The Students' Guide in Quantitative Analysis - Free Ebooks Library

70
QUANTITATIVE ANALYSIS.
ficiently washed, a red residue of oxide of iron may remain
on the filter, in which case pour dilute HNO3 upon it
allow it to pass into the ammoniacal solution, acidulate
that with HNO3, warm, add more of the precipitant, and
set aside as before; filter and wash several times with the
diluted precipitant, then dissolve the precipitate on the
filter and that adhering to the beaker in as little dilute
NH^HO as possible.
The yellow granular precipitate of ammonium phospho-
molybdate is not sufficiently constant in composition to
admit of directly weighing it in exact analysis ; it is there-
fore dissolved in NH,HO and the phosphoric acid thrown
down with magnesia mixture as just detailed. According
to Muntzinger's analysis, after drying at loo'^ C, it contains
3-577 percent. NH^HO
3.963 " P,Os
92.461 " MoO,
100.000
Lipowitz says the precipitate dried at 20" to 30" C. con-
tains 3.607 per cent, of P.Oj, and Eggertz ^.j to 3.8 per
cent. P,0,. When dried at 120'' C, Sonnenschein found
about 3 per cent. For properties of this precipitate sec
also Fres., § 93, i, foot-note. Consult also Finkener's
paper in Bericht d. d. chem. Ges XI, p. 1638 (1878}, and
Chem. News, X L VII , p. 66 ( 1 88 3),
Note II. Washing of Fe,0,3H,0.—Wash this precipi-
tate by boiling up with water and decanting until the wa.sh
water shows very little alkaline reaction with litmus paper,
and gives very little precipitate with solution of AgNOj.
Then transfer to filter, and wash thoroughly with boiling
water.
Note 16. Determination of Mn.—(Gibbs' process. Am