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^00                     METALLURGY   OF   CAST   IRON.
well maintained, I would advise the two tuyeres being about two inches diameter, and give this plan the preference over one-inch tuyeres with higher blast pressures.
The cupola should have its bed of coke well on fire before the iron is charged, and the latter should be distributed evenly all over the surface of the bed, the largest pieces being placed in the middle. I have melted one-quarter of a common-sized pig all down in fifteen minutes from the time it was charged. This is mentioned merely to show that the baby-cupola can deal very rapidly with chunks of iron.
The melted iron should be held in the cupola until           j
one charge is thought to have been all melted down,           j
before it is tapped out.    A charge of iron may range           j
from 20 to 50 pounds; and  several  charges may fol-           j
low, having a layer of coke between them, from four           !
to five inches in thickness.     For a heat over twenty        ^^,
minutes long, some good flux may be advantageously           ]
used to make a thin slag, which could be run off at           <
the tap-hole or at a slag-hole, provided for the purpose,           j
about two inches above the level of the tap-hole.     To           j
start the blast  it  is  usually  best  to  let  the   lowest           j
pressure of blast found permissible with utility left on, up to the time that about two pounds of melted iron run out of the tap-hole. After this flowing of metal, plug up the hole and increase the blast pressure a few ounces, so as to bring down the iron quickly, and collect it in a good body, which will maintain its fluid-ity while it remains on the bottom bed before being-tapped. In letting out the fluid metal, make a large hole and have a warm ladle to receive the liquid iron. The lining used for the cupola is simply a coating ofnovice desires to use the smallest cupola practical for melting small samples. "............      "        "   i in square hnrH........................