96 REMOVAL OF PBOSPHATE IONS FROM THE 



3. The precipitate with NH^OH under ordinary conditions 

 would consist only of hydroxides of Fe, Al and Cr. If however PO^'" 

 ions are present, it may also contain phosphates of the above metals 

 and also of Ca, Ba, Sr and Mg. 



2. Procedure. — Dissolve a small portion of the NH4OH 

 precipitate in HNO3 (Sp. g. 1.2) and test for P O/'' ions 

 with (NH4)2Mo04. If a yellow precipitate forms, dissolve 

 the remaining portion of the precipitate in dilute H CI (Sp. g. 

 l.]2). Test a small portion of the solution for Fe with 

 K4re(CN)e. To the remaining solution add Fe CI.., solution, 

 drop by drop, until (after careful stirring) , a drop of the solu- 

 tion removed by means of a stirring rod gives a broton precipi- 

 tate of Fe(0 H),3 with N H^OH on a porcelain plate. 



Notes. — 1. The test for Fe must be made at this point since Fe d.^ 

 is added to^^^the solution later on. 



2. The addition of Fe CI, causes a precipitation of Fe P O^ (white) 

 when the solution is made alkaline by NH^OH. When a sufficient 

 amount of Fe ions has been added to combine with ail 

 P O^'" ions, an excess of FeClg causes a precipitation of the brown 

 Fe(0H)3 



3. Procedure. — To the HCl solution containing an excess 

 of Fe CI3 add NH4Ci solution and a slight excess of 

 NH4OH. Filter. Save the filtrate. 



Notes. — 1. After the addition of NH^OH, the precipitate will 

 contain, Fe P O^, and hydroxides of Fe, Cr, and Al, all the P O^'" ions, 

 remaining in the precipitate. The filtrate may contain ions of Mn, Ni,. 

 Co, Ba, Sr, Ca, and Mg. 



4. Procedure. — Dissolve the above precipitate in dilute 

 HCl (Sp. g. 1.12) and add an excess of NaO H and HA 

 Filter. 



Notes.— 1. By the addition of Na H and H.,0 the A1(0 H), 



is converted into the soluble Na^^AlO^, and the Cv(6 H)., is oxidized 

 to Na^CrO^, the iron precipitate remaining behind on the filter. 



