~Determination of Iron in Brown or Red Ores or Magnetite.~--Weigh up 0.5
gram of the ore (powdered and dried at 100° C.), and dissolve in from 10
to 20 c.c. of strong hydrochloric acid, boiling until all is dissolved,
or until no coloured particles are left. Dilute, reduce, and titrate.
~Determination of Iron in Pyrites.~--Weigh up 1 gram of the dry powdered
ore, and place in a beaker. Cover with 10 c.c. of strong sulphuric acid,
mix well by shaking, and place on the hot plate without further handling
for an hour or so until the action has ceased. _Allow to cool_, and
dilute to 100 c.c. Warm until solution is complete. Reduce and titrate.
~Determination of Iron in Substances Insoluble in Acids.~--Weigh up 1
gram of the ore, mix with 5 or 6 grams of carbonate of soda and 0.5 gram
of nitre by rubbing in a small mortar, and transfer to a platinum
crucible. Clean out the mortar by rubbing up another gram or so of soda,
and add this to the contents of the crucible as a cover. Fuse till
tranquil. Cool. Extract with water. If the ore carries much silica,
evaporate to dryness with hydrochloric acid to separate it. Re-dissolve
in hydrochloric acid, and separate the iron by precipitating with
ammonia and filtering. If only a small quantity of silica is present,
the aqueous extract of the "melt" must be filtered, and the insoluble
residue washed and dissolved in dilute hydrochloric acid.
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