152 
Jars has given the steel furnace, and the foundery fur- 
nace of England, but not the blast furnace. 
17thly, Thus it appears, that a smelting furnace may 
be considered as divided into three parts ; viz. the up- 
permost portion from the opening at top, downward to 
the narrow part of the boshes wherein the process of ce= 
menting goes on ; that is, where the crude ore is gradu- 
ally deprived of the oxygen, or substance that demetallizes 
it, by means of the carbon of the coals. Whether this 
be compleatly effected, depends first on the charge of the 
furnace ; whether the coal, the iron-stone, and the blast, 
be each in due proportion to each other, so that no part of 
either shall escape the action of the other : secondly, on 
the degree of heat given to the charge, for this union of 
the carbon of the coal, with the oxygen of the iron, does 
not take place, but in a full red heat : thirdly, upon the 
size of the particles of ore, coal and limestone : and 
fourthly, upon the time the charge takes in descending 
from the top of the chimney to the bottom of the boshes, 
where the fusion or melting takes place ; for, if it descend 1 
too quickly, the iron will not be sufficiently carbonated ; 
part of it, in the form of ore, or oxyd, will be turned into 
glass with the slag, and the iron in the hearth will be im- 
perfect white iron without a regular grain. On the con- 
trary, if the proportion of coal be considerable, and the de- 
scent of the charge protracted, the iron will be smooth- 
faced pig ; carburetted or supersaturated with carbon ; 
it will be extremely fusible, more so than cast steel, which, 
in many properties, it greatly resembles; and a substance 
like plumbago or black lead, called kish, will float on its 
surface. This kind of pig, however, is very valuable, 
being used for castings of all kinds : where the coal, the 
heat, and the stone, have been in due proportion, the iron 
will be saturated with carbon, or nearly, so as to be me- 
tallic throughout. This is forge pig; a kind of iron uni- 
