208 ASH OF THE REFINING HEARTH. 



When dry, it is very gradually heated in a shallow 

 platinum dish to expel the ammonia, and the residual 

 vanadic acid is fused at a low red heat. If pure, it 

 solidifies, on cooling, to a dark brown-red, very 

 crystalline mass. 



The solution filtered from the vanadate of ammonia 

 is mixed with ammonia, and afterwards with a solution 

 of chloride of magnesium, which precipitates all the 

 phosphoric, and most of the arsenic acid. After 

 twenty-four hours, the precipitated double salts are fil- 

 tered oft', washed with dilute ammonia, dissolved in 

 hydrochloric acid, the solution heated to 50, and the 

 arsenic precipitated by a stream of sulphuretted hydro- 

 gen-gas. In the filtrate from the sulphide of arsenic, 

 the phosphoric acid may again be precipitated as a 

 double salt by adding ammonia. 



The solution filtered from the magnesia precipitate, 

 which still contains the chromic and molybdic acids, 

 is saturated with sulphuretted hydrogen and heated, 

 when all the chromium is precipitated as green sesqui- 

 oxide. 



From the solution filtered from this precipitate, the 

 molybdenum is precipitated by dilute sulphuric acid 

 as a brown sulphide of molybdenum, from which, 

 when heated in a tube, a mixture of sulphur and sul- 

 phide of arsenic sublimes, while black lustrous MoS 2 

 remains behind. 



The residue of sesquioxide of iron which is left 

 after ignition with nitre and alkali, and extraction 

 with water, is partly dissolved by digestion with con- 

 centrated hydrochloric acid, and if sulphuretted hydro- 

 gen be passed through the solution, the copper will be 

 precipitated. 



The solution filtered from the precipitate is heated 

 to the boiling-point, and a sufficient quantity of 

 chlorate of potassa gradually added, to convert the 

 protochloride of iron into sesquichloride. The small 

 quantities of nickel, cobalt, and manganese which are 



