536 MANGANESE. 



posed to consist of 1 eq. of deutoxide, and 2 eq. of peroxide 

 with 1 eq. of water (Dr. Turner) ; its formula is, therefore, 

 Mn 2 O 3 , Mn 2 O 4 



VALUATION OF PEROXIDE OF MANGANESE. 



The numerous applications of the higher oxides of manganese 

 depending upon the oxygen which they can furnish, render it 

 important to have the means of estimating expeditiously and 

 without difficulty their value for such purposes. The value of 

 these oxides is exactly proportional to the quantity of chlorine 

 which they produce, when dissolved in hydrochloric acid, and 

 the chlorine can be estimated by the quantity of protosulphate 

 of iron, which it peroxidises. Of pure peroxide of manganese 

 545.9 parts (1 eq.) produce 442.6 parts of chlorine, which per- 

 oxidise 3456 parts (2 eq.) of crystallized protosulphate of iron 

 (page 502). Hence 50 grains of peroxide of manganese yield 

 chlorine sufficient to peroxidise 317 grains (more exactly 316.5 

 grs.) of protosulphate of iron. 



Fifty grains of the powdered oxide of manganese to be ex- 

 amined are weighed out, and also any known quantity, not less 

 than 3 1 7 grains, of the sulphate of iron (copperas) employed in 

 chlorimetry. The oxide of manganese is thrown into a flask 

 containing an ounce and a half of strong hydrochloric acid, 

 diluted with half an ounce of water, and a gentle heat 

 applied. The sulphate of iron is gradually added in small 

 quantities to the acid, so as to absorb the chlorine as it is 

 evolve^, and the addition of that salt continued till the liquid, 

 after being heated, gives a blue precipitate with the red prussiate 

 of potash, and has no smell of chlorine, which are indications 

 that the protosulphate of iron is present in excess. By weigh- 

 ing what remains of the sulphate of iron, the quantity added is 

 ascertained ; say m grains. If the whole manganese were 

 peroxide, it would require 317 grains of sulphate of iron, and 

 that quantity would, therefore, indicate 100 per cent of peroxide 

 in the specimen ; but if a portion of the manganese only is 

 peroxide, it will consume a proportionally smaller quantity of 

 the sulphate, which quantity will give the proportion of the 

 peroxide, by the proportion : as 317 100 :: m : per centage 

 required. The per centage of peroxide of manganese is thus 

 obtained by multiplying the number of grains of sulphate of 

 iron peroxidised, by 0.317- 



