The percentage of magnesia found is multiplied by 1.4, and the
result is deducted from the apparent percentage of lime got by
titrating.
~Magnesia.~--Dissolve 2 grams of the limestone in hydrochloric acid, and
separate the lime with ammonia and ammonium oxalate. The filtrate is
treated with sodium phosphate, and the magnesia is weighed as
pyrophosphate, or titrated with uranium acetate.
~Iron.~--Dissolve 2 grams in hydrochloric acid, reduce, and titrate with
standard permanganate of potassium solution. This gives the total iron.
The ferrous iron is determined by dissolving another 2 grams in
hydrochloric acid and at once titrating with the permanganate of
potassium solution.
~Manganese.~--Dissolve 20 grams in hydrochloric acid, nearly neutralise
with soda, add sodium acetate, boil, and filter. To the filtrate add
bromine; boil, and determine the manganese in the precipitate. See page
300.
~Phosphoric Oxide.~--This is determined by dissolving the ferric acetate
precipitate from the manganese separation in hydrochloric acid, adding
ammonia in excess, and passing sulphuretted hydrogen. Filter and add to
the filtrate "magnesia mixture." The precipitate is collected, washed
with ammonia, ignited, and weighed as pyrophosphate.
THE ALKALIES.
The oxides of sodium, potassium, lithium, c?sium, and rubidium and
ammonia are grouped under this head.
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