Afialysis of Chromic Iron Ore. 245 



ingly difficult solution by chemical analysis. Supposing the iron, 

 however, to be in the state of protoxide, the .172 will be reduced 

 to .1544 of protoxide. Now if ignition with carbonate of soda 

 and caustic potassa, left a portion of the mineral undecomposed, 

 it may without great error be assumed that the iron in this por- 

 tion has not been peroxidized by that operation, and that tlieie- 

 fore .353 is the correct weight of the undecomposed portion of 

 the mineral. By adding the several weights obtained, we have, 

 Oxide of chrome, - . - - .2440 

 Protoxide of iron, - - - - .1544 



Alumina, ------ .1414 



Magnesia, - - - - - - .0900 



Undecomposed ore, - - . - .3530 



.9828 

 This shows a loss of 1.72 per cent., which may be ascribed in 

 part to errors in analysis, and partly, without impropriety, to a 

 partial peroxidation either of the iron or chrome. 



By omitting the undecomposed matter, and calculating the per- 

 centage of each ingredient, we find the mineral to consist of 

 Oxide of chrome, - - - - 38.742 

 Protoxide of iron, - - - - 24.516 

 Alumina, - - - - - 22.452 



Magnesia, - - - - - 14.290 



100.000 

 This result indicates that a portion of the talcose matter was 

 included in the specimen, notwithstanding the care exercised in 

 its separation. Yiewing the alumina, with a little silica included 

 in it and the magnesia, as belonging to the talc, we find the for- 

 mula for the oxides of chrome and iron, to be 2 : 3, or 3(FeO)-l- 

 2(Cr=0^). The formula generally received for the pure mineral 

 is 2Cr + Fe, and leads to the supposition, that in the present case, 

 a portion of the iron exists as peroxide, a view which is strength- 

 ened by the brown streak of the mineral. 



Philadelphia, Dec. 5, 1839. 



