Mr. Brown on the Commercial Value of Black Oxide of Manganese. 185 



XXII. — On the Estimation of the Commercial Value of some Specimens 

 of Black Oxide of Manganese. By Mr. George William Brown. 



The value of binoxide of manganese may be estimated in various ways, 

 all of which depend on the determination of the amount of oxygen which 

 they contain. The first of these is the method by oxalic acid, and con- 

 sists in the oxygon of the manganese giving oxygen to the carbonic oxide 

 of the oxalic acid, and converting it into carbonic acid. The first 

 method of accomplishing this was proposed by Berthier, who disengaged 

 the carbonic acid in a flask from which a bent tube passes into another 

 flask containing barytes water; the carbonic acid being disengaged, 

 passes through the barytes water, and precipitates the barytes in the 

 form of carbonate. The precipitate is then weighed, and from the 

 amount of oxalic acid decomposed, the amount of oxygen is calculated. 



A modification of this plan was made by Dr. Thomson, who, 

 instead of estimating the amount of oxalic acid decomposed by weighing 

 the carbonic acid, calculated it by the loss sustained in the flask contain- 

 ing the oxalic acid, &c. This method is much more convenient, as one 

 small flask is only employed, while, by Berthier 's plan, two flasks are 

 necessary. Less time is also required to calculate the value of the 

 manganese by this plan than the former The mode of applying this 

 method is, to fit a light flask with a cork, through which a small tube 

 containing chloride of calcium passes. The oxide of manganese is then 

 weighed out in the tube which is suspended from the cork by a thread; 

 the oxalic acid, with a small portion of sulphuric acid and water, being 

 first introduced into the flask. The whole is weighed, and then the tube 

 containing the manganese is allowed to drop into the oxalic acid. Car- 

 bonic acid is immediately disengaged. When the action is over the 

 apparatus is weighed again ; the difiierence between the first and second 

 weights gives the quantity of carbonic acid which has escaped. From 

 this weight the oxygen in the manganese is calculated. Then, since 

 there are two atoms of carbonic acid driven ofl^, and the weight of two 

 atoms of carbonic acid exactly equals the weight of one atom of binoxide 

 of manganese, the amount of loss between the first and second weighing 

 will be equal to the amount of binoxide in the specimen. 



I have made two analyses of a specimen of sesquioxide of manganese 

 from New Brunswick, the results of which are as follows : — 



50 grains was the amount worked on. 



First analysis. 



Weight of apparatus before disengaging CO2, = 1105'16 



Weight of apparatus after disengaging CO™, = 1077*10 



MnO, in 50 grains, = 2806 



MnOo per cent, = 56-12 



