2. The dross found on the bottom of the reverberatory furnace, after
re-melting the tin to refine it.
The scoriæ C, are smelted without any preparation; but those marked B,
are stamped in the mill, and washed, to concentrate the tin grains; and
from this rich mixture, called _prillion_, smelted by itself, a tin is
procured of very inferior quality. This may be readily imagined, since
the metal which forms these granulations is what, being less fusible
than the pure tin, solidified quickly, and could not flow off into the
metallic bath.
Whenever all the tin blocks have thoroughly undergone the process of
liquation, the fire is increased, to melt the less fusible residuary
alloy of tin with iron and some other metals, and this is run out into a
small basin, totally distinct from the refining basin. After this alloy
has reposed for some time, the upper portion is lifted out into block
moulds, as impure tin, which needs to be refined anew. On the bottom and
sides of the basin there is deposited a white, brittle alloy, with a
crystalline fracture, which contains so great a proportion of foreign
metals, that no use can be made of it. About 3-1/2 tons of coal are
consumed in producing 2 of tin.
_Smelting of tin by the blast furnace._--This mode of reduction employs
only wood charcoal, and its object is to obtain tin of the maximum
purity to which it can be brought by manufacturing processes. The better
ores of the stream-works, and the finer tin sands, are selected for this
operation. The washings being always well performed, the oxide of tin is
exempt from every arsenical or sulphureous impurity, and is associated
with nothing but a little hematite. It is therefore never calcined.
The smelting is effected without addition; only, in a few cases, some of
the residuary matters of a former operation are added to the ore. About
a ton and six-tenths of wood charcoal are burned for one ton of fine
smelted tin. The only rule is, to keep the furnace always full of
charcoal and ore. The revived tin is received immediately in the first
basin; then run off into the second, where it is allowed to settle for
some time. The scoriæ that run off into the first basin, are removed as
soon as they fix. These scoriæ are divided into two classes; namely,
such as still retain tin oxide, and such as hold none of the metal in
that state, but only in granulations. The metallic bath is divided, by
repose, into horizontal zones, of different degrees of purity; the more
compound and denser matters falling naturally to the bottom of the
basin. The tin which forms the superior zones, being judged to be pure
enough, is transvased by ladles into the refining basin, previously
heated, and under which, if it is of cast-iron, a moderate fire is
applied. The tin near the bottom of the receiving basin is always laded
out apart, to be again smelted; sometimes, indeed, when the furnace is
turning out very impure tin, none of it is transvased into the second
basin; but the whole is cast into moulds, to be again treated in the
blast furnace.
In general they receive no other preparation, but the green wood
ebullition, before passing into the market. Sometimes, however, the
block of metal is heated till it becomes brittle, when it is lifted to a
considerable height, and let fall, by which it is broken to pieces, and
presents an agglomeration of elongated grains or _tears_; whence it is
called _grain tin_.
On making a comparative estimate of the expense by the _blowing-house_
process, and by the reverberatory furnace, it has been found that the
former yields about 66 per cent. of tin, in smelting the stream or
alluvial ore, whose absolute contents are from 75 to 78 parts of metal
in the hundred. One ton of tin consumes a ton and six-tenths of wood
charcoal, and suffers a loss of 15 per cent. In working with the
reverberatory furnace, it is calculated that ore whose mean contents by
an exact analysis are 70 per cent., yields 65 per cent. on the great
scale. The average value of tin ore, as sold to the smelter, is 50
pounds sterling per ton; but it fluctuates, of course, with the market
prices. In 1824, the ore of inferior quality cost 30_l._, while the
purest sold for 60_l._ One ton of tin, obtained from the reverberatory
furnace, cost--
1-1/2 tons of ore, worth _£_75 0 0
1-3/4 tons of coals, at 10_s._ per ton 0 17 6
Wages of labour, interest on capital, &c. 3 0 0
---------
78 17 6
On comparing these results with the former, we perceive that in a
_blowing-house_ the loss of tin is 15 per cent., whereas it is only 5 in
the reverberatory furnace. The expense in fuel is likewise much less
relatively in the latter process; for only 1-3/4 tons of coals are
consumed for one ton of tin; while a ton and six-tenths of wood charcoal
are burned to obtain the same quantity of tin in the blowing-house; and
it is admitted that one ton of wood charcoal is equivalent to two tons
of coal, in calorific effect. Hence every thing conspires to turn the
balance in favour of the reverberatory plan. The operation is also, in
this way, much simpler, and may be carried on by itself. The scoriæ,
besides, from the reverberatory hearth, contain less tin than those
derived from the same ores treated with charcoal by the blast, as is
done at Altenberg. It must be remembered, however, that the grain tin
procured by the charcoal process is reckoned to be finer, and fetches a
higher price; a superiority partly due to the purity of the ore reduced,
and partly to the purity of the fuel.
To test the quality of tin, dissolve a certain weight of it with heat in
muriatic acid; should it contain arsenic, brown-black flocks will be
separated during the solution, and arseniuretted hydrogen gas will be
disengaged, which, on being burned at a jet, will deposit the usual gray
film of metallic arsenic upon a white saucer held a little way above the
flame. Other metals present in the tin, are to be sought for, by
treating the above solution with nitric acid of spec. grav. 1·16, first
in the cold, and at last with heat and a small excess of acid. When the
action is over, the supernatant liquid is to be decanted off the
peroxidized tin, which is to be washed with very dilute nitric acid, and
both liquors are to be evaporated to dissipate the acid excess. If, on
the addition of water to the concentrated liquor, a white powder falls,
it is a proof that the tin contains bismuth; if on adding sulphate of
ammonia, a white precipitate appears, the tin contains lead; water of
ammonia added to supersaturation, will occasion reddish-brown flocks,
if iron is present; and on evaporating the supernatant liquid to
dryness, the copper will be obtained.
