EXAMINATION OF CLAYS.
~Moisture.~--Take 5 grams of the carefully-prepared sample and dry in
the water-oven till the weight is constant.
~Loss on Ignition.~--Weigh up 2 grams of the sample used for the
moisture determination, and ignite in a platinum-crucible to redness,
cool, and weigh.
~Silica and Insoluble Silicates.~--Weigh up another 2 grams of the dried
sample, and place them in a platinum dish; moisten with water, and cover
with 20 c.c. of sulphuric acid. Evaporate and heat gently to drive off
the greater portion of the free acid. Allow to cool; and repeat the
operation. Extract by boiling with dilute hydrochloric acid, filter,
wash, dry, ignite, and weigh. The quantity of insoluble silicates is
determined by dissolving out the separated silica with a strong boiling
solution of sodium carbonate. The residue (washed, dried, and ignited)
is weighed, and reported as "sand."
~Alumina and Ferrous Oxide.~--To the filtrate from the silica add "soda"
solution till nearly neutral, and then sodium acetate. Boil and filter
off the precipitate. Reserve the filtrate. Dissolve the precipitate in
hydrochloric acid, and dilute to exactly 200 c.c. Divide into two parts
of 100 c.c. each. In one determine the iron by reducing and titrating in
the way described under volumetric iron. Calculate the percentage as
ferrous oxide, unless there are reasons to the contrary, also calculate
its weight as ferric oxide.
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