05 per cent. of
manganese. If the percentage of dioxide is required it may be calculated
by multiplying the percentage of manganese by 1.582. It must be borne in
mind that the manganese should never be calculated to dioxide except
when it is known to exist in the ore only in that form.
VOLUMETRIC METHODS.
The two methods are based on the oxidising effect of manganese dioxide;
and if the metal does not already exist in this form it will require a
preliminary treatment to convert it. The following method due to Mr. J.
Pattinson[82] effects this: A quantity of the ore containing not more
than .25 grams of the metal (Mn), is dissolved in hydrochloric acid in a
pint beaker, and, if necessary, 3 or 4 c.c. of nitric acid are added to
peroxidise the iron, and ferric chloride is added if required, so that
there may be at least as much iron as manganese. Calcium carbonate is
added till the solution is slightly red; and next the redness is removed
by the cautious addition of acid; 30 c.c. of zinc chloride solution
(containing 15 grams of zinc per litre) are added, the liquid is brought
to boil and diluted to about 300 c.c. with boiling water; 60 c.c. of a
solution of bleaching powder (33 grams to the litre and filtered),
rendered slightly greenish by acid, are then run in and are followed by
3 grams of calcium carbonate suspended in 15 c.
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