ASH OF THE REFINING HEARTH. 207 



above enumerated, in combination with oxide of lead. 

 It is filtered off and washed once or twice. 



Chromic and vanadic acids cannot be completely 

 separated from oxide of lead by means of sulphuric 

 acid. The precipitate is therefore treated, while still 

 moist, with a mixture of fuming hydrochloric acid and 

 strong alcohol, with which it is heated nearly to ebul- 

 lition, when all the lead and silica are separated in an 

 insoluble state, and the metallic acids are converted 

 into green chlorides, and dissolved together with the 

 phosphoric and arsenic acids. The chloride of lead is 

 filtered off and washed with alcohol ; the green solu- 

 tion is evaporated to the consistency of a syrup, mixed 

 with a slight excess of a concentrated solution of po- 

 tassa, and chlorine passed into it until the metallic 

 oxides have redissolved in the form of acids, imparting 

 a yellow color to the solution.* The liquid is then 

 neutralized with ammonia, concentrated as far as pos- 

 sible by evaporation, allowed to cool, and a fragment 

 of chloride of ammonium placed in it, so large as not 

 to be entirely dissolved. The vanadic acid is thus 

 almost completely precipitated as an ammonia salt, in 

 the form of a white or yellow crystalline powder. 

 After twenty-hours it is filtered off and washed, first 

 with a saturated solution of sal-ammoniac, afterwards 

 with alcohol. It may be purified by dissolving in 

 boiling water with the addition of^some ammonia.f 



* Phosphate of alumina may precipitate here, and must be ana- 

 lyzed separately. (See No. 19.) 



f It is possible that, if molybdenum be present, a yellow com- 

 pound of phosphoric acid, molyLdic acid and ammonia might be 

 precipitated here. It is insoluble in hot dilute nitric acid. This 

 circumstance might be made use of for separating the molybdic 

 acid at once from the solution after treatment with chlorine. The 

 solution would be mixed with ammonia, and afterwards boiled, 

 with addition of nitric acid in slight excess, when the compound 

 would separate as a yellow powder. It contains 3 per cent, of phos- 

 phoric acid. 



