F U R N 
branching from the notch of the tiam, ami eniitfing from 
, its dream beautiful fparks of ignited carbon, refembling 
thofe ejeiSbed from*’’a crucible of cad deel in fufion, ex- 
pofed to external air, or to the combaftion of fine deel 
filings in a white flame; if, when ilfning from the orifice 
of the furnace, it is of the pured white colour, polfeding 
no tenacity, but in a date of the greated fluid divifion, 
and, when cold, refembies a mafs of heavy torrefied fpar, 
Void of the fmalled vitrid appearance, hard and durable, 
it is then certain th.at the furnace contains fulpluiry iron, 
i, e. fuper-carbonated iron. At hlad-furnaces, where a 
great quantity of air is thrown in per minute, fuper- 
carbonated crude iron will be obtained with a cinder of a 
longer form, with a rough flinty fracture towards the 
outfide of the column. 
That cinder or lava, which indicates the prefence of 
carbonated iron in the hearth of the furnace, forms itfelf 
into circutar compact dreams, whicli become confolidated 
and inferted into each other; thefe are in- length from 
three to nine feet. Their colour, when the iron ap¬ 
proaches the drd quality, is a beautiful variegation of 
white and blue enamel, forming a wild profufion of the 
elements of every known figure; the blues are lighter or 
darker according to the quantity of the metal and the 
action of the external air while cooling. When the 
quality of the pig-iron is fparingly carbonated, the blue 
colour islefs vivid, lets delicate; and theexternal furface 
rougher, and more fullied tvith a mixture of colour. The 
fame Icoria, when fufed in velfeis whicli are allowed to 
cool gradually, parts with all its variety of light and 
lliade, and becomes of a yellowifh colour, fometimes 
nearly white when the quantity of incorporated metal has 
been fmall. 
The lava or cinder widch is emitted from the blad- 
fnrnace when carbo-oxygenated (or N° 3) iron is pro¬ 
duced, affiimes a long ziz-zag form. The dream is 
flightly convex in the middle; broad, flat, and obliquely 
furrowed, towards the edges. The end of the dream fre¬ 
quently rears itfelf into narrow tapered cones, to the 
height of dx or eight inches: thefe are generally hollow 
in the centre, and are eafily demolidied, owing to their 
exceflive brittlenefs. The colour of this lava is very 
various; for the mod p.art it is pale yellow mixed with 
green. Its tenacity is fo great, that if, while fluid, a 
ftnall iron hook is inferted into it at a certain degree of 
heat, and then drawn from it with a quick but deady 
motion, twenty to thirty yards of fine gdafs thread may 
be formed with eafe. If the colours are vivid and vari¬ 
egated, the thread will podefs, upon a minute fcale, all 
the various tints of colouring which is found in the co¬ 
lumnar mafs. When by accident a qtiantity of this lava 
runs back upon the clifeharging-pipe, it is upon the re- 
itirn of the blad impelled with fiich velocity as to be 
blown into minute delicate fibres, fmaller than the mod 
duftile wire ; at fird they float upon the air like wool, 
and w’hen at red very much refemblethat fubdance. 
The'prefence of oxygenated crude iron (N° 4) on the 
furnace-hearth, is indicated by the lava refolving itfelf 
into long dreams, fometimes branched, fometimes co¬ 
lumnar, extending from the notch to the lowed part of 
the declivity; here it commonly forms large, flat, hol¬ 
low cakes, or inclines to form conical figures; thefe are, 
however, feldom perfe6t; for the quantity of fluid lava, 
eotiveyed through the centre of the column, accumulates 
fader than the external (ides of the cone are confolidated; 
and thus, when the drudfure is only half finifhed, the 
fmall crater vomits forth its fuperabundant lava, and is 
dCmolilhed. The current of fuch lava falls heavily from 
the dam as if furcharged with metal, and emits dark red 
fparks refembling the agitation of draw embers. Its 
colour is dill more varied than the former deferiptions of 
fcoriae, and is found changing its hues through a great 
variety of greens diadedwith browns. Another variety 
of fcoria, which indicates the fame quality of iron, af- 
ftimes a fimilar form; but has a black ground colour 
ACE. 135 
mixed with browns, or is entirely black. When the 
latter colour prevaiks, the texture of the cinder becomes 
porous ; tlie qnaniily qfiroti left is now very conliderable, 
and fuch as will be eadly extradled in the alfity-furnace 
witli proper fluxes. In cafes of total derangement in the 
furnace, the fcoria will dill retain this black colour, 
although the quantity of metal may amount to 25 per 
cent, tlie fracUire, however, becomes denfe, and yts 
fpecidc gravity increafes in proportion to the quantity of 
metal it holds incorporated. 
