BOG IRON ORE. 49 



nesia may be separated, by very dilute nitric acid from 

 the oxide of manganese, which is insoluble in the acid. 



26. BOG IRON-ORE. 



Fe 2 3 , 3 HO, with MnO, A1 2 3 , CaO, MgO, Si0 3 , P0 5 , 

 As0 5 . 



If the amount of iron only is to be determined, the 

 process with copper may be employed, as in the case 

 of magnetic iron; or the ore may be subjected to the 

 dry assay. The complete analysis is effected in the 

 following manner: 



The mineral, dried at 100, is ignited, and the water 

 determined. 



Another portion, which has not been ignited, is 

 coarsely powdered, and dissolved in hydrochloric acid ; 

 the solution is evaporated to perfect dryness on the 

 water-bath, the mass dissolved in warm dilute hydro- 

 chloric acid, and the sand and silicic acid removed by 

 filtration. The latter may, after ignition and weigh- 

 ing, be separated from the sand by boiling with carbo- 

 nate of soda. 



The hydrochloric solution is boiled with an alkaline 

 sulphite, until it no longer smells of sulphurous acid, to 

 reduce the sesquichloride of iron to protochloride, and 

 the arsenic acid to arsenious acid, which is then pre- 

 cipitated by sulphuretted hydrogen, as tersulphide of 

 arsenic; sometimes mixed with a little sulphide of 

 copper. 



The solution is boiled till the sulphuretted hydrogen 

 is completely expelled, precipitated by carbonate of 

 soda, mixed with an excess of caustic soda, and boiled 

 until the precipitate becomes pulverulent. 



The solution is filtered off. It contains all the alu- 

 5 



