MANUFACTURE OF IRON AND STEEL. 
603 
level, and a light frothy slag makes its appearance, and is 
thrown out in large foam-like masses. This violent eruption 
of cinder generally lasts five or six minutes, when all further 
appearance of it ceases — a steady and powerful flame replacing 
the shower of sparks and cinder which always accompanies 
the boil. The rapid union of carbon and oxygen which thus 
takes place adds still further to the temperature of the metal, 
while the diminished quantity of carbon present allows a part 
of the oxygen to combine with the iron, which undergoes 
combustion, and is converted into an oxide. At the excessive 
temperature that the metal has now acquired, the oxide, as 
soon as formed, undergoes fusion, and forms a powerful 
solvent of those earthy bases that are associated with the iron. 
The violent ebullition which is going on mixes most intimately 
with scoriae and metal, every part of which is thus brought 
into contact with the fluid, which will thus wash and cleanse 
the metal most thoroughly from the silica and other earthy 
bases which are combined with the crude iron, while the 
sulphur and other volatile matters which cling so tenaciously 
to iron at ordinary temperatures are drawn off, the sulphur 
combining with the oxygen, and forming sulphurous acid gas. 
The loss in weight of crude iron during its conversion into an 
ingot of malleable iron, was found, on a mean of four experi- 
ments, to be 12| per cent., to which will have to be added 
the loss of metal in the finishing rolls. This will make the 
entire loss probably not less than 18 per cent., instead of 
about 28 per cent., which is the loss on the present system. 
A large portion of this metal is, however, recoverable, by 
treating with carbonaceous gases the rich oxides thrown out 
of the furnace during the boil. These slags are found to 
contain innumerable small grains of metallic iron, which are 
mechanically held in suspension in the slags, and may be 
easily recovered, by opening the tap-hole of the converting 
vessel, and allowing the fluid malleable iron to flow into the 
iron ingot moulds placed there to receive it. The masses of 
iron thus formed will be perfectly free from any admixture of 
cinder, oxide, or other extraneous matters, and will be far 
more pure, and in a sounder state of manufacture than a pile 
formed of ordinary puddle bars. And thus it will be seen, 
that by a single process, requiring no manipulation or parti- 
cular skill, and with only one workman, from three to five 
tons of crude iron passes into the condition of several piles of 
malleable iron in from thirty to thirty-five minutes, with the 
expenditure of about one third part the blast now used in a 
fiery furnace with an equal charge of iron, and with the con- 
sumption of no other fuel than is contained in the crude iron. 