Tlie next foiirce of information, as to tlie quality of 
the iron in the furnace, is to be got from the colour of 
the fcoria upon the working bars, which are from time 
to time inferted to keep tlie furnace free from lumps, and 
to bring forward tlie fcoria. When foper-carbonated 
crude iron is in the hearth, the vitrid crufiupon the bars 
will be of a black colour and fmootli furface, fully co¬ 
vered with large and brilliant plates of plumbago, As 
the quality of the metal approaches to N° 2 (carbonated), 
the carburet upon the fcoria decreafes both in point of 
quantity and dze, Wlien carbo-oxygenated iron, or 
N° 3, is in the furnace, the working barsare always coated' 
with a lighter coloured fcoria than when the former va¬ 
rieties- exid ; a- fpeck of plumbago is now only found 
here and there, and that of the fmalled fize. When the 
quality of the metal is o.xygenated, as 4, not onljr 
have the plates of carburet difappeared, but alfo the 
coally colour on the external furface of the fcoria ; what 
now attaches to the bars, is nearly of the fame nature and 
colour as the lava emitted at tlie notcli of the dam. 
Thefe criterions are infallible ; for, as the fufibility or 
carbonatioii of the metal is promoted in a clirefl:'ratio to 
the comparative quantity of the coally principle prefent 
in the furnace, fo in the fame proportion will the vitrid 
criid encircling the working bars exliihit the prefence of 
that principle in the furnace. 
Thu-s combudion, in tJie blad furnace, confids in tlTe 
rapid ignition of a given quantity of fuel, and its ac¬ 
companying portion of ore, in a certain given time. 
That furnace which can in the diortedr time reduce the 
greatedquantity of fuel, all things el febeing in proportion, 
will condantly nianufadliire the greated^quantity of iron-. 
In common, before the introdudfion of the blad, the fur¬ 
nace is filled with alternate drata of coke, iron-done, and 
limedone, heated by fimple atmofpheric preflaire to a 
bright red or wdiite heat, and the iron done to a melting 
heat. This temperature is then quickly increafed through¬ 
out the furnace, by the application of the bla(l. The 
blowing orifices or tuyeres of the furnace, exliibit the 
fuel increafing in whitenefs, and the iron-done rapidly 
didblving before the blad, of a blackidi colour. At 
this period, the lava which flows from the furnace, in 
confequence of the redmftion of the ore and lime-done, 
is confi'derably charged with iron, and is of a blackiih 
brown, or greenidi brown, colour. Thefe appearances 
continue for twelve, twenty-four, or thirty-fix, hours, ac¬ 
cording to the mode of treatment in bringing forward the 
furnace after blowing. The tuyere (if a bright tuyere 
furnace) will appear like a blaze of pure light, at times 
very opprefllve to the eye; it foon, however, becomes 
accudomed to it, and will with facility difeern the indi¬ 
vidual mafiTes of coke, as they are forced away, witli the 
rapidity of lightning, before the concentrated force of the- 
air. The concrete ore and lime-done are no longer vid- 
ble ; but a fine metallic fpray is condantly defeending, 
and, forced from the fuel, precipitates itfelf to the bot¬ 
tom of the furnace. The fcoria formed by the fufion 
and union of the lime-done, with the immetallic parts of 
the ore, is carried before the blad in a fimilar manner and 
form, but eafily didinguidiable from the fluid metal by 
its buoyancy, want of velocity when impelled, and by its 
opaque colour. In this date, the furnace is confidered in 
excellent fmelting order. The iron is generally revived 
with little lofs ; and the colour and purity of the cinder 
or lava fufficiently indicate the peffeflion of the fepara. 
tion. 
4 
