This structure at Foster Falls is called a cold blast iron furnace. Everything in the area was dependent on its use. It was the center of the area's economy.
Here's how it worked: In order to turn iron ore into iron (and later steel) the raw material had to be heated to melting temperature. To heat the ore timber was turned into charcoal and was then used to stoke the furnace to 500 degrees centigrade (today plants use coke and "hot blast" to smelt iron ore; it's cheaper and far less labor intensive).
Required for production were (a) iron ore (hematite - iron oxide), (b) limestone, (c) heat (charcoal or coke), (d) water, and (e) air.
The water (diverted from the New River) was needed to turn a wheel that operated a huge bellows that forced air into the lower unit of the furnace.
Train car loads of iron ore were hauled in on tracks above and behind the furnace. Workers then wheelbarrowed the ore - mixed with limestone - to the stack at the top and shoveled the mixture in. Generally when the furnace was started it ran 24 hours a day, 7 days a week.
At melting temperature the iron ore (Fe2O3) separated into iron (Fe), carbon dioxide (CO2) and refuse (slag).
The melted iron flowed into molds that were located on the lower left side of the furnace, the slag flowed into a catch basin to the lower right.
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This is an old photo of the Foster Falls Mining and Manufacturing Company's iron furnace in its heyday.
In the foreground can be seen piles of timber hauled in to heat the furnace.
At its peak the furnace employed 90 men.
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* The process that turned trees into charcoal was an elaborate process in itself. Trees were hauled in, sawed into logs, piled high and set on fire. Once the fire was going the logs were covered up with dirt and left to burn (airless) for up to a week. Charcoal was the end product. It required 2.5 tons of ore and 140.9 bushels of charcoal to produce one ton of iron. At its peak the furnace produced 12 tons of pig iron a day.
** Limestone was used in the process to bind with the impurities that were in the raw ore.
*** The bound byproduct - slag - was later used to line railroad beds (in lieu of gravel).
***** I'm sure you all remember your chemistry from high school. The balanced equation: 2Fe2O3 + 3C → 4Fe + 3CO2. The 3C being the charcoal or carbon. Fe being iron and O being oxygen.
***** The cold blast process was found, over time, to be less effective than the hot blast smelting process that is in use today. Thus, all cold blast furnaces in the U.S. were gone by the 1920's.
****** The end product - pig iron - a poorer quality product, was used in the manufacture of such things as railroad car wheels. During the Civil War it was attempted to use pig iron for artillery tubes (cannon) by the Confederate government but testing proved that the barrels kept failing.