186 BROWN IRON ORE. 



is produced. The precipitate, consisting of the baryta- 

 salts of the above-mentioned acids, is filtered off* 

 washed and boiled while yet moist, with dilute sulphuric 

 acid, which must not be added in too great excess. 

 The reddish-yellow acid filtrate is neutralized with 

 ammonia, concentrated by evaporation, and a fragment 

 of chloride of ammonium is placed in it. In propor- 

 tion as the solution becomes saturated with chloride of 

 ammonium, vanadate of ammonia is deposited as a 

 white or yellow crystalline powder, which is allowed to 

 separate completely, filtered oft) and washed with a 

 saturated solution of chloride of ammonium. When 

 gradually heated with full access of air, it leaves dark 

 red vanadic acid, which fuses when heated more 

 strongly, and solidifies, on cooling, to a very crystal- 

 line mass. 



The solution obtained by lixiviating the mass after 

 fusion with nitre, may also be mixed with sal- ammo- 

 niac, and boiled, in order to neutralize the free alkali, 

 and to precipitate silica and phosphate of alumina. 

 This precipitate usually contains also vanadic acid, 

 which may be converted into sulphide by! fusion with 

 an equal weight of carbonate of potassa and sulphur; 

 the fused mass is extracted with water, and the brown 

 sulphide of vanadium precipitated from the filtered 

 solution by dilute sulphuric acid. 



If the iron-ore be reduced by fusion with borax 

 (see Iron Assay), in a crucible lined with charcoal, a 

 well-fused, crystalline regulus of iron is obtained, 

 which contains vanadium, chromium, arsenic, phos- 

 phorus, silicon, and carbon. 



Moreover, see Ash of the Kefining-hearth. 



