~Estimation of "Silica and Insoluble Silicates" in an Ore.~--Take 2
grams of the powdered mineral, evaporate with nitric acid (if sulphides
are present), treat the dried residue (or the original substance if
sulphides are absent) with 10 or 20 c.c. of hydrochloric acid; again
evaporate to dryness, take up with dilute hydrochloric acid, filter,
wash, ignite, and weigh.
~Estimation of Silicon in Iron.~--Place 2 grams of the metal (borings or
filings) in a four-inch evaporating dish, and dissolve (with aid of
heat) in 25 c.c. of dilute nitric acid. Evaporate to complete dryness,
take up with 20 c.c. of hydrochloric acid, and allow to digest for one
hour. Boil down to a small bulk, dilute with a 5 per cent. solution of
hydrochloric acid, boil, and filter. Wash with acid and water, dry,
ignite in a platinum crucible, and weigh the SiO_{2}. This, multiplied
by 0.4673, gives the weight of the silicon. The percentage is calculated
in the usual way.
PRACTICAL EXERCISES.
1. A certain rock is a mixture of 70 per cent. of quartz, 25 per cent.
of potash-felspar, and 5 per cent. of potash-mica. What per cent. of
silica will it contain?
2. Two grams of a mixture of silica and cassiterite left, after
reduction in hydrogen, 1.78 grams. Assuming all the oxide of tin to have
been reduced, what will be the percentage of silica?
3.
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