IRON. 
merits of a convenient size for melting. The 
mineral is melted or run down, in large fur- 
naces, from sixteen to thirty feet high ; 
and variously shaped, either conical or el- 
liptical, according to the opinion of the 
iron-master. Near the bottom of the fur- 
nace is an aperture for the insertion of the 
pipe of large bellows, worked by water or 
steam, or of other machines for producing 
a current of air ; and there are also holes at 
proper parts of the edifice, to be occa- 
sionally opened, to permit the scoriae and 
the metal to flow out, as the process may 
require. Charcoal or coke, with lighted 
brushwood, is first thrown in ; and when 
the whole inside of the furnace has ac- 
quired a strong ignition, the ore is thrown 
in by small quantities at a time, with more 
of the fuel, and commonly a portion of 
limestone, as a flux : the ore gradually sub- 
sides into the hottest part of the furnace, 
where it becomes fused ; the earthy part 
being converted into a kind of glass, while 
the metallic part is reduced by the coal, 
and falls through the vitreous matter to the 
lowest place. The quantity of fuel, the 
additions, and the heat, must be regulated, 
in order to obtain iron of any desired qua- 
lity ; and this quality must likewise, in the 
first product, be necessarily different, ac- 
cording to the nature of the parts which 
compose the ore. 
The iron which is obtained from the smelt- 
ing furnaces is not pure ; and may be dis- 
tinguished into three states : white crude 
iron, which is brilliant in its fracture, and 
exhibits a crystallized texture, more brittle 
than the other kinds, not at all malleable, 
and so hard as perfectly to withstand the 
file : grey crude iron, W'liich exhibits a 
granulated and dull texture when broken ; 
this substance is not so hard and brittle as 
the former, and is used in the fabrication 
of artillery and other articles which require 
to be bored, turned, or repaired : ■ and 
black cast iron, which is still rougher in its 
fracture ; its parts adhere together less per- 
fectly than those of the grey crude iron : 
this is usually fused again with the white 
crude iron. 
Whenever crude iron, especially the grey 
sort, is fused again in contact with air, it 
emits sparkles, loses weight, and becomes 
less brittle. In order to convert it into 
malleable iron, it is placed on a hearth, in 
the midst of charcoal, urged by the wind of 
two pair of bellows. As soon as it becomes 
fused, a workman continually stirs it with a 
long iron instrument. During the course of 
several hours it becomes gradually less fusi- 
ble, and assumes the consistence of paste. 
In this state it is carried to a large hammer, 
the repeated blow's of which drive out all 
the parts that still partake of the nature of 
crude iron so much as to retain the fluid 
state. By repeated heating and hammer- 
ing, more of the fusible iron is forced out ; 
and the remainder, being malleable, is form- 
ed into a bar or other form for sale. Crude 
iron loses upwards of one fourth of its 
weight in the process of refining; some- 
times, indeed, one half. 
Purified, or bar iron, is soft, ductile, flexi- 
ble, malleable, and possesses all the quali- 
ties which have been enumerated under 
this article as belonging exclusively to iron. 
When a bar of iron is broken its texture 
appears fibrous ; a property which depends 
upon the mechanical action of the hammer 
while the metal is cold. Ignition destroys 
this fibrous texture, and renders the iron 
more uniform throughout ; but hammering 
restores it. 
If the purest malleable iron be bedded in 
pounded charcoal, in a covered crucible, 
and kept for a certain number of hours in 
a strong red heat, (which time must be 
longer or shorter, according to the greater 
or less thickness of the bars of iron) it is 
found that by this operation, which is called 
cementation, the , iron has gained a small 
addition of weight, amounting to about the 
hundred and fiftieth, or the two hundredth 
part, and is remarkably changed in its pro- 
perties. It is much more brittle and fusible 
than before. Its surface is commonly blis- 
tered when it comes out of the crucible; 
and it requires to be forged to bring its 
parts together into a firm and continuous 
state. This cemented iron is called steel. 
It may be welded like bar iron if it have not 
been fused or over-cemented ; but its most 
useful and advantageous property is that of 
becoming extremely hard When ignited and 
plunged into cold water. The hardness 
produced is greater in proportion as the 
steel is hotter, and the water colder. The 
colours which appear on the surface of steel 
slowly heated are yellowish-white, yellow, 
gold colour, purple, violet, deep blue; after 
which the ignition takes place. These signs 
direct the artist in tempering or reducing 
the hardness of steel to any determinate 
standard. If steel be too hard it will not 
be proper for tools which are intended to 
have a fine edge, because it will be so brit- 
tle that the edge will soon, become notched 
if it be too soft it is evident that (lie ed£<c 
