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crystals of which are small, and assume a soft or greasy 
appearance. The colour is also very light. Pigs made 
from charcoal often contain in their centre patches of white 
iron, which is highly carbonized ; so that the general formula 
must be considered as correct only in reference to irons made 
from coal or coke. 
Until within the last twenty years, the pig iron for good 
qualities of bars was re-melted in a furnace called a refinery, 
blown with a blast of air, and run into thick plates, which 
plates were afterwards broken and then put into the puddling 
or reverberatory furnace. This refining process is not simply 
a re-melting one, as the iron, when melted, being exposed to 
the action of a blast of air, the oxygen thereof combines 
with some of its carbon, and thus partially effects the opera- 
tion subsequently perfected in the puddling furnace. More- 
over, it is probable that some of the impurities of the pig 
were got rid of, as well as a portion of the carbon, such, at 
least, as, being lighter than the iron, floated on the surface, 
and when run into the slabs or plated, flowed off into a hole 
scooped out at the foot. 
The intermediate process of refining is now generally 
abandoned in Staffordshire, the same objects being attained 
much more economically by an improved method of puddling, 
termed boiling. 
Heating the air before it is driven into the blast furnace, 
commonly called " hot blast," has effected most extraordinary 
results in increasing the quantity of iron by economy of fuel. 
I well remember the protracted discussions to which the hot 
blast question gave rise in this society some years since, and 
I have no desire to renew them ; but I must state my con- 
viction founded on long experience, that the hot blast does 
in some respects, and for certain special purposes, deterio- 
rate the quality of the iron made. It is conjectured that 
this arises from the greater heat of the blast furnace 
