The Students' Guide in Quantitative Analysis - Free Ebooks Library

gg QUANTITAXrVE ANALYSIS,
hot cone. H,SO,, pour into cold water, and collect the pre
cipitate as before.
Naie 9. Separation of SiO,.—Evaporate as in Note 5.
Then add HCI quite freely and warm for some time before
adding any water, as the high heat may have produced
anhydrous Fe.Oj, forming an oxychloride which is very
slow to dissolve, especially in dilute acid. Should the acid
already added be too dilute, concentrate by evaporation,
add cone. HCI, and digest at a moderate heat.
Note II. pRECtP[TATEON OF THE BASIC ACETATES.—^^iV-
//-(T/^/ combined with Solutions li and cV must be very
carefully neutralized with sodium carbonate. (If ammonium
carbonate were used, bromide of nitrogen might form in
Filtrate g.) To neutralize the greater portion of the acid
use crystallized sodium carbonate, and complete the neu-
tralization with a very dilute solution of the carbonate, add-
ing it drop by drop, agitating to dissolve the precipitate,
until the liquid assumes a deep mahogany-red color. If a
permanent precipitate forms, add a little hydrochloric acid,
and repeat as above. Then dilute the solution to about i
litre for each gramme of the sesquioxide present, add about
20 grammes sodium acetate dissolved in a small quantity of
water, and heat the whole to boiling.
It is sufficient to boil from ten to fifteen minutes for the
complete precipitation of the acetates. The fdtcring should
be done rapidly on a ribbed filter, keeping the fluid hot. and
disturbing the settled precipitate as little as possible.
When available the Bunsen pump may here be used with
advantage. After the supernatant fluid has been poured
through the filter, throw on the precipitate and wash it with
boiling water containing a little sodium acetate. Should
any basic acetate separate upon concentrating the filtrate,
add some sodium acetate, boil, filter, dissolve the prccip
itate in HCI, and unite to the solution of the main body.