IRON MANUFACTURE. 493 
several thousand tons of ore. They are usually about 10 feet high, 
from 10 to 20 feet broad at the base, sloping upward to the top, which 
is flat, and so long, often, that while the burnt ore is being removed from 
one end fresh ore is being added at the other. The time necessary for 
the calcination depends evidently upon the size of the pile, and also 
the need in which the furnace stands in reference to a supply of ore. 
They answer thus at the same time as calcination heaps and storage 
piles. Sometimes they burn for 6 or 8 months, though it is impossible 
to obtain any accurate information regarding the time, labor, expense of 
fuel, etc., consumed in the operation. By burning, the ores lose about 
20 to 30 per cent. of their original weight, and are Sy en- 
riched in their yield of iron. 
As regards the fuel of the region, mention has already been made 
that charcoal forms the exclusive material used in 34 of the 41 furnaces, 
and that it is only within a few years that attention has been turned to 
the employment of the coals in smelting the ores of the region. The 
varieties of wood, most common in the region, are oak, hickory, maple, 
beech, ash, poplar, walnut, and some pine. The magnificent forests 
have furnished an abundant supply of charcoal, but its rapid consump- 
tion, as stated, has caused the abandonment of some furnaces, while 
others more provident, permitting the growth of new timber, after the 
lapse of 20 or 25 years, are now cutting a second growth for charcoal. 
It is reported also that in some instances a third growth is being 
obtained from the same land. The amount of charcoal consumed 
annually by a furnace, may be illustrated by the following statements 
kindly furnished by the proprietors of the Pine Grove and Hecla 
furnaces: Pine Grove, hot-blast furnace, in 1869, produced 3,102 tons 
(of 2,268 lbs.) of iron, and consumed 11,045 cords of wood, which yielded 
36.8 bushels per cord, or 406,456 bushels, or at the rate of 131 bushels 
of charcoal, or 3.56 cords of wood per ton of iron. The Hecla, cold- 
blast furnace, in 1867, for a blast of 2.8 days, made 1,980 tons (2,268 
lbs.) of iron, and consumed 393,000 bushels of charcoal, or 201 bushels 
per ton of iron. It is usually stated that a furnace will consume the 
wood from 250 acres of land per year, hence to ensure a perpetual 
supply of timber by allowing its regrowth where once cut, such a furnace 
would require from 800 to 1,000 acres of wooded land. The wood is 
valued at about 50 cents per cord in the tree. The charcoal made and 
delivered at the furnace was estimated in 1870-71 to cost on an average 
