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458 METALS—THE NOBLER.
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cooled
in iron moulds for becoming Block Tin ; which may be made into pure
Tin, and then sold as '' grain Tin." It does not tarnish in the air,
and is proof against the action of acids, such as vinegar, and the
like. But this pure Tin would be too costly for use in making domestic
receptacles for the hundred and one articles of common daily
consumption, such as biscuit tins, coffee tins, sardine boxes, tin
kettles, etc.; likewise it would be too heavy, if these receptacles are
to be of stable form ; therefore for such vessels sheet iron (or sheet
copper) is used, with a thin protective coating of pure Tin, on both
the inner and outer surfaces thereof.
To
make " tin plate " (in Scotland, " white iron") the sheet-iron plates
are immersed in the acidulated water, and next scoured completely
bright. Each plate is then plunged into a vessel filled with melted
Tin, the surface of which is covered with suet, pitch, or resin, for
preventing any formation of bubbles thereupon. Some of the Tin not
only covers the surfaces of the Iron, but completely penetrates it,
giving to its whole substance a white colour. " Block Tin " is made by
pouring the melted ore (after it has been first washed, and then
roasted), into quadrangular moulds of stone, each containing about
three hundred and twenty pounds weight thereof. These " blocks " are
stamped by officers of the Duke of Cornwall with the impression of a
lion, the arms of that Duchy. A duty of four shillings per
hundredweight has to be paid, on stamping, to the Prince of Wales.
Speaking
as above of vinegar, incidental mention may be made of the circumstance
that at the time of the Great Plague in this country (1665-1666), Dr.
Robert Cvedale caused the whole of his household to escape that dire
malady by a remedy which he discovered, and
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