The
precipitate after ignition is stannic oxide (SnO_{2}). It is a
yellowish-white powder (darker whilst hot), insoluble in acids, and
contains 78.67 per cent. of tin. Cold dilute nitric acid dissolves tin
to a clear solution, which becomes a white enamel-like jelly on heating;
this (filtered off, washed, and dried) forms an opal-like substance,
which is converted on ignition into stannic oxide with evolution of
nitrous fumes. Stannic oxide when ignited with chlorides is more or less
completely converted into stannic chloride, which volatilises. The
presence of chlorides during the evaporation with nitric acid causes a
similar loss.
~Determination of Tin in an Alloy.~--(_Bronze._)--Take 2 grams, and
attack with 20 c.c. of dilute nitric acid in a covered beaker with the
aid of heat. Boil till the bulk is reduced by one-half, dilute with 50
c.c. of water, allow to settle for a few minutes, and filter; wash well
first with water acidulated with a little nitric acid, and afterwards
with water; dry, ignite, and weigh as stannic oxide.
~Determination of Tin in Tin Ore.~--Treat 5 grams of the dried and
finely-powdered ore with 30 c.c. of hydrochloric acid in a four-inch
evaporating dish. After the soluble oxides have been dissolved add 1 or
2 c.c. of nitric acid, boil off nitrous fumes, dilute, and filter.
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