1. Tin is a whitish metal, less elastic, and less sonorous than any
other metal, except lead. It is found in the mountains which separate
Gallicia from Portugal, and in the mountains between Saxony and
Bohemia. It also occurs in the peninsula of Molucca, in India, Mexico,
and Chili. But the mines of Cornwall and Devonshire, in England, are
more productive than those of all other countries united.
2. There are two ores of tin, one of which is called _tin stone_, and
the other _tin pyrites_; the former of these is the kind from which
the metal is extracted. The ore is usually found in veins, which often
penetrate the hardest rocks. When near the surface of the earth, or at
their commencement, they are very small, but they increase in size,
as they penetrate the earth. The direction of these veins, or, as the
miners call them, _lodes_, is usually east and west.
3. The miners follow the lode, wheresoever it may lead; and, when they
extend to such a depth, that the waters become troublesome in the
mine, as is frequently the case, they are pumped up with machinery
worked by steam, or drawn off by means of a drain, called an _adit_.
The latter method is generally adopted, when practicable.
4. The ore is raised to the surface through shafts, which have been
sunk in a perpendicular direction upon the vein. At the top of the
shaft, is placed a windlass, to draw up the _kibbuts_, or baskets,
containing the ore. Near St. Austle, in Cornwall, is a mine which has
not less than fifty shafts, half of which are now in use. Some of the
veins have been worked a full mile, and some of the shafts are nearly
seven hundred feet deep.
5. At St. Austle Moor, there is a mine of _stream tin_, about three
miles in length. The tin, together with other substances, has been
deposited in a valley, by means of small streams from the hills. The
deposite is about twenty feet deep, and the several materials of which
it is composed, have settled in strata, according to their specific
gravity. The ore, being the heaviest, is, of course, found at the
bottom.
6. The ore, from whatever source it may be obtained, is first
pulverized in a stamping mill, and then washed, to free it from the
stony matter with which it may be united. The ore, thus partially
freed from foreign matter, is put into a reverberatory furnace, with
fuel and limestone, and heated intensely. The contents of the furnace
having been brought to a state of fusion, the lime unites with the
earthy matters, and flows with them into a liquid glass, while the
carbon of the coal unites with the tin. The metal sinks, by its
specific gravity, to the bottom of the furnace, and is let out, after
having been exposed to the heat about ten hours.
7. The tin thus obtained, is very impure; it therefore requires a
second fusion, to render it fit for use. After having been melted a
second time, it is cast into blocks weighing about three hundred
pounds. These blocks are taken to places designated by law, and there
stamped, by inspectors appointed for the purpose by the Duke of
Cornwall. In performing this operation, the inspector cuts off a
corner, and stamps the block at that place, with the proper seal, and
with the name of the smelter. These precautions give assurance, that
the metal is pure, and that the duty has been paid.
8. The duty is four shillings sterling per hundred weight, which is
paid to the Duke of Cornwall, who is also Prince of Wales. The revenue
from this source amounts to about thirty thousand pounds a year. The
owner of the soil also receives one sixth, or one eighth of the ore as
his _dish_, as the miners call it. The miners and the smelters receive
certain proportions of the metal for their services.
9. Tin was procured from Britain at a very early period. The
Phoenicians are said by Strabo to have passed the Pillars of Hercules,
now the Straits of Gibraltar, about 1200 years before Christ. But the
time at which they discovered the tin islands, which they denominated
_Cassorides_, cannot be ascertained from history, although it is
evident from many circumstances, that the Scilly Islands, and the
western ports of Britain, were the places from which these early
navigators procured the tin with which they supplied the parts of the
world to which they traded.
10. For a long time, the Phoenicians and the Carthaginians enjoyed the
tin trade, to the exclusion of all other nations. After the
destruction of Carthage by the Romans, a colony of Phocean Greeks,
established at Marseilles, carried on this trade; but it came into the
hands of the Romans, after the conquest of Britain by Julius Cæsar.
11. The Cornish mines furnish incontestable proofs of having been
worked many hundred years ago. In digging to the depth of forty or
fifty fathoms, the miners frequently meet with large timbers imbedded
in the ore. Tools for mining have also been found in the same, or
similar situations. The mines, therefore, which had been exhausted of
the ore, have, in the course of time, been replenished by a process of
nature.
12. To what purposes the ancients applied all the tin which they
procured at so much labor and cost, is not precisely known. It is
probable, that the Tyrians consumed a portion of it, in dyeing their
purple and scarlet. It formed then, as it now does, many important
alloys with copper. The mirrors of antiquity were made of a
composition of these metals.
13. The method of extracting tin from its ores was probably very
defective in ancient times. At least, it was so for several centuries
before the time of Elizabeth, when Sir Francis Godolphin introduced
great improvements in the tin works. The use of the reverberatory
furnace was commenced, about the beginning of the eighteenth century,
and soon after pit-coal was substituted for charcoal.
14. This metal, in its solid state, is called _block-tin_. It is
applied, without any admixture with any other metal, to the formation
of vessels, which are not to be exposed to a temperature much above
that of hot water. A kind of ware, called _biddery ware_, is made of
tin alloyed with a little copper. The vessels made of this
composition, are rendered black by the application of nitre, common
salt, and sal ammoniac. _Foil_ is also made by pressing it between
steel rollers, or by hammering it, as in the case of gold by the
gold-beaters.
15. But tin is most extensively applied as a coating to other metals,
stronger than itself, and more subject to oxydation. The places which
are usually denominated tin, are thin sheets of iron coated with this
metal. The iron is reduced to thin plates in a rolling-mill, and these
are prepared for being tinned, by first steeping them in water
acidulated with muriatic acid, and then freeing them from oxyde by
heating, scaling, and rolling them.
16. The tin is melted in deep oblong vessels, and kept in a state of
fusion by a charcoal fire. To preserve its surface from oxydation, a
quantity of fat or oil is kept floating upon it. The plates are dipped
perpendicularly into the tin, and held there for some time. When
withdrawn, they are found to have acquired a bright coating of the
melted metal. The dipping is performed three times for _single tin
plate_, and six times for _double tin plate_. The tin penetrates the
iron, and forms an alloy.
17. Various articles of iron, such as spoons, nails, bridle-bits, and
small chains, are coated with tin, by immersing them in that metal,
while in a state of fusion. The great affinity of tin and copper,
renders it practicable to apply a thin layer of the former metal to
the surface of the latter; and this is often done, as stated in the
article on the coppersmith.
18. Tin and quicksilver are applied to the polished surface of glass,
for the purpose of forming mirrors. In silvering plain looking-glasses,
a flat, horizontal slab is used as a table. This is first covered with
paper, and then with a sheet of tin foil of the size of the glass. A
quantity of quicksilver is next laid on the foil, and spread over it
with a roll of cloth, or with a hare's foot.
19. After as much quicksilver as the surface will hold, has been
spread on, and while it is yet in a fluid state, the glass is shoved
on the sheet of foil from the edge of the table, driving a part of the
liquid metal before it. The glass is then placed in an inclined
position, that every unnecessary portion of the quicksilver may be
drained off, after which it is again laid flat upon the slab, and
pressed for a considerable time with heavy weights. The remaining
quicksilver amalgamates with the tin, and forms a permanent,
reflecting surface.