~Stannic Oxide.~--Dry, ignite, and weigh the insoluble residue. Transfer
to a porcelain boat, and reduce in a current of hydrogen at a red heat
for half an hour. Allow to cool whilst the hydrogen is still passing.
Transfer the boat to a beaker, and dissolve up the tin in 10 c.c. of
hydrochloric acid and a c.c. or so of nitric. Wash out the combustion
tube with some acid and add the washing to the contents of the beaker.
Warm gently, dilute with water, and filter. Collect, dry, ignite, and
weigh the insoluble residue. Through the filtrate pass a rapid current
of sulphuretted hydrogen, allow to settle, and filter. Wash the
precipitate with hot water, dry, calcine gently; ignite with ammonium
carbonate, and weigh as stannic oxide, SnO_{2}. The insoluble residue
will in most cases retain some tin. Fuse it with fusion mixture, take up
with hydrochloric acid, filter, pass sulphuretted hydrogen through the
filtrate, collect and wash the sulphide of tin. Ignite and weigh as
stannic oxide, and add it to that previously obtained.
~Copper.~--Pass sulphuretted hydrogen through the acid filtrate obtained
in the first cleaning of the ore, collect the precipitate, and wash
first with soda solution and then with hot water. Dry, ignite, and weigh
as cupric oxide, CuO. Mix the filtrate with that from the main portion
of the sulphide of tin.
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