CAST IRON". 203 



nitric acid expelled by evaporation, and the arsenic 

 reduced in Marsh's apparatus. 



The solution of iron filtered from the black residue 

 is neutralized with carbonate of soda, mixed with a 

 few drops of sesquichloride of iron, and then with 

 acetate of soda, when arseniate of sesquioxide of iron 

 is precipitated, may be easily decomposed by sulphide 

 of ammonium. 



For the quantitative determination of the arsenic, 

 the cast-iron is dissolved in hydrochloric acid, with 

 gradual addition of nitric acid, the solution filtered 

 from the carbon, and heated with sulphurous acid till 

 all the sesquichloride of iron is converted into pro- 

 tochloride; the excess of sulphurous acid is then 

 expelled by heat, and the solution saturated with 

 sulphuretted hydrogen, and allowed to stand for twenty- 

 four hours in a closed vessel ; the excess of gas is 

 afterwards evaporated, and the precipitate filtered off. 



V. COPPER. This metal is contained in the preci- 

 pitate produced as above, by sulphuretted hydrogen. 

 After drying, it is distilled in a tube, when sulphide 

 of copper remains behind. Or the sulphide of arsenic 

 may be dissolved out by solution of potassa, or more 

 completely, by solution of monosulphide of potassium. 



VI. MANGANESE. The solution filtered from the 

 precipitate produced by sulphuretted hydrogen, in Y. 

 is heated to the boiling-point, and the protoxide of iron 

 entirely converted into sesquioxide by adding chlorate 

 of potassa or hydrochlorite of soda. The oxide of 

 manganese and sesquioxide of iron are then separated 

 from each other by means of bicarbonate of soda, as 

 in No. 25. 



VII. ALUMINUM. The alumina is contained in the 

 sesquioxide of iron which is then precipitated and may 

 be separated from it as in No. 21. 



VIII. MAGNESIUM AND CALCIUM remain, together 

 with the protoxide of manganese, in the solution fil- 



