Analysis 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, 
itmay without great error be assumed that the iron in this por- 
tion has not been peroxidized by that operation, and that there- 
fore .353 is the correct weight of the undecomposed portion of 
the mineral. By adding the several —_— obtained, we have, 
Oxide of chrome, - - .2440 
Protoxide of iron, - - - - 1544 
Alumina,’ <>: “= tose = eS Btw ot 
Magnesia, - - - - - - -0900 
Undecomposed ore, - - -  - 3530 
.9823 
This shows a loss of 1.72 per cent., which may be ascribed in 
part to errors in analysis, and partly, without impropriety, toa 
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, - . - - 
Protoxide of iron, - - - - 24.516 
Alumina, - - - - - 22.452 
Magnesia, - - - - - . 14.290 
100.000 
This result failteatess that a portion of the talcose matter was 
included in the specimen, notwithstanding the care exercised in 
its separation. Viewing the alumina, with a little silica included 
in it and the magnesia, as belonging to the tale, we find the for- 
mula for the oxides of chrome and iron, to be 2 : 3, or 3(F'eO)+ 
%Cr?O2), The formula generally received for the pure mineral 
is 2Cr+Fe, and leads to the supposition, that in the present case, 
4 portion of the iron exists as peroxide, a view which is strength- 
€ned by the brown streak of the mineral. 
Philadelphia, Dec. 5, 1839. 
