132 
Iron, 
for some time is the consequence, yet, as the quality of 
the iron is impaired, and as in the end the furnace will 
return to its old consumption of materials as to quan- 
tity, the effects of a loose soft blast are conclusively per- 
nicious* 
It sometimes happens, that when a loose blast is sur- 
charged with a considerable portion of moisture, or comes 
In contact with coaks which had been wet when intro - 
duced into the furnace, the inflammation which takes place 
at the tuyere is prodigious : fine fire-clay will be melted 
down and blown to slag in a few minutes; the sides of 
the furnace, composed of very infusible fire-stone, is next 
attacked, and in a few hours will be so completely destroy- 
ed as to stop the working, and require immediate repair* 
Effects similar to those now described will be felt when 
blast is improperly proportioned to coal of a stronger con- 
tinuity of fracture and superior quality* Besides the ef- 
fects produced by the sudden decomposition of iron, others 
of like nature are produced where a soft coal is used, a 
small furnace and a great discharge of blast, m 
It has been found that crude iron, to be properly ma- 
tured, ought to remain in the blast furnace, according to 
eircumsances, 48 to 60 hours ; that is, from the period 
that the iron-stone is introduced till such time as the me- 
tal begins to occupy its place in the hearth in a state of 
perfect separation* When the contrary is the case, the 
mixtures arrive at the hottest parts of the furnace before 
the metal has taken up a sufficient quantity of carbon from 
the fuel ; the action of the blast, and the immediate heat 
by which the ore is surrounded, forces the iron from its 
connections to the bottom of the furnace* The quality 
is de- carbonated, and reduced in its value : to restore this 
again, the local portion of fuel is increased ; this adds to 
the expence of manufacturing, and diminishes, in some 
measure, the smelting of the furnace* 
