154 § 93. SPECIAL METHODS OF ANALYSIS. * 



1. Case in which there is enough alumina and ferric 

 oxide present to combine with all the phosphoric acid. 

 The filtrate from the precipitate by sodic acetate, obtained 

 in a qualitative test in the manner described below, gives 

 no reaction for phosphoric acid with ammonic molybdate. 



To the not too concentrated solution add sodic carbon- 

 ate with constant stirring, until a few scattered flakes of a 

 precipitate remain permanent, heat to boiling, remove the 

 lamp, and add immediately an excess of a boiling hot so- 

 lution of sodic or ammonic acetate ; this reagent precipi- 

 tates all the Al^Og, Fe^Og, and P^O^ ; filter rapidly while 

 hot, and wash the contents of the filter with boiling water, 

 containing a little ammonic acetate ; dissolve the precipi- 

 tate, without drying it, in hot, dilute hydrochloric acid, 

 wash the filter out well, mix the solution and washings by 

 vigorous stirring, add water, if it is necessary, to bring 

 the liquid to such a volume that it can be conveniently 

 divided in two equal parts, and mix carefully again by 

 stirring, divide it accurately, precipitate one part with 

 ammonia in slight excess, as directed for the precipitation 

 of alumina (§ 51), filter, wash with hot water, dry, ignite 

 precipitate and filter separately, and weigh ; the result, 

 multiplied by two, gives the total amount of Al^Og, Fe^Og, 

 and PjOg in the undivided solution. 



Reduce the ferric to ferrous oxide in the other half of 

 the solution, and estimate the iron with potassic perman- 

 ganate (§ 52, 5) y or, as a sulphuric-acid solution is better 

 adapted for that process, this half of the solution may be 

 precipitated with ammonia also, and the precipitate wash- 

 ed, and dissolved, without drying it, in dilute sulphuric 

 acid. The amount of ferric oxide being estimated from 

 the result, multiply by two and thus get the quantity of 

 Fe^Og in the undivided solution. 



The difterence between the total weight of Al^O^, 

 Fe^Og, and P^O,^, and the sum of the Fe^Og, as determined 

 above, and the P^O^ to be determined in another portion 



