Jean-Claude Mougin (pdf) - Picto Benelux

• Allow the mixture to settle for at least 4 hours in the tubes. The ferric
oxalate starts to decant as an emerald green liquid, clearly separated from
the iron that wasn’t reduced by the acid.
• Filter the iron oxalate through a funnel having its tip filled with cotton
wool. The Büchner vacuum pump can be reused here to speed up filtering.
• Repeat the filtering several times if necessary, until you get a perfectly
clear liquid.
3.3 Determining the ferric oxalate concentration
The percentage can be read on the specific gravity chart printed below.
This chart shows for example that a gravity coefficient of 1.17 corresponds to a
27 % concentration. The simplest way of measuring this concentration is to use an
hydrometer. A 24 % instead of a 27% concentration will not show any real
difference in the resulting print.
Another way of proceeding is to weigh the same volumes of water and of ferric
oxalate: the ratio between both results has to be 1.174.
When getting a density higher than 1.17, add water. When getting a density lower
than 1.15, as the ferric oxalate cannot be heated without damage, the whole
procedure has to be started over again, and more water has to be extracted in
order to get a less humid iron hydrate.
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