John Blankenbaker's Germanna History Notes

Note 1515

Recent discussions raise good points about iron making.  The use of copper vessels would not work for smelting iron.  Copper melts at about 2000 degrees Fahrenheit, and iron does not melt until it reaches a temperature closer to 3000 degrees.  The use of natural draft to move the air through the charge (iron ore, limestone, and charcoal) went out about 500 B.C.  The old furnaces found in the Siegen from this date used natural draft, but it was always a problem.  Even the Egyptians had learned to use goat skin bellows to force the air.  Blast furnaces in the modern form began to appear about 1340 A.D. in Central Europe.

Yes, the smelting furnace had to run continuously, day and night, seven days a week, for months on end.  Only a major problem could force them to shut down.  Such a problem might be a lack of water to drive the bellows, or a shortage of charcoal to fire the furnace.  If a furnace went cold, it was a problem to get it back into "blast".

Coke was not in wide use when the Tubal furnace started about 1721.  [Coke is made by pre-heating coal, which removes the impurities, mainly sulphur, which would contaminate the iron.]  [Limestone is also added because it helps to remove impurities from the iron ore during smelting.]  Therefore, wood was used to make charcoal, and it took a lot of wood.  The first use of coke was in England in 1709.  [The use of coke was pioneered by Abraham Darby .]  A large work crew about the furnace were the colliers who made charcoal from wood.  In a self-contained furnace operation, the supply of food took even more labor.  At one furnace in New Jersey, they used to shut down in the harvest season so everyone could work in the harvest.
[For more information on iron making, see Iron Smelting, A Beginners Guide .]

At this time (early 1700s), England had been so denuded of trees that they could not produce as much iron as they needed.  They had to buy iron from the Baltic nations.  Gov. Spotswood recognized this problem and gave that as a reason for producing iron in Virginia.  But the short-sighted English merchants were afraid that, if Virginia produced iron, they would start making iron objects in Virginia and not buy them from England.

Spotswood argued that Virginia had everything that was needed, and it would reduce the dependence on the foreign iron.  He, of course, was correct.  Perhaps this is the reason that, when he did start making iron, the objections were minimal.  The merchants in England, though, said that Virginia should ship the pig iron to England and not make any final products in Virginia.

I erred slightly in the last note.  The oxygen in the air is not entirely consumed by the charcoal.  Generally, the charcoal and oxygen make carbon monoxide, and this combines with oxygen in the iron ore, producing carbon dioxide and iron.  This last chemical combination is aided by the limestone which acts as a catalyst in reducing the iron ore.

I spoke of the pouring the molten iron onto the ground where it was cast into pigs or useful products.  Probably I should have said the sand beds (sand molds) not the ground.  The sand was filtered and rotated in service to clean it up.
(02 Nov 02)