The uses of tin are very numerous. Combined with copper, in different
proportions, it forms bronze, and a series of other useful alloys; for
an account of which see COPPER. With iron, it forms tin-plate; with
lead, it constitutes pewter, and solder of various kinds (see LEAD).
Tin-foil coated with quicksilver makes the reflecting surface of glass
mirrors. (See GLASS.) Nitrate of tin affords the basis of the scarlet
dye on wool, and of many bright colours to the calico-printer and the
cotton-dyer. (See SCARLET and TIN MORDANTS.) A compound of tin with
gold, gives the fine crimson and purple colours to stained glass and
artificial gems. (See PURPLE OF CASSIUS.) Enamel is made by fusing oxide
of tin with the materials of flint glass. This oxide is also an
ingredient in the white and yellow glazes of pottery-ware.
An ACCOUNT of TIN coined in Cornwall and Devon, from 1817 to 1829
inclusive:--
+------+-------+---------+
|Years.|Blocks.|Tons. |
+------+-------+---------+
| 1817 | 25,379|4,120 |
| 1818 | 23,048|3,745-1/3|
| 1819 | 18,881|3,065 |
| 1820 | 17,084|2,773-1/2|
| 1821 | 19,273|3,128 |
| 1822 | 18,732|3,137 |
| 1823 | 24,077|4,031 |
| 1824 | 28,602|4,819 |
| 1825 | 24,902|4,170 |
| 1826 | 26,299|4,406 |
| 1827 | 31,744|5,316 |
| 1828 | 28,179|4,696 |
| 1829 | 26,344|4,396 |
+------+-------+---------+
+---------------------+-------------+
| Tin imported. |Tin exported.|
|Duty, 50_s._ per cwt.| |
+-------+-------------+-------------+
| | _Cwts._ | _Cwts._ |
| 1827 | 2,217 | 2,938 |
| 1828 | 3,386 | 3,258 |
| 1829 | 2,674 | 2,581 |
| 1830 | 15,539 | 10,426 |
| 1831 | 8,099 | 12,226 |
| 1832 | 29,203 | 21,720 |
| 1833 | 35,124 | 39,850 |
| 1834 | 46,769 | 46,685 |
| 1835 | 17,705 | 23,796 |
| 1836 | 23,236 | 17,231 |
+-------+-------------+-------------+
The principal importations are from the East India Company’s territories
and Ceylon:--they amounted in 1832 to 24,585 cwts.; in 1833 to 27,928;
in 1834 to 33,611; in 1835 to 10,104; and in 1836 to 17,729. From
Sumatra and Java 1961 cwts. were imported in 1832, and 1145 in 1834, but
in the other years greatly less.
Declared } | | | |
value of } 1827. | 1829. | 1831. | 1833. | 1835.
tin and }302,255_l._|235,178_l._|239,143_l._|282,176_l._|381,076_l._
pewter } | | | |
wares and } | | | |
tin-plates} 1828. | 1830. | 1832. | 1834. | 1836.
exported }266,651_l._|249,657_l._|243,259_l._|337,056_l._|387,951_l._
in } | | | |
Of these goods, from two-fifths to three-fifths go to the United States
of America.
ABSTRACT of TIN coined in Cornwall and Devon, in the year ending June
30, 1835; from the _Mining Review_, vol. iii.
+---------------------------+-----------+-------------+------------+
| |Blocks of | Blocks of | |
| |Grain Tin. | Common Tin. | Totals. |
| Smelters. +-----+-----+------+------+------+-----+
| |1834.|1835.|1834. |1835. |1834. |1835.|
+---------------------------+-----+-----+------+------+------+-----+
|Daubuz and Co. | 728 | 875 | 6114 | 4494 | 6842 | 5369|
|Grenfell and Boase | 344 | 196 | 3776 | 3097 | 4120 | 3293|
|Bolitho and Sons | 229 | 153 | 3829 | 3099 | 4058 | 3252|
|R. and J. Michell | 101 | 75 | 709 | 575 | 810 | 650|
|Wheal Vor Adventurers | -- | -- | 3925 | 4069 | 3925 | 4069|
|Taylor, Sons and Co. | -- | 112 | -- | 1250 | -- | 1362|
|John Batten and Son | 28 | 49 | 2352 | 2351 | 2380 | 2400|
|Joseph Carne | -- | -- | 896 | 851 | 896 | 851|
|William Cornish | -- | -- | 622 | 574 | 622 | 574|
|Gill and Co. (at Morwelham)| -- | -- | 758 | -- | 758 | --|
| Ditto (at Calstock) | 60 | -- | 605 | -- | 665 | --|
|Rundle, Paul and Co. | -- | 12 | -- | 1545 | -- | 1557|
| +-----+-----+------+------+------+-----+
| Total |1490 |1472 |23586 |21905 |25076 |23377|
+---------------------------+-----+-----+------+------+------+-----+