxide of Manganese. 413 



The loss of weight which the flask has sustained is exactly 

 equal to the quantity of binoxide of manganese in the pow- 

 der examined. Thus, let the loss of weight he 34 grains ; 

 the quantity of binoxide of manganese in the 50 grains of 

 the powder which was tested will be 34 grains ; or it will 

 contain 68 per cent, of pure binoxide of manganese, and 32 

 per cent, of impurity. 



To understand what takes place, it is necessary to recol- 

 lect that oxalic acid is composed of 



2 atoms carbon 1-5 



3 atoms oxygen 3 



4-5 

 and that binoxide of manganese is composed of 



1 atom manganese 3*5 



2 atoms oxygen 2 



5-5 



The oxalic acid acts on the binoxide by abstracting one- 

 half of its oxygen, which converts it into carbonic acid ; 

 hence the effervescence. 55 grains of pure binoxide of 

 manganese would give out 10 grains of oxygen, which 

 would convert 45 grains of oxalic acid into 55 grains of 

 carbonic acid ; which escaping, indicate, by the loss of 

 weight, the quantity of carbonic acid formed. Now, it 

 happens that the weight of the carbonic acid formed is 

 exactly equal to the quantity of binoxide of manganese 

 which gives out its oxygen to the oxalic acid. Hence, the 

 reason of the accuracy of the test. 



In other words, an integral particle of binoxide of man- 

 ganese, which weighs 5*5, gives out 1 atom of oxygen. This 

 atom of oxygen combines with an integrant particle of oxalic 

 acid, weighing 4*5, and converts it into two integrant par- 

 ticles of carbonic acid, which both together weigh 5*5. As 

 this carbonic acid escapes, the loss of weight must be just 

 equal to the quantity of binoxide of manganese in the pow- 

 der subjected to experiment. 



In practice, I find that a small quantity of the binoxide 

 of manganese sometimes escapes the action of the oxalic 

 acid, being probably screened by the great quantity of im- 

 purity with which it is mixed. But the deficiency of car- 



