The Students' Guide in Quantitative Analysis - Free Ebooks Library

NOTES TO THE PRECBDISG SCHEME,
Vonr Sci. [2] XLIV, p. 216.) To the HCl solution add
NI i-lO in Lccss and solution of Na,HPO, m large
LceW. ThenaddcUIutcH.SO,or HCl until the wh.te
precipitcite redissolvcs, heat to boilmg, and add NH.HO m
Lcess Digest near the boiling point about an hour, when
the precipitate, at first white and gelatinous, becomes
rose-colored and forms crystalline scales. Filter and wash
with hot water. If tinged red, redissolve the precipitate m
dilate HCl. aad repeat the process, On ignitwn the pre-
cipitato is converted into Mn.P.O,, a nearly white powder.
IE Zn is present, it must first be separated as in
Scheme I, Am. Clum., Vol. I, p. 323-
Note iS Volumetric Determination of Fe.— 1 ut
Solution k\ which must be completely free from the KClOj
used to oxidize Filtrate k, into a wide-mouthed reduction
bottle hoidmg about 250 c. c. Carefully let down mto the
bottle a lump of amalgamated zinc, free from iron, and a
strip of platinum foil resting upon it, add about lO c. c.
cone H SO,, cover with a watch-glass and set aside over
nio-ht To ascertain if the reduction is complete test the
solution with ammonium sulpho^yanide. which should
e'ive only a trace of pink color.
^
Then introduce into a flask holding about 200 c. c., and
fitted with a Kronig valve, exactly 0.2 gramme iron piano-
forte wire, add dilute H.SO,, and heat untd complete
solution of iron. Cool the flask, pour and wash out the
contents of the flask into a large beaker containing about
400 c. c. cold water, add a little concentrated II.SO, and
titrate with a solution of K.Mn.Os ^^3 grms. ui 2 litres
water) to determine its strength. Repeat, and average
'''now nour and wash out the contents of the reduction-
bottle into a large beaker, add cone. H.SO,. and tilmte
with the standard K.Mn.O, as before. H the HCl was not
7'