Pig iron is the resultant product when molten iron from a furnace is funneled into small molds and allowed to cool. When the furnace is tapped, the molten iron flows out into a channel which has side branches. One of these side branches could be the size of an ear of corn, perhaps larger. The central channel with the branches reminded early workers of a nursing sow and piglets. They called the resultant product pig iron.
As Gene has pointed out, it takes a lot of energy to smelt iron. The heat, in Spotswood's time, was derived from charcoal made from wood. In the Siegen area, at the time our ancestors left, the item in short supply was wood, for it takes about fifty pounds of wood to make the charcoal necessary to smelt out one pound of iron. The charcoal is close to being pure carbon, and it burns with oxygen from the air, releasing heat and making carbon dioxide. The fifty pounds of wood would have lost a lot of weight in being converted into charcoal. It takes two oxygen atoms for every carbon atom to produce carbon dioxide. Air is not pure oxygen; it is about twenty percent oxygen, and the other elements are inert. Another way to look at the wood needed is to note that a furnace like Tubal, producing a few tons of iron per day, consumed the trees from one acre of ground.
All of that wood, now converted into charcoal, was fed through the furnace. Several times this much air, by weight, had to be forced through the furnace also. It did not flow naturally. Large bellows were used, and these were driven by waterpower. This was a second source of energy, and sometimes the process ground to a halt because the water flow was not sufficient. The furnace had to be sited at a location where there was lots of water falling through a significant drop. This was used to drive a waterwheel which drove the bellows.
The molten iron was sometimes allowed to flow into a mold to make useful products such as pots and pans. Sometimes it might flow over a wide, level mold to make something like a fireplace backing or the parts of a five-plate stove. This is casting directly from the furnace. Instead of calling this pig iron, it was called cast iron, though the properties of cast iron and pig iron are essentially the same. By either name, one property that they share is that the product is brittle. It could not make an axe, or a sledge, or a wedge, which are subject to tremendous forces. Nor is the cast iron malleable or useable directly by a blacksmith.
Bar iron and wrought iron are essentially the same thing. This takes another stage of processing beyond cast iron to produce. The furnace operation at Saugus, Massachusetts, which preceded the Tubal furnace, did not produce molten iron. The temperatures were lower and the resultant iron was never truly melted but was a sponge like mass after the impurities had been burned out. By beating and working this, iron could be produced that was malleable.
[to be continued]
(01 Nov 02)
We gratefully acknowledge the work of John Blankenbaker who published over 2,500 Germanna History Notes via the Germanna-L@rootsweb.com email list from 1997 to 2008. We are equally thankful to George Durman (Sgt. George) for hosting the list and republishing the notes via rootsweb.com.