534 On the Produétion of Caft Iron, &e. 
farnace-hearth, is indicated by the Java refolving itfelf into 
long {treams, fometimes branched, .fometimes columnar, 
extending from the notch’ to the lowelt part of the declivity 5 
here it commonly forms large, flat, hollow cakes, or melines 
to form.conical figures: thefe are, however, feldony perfect; 
for the quantity of fluid Java, conveyed through the eentre of 
the column, accumulates fafter than the external fides of the 
cone are confolidated; and thus, when the ftructure is. only 
half finifhed, the fmall crater vomits forth its fuperabundant 
Java, and-is demolifhed. The current of fuch lava falls hea- 
vily from the dam as if furcharged with metal, and emits 
dark red fparks refembling the agitation of ftraw embers. 
Its colour is ftill more didien than the former defcriptions of 
fcoriz, and is found changing its hues through a g@reat va- 
riety of greens thaded with browns. iAivother’ variety of feo- 
ria, W hich indicates the fame quality of tron, affumes a fimi- 
jar form; but has a black ground colour mixed with browns, 
or is entirely black. When the latter colour prevails, the 
texture of the cinder becomies porous; the quantity of iron 
left is now very confiderable, and. fuch as will be eafily ex- 
tracted in the aff: av-furnace with proper fluxes. In cafes of 
total derangement i in the furnace, the fcoria will {till retain 
this black Gee: ur, although the quantity of metal may amount 
to 25 per cent.; the freeones however, becomes denfe, and ° 
its {pecific sai mereafes in proportion to the quantity of 
metal it holds incorporated. 
The next fource of information, as to the quality of the 
iron in the furnace, is to be got from the colour of the feoria 
upon the working bars, which are trom time to time inferted. 
to keep the furnace free from lumps, and to bring forward 
the feoria. When fuper-carbonated crude iron is in the 
hearth, the vitrid cruft upon the bars will be of a black co- 
lour and fmooth furface, fully covered with large and_ brik 
jiant plates of phambago. 
As the quality of the metal approaches to No. 2 (carbo- 
nated), the carburet upon the feoria decreafes both in point 
of quantity and fize. 
When carbo-oxygenated iron (No.3) is in the furnace, 
the ‘working hars are always coated’ witha lehter co- 
9 loured 
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