APPENDIX. 
3Ô3 
Tritoxide of iron .... 0,336 
Alumine 0,400 
Silex 0,020 
Oxide of chrome - - - - a trace 
Oxide of manganese - - - none 
Water 0,247 
1 ,003 
There was reason to suppose that the alumme existed in this ore, 
as in wavellite, combined with phosphoric and fluoric acid : but not 
the least indication of either of these acids could be detected. It 
was also ascertained, that it contained neither sulphuric acid nor 
glucine, and by treating it with sulphuric acid and sulphate of 
ammonia, it was entirely Converted into beautiful octahedral crystals 
of alum. 
From these results it appears indubitable, that this ore is a mix- 
ture of hydrate of alumine, a small quantity of argil tritoxide 
of iron, and perhaps hydrate of iron ; we cannot, however, hence 
deduce the composition of the hydrate of alumine, because we do 
not know the proportion of this earth in the argillaceous mixture, 
and it is also possible, that a small part of water may be combined 
with a portion of the oxide of iron. 
The first variety is certainly a mixture of tritoxide and hydrate 
of iron, hydrate of alumine, and argil. 
Similar ores have not yet been met with in Europe. If all 
those of Fouta Diallon were of the same nature, it would be impos- 
sible to conceive how the Negroes could extract iron by the method 
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