COBALTITE. 105 



tion of the small amount of iron contained in it be 

 neglected ; or it is dissolved in water acidulated with 

 hydrochloric acid, and the solution precipitated at a 

 boiling heat by caustic potassa. The small amounts 

 of nickel and iron contained in the oxide of cobalt 

 are then determined as in No. 66. 



The sulphuric acid is determined by means of chlo- 

 ride of barium, and the excess of baryta removed by 

 sulphuric acid. The filtered solution is concentrated 

 by evaporation, and the arsenic acid precipitated by 

 sulphate of magnesia and ammonia as in No. 65. 



II. The mineral is dissolved in concentrated hydro- 

 chloric acid, with gradual addition of nitric acid, until 

 it is completely dissolved, or the undissolved sulphur 

 is left behind with a fine yellow tint. The latter is 

 then collected on a weighed filter, dried at 100 and 

 weighed. 



From the solution the sulphuric acid is precipitated 

 by chloride of barium, and the amount of sulphur 

 calculated from the precipitate, is added to that directly 

 determined. 



The excess of baryta is removed from the solution 

 by sulphuric acid. 



The filtrate is mixed with sulphurous acid, allowed 

 to stand for twenty-four hours, then heated to boiling 

 until the excess of sulphurous acid is completely driven 

 off", and when cooled down to about 50, saturated with 

 sulphuretted hydrogen. Thus saturated, it is left to 

 stand for twenty-four hours, the sulphuretted hydrogen 

 removed by gentle evaporation, and the sulphide of 

 arsenic collected on a weighed filter and dried at 100. 

 It is then treated as in No. 52. 



The solution of cobalt filtered from this precipitate 

 is heated to boiling, mixed with a little chlorate of 

 potassa, in order to bring the iron to a higher state of 

 oxidation, carefully neutralized with carbonate of soda, 



