MANUFACTURES.
anical
esses.
Z-'
1 tures 10 " ^ rSt me * ts > an( ' * s drawn off. This forms grain tin ;y — . what is left behind is common tin, still containing a
small portion of iron, copper, and arsenic.
The water employed in the second washing con-tains a considerable quantity of sulphate of copper, onwhich account it is preserved to be afterwards decom-posed by iron, and the scoria separated from the tinwhen drawn from the furnace, retains a good deal ofthe metal; this, therefore, is also reserved to be againstamped and re-melted with fresh ore. .
^'hiction The above process is followed only for the raised ore ;ti n Stream w hat is called the stream tin undergoes a different pro-cess. As the ore is here in a state approaching to powderby its first washing, and as a great many of the im-purities with which it is combined in the other state arealready removed, the first operation is to bruise itand pass it through wire sieves ; it is then thrown withalternate layers of charcoal into a blast furnace, in whichit is reduced and runs out, through a channel in thebottom, into pits, the scoria being removed as it collectsand thrown again into the furnace. After this the metalis put into a large iron pot, in which it is kept in a state offusion ; and while in this state, pieces of charcoal areplunged into it, which cause a fresh quantity of scoria tobe formed, and separated from the metal. It is then triedor tested by removing a quantity in a ladle and pouringit into the pot, and if it appears bright like silver and ofuniform consistence, it is considered pure, and is pouredinto moulds, being in a state fit for the market.
The following Table shows the Quantities of British Tin exported from the United Kingdom , Jrom 1820to 1831.
1820
1821
1822
1823
1824
1825
1826
1827
1828
1829
1830
1831
Exported.
blks. cwts.
qvs.
lbs.
blks.
cwts. qrs.
lbs.
cwts.
qrs.
lbs.
16,800 50
639
2
18
. .
25
,852
i
15
18,135 54
851
3
1
. .
, .
29
229
i
15
18,720 56
678
3
13
61
201
2
20
35
843
2
3
22,326 67
902
1
0
80
252
1
4
26
364
1
27
28,465 87
125
2
15
279
836
2
3
36
890
0
13
25,063 77
699
2
14
389
i
,180
0
14
34
237
3
19
24,555 76
674
1
1
400
i
,200
2
■20
43
645
0
0
30,544 95
882
1
14
602
i
,869
3
7
49
474
0
21
28,98391
387
3
19
547
i
,739
3
23
41
426
2
13
25,761 83
469
2
11
543
i
,827
1
22
33
215
0
8
24,306 80
979
3
26
589
2
,064
0
24
30
425
1
8
24,016|79
971
1
9
462
1
,651
0
12
21
762
2
0
»he re ° re ’ (53S.) Another useful metal found in England, is lead ;
Un< ^' it isfo S ° cornmon * n most Countries. In Englandham °T n< * ’ n Cornwall , Devonshire , Somersetshire , Dur-tiallv’ an . cas h' re > Cumberland, Westmoreland, and par-shire ln r er ^' ount ’ es 5 iu Wales, in Flintshire, Denbigh-Scotla rl e r ionet * ls * 1 ire, and Montgomeryshire; and inAro-vleV - m ^L um fr' es -shire, Lanarkshire, Ayrshire, andt>. « ire. The only ore of lead from which the metal
413
is extracted is galena, the smelting of which is very simple. Mt ', naiitalThis is performed either by a blast furnace, called an ore l >rocessi;s -hearth, or in a reveberatory furnace. In the former -“■"v—method, the ore and fuel are mixed together and ex-posed to the action of the blast, which quickly fuses themetal and causes it to fall into the lower part of thehearth, where it is protected from the oxygen of theblast by the scoria which floats upon its surface. Whenthe fluid is drawn off, a sufficient quantity of it is left inthe furnace to float the scoria, but when the whole isdrawn off, the blast is stopped, and some lime is throwninto the furnace to concrete the scoria while the heat isbeing discharged. In the reverberatory furnace, whichis preferred in places where there is a plentiful supplyof coals, the fire is made at one end, and the flamepasses over the hearth and up a flue, as already describedfor such furnaces in general.
In the latter case, the ore being already stamped andfreed from as much earthy matter as possible, is put into ariddle or sieve and placed in a large vessel full of water;when by a certain motion obtained, by practice, the lighterand earthy particles are separated and thrown over theedges of the riddle, while the metallic part, being of courseheavier, is retained at the bottom. With this, however,there are many impurities which can be separated onlyin the furnace.
Here commences the smelting process. The cleansed Processore is spread upon the concave hearth, so that the flame of smelting,may act upon it and release the sulphur; when this hasescaped, the lead combines with the oxygen, and theoxide of lead thus formed combines with and reducesthe earthy matter to a liquid which floats upon the sur-face of the metal, and for the rest of the operation pro-tects it from the action of the oxygen. The temperatureof the furnace is now considerably raised to separate asquickly as possible the lead from the liquid scoria; afterwhich a great portion of the scoria is tapped off, leavingonly so much behind as is necessary to protect themetal from the action of the oxygen. The fire is nowslackened and a quantity of slack, or refuse pit-coal,is thrown into the furnace, which serves to diminish theheat, and to concrete the melted scoria; though thislast part of the process is not well done unless powderedlime be also added. The scoria being now hardened,is broken to pieces by a rake, and thrust to the oppositeside of the furnace, where it is taken out throughapertures formed for the purpose. The lead is nowtapped, in a manner similar to that described in themanufacture of iron, and is allowed to run into a largeiron pan, where it is laded into moulds to be cast into pigs.
When the ores abound with sulphate of iron, it becomesnecessary to add the fluate of lime as a flux.
The scoria is still found to contain some lead, inde-pendently of that in the state of oxide, and chemicallycombined with it; it is therefore exposed to the heat ofanother furnace, being a species of blast furnace, calleda slag hearth, which fuses the scoria, and causes themetal to penetrate through it, and fall into a cavity,where it is protected from the agency of the blast, andwhence it is taken and cast into pigs.
v
3 H
VOL, VJI.