The Students' Guide in Quantitative Analysis - Free Ebooks Library

In boilinc?
NOTliS TO THE PRECEDING SCHEME. 69
Filtrate e with KCIO3 to oxidize FeO. be
c^u-eful to decompose the whole of the chlorate by heat-
incr with excess of HCl.
"Note 1 2 Determination of P.O^.-To remove the HCl
in Solutkn r' add NHJIO in large excess, wash the pro
cipitates of ferric hydrate and ferric phosphate by decantation
two or three times, and redissolve in hot cone. HNO,.
Evaporate this solution down to small bulk ( 1 50 c.c. to 100
cc ) partially neutralize with NH.HO, and add about 50
c c" of solution of ammonium molybdatc in nitric acid. If
the solution is very acid, ammonium nitrate is formed by
the partial neutralization as above, otherwise add a small
quantity of the salt. Warm the solution, do not bod, aad
let stand 24 hours or more. Then filter from the yellow
granular precipitate of ammonium phospho-molybdate with-
out brin-ing it all on the filter, and wash the precipitate
with a solution prepared by mixing 100 parts of the precipi-
tant with 20 parts of HNO, (sp. gr.=i.2) and 80 parts of
water. Dissolve the yellow precipitate by pouring a small
quantity of dilute NH.HO through the filter into the
original beaker, and determine the phosphoric acid m the
ammoniacal solution by means of mag:nesia mixture (5 c.c.)
in the usual manner. Magnesia mixture is preferably made
with magnesium chloride. If the crystalline ammoniomagnesium
phosphate falls mixed with flocculent magne-
sium hydrate, add HCl until dissolved and reprecipitate
with NHJ-IO.
Reserve the filtrate and washings of the yellow precipitate,
and test for phosphoric acid by adding a little more
of the ammonium molybdate solution, heating and allowing
to stand 12 hours. If a yellow precipitate forms, pour
through a separate filter, dissolve in dilute NH4HO and
add to the ammoniacal solution.
Tf the yellow precipitate first obtained was not suf