S68 Lieut.-Col. Yorke on Br&wfi Iron Ore. 



In 100. 



Silica 0-26 2'4.2 



Water . 1-57 14.-28 



Sesquioxide of iron .... 9'03 82*16 



... of manganese . . 0*1 24' 1*13 



Trace of alumina, tin, loss . . 0*006 



10-99 99-99 



Deducting the silica and using the same atomic numbers as 

 before, SFeaOg+SHO would contain in 100, — 



Theory. Experiment. 



Peroxide of iron. 85'57 r*.. ,.1^?- 85*4)7 



84.*32\, 

 g* 1'15/' 



Ox.manf 



Water. . . . 14*43 14-53 



100* 100* 



This, then, is the substance called limonite by Beudant, 

 and the analysis of D'Aubuisson commonly attached to the 

 crystallized mineral first described refers to this species. 



C. 



I have also examined a specimen of fibrous brown iron orej 

 which was ticketed " Brauner Glasskopf " from Wansiedel. 

 This specimen was covered externally by a blackish, brilliant 

 substance about one-tenth of an inch thick, which separated 

 from the body of the specimen on hammering it, and broke 

 off in small, brilliant, concretionary masses, which might at 

 first sight be mistaken for crystals. The powder of this sub- 

 stance was of a purplish red. It lost 5-3 per cent, of its 

 weight by ignition. 



19835 grs. of the body of the specimen which had a fibrous 

 structure, separated from the external coating, yielded on 

 analysis — 



In 100. 



Silica 0-29 1*46 



Water 2-46 12*42 



Red oxide of iron .... 17-02 85*80 

 I Oxide of manganese . . . 0-26 1-30 



Excess 0*20 ___ 



19-835 100-98 

 This analysis agrees with the hypothesis that the substance 

 is composed of single equivalents of the two mineral com- 

 pounds just described, but it would be altogether premature 

 from this single result to assume the existence of such a defi- 

 nite compound. 



Indeed these experiments seem to me to lead rather to the 

 notion that all the brown iron ores having a crystalline struc- 



