Burden
The burden in the cupola or blast-furnace is supposed to be light when the proportion of fuel to ore or iron is large. When the fuel is proportionately small in the charge, the burden is then called heavy. See CHARGING THE COMMON CUPOLA.
Twelve hundred entries from the golden age of cast metal — how bells are founded, why brass is not bronze, what a cupola melts and a core withstands — by Simpson Bolland, the trade's great teacher.
The burden in the cupola or blast-furnace is supposed to be light when the proportion of fuel to ore or iron is large. When the fuel is proportionately small in the charge, the burden is then called heavy. See CHARGING THE COMMON CUPOLA.