EXAMINATION OF ASH CONSTITUENTS 9 



The ash is dissolved in a small quantity of con- 

 centrated hydrochloric acid, and evaporated to dryness 

 on the water-bath, the evolution of carbon dioxide on 

 treatment with acid showing the presence of metallic 

 carbonates. Any silicates present are thus converted 

 into insoluble silica ; hence, on dissolving the residue in 

 dilute hydrochloric acid and filtering, the silica is 

 removed. After washing this on the filter paper, the 

 presence of silica in the residue may be confirmed by 

 its insolubility in a fused borax bead. 



The filtrate after removal of silica is rendered 

 alkaline with ammonia, boiled, and filtered. All the 

 phosphoric acid, together with all or part of the iron, 

 calcium, and magnesium, is thus obtained on the filter 

 paper, and may be examined for iron, calcium, and 

 phosphates by the usual methods of precipitation as 

 follows :^ 



Iron. — A portion of the precipitate is dissolved in 

 dilute hydrochloric acid, and treated in two portions 

 with potassium ferrocyanide and potassium thio- 

 cyanate respectively. A blue precipitate in the first 

 case, and a blood-red coloration in the second, confirm 

 the presence of iron. 



Calcium. — A small quantity of the moist precipitate 

 is dissolved in dilute acetic acid and ammonium oxalate 

 added. The production of a white precipitate of calcium 

 oxalate, soluble in hydrochloric acid, shows the presence 

 of calcium. 



Phosphoric Acid. — On dissolving a third portion in 

 concentrated nitric acid and warming, .the characteristic 

 canary-yellow precipitate of ammonium phospho- 

 molybdate is produced. 



The filtrate from the precipitation with ammonia 

 contains all the sodium, potassium, chloride, and part 



